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Trevor Marshall VCA/Ring modulator - Eurorack
MUFF WIGGLER Forum Index -> Music Tech DIY Goto page 1, 2  Next [all]
Author Trevor Marshall VCA/Ring modulator - Eurorack
whoop_john
I have started work on the ETI VCA, which I am calling the Trevor Marshall VCA/RING MOD, out of deference to the designer rather than the magazine.

Trevor worked with Kim Ryrie, founder of ETI and later the father of the Fairlight, so it's just possible it should be the Marshall/Ryrie VCA/RING MOD.

However, http://www.trevormarshall.com/eti.htm does not credit Ryrie with any circuit design involvement.

I am starting this thread to establish whether there is any interest in a PCB for this. I may also need some advice from the experts in due course.

Here is a new scan of the circuit, upon which I have placed the component values. On my PCB I am also adding an input pot for both inputs and a voltage follower buffer for each.



whoop_john
The lack of enthusiasm speaks volumes. It's a versatile little module, being both a VCA and ring modulator in one package - I thought it might garner more interest, but what do I know?

I guess you all just built the 100m module using the same chip, which is only a ring mod.
sammy123
I'm interested. I have the jacks for your design so that is a bonus too. Any plans for sharing a panel design or selling panels?
whoop_john
sammy123 wrote:
I'm interested. I have the jacks for your design so that is a bonus too. Any plans for sharing a panel design or selling panels?

The general idea is to get some interest and if there is enough, to manufacture a PCB.

Front panels are an issue, I know. What is the best way of getting them made? I have no problem with supplying accurate artwork. From what I understand, front panels are the most expensive part of any DIY module.
sammy123
I really can't say. I've never done a run of panels. I've used .fpd or .svg files that others have provided and had them made at Ponoko or Front panel Express here in the US.
Larrea
Actually I'm very interested, especially as a pair with the Maplin/Transient module; I think I said so in that thread.

I'd love to see this develop.
whoop_john
Larrea wrote:
Actually I'm very interested, especially as a pair with the Maplin/Transient module; I think I said so in that thread.
You did indeed.
KSS
You can make this fit in shallower cases by moving the 1K, 100K above the 3x12K upward into the space between the Switch and the Sig In jack. The trace then moves and becomes shorter and more direct which means the 4.7uF cap to their right can also slide upwards into that space. Everything else below now can also slide upwards.
Slide Mr. Neuman's head and character reference up and if you either rotate the Power input components and hdr 90 like many doepfer (which is what I would do) or just slide them up as well between the Mtg holes and move your module title to above or near Miscreant you can shave .250" (6mm) without sacrificing ease of assembly.

May not seem much, but in this era of shallow cases even a perception of too deep can hurt your sales prospects.

Personally I'd rather have sigin and sigout next to each other with CV above or below. With these changes all three extra wiring pads could be at the extreme left for those doing non-Euro builds. A 4 to 6 pin .100 hdr there (3 sets 2pins with GNDs) would be a nice MOTM style touch.

Be careful with your 5 hole pot footprint. The middle lug (wiper) of an alpha 16 style pot will often short to the two pads that will be next to it. If you offset the 3 inner .100 pins away from the PCB edge .100, and add a new middle pin for the .200 alpha type footprint, this is solved. Pots with .100 spacing have pins farther from their face so it all works out.
KSS
One more thing. There's no good reason not to have all the ElCaps face the same way. + down in this case. Even works with the 90 rotated power HDR and parts.
Can't hurt, is easier to support DIY and adds a pro touch.
KSS
Sorry, one more. You can swap the two upper 074 sets of pins and components. The 4148 and 12K will bridge the pot wiper and you can eliminate the trace going between the IC pads.

I didn't check any of this for agreement with the schematic. It's all based on my assumption that your layout is already electrically correct.
KSS
whoop_john wrote:
The lack of enthusiasm speaks volumes. - I thought it might garner more interest, but what do I know?

Saw a similar comment by Jorg recently.
It's Spring. Summer is coming, School is ending. Thoughts are moving outdoors. Happens every year. Add to that the pure hell MW has been to use getting logged out and you shouldn't be surprised that there's a dip in activity and response here. It's not personal. Patience is a good thing this time of year. Thank you for the Trevor Marshall link!
niicholas
I'm interested and would order a board if you make them w00t
fitzgreyve
I have these in one of my synths from the early 80's, the only thing I would have advised I see that you've already done - made RV1 a multiturn preset - I recall that they are slightly finicky at getting minimum breakthrough in VCA mode.
whoop_john
KSS wrote:
You can make this fit in shallower cases by moving the 1K, 100K above the 3x12K upward into the space between the Switch and the Sig In jack. The trace then moves and becomes shorter and more direct which means the 4.7uF cap to their right can also slide upwards into that space. Everything else below now can also slide upwards.
Slide Mr. Neuman's head and character reference up and if you either rotate the Power input components and hdr 90 like many doepfer (which is what I would do) or just slide them up as well between the Mtg holes and move your module title to above or near Miscreant you can shave .250" (6mm) without sacrificing ease of assembly.

May not seem much, but in this era of shallow cases even a perception of too deep can hurt your sales prospects.

Personally I'd rather have sigin and sigout next to each other with CV above or below. With these changes all three extra wiring pads could be at the extreme left for those doing non-Euro builds. A 4 to 6 pin .100 hdr there (3 sets 2pins with GNDs) would be a nice MOTM style touch.

Be careful with your 5 hole pot footprint. The middle lug (wiper) of an alpha 16 style pot will often short to the two pads that will be next to it. If you offset the 3 inner .100 pins away from the PCB edge .100, and add a new middle pin for the .200 alpha type footprint, this is solved. Pots with .100 spacing have pins farther from their face so it all works out.

Thank you for the constructive comments, much appreciated. I have tried to take on-board your suggestions. I have shaved 6.5mm off the height, which is now 43.5mm.

I wish I knew why my uploaded pictures always look so horrible and fuzzy - they are clear as a bell when I send them.

masterofstuff124
this interests me!

im down for a PCB/panel combo!
whoop_john
masterofstuff124 wrote:
this interests me!

im down for a PCB/panel combo!

Can somebody put me straight on the best way to produce panels please. It seems to be the big problem area - the panels end up costing more than the PCB and components.

I am trying to provide things for cheap. Why? Because I am a cheapskate. I cannot afford major investment in what are, for me, toys.

I appreciate that many of you want a Gucci job, Schaeffer etc., but I cannot order and stock this for people in advance. I am happy to provide artwork.

Cheapest method I can think of is 2mm acrylic with a brushed ali custom printed sticker, but how durable this is, I have no idea. I may try it out soon. I am also considering using laser-cut acrylic, which can then be used as a routing template for an ali panel. That still leaves the problem of how to add artwork to the front.

I wish I still had my silkscreening equipment.
masterofstuff124
pcbway.
aluminum pcb panels.
will be something like $5 a panel.

got to design the panel in PCB software but the results are very nice.
whoop_john
masterofstuff124 wrote:
pcbway.
aluminum pcb panels.
will be something like $5 a panel.

got to design the panel in PCB software but the results are very nice.

05 single-sided panels 128.5mm x 5HP are $60 - $12 each
10 single-sided panels 128.5mm x 5HP are $63 - $6.3 each
20 single-sided panels 128.5mm x 5HP are $71 - $3.55 each

This is at cost, with nothing to cover any losses or contingencies such as damage or cost of posting on to final destination.
ricko
Nice to see Dr Marshall's designs getting some love.

I have an ETI 4600 (linear CV and keyboard fatally flawed designs) and I really think you are better off using a high quality modern op-amp in the audio chain instead of the 301a (or even the tl074), which is more of a noise generator than an op-amp. Especially the mixers, the output and the output buffers of modules. So IC3 of this VCA.

I think this is generally true for any synth: you want low noise opamps on any ungated audio signal (I.e all down the path from the last VCA to the final output) so there is silence when there is no note. And also for mixers where you have multiple opamp in parallel. Internally, earlier in the signal chai , begore gating/enveloping noise is not so much a problem.

Rick
KSS
Looks nice. Good to know you found it helpful. Always an unknown how someone will take comments.
Looks like the 33uF cap near the module title resisted rotation. Measuring pots instead of just trusting memory shows that the alpha 3 pin line should be 150 mils from the board edge and the .100 spaced 3 pins behind will be 225mils from the edge. This will put the alpha 16mm style mtg face plane at the PCB edge. The usual star washer behind the panel will be enough spacer.
I miss Trevor Marshall's name and it looks it will still fit above the VCA/Ringmod label?
Standard Doepfer Pot spacing is 20mm which is close enough that 800 mils can be used. FC-UK uses 700 to fit 6 pots vertically so maybe that's why you've used 700mils. There is room to drop the 2nd pot 87 or 100mils toward the switch which will please the Doepfer crowd and maybe disappoint those with much Freq Central.
Finally, if you always add a fourth pin to trimpot/preset footprints the parts that fit is vastly expanded. 3 inline, 4th middle pin 100mils offset, for a T shape. Link the middle two pins and many more trims will work. Most trims with only 3 inline pins have those pins nearer one face than your footprint shows. Shifting them to add a 4th pin will actually put the trim closer to your silkscreen of it.

I still like the idea of 6 pins (3 GNDs for RG174 coax to the jacks) across the bottom for the MOTM DIY. But you could easily add three two pin .100 footprints to allow this mid board and gain the added advantage of room for holes to ziptie the RG174. You could put pads for OUT and VC between the jacks where their traces already exist. And only a GND pin next to the existing IN pin (Slide 100K,12K pair up another 100mils). Little things like this make your PCB more easily useful to more of the SDIY population. Since you've already done the power and mtg holes, these might be worthwhile too. A few extra holes will add nothing to the cost of a board with so few already.

You may rather put the added non-Euro format pads under the Jacks since both wouldn't normally be used at the same time and having them unused may lead to questions. Never underestimate the time support of a project will take and therefore do your best to minimize it. You're going to have questions either way. So do what makes sense for you. I'd have them in place so that they may be used in addition to the jacks.

The line you have between the 0.47uF cap and its label might better be above the + for the PWR connector. If the label is moved up towards the 8K2, the line will no longer visially separate the + from the Connector.

You asked about front panels. The bitter truth is that there is no really good answer unless you make more than a few. Even your listing of the PCB prices shows this. Some have found that PCBs as front panels work great and others have found poor print quality and scratching acceptable in a PCB but not when that PCB is a Panel. So be clear with both the PCB maker you choose and the customers if you choose this route. Ask Andrew NLC and others who seem to successfully go this way.

First, accept that front panels simply are going to be costly relative to the rest. But also accept that having a front panel available is going to make your project much more desirable. Even those buying to repanel for another format will be drawn in by a front panel layout.
At an absolute minimum, provide a drawing of a suggested panel layout with dimensions if these matter. As they do in the Eurorack version. Make a PCB panel layout and an FPD. Even if you don't actually offer the panels having these will help your sales. But do try to figure a way to offer panels if you can. It really will make a difference in your return.
Next, do everything you can to increase the number of buyers so that the price of the front panel comes into reasonable range. Consider a call to Synthcube and/or Thonk to see if going that way makes sense.
Third, accept that others might feel less inhibited by a price you feel is too high. Considering their options, this makes sense. So find out what the price needs to be and charge what makes sense so that you can do another SDIY offer if you want. SDIY is always going to be filled with vocal critics of your price, regardless of what price you list. So be fair, but don't bow to the complaints in a way that is unfair to yourself. Truth is, panel prices suck. But despite the complainers, they *are* fair. And they are also the key to your success.
whoop_john
KSS wrote:
Looks nice. Good to know you found it helpful. Always an unknown how someone will take comments.

Someone who takes the trouble to comment in detail deserves consideration. Thank you. I am no Prima Donna. It is all most useful information for me.

Some of your comments are coming from the aspect of me perhaps marketing this stuff commercially and thus needing to be as versatile as possible. My approach is low cost, Eurorack, and to disfray my own costs by selling any spare inventory that accumulates. If I factored in time to layout PCBs and get them produced, it would never be an economic exercise unless I had a view to producing 100s.

Your suggestions can be incorporated and if they appeal to the non-euro brigade, then why not do them?

KSS wrote:
Looks like the 33uF cap near the module title resisted rotation.

Indeed it did. It was a surly little bugger from the outset. Personally I didn't like its attitude at all. It'll move, given a big enough crowbar.

KSS wrote:
Measuring pots instead of just trusting memory shows that the alpha 3 pin line should be 150 mils from the board edge and the .100 spaced 3 pins behind will be 225mils from the edge. This will put the alpha 16mm style mtg face plane at the PCB edge. The usual star washer behind the panel will be enough spacer.

I'll look into this further. I ordered the 3.5mm jacks but was sent ones without the mounting thread and nut. Have ordered more. These need to be in line with the pot and switch. I may change the switch to a 90º version - toggle up and down rather than across.
KSS wrote:
I miss Trevor Marshall's name and it looks it will still fit above the VCA/Ringmod label?

It didn't fit anywhere, so I shortened it. I may try typing it in a smaller font size.

KSS wrote:
Standard Doepfer Pot spacing is 20mm which is close enough that 800 mils can be used. FC-UK uses 700 to fit 6 pots vertically so maybe that's why you've used 700mils. There is room to drop the 2nd pot 87 or 100mils toward the switch which will please the Doepfer crowd and maybe disappoint those with much Freq Central.

Here I want to be somewhat selfish, as all the modules I have been producing for my own amusement - about 8 or so, so far - have been on the 700mil pitch, for the reason you stated, that 6 will fit vertically in Eurorack. It makes more sense to me.

KSS wrote:
Finally, if you always add a fourth pin to trimpot/preset footprints the parts that fit is vastly expanded. 3 inline, 4th middle pin 100mils offset, for a T shape. Link the middle two pins and many more trims will work. Most trims with only 3 inline pins have those pins nearer one face than your footprint shows. Shifting them to add a 4th pin will actually put the trim closer to your silkscreen of it.

There I was in bed last night, pondering life, as one does, and I remembered a build I did of someone's PCB - it was a 'scope clock as you ask - and the preset pins were offset and I had to kludge it. So yes this is a good idea, although the inline presets do seem more prevalent these days.

KSS wrote:
I still like the idea of 6 pins (3 GNDs for RG174 coax to the jacks) across the bottom for the MOTM DIY. But you could easily add three two pin .100 footprints to allow this mid board and gain the added advantage of room for holes to ziptie the RG174. You could put pads for OUT and VC between the jacks where their traces already exist. And only a GND pin next to the existing IN pin (Slide 100K,12K pair up another 100mils). Little things like this make your PCB more easily useful to more of the SDIY population. Since you've already done the power and mtg holes, these might be worthwhile too. A few extra holes will add nothing to the cost of a board with so few already.

I shall have to ponder this more to understand it fully.

KSS wrote:
You may rather put the added non-Euro format pads under the Jacks since both wouldn't normally be used at the same time and having them unused may lead to questions. Never underestimate the time support of a project will take and therefore do your best to minimize it. You're going to have questions either way. So do what makes sense for you. I'd have them in place so that they may be used in addition to the jacks.

I placed the dual purpose pins as per the Bissel PCB I just made. People suggested I do it this way

KSS wrote:
The line you have between the 0.47uF cap and its label might better be above the + for the PWR connector. If the label is moved up towards the 8K2, the line will no longer visially separate the + from the Connector.

This was quite last minute. I am sure you are right, there is a better placement for the legend.

KSS wrote:
You asked about front panels. The bitter truth is that there is no really good answer unless you make more than a few. Even your listing of the PCB prices shows this. Some have found that PCBs as front panels work great and others have found poor print quality and scratching acceptable in a PCB but not when that PCB is a Panel. So be clear with both the PCB maker you choose and the customers if you choose this route. Ask Andrew NLC and others who seem to successfully go this way.

I do have someone in the UK who makes really lovely engraved panels and can do black anodised 2mm or natural anodised with black infill. The prices were too steep for my el-cheapo build, but I think the mileage of others may vary. The problem here for me was also the up-front cost of getting the person to buy in a sheet of the material in the first place. I can reactivate the dialogue I had with the person.

KSS wrote:
First, accept that front panels simply are going to be costly relative to the rest. But also accept that having a front panel available is going to make your project much more desirable. Even those buying to repanel for another format will be drawn in by a front panel layout.
At an absolute minimum, provide a drawing of a suggested panel layout with dimensions if these matter. As they do in the Eurorack version. Make a PCB panel layout and an FPD. Even if you don't actually offer the panels having these will help your sales. But do try to figure a way to offer panels if you can. It really will make a difference in your return.

Again your assumption is that I wish to make a return. I have no problem in supplying an accurate template or artwork for anything I do. I trained as an architect and earned my living for many years as a graphic designer. I can draw accurately. In fact I still do all of Kenton Electronic's artwork for their products, and also their advertising, although I am now crusty and ostensibly retired.

KSS wrote:
Next, do everything you can to increase the number of buyers so that the price of the front panel comes into reasonable range. Consider a call to Synthcube and/or Thonk to see if going that way makes sense.

At this point I maybe need to talk to Thonk, I think, about things that go thunk, to use some alliterative assonance.

KSS wrote:
Third, accept that others might feel less inhibited by a price you feel is too high. Considering their options, this makes sense. So find out what the price needs to be and charge what makes sense so that you can do another SDIY offer if you want. SDIY is always going to be filled with vocal critics of your price, regardless of what price you list. So be fair, but don't bow to the complaints in a way that is unfair to yourself. Truth is, panel prices suck. But despite the complainers, they *are* fair. And they are also the key to your success.

I do agree. I am not going for robustness myself, but many others want durability.

I got slightly burned on costs when I did a transistor tester PCB offer here on Muffs, I didn't build in any extra costs. Paypal conversion fees, increased postal charges and two losses in the mail taught me that it is necessary to build in at least some potential profit, or I lose out.

I noticed in selling the Bissel board how easily costs mount. The international shipping is just slightly more than I anticipated, but the profit I built in on the PCBs covers it. I wish the cost could have been lower, but if people are working and earning, then they probably shouldn't mind and the costs are really no more than buying a drink or two in a bar. It's all relative.
dubtoms
It's too bad my only 1496 is about to be used in Fitzgreyye's Roland-ish ring mod for Eurorack. I hope you'll sort the panel issue as I really want that envelope follower of yours ! hihi

As far as masterofstuff's suggestion of using PCBway aluminium panels goes, i haven't mentioned in the other thread that Philip who run the "Pusherman" group buys on Facebook managed to break down his "retail" price for small panels to around 2 or 3 British Pounds. I think the key here is larger numbers. He has worked on deals with a few circuit designers who promote their stuff here like Timo Rozendal and Maté Szabo where they get a cut of the profit for each boards sold through the group buy. Maybe that's a solution you are willing to consider.
dubtoms
There's also Julian aka the Beast who provides custom aluminium panels manufacturing service in the UK.

Check this thread for more info
whoop_john
dubtoms wrote:
…i haven't mentioned in the other thread that Philip who run the "Pusherman" group buys on Facebook managed to break down his "retail" price for small panels to around 2 or 3 British Pounds.

I am already part of the Pusherman group - I should pay more attention to it perhaps.

Julian's panels are £2 per HP, so for a 5 HP panel that is £10. It only includes pilot holes, all at 3.3mm. Is that what people want?
whoop_john
ricko wrote:
Nice to see Dr Marshall's designs getting some love.

I have an ETI 4600 (linear CV and keyboard fatally flawed designs)…

If you thought the 4600 keyboard was fatally flawed, the 5600S was worse, with its binary weighted semitones - great on paper, nightmare in the real world, through cumulative errors and offsets in the addition chain of op-amps.
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