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WIGGLING 'LITE' IN GUEST MODE

Buffered mults
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Buffered mults
raisinbag
I'd like to make up a buffered mult on strip board for shits and giggles. I can't seem to find a decent schematic to learn from. I am guessing you basically run signal through an opamp at unity gain and then?????????
sduck
Boy am I glad you asked. I was thinking of building up a few also, but my powers of searching on this website are weak, so hopefully someone will post a schematic. Or I'll have to try doing the dreaded search...
roglok
this discussion is just going on over at e-m: http://electro-music.com/forum/topic-56272.html
Barcode
Here's another thread. This one has some layouts posted.

http://www.electro-music.com/forum/viewtopic.php?t=49356
raisinbag
sduck wrote:
Boy am I glad you asked. I was thinking of building up a few also, but my powers of searching on this website are weak, so hopefully someone will post a schematic. Or I'll have to try doing the dreaded search...


Ya I already did the dreaded search and found nothing frutful. I'll go check out the posts you other guys made and check back with more questions (when I'm off the ski hill, yipeeeeeee!)
russma
For the uninitiated, how is a buffered mult different than an un-buffered one?

I'm guessing it's something to do with maintaining the voltage level across all outputs?
hpsounds
https://www.muffwiggler.com/forum/viewtopic.php?t=46106

Hédi K.
raisinbag
Well from my understanding, you are running the signal through an opamp (or a few opamps) when buffering. When not buffering you just split the signals. Whole purpose of buffering is to retain signal strength and I think also takes care of impedance issues.
burdij
Here you go:



Place a temporary load, the 100K resistor with the dotted line, on one of the outputs. Put a steady voltage signal into the input. Adjust the potentiometer so that output voltage measured at the top of the load resistor equals the input voltage.
sduck
Thanks all!
burdij
I made a slight mistake in the schematic which has already been corrected. The potentiometer should be a 10K which will give a X1 +- 5% gain adjust range.
raisinbag
Yay thumbs up Thanks that is exactly what I was looking for!!!!!!!!!!!!!!!
EMwhite
How critical is the value of the 27pF cap (will 33 be ok?);

What about the 95.3K resistor. Naturally, I don't have that in my parts bin so how about 30+30+30+3.3+3.3... new at this so please bear with me.

Is the point that you can affect between a 90-something K resistance and a 105 or so amount of resistance thus boosting or cutting the voltage in order to dial in unity?

Final stupid question of the evening, how to wire the 10K pot? I've seen the 1,2,3 (ground,wiper/center,+xV) wiring, should two of the terminals be connected together, if so which? Thanks.
Barcode
EMwhite wrote:

What about the 95.3K resistor. Naturally, I don't have that in my parts bin so how about 30+30+30+3.3+3.3... new at this so please bear with me.


I'm guessing you have loads of 100k resistors laying around like me. And yes they will work. thumbs up
Luka
i built the one listed in this thread - the schematic provided by Big G resolved all my concerns with standard buffering circuits and works great

https://www.muffwiggler.com/forum/viewtopic.php?t=19142&highlight=buff ered+mult
glitchpop
Great thread thumbs up

I have a few more noob questions for you burdij once you cover EMwhites hihi

1. IC is listed as TL0XX. Does that mean any opamp will do?

2. +-12V is not shown on the schematic is that assumed to be connected to appropriate pins? Or is it/ will it work unpowered?

Thanks!
burdij
EMwhite wrote:
How critical is the value of the 27pF cap (will 33 be ok?);


The capacitor gives the circuit stability when the gain of the amp is set near X1. The value is not too critical. I would say anything between 22 and 100pF would be fine. If you go higher than that, you will be affecting the high frequency response.

EMwhite wrote:

What about the 95.3K resistor. Naturally, I don't have that in my parts bin so how about 30+30+30+3.3+3.3... new at this so please bear with me.


95.3K is the nearest value to 95K in 1%. A 82K and a 12K in series would work in 5% values.

EMwhite wrote:

Is the point that you can affect between a 90-something K resistance and a 105 or so amount of resistance thus boosting or cutting the voltage in order to dial in unity?


Yes, that is the reason. A common use of a buffered mult would be to distribute note CV values to multiple oscillators. The value of the gain needs to be as close to X1 as possible in order to maintain the 1V/Octave scaling. If the gain is not close to that value, you would be only able to tune all oscillators to be in tune at one value. The oscillators will stay relatively in tune with each other but all would go out of tune the further from that "in tune" value they got.

EMwhite wrote:

Final stupid question of the evening, how to wire the 10K pot? I've seen the 1,2,3 (ground,wiper/center,+xV) wiring, should two of the terminals be connected together, if so which? Thanks.


You could use only two of the three pot connections, the wiper and one of the end connections. I usually connect the wiper to one of the end connections and use that in conjunction with the other end connection in this sort of application. That way, there is always a DC path returning to the negative input from the output which prevents bumps in the gain of the amp as the wiper scraps along the surface of the resistance element. If the path opens briefly, the gain of the circuit will head for infinity and produce noticeably more noise in the output. I usually also arrange the connections so the higher resistance occurs in the clockwise direction which would produce higher gain but that is only a cultural bias toward right-handedness.
burdij
glitchpop wrote:
1. IC is listed as TL0XX. Does that mean any opamp will do?


I was suggesting using an op amp such as the TL062, TL064, TL072, TL074, TL082, TL084 series but any quality, low offset, high speed opamp will work. The capacitor assures stability so the choice of device shouldn't matter too much. I wouldn't use "old timey" op amps like 741s though as they just don't have very good frequency response.

glitchpop wrote:
2. +-12V is not shown on the schematic is that assumed to be connected to appropriate pins? Or is it/ will it work unpowered?


The op amp power pins do need to be connected to a power source. Whether it is +-12V or +-15V doesn't matter. You should use the same power as your other synth modules are powered with.
qfactor
burdij wrote:

The op amp power pins do need to be connected to a power source. Whether it is +-12V or +-15V doesn't matter. You should use the same power as your other synth modules are powered with.


Pardon, but could this buffer work off a 9v battery? Am looking at attempting a "portable" buffered mult! zombie
roglok
Luka wrote:
i built the one listed in this thread - the schematic provided by Big G resolved all my concerns with standard buffering circuits and works great

https://www.muffwiggler.com/forum/viewtopic.php?t=19142&highlight=buff ered+mult


so... how does burdij's single op-amp design with output compensation in the feedback path compare to Big G's circuit? I was under the impression that each output needs its own buffer.
burdij
roglok wrote:
Luka wrote:
i built the one listed in this thread - the schematic provided by Big G resolved all my concerns with standard buffering circuits and works great

https://www.muffwiggler.com/forum/viewtopic.php?t=19142&highlight=buff ered+mult


so... how does burdij's single op-amp design with output compensation in the feedback path compare to Big G's circuit? I was under the impression that each output needs its own buffer.


You can tie as many 101K loads (the equivalent load of the output resistor and one input load of the next stage) to the output of the opamp in the circuit shown as you like as long as the total load at the maximum output swing stays below the maximum current output of the op amp used. For a TL074, the maximum output swing is +-13.5 V with a 10K load. Ten parallel output loads of 101K is roughly 10K ohms. I don't know if I would use that many as the total capacitance of all the cables plugged into the outputs would start to become a significant value.
burdij
qfactor wrote:
burdij wrote:

The op amp power pins do need to be connected to a power source. Whether it is +-12V or +-15V doesn't matter. You should use the same power as your other synth modules are powered with.


Pardon, but could this buffer work off a 9v battery? Am looking at attempting a "portable" buffered mult! zombie


If you use two 9V batteries, one for positive and one for negative, the circuit should work properly. Remember that lowering the supply voltages will also lower your output voltage swing "headroom". For a TL074, the output voltage will swing to within about 1.5 volts of the power supply voltage values and, as mentioned in the previous post, will also be dependent on the load on the opamp output since the amplifier has some finite output impedance. You could look around for an opamp designed to do "rail-to-rail" output swing like an LT1677 for this application to fully utilize the available power supply range.
roglok
burdij wrote:
roglok wrote:
Luka wrote:
i built the one listed in this thread - the schematic provided by Big G resolved all my concerns with standard buffering circuits and works great

https://www.muffwiggler.com/forum/viewtopic.php?t=19142&highlight=buff ered+mult


so... how does burdij's single op-amp design with output compensation in the feedback path compare to Big G's circuit? I was under the impression that each output needs its own buffer.


You can tie as many 101K loads (the equivalent load of the output resistor and one input load of the next stage) to the output of the opamp in the circuit shown as you like as long as the total load at the maximum output swing stays below the maximum current output of the op amp used. For a TL074, the maximum output swing is +-13.5 V with a 10K load. Ten parallel output loads of 101K is roughly 10K ohms. I don't know if I would use that many as the total capacitance of all the cables plugged into the outputs would start to become a significant value.


Thanks, that sounds great! Still I don't understand why most buffered multiple designs are built around multiple op-amp buffers when it only requires one. What I understood from your reply is that with your design it's possible to use a single op-amp (e.g. TL071) for up to 10 outputs and still have an accurate 1:1 output scale. Are other designs overcomplicating the matter then?
Eric G
burdij wrote:
Here you go:





I don't see the point with all those components. One non-inverting OPamp will do fine, and skip all the resistors. Also skip the 1k resistors and you need no calibrations.
The 1k resistors are only for short-circuit protection, and if you happen to short and destroy an OPamp (I never did) then just replace it.
CJ Miller
When I saw the thread title, I thought it said: "Buttered Muffs"... lol
airfrankenstein
CJ Miller wrote:
When I saw the thread title, I thought it said: "Buttered Muffs"... lol


Looking forward to THAT module! thumbs up It's motherfucking bacon yo
sinemod
Ok so what is the good schematics
Does it need 2 op amp ?

and what about a simple inverting
airfrankenstein
why would it need two op amps?
Nantonos
burdij wrote:
Here you go:



Place a temporary load, the 100K resistor with the dotted line, on one of the outputs. Put a steady voltage signal into the input. Adjust the potentiometer so that output voltage measured at the top of the load resistor equals the input voltage.


Then place three more temporary loads on the other three outputs, what does the voltage read now.

In other words, that looks like a fine input circuit but shouldn't the outputs on a buffered mult be, well, buffered to isolate each them from the load on that output and on the other outputs.
daverj
Nantonos wrote:
burdij wrote:
Here you go:



Place a temporary load, the 100K resistor with the dotted line, on one of the outputs. Put a steady voltage signal into the input. Adjust the potentiometer so that output voltage measured at the top of the load resistor equals the input voltage.


Then place three more temporary loads on the other three outputs, what does the voltage read now.

In other words, that looks like a fine input circuit but shouldn't the outputs on a buffered mult be, well, buffered to isolate each them from the load on that output and on the other outputs.


Adding temporary loads to the other outputs won't change the voltage on the first output. The common point between outputs is the feedback point of the amplifier, which is constant.

However this circuit has a couple of other issues that make it a problem.

1 - If the load of the input you connect to is not the same as the temporary load that you tested with, the voltage will be wrong. And if two inputs connected to two of the outputs have different loads, they will get different voltages.

For example, if you calibrate it using a 100K resistor, but the module you connect it to has a 50k input load, the voltage on the input will be off by about 50mv at full scale (+5v or -5v). Or 100mv if feeding it +10v. That means 59 cents difference for a 5v signal (or 118 cents for a +10v signal)

2 - with 1% resistors the difference between two outputs could be about 1 cent different.

3 - With a gain of x2 and a TL07x amplifier, the worst case input offset voltage could make the outputs be off by 20mv, or about 24 cents, relative to what the input signal was. This will be the same amount for all outputs, and assuming that you are sending the voltages to a 1v/oct input on a VCO or filter, the frequency control of that module can be used to compensate. So this isn't that big of a deal, but something to be aware of.

The best way to do a buffered mult is to have one amplifier as the input stage to buffer the other stages, and then each output have it's own amplifier. Those amps should each have their own gain adjustment and should have the output resistor inside the feedback loop so that the load they are feeding becomes irrelevant.

Ideally they would also each have their own offset trim, though that isn't as important as long as everything they feed has a bias control (such as frequency on a VCO) to correct for offset differences.

It is possible to make one with a single output amp, if you put the protection resistor in the feedback loop and basically make a passive mult on the output. The problem with that is that as you plug additional modules in, if the cable momentarily touches ground it will short out all of the signals. By having separate amps for each output you eliminate that problem.
roglok
dave, would it be possible for you sketch this up? i think a schematic for your solution would be greatly appreciated by many... thumbs up
Ginko
Sounds like it would be quite a good DIY kit, if you need a couple of TL074s (to make 1:3) and trimpots, I reckon you could squeeze about 4 buffered mults into a 4hp panel - a stacked pair of PCBs maybe?
horstronic
Ginko wrote:
Sounds like it would be quite a good DIY kit, if you need a couple of TL074s (to make 1:3) and trimpots, I reckon you could squeeze about 4 buffered mults into a 4hp panel - a stacked pair of PCBs maybe?


That would be nice! I'm just a bit unsure if its worth the effort as you can do this on stripboard pretty easily.
Ginko
true, it would have to be convenient to build and priced conveniently
daverj
roglok wrote:
dave, would it be possible for you sketch this up? i think a schematic for your solution would be greatly appreciated by many... thumbs up


There's many ways to design a buffered mult. If I were designing one for my own use, this is probably what I would do:



The first stage has 7 percent gain. The trimpots ideally give +/-7% adjustment. With 1% resistors, the gains could be off by up to about +/-4.5%. With a 10% trimpot the adjustment range could be off by another 1.5%-2%. So the adjustment range of the trim will still cover all possibilities.

The feedback cap values are based on a printed circuit board. With point to point hand wiring or stripboard I might double those.

Since all amps are on the same die, if their offset voltages are similar then using two inverting amps in series may provide some cancellation of that voltage.

I didn't put in bias controls because 1) to make it temperature and supply voltage stable requires a bunch of extra parts, and 2) I am assuming the places these outputs go already have a bias control in the form of the frequency pot on a VCO or filter.

I did this using a Euro power connector and voltages. It would be identical except for the connector for a +/-15 system.

The two Schottky diodes provide power cable reversal protection and their small voltage drop won't effect the operation of the circuit.
diablojoy
hmm i did recently do a board for myself but certainly not as good as what dave is suggesting , there is no trimming provided for and the output resistors are not in the feedback loop so it isnt going to be as accurate.
it works but i am still testing it to see how well it works.
I still might revise it to improve on it, though there is no room left for anything extra component wise without going to SMT
board is 8HP , 8 inputs split into 2 groups of 4 to 2 groups of 4 buffered outputs using 6 dual opamps. (I used 6 x LF442)
output 4 normals to input 5
Its all on a single double sided board measuring 100 x 40 mm with 16 x erthenvar jacks but it also includes headers on the ins and outs for different formats so it is quite tight . mixed euro / motm power header and filter caps are silk screened on the back so power connection for either format is easy
I perhaps may have some spares going if anyone is absolutely desperate
Ginko
Nice!
cloudscapes
Individually buffered outputs is probably a better idea, like the schematic on electro-music. The one with the single opamp input buffer will work, but it won't be rock-solid when you start mixing the output "destinations". If you leave the outputs unbuffered and start passively mixing/stacking multiple outputs further down the line, you might have bleed interfering with your mixes. Buffered outputs ensure that you can do whatever you want down an output without it bleeding back and up another output. *

*speaking as a modular noob grin so I reserve the right of being totally wrong
roglok
daverj wrote:
roglok wrote:
dave, would it be possible for you sketch this up? i think a schematic for your solution would be greatly appreciated by many... thumbs up


There's many ways to design a buffered mult. If I were designing one for my own use, this is probably what I would do:


Thank you very much for the circuit and especially the great explanation, dave! thumbs up
qfactor
roglok wrote:
daverj wrote:
roglok wrote:
dave, would it be possible for you sketch this up? i think a schematic for your solution would be greatly appreciated by many... thumbs up


There's many ways to design a buffered mult. If I were designing one for my own use, this is probably what I would do:


Thank you very much for the circuit and especially the great explanation, dave! thumbs up


Indeed, thank you, daverj, for your insight and thoughts about having buffers in both inputs and outputs! thumbs up
we're not worthy
horstronic
I made a PCB design for the schematics daverj posted. Haven't tried it yet but I will soon. I'm pretty shure it's gonna work as it is a pretty simple design.

Here it is:
Bottom
Top silk
Top
roglok
horstronic wrote:
I made a PCB design for the schematics daverj posted. Haven't tried it yet but I will soon. I'm pretty shure it's gonna work as it is a pretty simple design.

Here it is:
Bottom
Top silk
Top


nice! are you planning to do a run?
horstronic
roglok wrote:
horstronic wrote:
I made a PCB design for the schematics daverj posted. Haven't tried it yet but I will soon. I'm pretty shure it's gonna work as it is a pretty simple design.

Here it is:
Bottom
Top silk
Top


nice! are you planning to do a run?


Not right now. Maybe if there is enough interest I can order a few boards but I have to test it first and I don't have the time right now.
horstronic
I finally had the time to build it. Here's the result:




It works pretty nice It's peanut butter jelly time!
The only thing you need to keep in mind when adjusting the outputs is that this circuit doesn't have offset trimmers, so you have to measure the offset first. It's not very high (+- 5mV on my build) but it can affect the results if you don't do it.
So here's what I did:
Leave the input unconnected and measure its voltage. Then measure the voltage on the output you want to adjust. Subtract the input voltage from the output voltage. That's your offset.
When you trim the output now, always add that to the voltage you measure.

Here's an example in case my explanation was too confusing (sorry, I'm not a native speaker):

First measurement with nothing connected to the input:
Input Voltage: +1mV
Output Voltage: +5mV

Output - Input = 4mV = Offset

Now connect the Input to a voltage source (I used a CVP). You can use any voltage, let's say we use 5V.
Measure the output voltage and adjust it to be like this:

Output = Input + Offset
Output = 5V + 4mV = 5.004V

Check if you get the same results in all voltage areas.
You're done.
horstronic
I'm thinking about doing a little run of PCBs/Panels for this.
Mostly because I need some more for myself and I want to make some experiences in that area as I'm planning to dive deeper in making my own modules.
So this is kind of a non-profit thing, a set of both will cost something around 10€. Panels will be made of black PCB material.
I improved the PCB design a bit, it's gonna be panel mounted, so no more wiring.
Would there be any interest in this?
Ginko
I would be interested, can you get it to 4hp?
Synthsense
I would be interested in something like 8 PCBs, maybe more, but I also think the panel should be squashed to 4HP

Nice project, there aren't many Buffered Multiples going around Muff nowadays, I have a Polyphonic Modular project in mind that would need a good quantity of those modules

Cheers Guinness ftw!
horstronic
Yes, I'm trying to make it 4HP, that's my plan anyway.
I'm pretty shure it should be possible, but I need to check it out before I can say that for shure.

I'm using these jacks:
http://www.thonk.co.uk/shop/pj302m/
Has anybody used them before and can tell me how much space they need, measured from the middle to the end of the pins?



It should be something between 9.5-11mm, I guess, but it's hard to tell.

To make a 4HP panel possible, it mustn't be more than 10mm, but guess it's doable by making a thin PCB and cutting off the legs.

Edit: BTW, I'm also open to suggestions for different right angled jacks!
roglok
i'm still interested as well.

however, i'd prefer separate 1>3 PCBs over a single dual PCB for more flexibility. but probably that's just me. if possible, please include mounting holes (at least two) for those who fashion their own panel designs.

Give somebody an inch, and he will take a mile.

oops
roglok
also, regarding your panel design: i would make it clear what is input and what is output. right now it looks like a passive mult. and also consider a normalling option. sorry i can't help with the jacks...
horstronic
roglok wrote:

however, i'd prefer separate 1>3 PCBs over a single dual PCB for more flexibility. but probably that's just me. if possible, please include mounting holes (at least two) for those who fashion their own panel designs.


I don't want to do seperate PCBs, but maybe I can make it possible to cut the PCB in half and include a power connector on both sides.
Mounting holes are not a problem.

Quote:
also, regarding your panel design: i would make it clear what is input and what is output. right now it looks like a passive mult. and also consider a normalling option. sorry i can't help with the jacks...


Actually this panel was designed to show the inputs and outputs, you just can't see it because I originally designed it for jacks with knurled nuts. The hex nuts are just too big. Here's how it should've looked like:


Normalling is a good idea, I will include that!
roglok
horstronic wrote:
roglok wrote:

however, i'd prefer separate 1>3 PCBs over a single dual PCB for more flexibility. but probably that's just me. if possible, please include mounting holes (at least two) for those who fashion their own panel designs.


I don't want to do seperate PCBs, but maybe I can make it possible to cut the PCB in half and include a power connector on both sides.


CGS style! That would be great!

Quote:

Mounting holes are not a problem.


thumbs up

Quote:

Actually this panel was designed to show the inputs and outputs, you just can't see it because I originally designed it for jacks with knurled nuts. The hex nuts are just too big. Here's how it should've looked like:


thumbs up

Quote:
Normalling is a good idea, I will include that!


thumbs up
SlowNova
Throwing another design in the mix. The schematic for Mutable Instruments Links is up on github:

https://github.com/pichenettes/eurorack/tree/master/links/hardware_des ign/pcb

The 1 to 3 section can be built with a single TL074, and the LED section could be replaced to make it a 1 to 4.

bartleby
roglok wrote:
i'd prefer separate 1>3 PCBs over a single dual PCB for more flexibility.

+1

horstronic wrote:
maybe I can make it possible to cut the PCB in half and include a power connector on both sides.

thumbs up

horstronic wrote:
Yes, I'm trying to make it 4HP, that's my plan anyway.

thumbs up

horstronic wrote:
I'm using these jacks:
http://www.thonk.co.uk/shop/pj302m/
Has anybody used them before and can tell me how much space they need, measured from the middle to the end of the pins?

i am currently on a vacation far away from my modular, so i can't provide any measurements. but 4ms uses those in their clocker modules (rcd and scm), which are 4hp.

horstronic wrote:
BTW, I'm also open to suggestions for different right angled jacks!

can't you just use regular kobiconn clones and mount them sideways on the pcb? i've been told that people have used them that way on their 4ms clocker modules as replacements for the ones you linked to.

if you can do it 4hp and separable twin pcb, i think i'm in for 2x full pcb+panel sets and another 3x just the double pcb...
daverj
It's not from the same manufacturer, but an identical looking jack, with all dimensions shown in the Thonk diagram the same, shows a measurement of 5.5mm from the center of the hole to the pcb surface. That would mean 10mm from the center of the hole to the tips of the pins.

Assuming that matches these, you would either have to cut the tips of the pins off, or place the holes off center to use them in a 4HP panel.

Kobiconn makes a connector that also looks like the Thonk one and has the same 10mm from hole to pin tips. So I'm going to guess the Thonk ones measure the same.

It's not so cheap, but this style:

http://www.mouser.com/ProductDetail/Switchcraft/35RAPC2AHN3/?qs=sGAEpi MZZMv0W4pxf2HiV3fTUvSc3cBdmeYlygX9eGc%3d

It sits lower on the board and is only 5.5mm from the hole to the pin tips. There are cheaper Kobiconn ones in that style, but they are stereo. Though you could still use them and just leave the ring contact disconnected.
mxmxmx
horstronic wrote:
I'm using these jacks:
http://www.thonk.co.uk/shop/pj302m/
Has anybody used them before and can tell me how much space they need, measured from the middle to the end of the pins?


i have a bunch of them here -- i'd say (using my geodreieck) it's 9.5mm, centre to tip. they only work properly with really thin panels though, 1.6mm or so.
horstronic
daverj wrote:
It's not from the same manufacturer, but an identical looking jack, with all dimensions shown in the Thonk diagram the same, shows a measurement of 5.5mm from the center of the hole to the pcb surface. That would mean 10mm from the center of the hole to the tips of the pins.

Assuming that matches these, you would either have to cut the tips of the pins off, or place the holes off center to use them in a 4HP panel.

Kobiconn makes a connector that also looks like the Thonk one and has the same 10mm from hole to pin tips. So I'm going to guess the Thonk ones measure the same.

It's not so cheap, but this style:

http://www.mouser.com/ProductDetail/Switchcraft/35RAPC2AHN3/?qs=sGAEpi MZZMv0W4pxf2HiV3fTUvSc3cBdmeYlygX9eGc%3d

It sits lower on the board and is only 5.5mm from the hole to the pin tips. There are cheaper Kobiconn ones in that style, but they are stereo. Though you could still use them and just leave the ring contact disconnected.


mxmxmx wrote:

i have a bunch of them here -- i'd say (using my geodreieck) it's 9.5mm, centre to tip. they only work properly with really thin panels though, 1.6mm or so.


Thanks guys, I will just try it out. Cutting the legs should be ok I guess, otherwise it will still be possible to use PJ301BMs or something like that. It's not that elegant as you would have to wire one connection per jack, but it's still doable. Maybe I can also put in an extra pad with a thinner hole per jack to make it easier to connect them with a piece of wire.
My OCD doesn't allow me to put the holes off center Dead Banana

I will update the layouts and put all the information in an order thread soon.
Dogue
I might be interested if you can get it down to 4hp. You might want to credit Dave for the circuit design.
horstronic
Dogue wrote:
I might be interested if you can get it down to 4hp. You might want to credit Dave for the circuit design.


Absolutely!
pmsr
I am interested, more so if it is 4hp.
urbanscallywag
mxmxmx wrote:
horstronic wrote:
I'm using these jacks:
http://www.thonk.co.uk/shop/pj302m/
Has anybody used them before and can tell me how much space they need, measured from the middle to the end of the pins?


i have a bunch of them here -- i'd say (using my geodreieck) it's 9.5mm, centre to tip. they only work properly with really thin panels though, 1.6mm or so.
This style of jack is available with different bushing lengths. Ours are 5mm long (same as the vertical jack). I use them with 2mm panels.

horstronic
@ you guys who want a PCB that can be cutted in half:
Here's my first attempt on this:

I just made some big pads with oval holes, I think that should work. Should be pretty easy to cut it with a dremel or something like that. Is this the way you want it or do you prefer to cut the board on your own?
mxmxmx
urbanscallywag wrote:
mxmxmx wrote:
horstronic wrote:
I'm using these jacks:
http://www.thonk.co.uk/shop/pj302m/
Has anybody used them before and can tell me how much space they need, measured from the middle to the end of the pins?


i have a bunch of them here -- i'd say (using my geodreieck) it's 9.5mm, centre to tip. they only work properly with really thin panels though, 1.6mm or so.
This style of jack is available with different bushing lengths. Ours are 5mm long (same as the vertical jack). I use them with 2mm panels.


oh, i'm sure they're available with 5mm bushing - i was referring to the ones linked above. the batch i got from thonk came with 3.5mm, which makes them unusable for many purposes (most blanks, acrylic etc).

@horstronic: i don't quite get the point of those slots. or, i guess, depending on where you get the pcbs made: wouldn't it make more sense to put one mult on a single board (<50mm) to be begin with rather than paying for the bigger size (100mm), just to break them apart again?
horstronic
mxmxmx wrote:

@horstronic: i don't quite get the point of those slots. or, i guess, depending on where you get the pcbs made: wouldn't it make more sense to put one mult on a single board (<50mm) to be begin with rather than paying for the bigger size (100mm), just to break them apart again?


Actually it's cheaper to do it this way, at least at the supplier I'm ordering.
Also I think most people may want to use the PCB in one piece (including me), which is better if you want to have a 2x 1->3 multiple, because you don't have to wire the two PCBs together.
I don't like this too much either, but I think it's a good compromise.
roglok
horstronic wrote:
@ you guys who want a PCB that can be cutted in half:
I just made some big pads with oval holes, I think that should work. Should be pretty easy to cut it with a dremel or something like that. Is this the way you want it or do you prefer to cut the board on your own?


Looks good to me! Thanks for taking this into account.
Ambriant
A great book for building simple circuits, like a non-inverting buffer for your mults module is the Make book by I think Ray Wilson at MFOS. You can download it from Amazon. I'd highly suggest it. Very useful.

I've built buffers and such from the information inside. They work great. It's a great reference to have for modular synth applications.
home_listening
I have an untested layout for Daverg's buffered mult if anyone wants a copy of the gerbers/eagle files.

Mancy bean
Ambriant, this one?

http://www.amazon.co.uk/Make-Analog-Synthesizers-Ray-Wilson-ebook/dp/B 00D3VEKH2/ref=sr_1_1?s=digital-text&ie=UTF8&qid=1404411806&sr=1-1&keyw ords=Make+Wilson
ersatzplanet
Ok - Now lets see the next step - Combining these circuits into a Buffered Matrix. Essentially each row would be a buffered mult that mixes with other rows for each column. The advantage of the standard matrix but without the mad crosstalk and level problems of a passive matrix.
horstronic
ersatzplanet wrote:
Ok - Now lets see the next step - Combining these circuits into a Buffered Matrix. Essentially each row would be a buffered mult that mixes with other rows for each column. The advantage of the standard matrix but without the mad crosstalk and level problems of a passive matrix.


That's a great idea Guinness ftw!
Do it!
horstronic
I made an order thread here:
https://www.muffwiggler.com/forum/viewtopic.php?t=116810

Could everybody who wants PCBs or panels write it there again?
That would make it a lot easier for me.

Thanks!
LeftyLogic
ersatzplanet wrote:
Ok - Now lets see the next step - Combining these circuits into a Buffered Matrix. Essentially each row would be a buffered mult that mixes with other rows for each column. The advantage of the standard matrix but without the mad crosstalk and level problems of a passive matrix.

So it's not exactly what you suggested, but your comment certainly piqued my interest, so I spent the afternoon drawing up a schematic for a sort of matrix unity mixer/mult thing!



What it does is combine a signal from each row with a signal from each column, giving 16 possible combinations: output A1 is a mix between the inputs of Row A and Column 1, output B3 is a mix between the inputs of Row B and Column 3, so on and so forth. You can also use it as four individual 1-to-4 buffered mults by plugging a signal in to each row, but leaving each column unconnected. (Or vice versa.) But where this module really starts to get interesting is when you plug one of the outputs into another input. For example, you can take the output at A1, and plug it into input B, which (if I'm imagining this right) will cause output B1 to be another mix of A and 1, but with 1 being at double the amplitude! In theory this chaining could be continued, increasing the gain by up to four times. Also, with A1 plugged into B, B2 will be a mix between A, 1, and 2, so there are a ton of possibilities for mixing. Also included is a mixer summing each row input, and another for each column input.
Now, obviously since I just drew this up today I haven't had a chance to build it, so I can't be 100% sure that it'll work as I'm hoping it will. If anyone sees any glaring errors, please point them out! Guinness ftw!
(Side note RE schematic nomenclature: all quad opamps should be TL074s, I just used lm324s on the inputs because the annotation was all screwed up otherwise)
horstronic
LeftyLogic wrote:
ersatzplanet wrote:
Ok - Now lets see the next step - Combining these circuits into a Buffered Matrix. Essentially each row would be a buffered mult that mixes with other rows for each column. The advantage of the standard matrix but without the mad crosstalk and level problems of a passive matrix.

So it's not exactly what you suggested, but your comment certainly piqued my interest, so I spent the afternoon drawing up a schematic for a sort of matrix unity mixer/mult thing!


What it does is combine a signal from each row with a signal from each column, giving 16 possible combinations: output A1 is a mix between the inputs of Row A and Column 1, output B3 is a mix between the inputs of Row B and Column 3, so on and so forth. You can also use it as four individual 1-to-4 buffered mults by plugging a signal in to each row, but leaving each column unconnected. (Or vice versa.) But where this module really starts to get interesting is when you plug one of the outputs into another input. For example, you can take the output at A1, and plug it into input B, which (if I'm imagining this right) will cause output B1 to be another mix of A and 1, but with 1 being at double the amplitude! In theory this chaining could be continued, increasing the gain by up to four times. Also, with A1 plugged into B, B2 will be a mix between A, 1, and 2, so there are a ton of possibilities for mixing. Also included is a mixer summing each row input, and another for each column input.
Now, obviously since I just drew this up today I haven't had a chance to build it, so I can't be 100% sure that it'll work as I'm hoping it will. If anyone sees any glaring errors, please point them out! Guinness ftw!
(Side note RE schematic nomenclature: all quad opamps should be TL074s, I just used lm324s on the inputs because the annotation was all screwed up otherwise)


If it works, this is gonna be awesome!
Sounds like a very nice tool.
LeftyLogic
horstronic wrote:

If it works, this is gonna be awesome!
Sounds like a very nice tool.

Thanks! Mr. Green I can't see why it wouldn't work, but I'll probably build a prototype in the next couple of weeks just to make sure.
daverj
ersatzplanet wrote:
Ok - Now lets see the next step - Combining these circuits into a Buffered Matrix. Essentially each row would be a buffered mult that mixes with other rows for each column. The advantage of the standard matrix but without the mad crosstalk and level problems of a passive matrix.


Are you talking about a matrix mixer, or matrix switcher?

If it's a mixer, then the fine tuning of signal level can be skipped, since the mixer pot gives adjustable levels already. Just set the first stage gain to more than 1 and attenuate as needed in the mix.

If a matrix switcher (no pots), then you would still want the fine tuning for the gain so that exact pitch scales match input to output, even though two inputs mixed would change the offset of the output pitch voltage.

With either one you could get rid of the output resistor on the stage driving the matrix, since there is not going to be much capacitance being driven. (saves one resistor per driver)
mikecameron
wow, this got out of hand. I like it!
euromorcego
maybe someone can enlighten me:

Quote:
The schematic for Mutable Instruments Links is up on github: The 1 to 3 section can be built with a single TL074, ...

So the TL074 is a suitable replacement for the OPA4171 that is shown in the schematics. And (I really have no clue, this is mainly out of curiosity): why does the Mutable Instruments achieve its goal without the trimmer? Also it does not use any resistor in the feedback.

I read through the early parts of the thread but it didn't seem covered. Probably I should google first, but i would really be interest to know.
SlowNova
euromorcego wrote:
So the TL074 is a suitable replacement for the OPA4171 that is shown in the schematics. And (I really have no clue, this is mainly out of curiosity): why does the Mutable Instruments achieve its goal without the trimmer? Also it does not use any resistor in the feedback.

I read through the early parts of the thread but it didn't seem covered. Probably I should google first, but i would really be interest to know.


No resistor in the opamp feedback is called a "Voltage Follower", here is a pretty good explanation: Voltage Follower

Quote:
The voltage follower with an ideal op amp gives simply
Vout = Vin
but this turns out to be a very useful service, because the input impedance of the op amp is very high, giving effective isolation of the output from the signal source. You draw very little power from the signal source, avoiding "loading" effects. This circuit is a useful first stage.

The voltage follower is often used for the construction of buffers for logic circuits.



I didn't mean to imply that the TL074 is a all purpose replacement for the OPA4171, but in this "links" topology I either would work fine. They are both general purpose opamps, although the TL074 will be slower and noisier. A LM348 would probably also be fine.

I think people tend to have the TL07X lying around since they are cheap, "good enough" and used in a lot of other diy circuits.
pmsr
SlowNova wrote:
I think people tend to have the TL07X lying around since they are cheap, "good enough" and used in a lot of other diy circuits.


Not to mention the OPA4171 doesn't come in DIP. The TL07x family is the de facto standard for opamps for this type of DIY circuits when you have to deal with both audio and cv in the same path. I call it the Goldilocks opamp. smile
horstronic
daverj wrote:
There's many ways to design a buffered mult. If I were designing one for my own use, this is probably what I would do:



The first stage has 7 percent gain. The trimpots ideally give +/-7% adjustment. With 1% resistors, the gains could be off by up to about +/-4.5%. With a 10% trimpot the adjustment range could be off by another 1.5%-2%. So the adjustment range of the trim will still cover all possibilities.

The feedback cap values are based on a printed circuit board. With point to point hand wiring or stripboard I might double those.

Since all amps are on the same die, if their offset voltages are similar then using two inverting amps in series may provide some cancellation of that voltage.

I didn't put in bias controls because 1) to make it temperature and supply voltage stable requires a bunch of extra parts, and 2) I am assuming the places these outputs go already have a bias control in the form of the frequency pot on a VCO or filter.

I did this using a Euro power connector and voltages. It would be identical except for the connector for a +/-15 system.

The two Schottky diodes provide power cable reversal protection and their small voltage drop won't effect the operation of the circuit.


One thing that just came to my mind:
The input stage has 7% gain. So if I plug in 10V, I get 10,7V.
According to the datasheet, the TL7X has a maximum peak output voltage of around 10,5V at a supply voltage of +/-12V. This would mean that after the second stage we will only have about 9,8V and that would be the maximum voltage output.
I checked it on my prototype and the maximum output is even lower, around 8,8V (I think because 10,5V is the maximum peak output, so the normal maximum voltage can be lower, right?). Damn, I never recognized that!
It's not too bad, as you normally don't have CVs in that range, but it could be a problem when it comes to gates.
So wouldn't it be better to make the first stage a voltage follower and have a gain at the second stage?
Or is there a better solution?
daverj
That's a simple change by just changing the value of the feedback resistors. You'll have to do the math to see if the resistor to ground on the trimpots needs changing too (after you pick the feedback resistor for the output sections). You want the trimpot to have enough range to cover all possibilities, without so much range that you're wasting a lot it.

The TL07x have a "typical" output high voltage of 1.5v below the rail, but worst case is about 3v below.
horstronic
daverj wrote:
That's a simple change by just changing the value of the feedback resistors. You'll have to do the math to see if the resistor to ground on the trimpots needs changing too (after you pick the feedback resistor for the output sections). You want the trimpot to have enough range to cover all possibilities, without so much range that you're wasting a lot it.

The TL07x have a "typical" output high voltage of 1.5v below the rail, but worst case is about 3v below.


Ok, that's what I was thinking. I just wanted to make shure I'm not messing it up.
Thanks again applause
euromorcego
Quote:
It's not too bad, as you normally don't have CVs in that range, but it could be a problem when it comes to gates.

Gates, by definition, shouldn't be too picky when it comes to the precise value. It is other CVs to worry about, there are some that extend in the 10V range, for example to select waveforms in some of the talking synths (maybe also some of the wavetable oscillators).
calaveras
This looks fun, I was going to buy a retail buffered mult anyway, but I think I have all the parts to just build this out on perfboard. The hard part is going to be making a panel!
(for me at least)
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