VCA Transistor matching

[Conboy]

Being newish to this I'm unsure how to match the BC547 transistor pair.

If they are from the same batch are they likely to be matched anyway?

If not how do I match them without any special equipment?

Tried to google it but got a bit

[LetterBeacon]

There's a circuit that you can use to match the transistors. Here's a link to the thread with a schematic: http://www.electro-music.com/forum/post-228566.html&highlight=#228566

[yusynth]

Here is a simple though efficient circuit to match transistors.
It is important that you do not handle the transistor with your fingers (because of temperature), work in a constant temperature place and wait for one or two minutes after powering the circuit before measuring the Vbe in order that the transistor temperature being stable.

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[Conboy]

Nice one Yves
Good and simple circuit ... I'll be off to buy a breadboard tomorrow then!

I did put the VCA together without matching but it sounds pretty bad! Splutter, distortion and cutting out on higher frequencies.

I am a little confused as to which components I should omit in the DC version. I left out C3 and C4 and fitted straps, but there are a number of other components with ** next to them (Q4, R24, C8, C9, D1) which I am unsure what to do with?

thanks

[Conboy]

I have once again discovered the depths of my ignorance and will tomorrow be building the AC coupled version.... being as that's what I need to do the job...

[yusynth]

[LetterBeacon]

Can the circuit that was posted by Yves earlier in the thread be used to match PNP trannies too?

How come that circuit is so much simpler than Moog's circuit?

Is the Moog circuit more accurate?

[yusynth]

Yes the circuit above is valid for PNP provided that you reverse the power supply polarity.

That is replace the NPN by a PNP with same connection Emitter for emitter , base for base, and collector for collector, and the +15V becomes ground and the ground becomes +15V.

The Moog's circuit provides a linear current source while here the current is defined by the collector resistor. When you need to match the Vbe of two trannies the same day, the simple circuit above is efficient enough.

[LetterBeacon]

That makes sense, thanks a lot!

[ultrashock]

Hi!

Kindly ask you to answer the next question (sorry for repeat), but anyway:

We can measure transistors by:
- Hfe (in you budget multimeter),
- Vbe (by the stated above schemes),
- or even as diodes (by connecting base-emitter).
All this values are completely different, that's why could you please answer by what values it is important to measure the transistors:
- for Moog VCA,
- for Moog VCF,
- VCO expoconvertor,
- other purposes.
and in what nodes it is critical?

Besides aforesaid and all known SSM2210/LM394/2SC1583/MAT02 NPN pairs there are also BCM847 and BCM857 transistors (M at the end means matched). And I noticed they are also cheap (out of stock at Digikey now). So, could they be used for our purposes without matching as such a ".1%" transistors?

[yusynth]

[MirlitronOne]

Apologies if this has been suggested before, but I haven't seen this idea in print.

When Vbe matching transistors, we are looking to measure about 600 mV to 1 mV or better accuracy, with a constant current source. This is exactly what the diode test facility on a cheap multimeter is designed to do. Hence, if you take an NPN transistor, connect the base to the collector, switch your DVM to diode test and connect the positive lead to collector and negative to emitter, the display will show Vbe in mV. The usual temperature and stability rules apply. For PNP transistors, just swap the leads over.

Considerations:

1. The test current is usually 1 mA, an order of magnitude greater than most circuits presented, but not, it seems, enough to cause measurement problems (at least not when I tried it).

2. Most DVMs will only measure to +/- 1 mV, only just about sufficient.

On the plus side:

1. It's cheap and simple.

2. It is a genuine constant-current measurement.

3. You're probably using that DVM to measure the Vbe anyway.

4. It's slightly better than Yves' simple rig, and you save on the power supply and resistor!

5. I've tried it and it appears to work pretty well.

[fluxmonkey]

MFOS has a relatively new page w/ a ton of info on matching transistors, including some more advanced circuits for matching: http://www.musicfromouterspace.com/analogsynth/TRANSISTORMATCHER/TRANSISTORMATCHER.php

[MirlitronOne]

Yes - the "GO - NO GO" tester has almost as many ICs as my Sound Lab.

[intoodeep]

Just to clarify Yves, for the VCA circuit on your site ("a simple but effective VCA"), the matched pair of transistors (Q1, Q2) needs to be matched for Hfe, not Vbe.

Also to what % do the transistors need to be matched?

Thanks!

[yusynth]

[ultrashock]

just to update the topic: I've made a universal transistor matcher - both for smd and thru holes ones both pnp and npn by the Yusynth's scheme.
smd transistors should be put and pressed to the board with some heat non-conducting material. thru holes resistors could be put directrly into collet-connectors. the direction of putting these transistors is stated as ")" or "D" with the rounded side

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print_pnp_matcher.pdf
Description:	template for negative photo-resist (two layers), should be printed as-is without scaling	Download (listen)
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[LektroiD]

[ultrashock]

It's not actually, HFE matching in Yusynth's (by Moog's) scheme above. It's more close like when you measure DIODES in Vbe in your ordinary multimeter (you can put transistors there with base and emitter pins). In what chains to which value to match see Yusynth's post above

[El Mop]

[yusynth]

Yes it will also work with +12V.

[El Mop]

Thank You!

[imguri]

hello,

excuse me but this post stay unclear for me. I need to match transistors for a yusynth VCA.

yusynth gives a schema to measure Vbe :

[isak]

Hi

For Yusynth vca Hfe will do.
Enjoy the project.

Cheers,
Isak E.

[imguri]

great ! now i can go on !
thank you !