Piggyback Si transistors to simulate Ger ???

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

Say a thread about this on DIY and a mention of it here by Modman. Was just wondering:

How did they sound?? Just like Ger, or so-so??

Thanks!

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Post by Greg »

I think the aim of the piggy backing is to reduce Hfe isn't it.
If you're looking for the softer response of a Germanium, a cap across the legs can help.
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Post by puppiesonacid »

Greg_G wrote:I think the aim of the piggy backing is to reduce Hfe isn't it.
If you're looking for the softer response of a Germanium, a cap across the legs can help.
which legs?

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Post by Greg »

puppiesonacid wrote:
Greg_G wrote:I think the aim of the piggy backing is to reduce Hfe isn't it.
If you're looking for the softer response of a Germanium, a cap across the legs can help.
which legs?
Collector to Base... something around 50 to 100pf works well.
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Post by gght »

From what I got, it was a method of imitating Ger. transistors with Si transistors, I thought sounded interesting, as I am going to build a FF type clone. Seems the idea died down.

Quoting modman's post here:

Postby modman on Thu Nov 01, 2007 3:29 am

sosodef wrote:I wonder could that range control work on a fet based boost?

Anyone find any success with silicone in the rangemaster?



My dad always told me and again last week: just act normal. But I can't. I was going to build a nice GE FUzz and GE Rangemaster to check out the mojo. Couldn't stick to that plan anymore once I read Brett's Piggybacking thread at diystbxes. I built a piggyback Fuzz and a piggyback Rangemaster

I couldn't believe that he thread died out on a 'oh we found some low gain si so we stopped experimenting.' This was the ticket to building a fuzz almost two random couples of cheapo transistors. Strange boutiquers haven't picked this up yet...

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...

Read more here:
https://www.diystompboxes.com/smfforum/i ... ic=49543.0

or try Brett suggestion of low gain SI for your Rangemaster?

Quote from: brett on 20-09-2006, 05:27:28
After word got out about the qualities of the 2N2369A (hFE about 70), I mostly lost interest.



allow me to quote from the above thread. Maybe I should do some clips with my piggybacked Rangemaster tomorrow....

RG wrote:« Reply #7 on: 20-09-2006, 22:30:54 »
It's only a suspicion, but I'll bet that the gain reduction does not remain constant across a range of values of base current.

Since the active base has an effective Shockley resistance and the passive one does not, it would be moderately amazing if the gain reduction was linear.

This is probably a Good Thing, in that it is even more asymmetrical than a transistor all by itself. It may be more Fuzz Face-y than a realy germanium FF.

It's worth some more testing.

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Post by gght »

Greg, how does the sound (using the cap on the legs) compare to a real Ger. tranny??

Thanks

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Post by Greg »

gght wrote:Greg, how does the sound (using the cap on the legs) compare to a real Ger. tranny??

Thanks
It takes a little of the biting sharp edge of a Si away...
Closer to the sound of a Germanium, but not exactly the same in feel, etc.

In a band situation you probably wouldn't pick the difference, but side by side on their own you would. Lots of people like the silicon for it's bite of course... I love a good Germanium FF, but they don't always sound good or cut through well in a band, especially if you don't cut the Bass a bit.
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Post by 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...

this is very intresting... i like the experiemental nature of this

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Post by Emanuele »

:hmmm: *starts to work on some ideas*

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Post by modman »

here I think was the original thread on
Relative importance of Gain in a Fuzz Face
for anybody who missed it.
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Post by Redhouse »

It was Bret's work originally, and it was to get a proper FF Hfe range from silicon, the resistor across the Emitters was originally small but was found to work best with values in the range of 2K-200K or so depending on your two Transistors and the Hfe you are trying to dial-in.

How does it sound? ...IMHO with the right resistor it sounds much better than Ge's, stays tight in the low end where Ge's start to mush-out, much less noise (hiss) and you get away from that temperature problem the Ge's have.

To find the right resistor for your two transistors temporarily install a 200k trimmer where the resistor goes, plug in your unit and play a playing volume (not bedroom levels) and dial in the trimmer untill you arrive at where you bet the best sound, remove the trimmers and install resistors.

I still have a small stash of AC128 and AC125 I got from a guy in the UK a few years ago (not selling any) I save for Ge builds that "must have" them, but IMHO the Bret-Piggyback thing sounds way better.

Here is a pic of a board I made for dialing-in piggyback's and the other FF parameters, it has trimmers and switchable caps to dial in things just right for a client/customer, sure it takes a little time to build a board like this BUT you never have to go back parts-swapping on finished boards to find a sweet spot for someone.
(the stuff in the lower left corner is for power)

Image

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Post by R.G. »

Redhouse wrote:It was Bret's work originally, and it was to get a proper FF Hfe range from silicon, the resistor across the Emitters was originally small but was found to work best with values in the range of 2K-200K or so depending on your two Transistors and the Hfe you are trying to dial-in.
Actually, I came up with piggybacking. I initially speculated that it would cut the effective gain of the active transistor in half. It turned out to reduce it much more than half, because the piggybacking transistor was working at such a low current level.

Brett did the work on the resistor between emitters to tailor the effective gain.

It's all there in the forum archives.

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Post by condorface »

How Identical do the two transistors have to be for piggybacking? Do you just need the same name transistors, or do you need to test them to find exact matches?

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Post by HydrozeenElectronics »

condorface wrote:How Identical do the two transistors have to be for piggybacking? Do you just need the same name transistors, or do you need to test them to find exact matches?
Just the same type. I tried it with some 2n0588 and it sounded pretty good. give it a shot and see what you think.

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Post by condorface »

HydrozeenElectronics wrote:
condorface wrote:How Identical do the two transistors have to be for piggybacking? Do you just need the same name transistors, or do you need to test them to find exact matches?
Just the same type. I tried it with some 2n0588 and it sounded pretty good. give it a shot and see what you think.
Thanks. I plan on actually doing this up right on the breadboard first to dial in the gains before soldering the resistor. I've got an old broken bogen PA with 2n5089s that I plan to salvage parts from. Not too mention tropical caps.... 8)

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Post by HydrozeenElectronics »

condorface wrote:
HydrozeenElectronics wrote:
condorface wrote:How Identical do the two transistors have to be for piggybacking? Do you just need the same name transistors, or do you need to test them to find exact matches?
Just the same type. I tried it with some 2n0588 and it sounded pretty good. give it a shot and see what you think.
Thanks. I plan on actually doing this up right on the breadboard first to dial in the gains before soldering the resistor. I've got an old broken bogen PA with 2n5089s that I plan to salvage parts from. Not too mention tropical caps.... 8)
A little trim pot works great that way you can strum with one hand and adjust with the other to dial in the best tone.

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Post by grrrunge »

I am insanely interested in this project. I like the overall sound of GE fuzzes, but i absolutely hate sloppy low end.
I want crushing palm mutes at all time, so "flart-flart" instead of "chunk-chunk" is simply not an option :lol:

Just to make sure I'm understanding the trick as described above: Is this schematic correct?
piggyback_ge_sim.png
piggyback_ge_sim.png (3.71 KiB) Viewed 1082 times
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Post by DrNomis »

Pretty interesting and cool ideas here, I must do some breadboarding of this someday.... :hmmm:
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Post by grrrunge »

DrNomis wrote:Pretty interesting and cool ideas here, I must do some breadboarding of this someday.... :hmmm:
I really want to get started as well! If it wasn't for all that damn painting i've got to get over with :slap: Moving is a pain in the ass :lol:
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Post by IvIark »

Something like this?

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