Piggyback Si transistors to simulate Ger ???

Frequently asked question on transistors: types, substitutions, how to test, use and misuse them.

Re: Piggyback Si transistors to simulate Ger ???

Postby sinner » 10 Jul 2012, 18:16

I'm thinking. That leakage simul resistor can bypass that small "miller" cap? I think this may not work in that configuration. I'll do that without this resistor, and I'll add it after to check what will happen
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Re: Piggyback Si transistors to simulate Ger ???

Postby Nocentelli » 10 Jul 2012, 18:25

Doesn't a Big Muff have a resistor AND cap from B-C in the same way? The miller cap still has an effect in that set-up, surely?

Really interested to hear the outcome of your experiments, by the way, Sinner.
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Re: Piggyback Si transistors to simulate Ger ???

Postby sinner » 10 Jul 2012, 18:30

Nocentelli wrote:Doesn't a Big Muff have a resistor AND cap from B-C in the same way? The miller cap still has an effect in that set-up, surely?

Really interested to hear the outcome of your experiments, by the way, Sinner.


Yeah, I was thinking about this in BMP too, it make sense. My knowledge in EE is limited, I'm a paramedic after all :D I'm still learning, but till today I was sure that resistor in parallel with a cap will limit cap functionality somehow....
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Re: Piggyback Si transistors to simulate Ger ???

Postby juanro » 10 Jul 2012, 19:54

What you call "miller cap"? I know of "miller effect"... the small interelectrode capacitance get's multiplied by a certain factor (usually the gain) when the stage is inverting, lets say: if a transistor base-to-collector capacitance is (static) 3pf (this is unreally high for a transistor, but for the sake of argument), and said transistor is used as an inverting (common emmiter) stage with a gain of 100, "aparent" capacitance from base to collector would be 300pf. This capacitance will hinder high frequency response, as it will allow a certain negative feedback from C to B thus reducing gain. If there's already a resistor from C to B it's mostly sure already providing some negative feedback, but it will have no effect over the capacitor and it's effect over high freq response, be that capacitor a real one or the "miller effect" interelectrode capacitance.
Does this makes sense or do I sound like I'm talking shit? :hmmm:

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Re: Piggyback Si transistors to simulate Ger ???

Postby Nocentelli » 10 Jul 2012, 20:25

That makes perfect sense - I've seen the term "miller cap" used to refer to a small value cap between base and collector e.g. in a bmp or modded silicon fuzzface, providing the high end reduction you describe. I believe I've seen culturejam use that term several times, and I believe sinner and i perhaps picked up this form of short-hand: If it's not a widely used term, i hold cj responsible for any confusion!
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Re: Piggyback Si transistors to simulate Ger ???

Postby juanro » 10 Jul 2012, 20:35

Or perhaps the cap is there to simulate the miller effect... wich I think in transistors is only important at radio frequencies. In vacuum triodes (but not penthodes) the aparent cap is in the range I mentioned (hundreds of pF) but in transistors @audio frequencies is almost negligible.
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Re: Piggyback Si transistors to simulate Ger ???

Postby sinner » 10 Jul 2012, 20:44

It makes sense juanro, thanks for advanced explanation :) I shouldn't ask really, as I'll do some experiments anyway, but it's cool to know technical background

Yeah, Nocentelli is right. I said "Miller Cap" as a kind of shortcut from saying "that capacitor between base and collector creating Miller Effect" :mrgreen: It's just shorted version. I believe since I'm a noob I'm allowed to be lame ;)

Anyway, update as fallows. All I did is just enclosure drilling, and hardware instalation (pots, knobs, switch, ins/outs, power socked and initial wiring. No vero designed yet, as I left all my transistor stash at work, and I'm unsure what I have in low-gain transistors, and to avoid fuckarounding with random pin-outs I'll left it to tomorrow-ish work

I had some 2N3440 transistors with gain around of 40-60hfe, and I believe they would be perfect, as typically used germanium OC71's was in that range typically. Should be perfect for Q1 and Q2, not sure about Q3 piggiback pair... Anyway, by last few months I've give away so much parts to my blokes I'm not sure do I still have them.

I may have large quantity of other low-hfe silicons I've scored from CultureJam back in the days he was running Caps N Such, but I really must to check again, my memory is tricky recently
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Re: Piggyback Si transistors to simulate Ger ???

Postby sinner » 10 Jul 2012, 21:12

Guys, do you think I should change the bias for darlington pair? Any technically explained background of pros and cons?
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Re: Piggyback Si transistors to simulate Ger ???

Postby sinner » 12 Jul 2012, 18:07

Back on it again. The circuit is ready, I'm using 2n3019 all the way - gain of 95 or around

I've changed few places with miniturrets to make changes easier. I'm not using Miller Effect Capacitor for Q3 pair right now, I want to know what it sounds without

I'm using early mk3 spec. The only difference is 100uF filtering cap in place of 25uF, piggyback trannies and that turrets (i'm using pots with resistors in line tunned to stock spec - 220k, 18k and so on)

Stay tuned
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Re: Piggyback Si transistors to simulate Ger ???

Postby jubal81 » 20 Jul 2012, 17:47

I made a Tonebender board this way. I used 5088s and with a little dialing in it sounds pretty great. I've been having a migraine attack so I haven't had a chance to experiment much with it.
I also added test points so you can see how you're dialing in the trannies.

I call it the Antiseptic. A no-germ bender.
I'm attaching the Eagle files. Feel free to do whatever you like with 'em.

Ah. Won't let me attach BRD file.

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Re: Piggyback Si transistors to simulate Ger ???

Postby Cub » 08 Sep 2012, 07:26

Bumpity bump, bump, bump.
Hello lads, how's this coming along ? :)
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Re: Piggyback Si transistors to simulate Ger ???

Postby grrrunge » 08 Sep 2012, 10:50

reeeal slow! :D i haven't had time to experiment lately...
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Re: Piggyback Si transistors to simulate Ger ???

Postby Cub » 09 Sep 2012, 22:28

All right then, do keep us posted if you make any progress. :thumbsup
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Re: Piggyback Si transistors to simulate Ger ???

Postby grrrunge » 10 Sep 2012, 21:07

Cub wrote:All right then, do keep us posted if you make any progress. :thumbsup
The sound of germs with the reliability and consistency of sillies, ooh ! [smilie=vibes.gif]

not to mention availability and lower cost... :thumbsup
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Re: Piggyback Si transistors to simulate Ger ???

Postby Cub » 13 Sep 2012, 16:27

grrrunge wrote:
Cub wrote:All right then, do keep us posted if you make any progress. :thumbsup
The sound of germs with the reliability and consistency of sillies, ooh ! [smilie=vibes.gif]

not to mention availability and lower cost... :thumbsup

Indeed ! Everybody wins, except for the sellers of "mojo" germs. 8)
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Re: Piggyback Si transistors to simulate Ger ???

Postby atreidesheir » 02 Dec 2012, 05:08

[quote="puppiesonacid"]
Code: Select all
1. Take two identical random silicon transistors (for more mojo: your fav fuzz silicons
2. Tie the BASES together,
3. Cut off one COLLECTOR
4. connect a 3k to 6k resistor between the EMITTER of the collectorless devicr and the EMITTER of the other transistor.

By varying the resistance, you can dial in the gain you want...



I have tried this and get no hfe reading from the transistor on my multimeter. So the experiment stops there for me.
Has anyone had similar experience?
I figure if I put it in circuit at that point i'm wasting my time.

I work so slowly these days I cannot afford to waste two hours for nothing. Family situation makes time too precious to waste at the moment.

Could someone please post pics of a properly piggybacked silicon pair with a resistor? so I can compare and learn. It would be awesome
I hate to ask, but I really need a visual to know if I am really doing this wrong. Thanks in advance to anyone that can help.
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Re: Piggyback Si transistors to simulate Ger ???

Postby grrrunge » 02 Dec 2012, 12:06

Something like this should do the trick ;)

GE_sim.png
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arikam (26 Jan 2013, 18:55), atreidesheir (02 Dec 2012, 16:34), ezugaru (03 Dec 2012, 01:05)
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Re: Piggyback Si transistors to simulate Ger ???

Postby atreidesheir » 02 Dec 2012, 16:35

thanks
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Re: Piggyback Si transistors to simulate Ger ???

Postby ezugaru » 03 Dec 2012, 01:50

Would be good if i try with some KT132 I have? :D
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Re: Piggyback Si transistors to simulate Ger ???

Postby atreidesheir » 03 Dec 2012, 02:11

Can someone give me a simple overview of how to calculate appropriate capacitor and resistor values for the miller effect. I get the gist of it. But I have not been able to find any clues to the math of it.
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