matching transistors - DIY

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Synthiq
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Post by Synthiq » Sat Mar 17, 2018 2:35 pm

cyrdun wrote:What is weird is that my multimeter gives me changing random values when in DC mode and not connected to anything? Shouldn't it be 0mV too?
Your test leads can act as antennas and pick up 50/60 Hz noise large enough to noticeable on the lowest voltage range. I see it, too and it is much worse on a multimeter with >1Gohm input impedance. If it bothers you, disconnect the leads to see if the reading go to zero.

cyrdun
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Post by cyrdun » Mon Mar 19, 2018 12:10 pm

Synthiq wrote: Your test leads can act as antennas and pick up 50/60 Hz noise large enough to noticeable on the lowest voltage range. I see it, too and it is much worse on a multimeter with >1Gohm input impedance. If it bothers you, disconnect the leads to see if the reading go to zero.
I've disconnected the leads, it didn't change anything? Does it mean my multimeter is faulty for this function?
It gives me 9V all right though when I check on the two sides of the capacitor...

Synthiq
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Post by Synthiq » Mon Mar 19, 2018 12:52 pm

cyrdun wrote:I've disconnected the leads, it didn't change anything? Does it mean my multimeter is faulty for this function?
It does my a difference on my multimeter. You can try to generate a voltage below 400mV to test that specific range, for instance by dividing the 9V you have with a 100kohm and 1kohm resistor divider and see if you get a stable 90mV. If not, there is probably a problem with your multimeter.

cyrdun
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Post by cyrdun » Fri Mar 23, 2018 10:30 am

I've checked mi circuit, it seems ok to me, but well i'm a noob, maybe there is a mistake i've overseen?

Image
Image

Synthiq
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Post by Synthiq » Fri Mar 23, 2018 11:38 am

One simple test you can do is to remove one of the two transistors and see if you still measure 0mV. If this is the case, remove both transistors and measure the resistance between the two connections for the emitters to see if there is a short or if you see the correct 200kohm from the two 100kohm resistors in series.

cyrdun
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Post by cyrdun » Fri Mar 23, 2018 11:49 am

Gosh I am so stupid lol. I was measuring it the wrong way all along.
(I won't tell you how, even the stupidest way you could think about, it was stupider)
Now I have values like 0.6mV, 0.558mV, etc.
Seems more like it should be.
Thanks a lot Synthiq for the help, much appreciated :).

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Post by aabbcc » Wed Mar 28, 2018 6:39 am

So if I want to run this on a 9v battery or power supply (have a switching one that ranges up tp 12v) would I need to modify/change the resistor values? Don't have any euro gear.

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thresholdpeople
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Post by thresholdpeople » Wed Mar 28, 2018 6:43 am

If you're running the Dave Jones modification of Ian Fritz's circuit - it's mean to run off a 9 or 12v power source.

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kid303
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Post by kid303 » Wed Mar 28, 2018 7:13 am

No you should be ok

The original Ian Fritz post says its 10v but anything around there should be ok.

To be honest I've not built mine yet.

Just look at the start of the thread and you will get the info you seek.

I cant remeber off hand the details but its all there in the early part of this thread.

Take it easy

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Post by aabbcc » Wed Mar 28, 2018 7:24 am

thresholdpeople wrote:If you're running the Dave Jones modification of Ian Fritz's circuit - it's mean to run off a 9 or 12v power source.
Ah okey, I'm doing the one availble through oshpark

https://oshpark.com/shared_projects/XHWPvGBc
kid303 wrote:No you should be ok

The original Ian Fritz post says its 10v but anything around there should be ok.

To be honest I've not built mine yet.

Just look at the start of the thread and you will get the info you seek.

I cant remeber off hand the details but its all there in the early part of this thread.

Take it easy
Thanks, will check beginning of thread again :)

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thresholdpeople
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Post by thresholdpeople » Wed Mar 28, 2018 7:30 am

It looks like the oshpark board needs bipolar power, but I'm not personally familiar with that board.

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kid303
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Post by kid303 » Wed Mar 28, 2018 9:45 am

Yes the oshpark needs a bipolar supply so when you flip the switch it goes to the negative voltage.

If nothing else put some batteries in series or parallel, can never remember which is which, just look it up so you get a + and a minus.

I have a dc power supply and Im just gonna make a MOTM cable to hook up to an ATX computer bench top power thing for this job so i can have my dc power supply free, i have got one of those cheap kit things for about ten bucks with a variable power supply up to 12v, they are ok for something like this, the supply doesnt have to be critically spot on just in the ball park. At the end of the day you are reading the difference (if any).

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LektroiD
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Post by LektroiD » Thu Mar 29, 2018 12:26 pm

Have I missed the boat for the PCBs, or are orders still being taken?

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analogdata
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Post by analogdata » Mon Apr 02, 2018 6:13 am

I have three pcbs left made from the files found on midisizer.
Image

Image

$6+postage
(Also have the needed LM 4040 if you want it as well. $1,5 a piece)

Will be sent from Sweden.

Pm if interested.

:bananaguitar:

cyrdun
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Post by cyrdun » Sat Apr 14, 2018 12:01 pm

Hi
I'm using Dave Jones' tweak on Ian Fritz circuit. Hopefully I'm using it the right way now :D.
Still I have readings that don't make any sense to me : the values I read seem to slowly oscillate at the rate of 0.1 mV every 5 to 10 seconds. For the two transistors I am testing right now, the minimum and maximum seem to be 1.8mV and 3.3mV. The variations are quite smooth and it clearly follows a pattern, sinusoidal or triangular (no random jumps).
So I'm lost. I don't get what could cause these variations. And, needless to say, I can't match any transistor with that.
Any help and advice welcome,
Thanks in advance! :)

Alternatively, as I am slowly losing hope of doing it myself, where could I buy matched transistors for a fair price ?

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cygmu
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Post by cygmu » Sun Apr 15, 2018 1:02 am

cyrdun wrote:Hi
the values I read seem to slowly oscillate at the rate of 0.1 mV every 5 to 10 seconds. For the two transistors I am testing right now, the minimum and maximum seem to be 1.8mV and 3.3mV. The variations are quite smooth and it clearly follows a pattern, sinusoidal or triangular (no random jumps).
Don't they settle after a while? As they conduct current the transistors will heat up, presumably not quite at the same rate if they are not perfectly matched and at an identical temperature in the beginning. But it should settle.

cyrdun
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Post by cyrdun » Sun Apr 15, 2018 8:15 am

cygmu wrote: Don't they settle after a while? As they conduct current the transistors will heat up, presumably not quite at the same rate if they are not perfectly matched and at an identical temperature in the beginning. But it should settle.
Thanks for your answer.
However I've left the circuit powered for two hours or so and I still can see the values going back and forth between min and max values. :/

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Post by jimfowler » Mon May 07, 2018 8:32 pm

Just ordered a trio of boards from Oshpark and should have them within the week. If anybody in the USA needs one (or two) let me know. They'll be like 5 bucks shipped.

- Jim

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KlangGenerator
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Post by KlangGenerator » Tue May 08, 2018 4:23 am

I'd like a board from OSH Park, but am based in Europe. :help:

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emmaker
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Post by emmaker » Tue May 08, 2018 12:21 pm

cyrdun wrote:Hi
I'm using Dave Jones' tweak on Ian Fritz circuit. Hopefully I'm using it the right way now :D.
Still I have readings that don't make any sense to me : the values I read seem to slowly oscillate at the rate of 0.1 mV every 5 to 10 seconds. For the two transistors I am testing right now, the minimum and maximum seem to be 1.8mV and 3.3mV. The variations are quite smooth and it clearly follows a pattern, sinusoidal or triangular (no random jumps).
So I'm lost. I don't get what could cause these variations. And, needless to say, I can't match any transistor with that.
Any help and advice welcome,
Thanks in advance! :)

Alternatively, as I am slowly losing hope of doing it myself, where could I buy matched transistors for a fair price ?
The transistors are VERY sensitive to heat/cold. Breathing on them or the heater in the room can make things very considerably. Also it take some time for the temperature to stabilize.

Might try putting the tester in a closed box with the meter outside to try and avoid temperature changes.

Make sure you got a good, stable power supply.

Might want to check the transistor connectors. Maybe wiggle the transistors a bit when you insert them to get a good connection.

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Post by aabbcc » Wed May 23, 2018 9:02 am

So I got a psu in the derarbox lil erebus kit, this one is +/-15v, will it work properly with the Ian fritz board on oshpark?
cyrdun wrote:
cygmu wrote: Don't they settle after a while? As they conduct current the transistors will heat up, presumably not quite at the same rate if they are not perfectly matched and at an identical temperature in the beginning. But it should settle.
Thanks for your answer.
However I've left the circuit powered for two hours or so and I still can see the values going back and forth between min and max values. :/
Same thhing for me, it's been plugged in now for an hour and the values are never stable but keep constantly switching between 1.555-1.780 MV, :s

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fuzzbass
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Post by fuzzbass » Wed May 23, 2018 5:33 pm

I'm not denigrating any of these nice PCBs being offered, but a real productivity improvement is to include a ziff socket for the transistors. You can pick up DUTs with plastic tweezers and insert them, test them, without polluting them with heat from your fingers. Body heat is a big factor when working at this level of sensitivity. Everything goes much faster. I credit Ray Wilson with this suggestion.
Wired for weird

aabbcc
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Post by aabbcc » Mon May 28, 2018 2:46 pm

KlangGenerator wrote:I'd like a board from OSH Park, but am based in Europe. :help:
PM ;)

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Fernando
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Post by Fernando » Sun Jul 29, 2018 7:51 am

When using +-15V supply (instead of +-12V),
should the two 3k9 resistors be changed to a higher value so one still gets 0.6V at the other end?
I assume the diodes are 1N4148.

I'll be using OSH boards (Fonik layout)



PS: if someone in Europe needs a pcb, just PM me. I can let go 1 pcb (I had to buy 3 at OSH) Will be actual cost /3, plus actual shipping cost.
.

Fer

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cygmu
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Post by cygmu » Sun Jul 29, 2018 10:54 am

It’s the diode that gives you the 0.6v. The resistor sets the current and you’ll be fine with 3k9 but you could go a little higher if you like, e.g. 4k7.

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