I'd like to build a simple germanium preamp. I already have a lot germanium transistors.
Are there any sonic benefits to germanium or is it all hype?
Are there any sonic benefits to germanium or is it all hype?
Not sure about "benefits" , many sound somewhat dull but some people perceive that as "warm", "smooth", etc. so yes, some like them, you might too.
So no "magic" but hey!!! build some project and YOU tell US 🙂
So no "magic" but hey!!! build some project and YOU tell US 🙂
If its guitar preamp you want to build they are ideal.
They're not dull at all if you surround them with modern passive components and they're certainly not warm or any different sounding than a silicon transistor if you choose the right circuit for them.You'll even find some advantages over silicon transistors in niche areas . Besides there are tons of very different germanium transistors outhere and they don't behave all the same nor have the same parameters so you need careful selection and even simulations if models are available for your particular design.
The only downside of germanium transistors in a preamp is noise and current leakage.Current leakage can be minimised with pnp transistors supplied at lower voltages.Making the bias base resistor as high as possible for your circuit also work, but current noise needs to be taken into account so look for good compromise .60's phono preamps prefferably used a silicon transistor for the input stage due to noise issue.
At line and headphones level they are ideal and their sound is not dull at all.You can apply any distortion reduction technique employed with silicon transistors and it will work very well.I did it in my headphones amp and i couldn't make a difference between tpa6120 and my germanium amp on 250 ohms bayerdynamic dt880 headphones.Maybe I'm deaf....
When getting into high power area you need to take current drift due to temperature into account and find the right compensation.Also consider the max voltage and heat dissipation cause germanium isn't too great in that redpect nor you'll be able to easily find high power complementary transistors if at all... .Complementary stages with Ac 180/81/87/88 are prefferable to transformer driven solution only if you have enough transistors to make good pairs.Higher power transistors with good FT are hard to find or expensive.
Do not believe anyone until you get to experiment yourself with them because they do not behave like silicon transistors and don't forget, you can try any diabolicaly complicated schematic you can think of. By the way , ac187/ac188 have been reported to have pretty low voltage noise so they can provide good SNR with low input impedance sources like DAC outputs.Some of the aspects of germanium transistors were never explored by our modern standards or the information is hard to find in some cases.
Nobody ever considered for example an i/v converter based on germanium transistors after a DAC as there was no audio DAC in the 50's or 60's or 70's so many things can be tried.
The low FT of germanium transistors argument that people usually bring into discussion is wrong with emitter followers and low gain common emitter stages and you'll find that by yourself as they don't have the same effect as gm doubling has in silicon transistors.Due to the lower BE voltage needed to open the transistor a 0.5 ohm emitter resistor used with germanium transistors will have 2...4 times higher distortion reduction effect that the same 0.5 ohms resistor has with silicon transistors depending on how high the collector current is.Besides you can aplso use PTC resistors as emitter resistors to insure thermal runaway compensation too instead of the classical NTC resistor placed in the base bias circuit.
This doubling gm effect in germanium trz is also milder , has less agressive slope and that makes germanium transistors more suitable for class B amplifiers which will naturally present lower current drift with temperature .Accompanied by modern op-amps their crossover distortions are theoretically much lower than in their silicon counterparts, but their inherent higher junction capacitance ask for more current drive yet that is not true with all transistors.Think about AC187/188 having max hfe=500 at 300mA while 1000mA is possible to get out of them with the right heatsink.You won't find easily transistors with such high hfe at these currents in silicon transistors.That can be a downside too in some applications, but generally i encourage anyone to think more about the use of germanium transistors in modern circuits even using simullators where it is possible.
You can also use superdiode circuits similar to those used in silicon circuits for thermal compensation, but you need to make sure that they will have very good thermal coupling with the final stage transistors because thermal runaway in germanium transistors is a lot quicker than it is in silicon transistors so big liquid or freon cooled heatsinks are better for high power germanium trz .You find them a lot in scraped computer cooling systems anyway.
They also have a very big advantage that others talked about too: they'll work even with 0.2 volts over CE junctions in some cases so battery supplied circuits can work very well with just one 1.2v battery while their CB and CE leakage current also drops with applied CE voltage so battery drain is better with lower voltages.
They're not dull at all if you surround them with modern passive components and they're certainly not warm or any different sounding than a silicon transistor if you choose the right circuit for them.You'll even find some advantages over silicon transistors in niche areas . Besides there are tons of very different germanium transistors outhere and they don't behave all the same nor have the same parameters so you need careful selection and even simulations if models are available for your particular design.
The only downside of germanium transistors in a preamp is noise and current leakage.Current leakage can be minimised with pnp transistors supplied at lower voltages.Making the bias base resistor as high as possible for your circuit also work, but current noise needs to be taken into account so look for good compromise .60's phono preamps prefferably used a silicon transistor for the input stage due to noise issue.
At line and headphones level they are ideal and their sound is not dull at all.You can apply any distortion reduction technique employed with silicon transistors and it will work very well.I did it in my headphones amp and i couldn't make a difference between tpa6120 and my germanium amp on 250 ohms bayerdynamic dt880 headphones.Maybe I'm deaf....
When getting into high power area you need to take current drift due to temperature into account and find the right compensation.Also consider the max voltage and heat dissipation cause germanium isn't too great in that redpect nor you'll be able to easily find high power complementary transistors if at all... .Complementary stages with Ac 180/81/87/88 are prefferable to transformer driven solution only if you have enough transistors to make good pairs.Higher power transistors with good FT are hard to find or expensive.
Do not believe anyone until you get to experiment yourself with them because they do not behave like silicon transistors and don't forget, you can try any diabolicaly complicated schematic you can think of. By the way , ac187/ac188 have been reported to have pretty low voltage noise so they can provide good SNR with low input impedance sources like DAC outputs.Some of the aspects of germanium transistors were never explored by our modern standards or the information is hard to find in some cases.
Nobody ever considered for example an i/v converter based on germanium transistors after a DAC as there was no audio DAC in the 50's or 60's or 70's so many things can be tried.
The low FT of germanium transistors argument that people usually bring into discussion is wrong with emitter followers and low gain common emitter stages and you'll find that by yourself as they don't have the same effect as gm doubling has in silicon transistors.Due to the lower BE voltage needed to open the transistor a 0.5 ohm emitter resistor used with germanium transistors will have 2...4 times higher distortion reduction effect that the same 0.5 ohms resistor has with silicon transistors depending on how high the collector current is.Besides you can aplso use PTC resistors as emitter resistors to insure thermal runaway compensation too instead of the classical NTC resistor placed in the base bias circuit.
This doubling gm effect in germanium trz is also milder , has less agressive slope and that makes germanium transistors more suitable for class B amplifiers which will naturally present lower current drift with temperature .Accompanied by modern op-amps their crossover distortions are theoretically much lower than in their silicon counterparts, but their inherent higher junction capacitance ask for more current drive yet that is not true with all transistors.Think about AC187/188 having max hfe=500 at 300mA while 1000mA is possible to get out of them with the right heatsink.You won't find easily transistors with such high hfe at these currents in silicon transistors.That can be a downside too in some applications, but generally i encourage anyone to think more about the use of germanium transistors in modern circuits even using simullators where it is possible.
You can also use superdiode circuits similar to those used in silicon circuits for thermal compensation, but you need to make sure that they will have very good thermal coupling with the final stage transistors because thermal runaway in germanium transistors is a lot quicker than it is in silicon transistors so big liquid or freon cooled heatsinks are better for high power germanium trz .You find them a lot in scraped computer cooling systems anyway.
They also have a very big advantage that others talked about too: they'll work even with 0.2 volts over CE junctions in some cases so battery supplied circuits can work very well with just one 1.2v battery while their CB and CE leakage current also drops with applied CE voltage so battery drain is better with lower voltages.
Look at the curves.
It also depends on what you want. For a dreamth mentioned guitar amp, maybe you want a sonic signature as past of the instrument. Think old Fender and a Strat. But if a line preamp, maybe you don't want any signature. I use "signature" not as a bad term, but as the sum of all the differences, ne, distortions, added to the signal. Bad, or desirable is your choice.
FWIW, the entire industry ran screaming away from them as soon as silicon was available. Maybe there is a reason. Maybe something was overlooked.
It also depends on what you want. For a dreamth mentioned guitar amp, maybe you want a sonic signature as past of the instrument. Think old Fender and a Strat. But if a line preamp, maybe you don't want any signature. I use "signature" not as a bad term, but as the sum of all the differences, ne, distortions, added to the signal. Bad, or desirable is your choice.
FWIW, the entire industry ran screaming away from them as soon as silicon was available. Maybe there is a reason. Maybe something was overlooked.
Germanium degrades over time, and that is accelerated by enclosures which are not hermetically sealed.
Part of the reason, you can read up.
After that, trying to get the devices will convince you that your effort is a waste, you are better off doing something else.
Part of the reason, you can read up.
After that, trying to get the devices will convince you that your effort is a waste, you are better off doing something else.
After all, while silicon is abundant on earth, hence cheap, germanium is rather scarce (rank 46 in the mass related list of occurence vs. rank 2 for silicon).
Best regards!
Best regards!
I have about a hundred ac181...188 that measure up to their initial specs.It depends probably on how they were kept away from moisture, production batch, quality control, manufacturer...etc.I for one found very few transistors affected by the time passed over them so careful screening for their sources might help.
All hype - its simply another semiconductor with a lower bandgap, nothing qualitatively different (other than most Ge devices being ancient and thus with more impurity issues like noise, low avalanche breakdown, reliability).
Ge has the disadvantage of needing more attention to thermal issues due to its max operating temp being very low.
Ge does have an advantage in low voltage circuitry - the lower bandgap allow Ge transistor circuitry it to be used from as low as a 1.5V supply.
Not in preamplifiers though...the author of this thread wants to make a preamp.
Thermal drift can still affect preamps - you don’t have a lot of wiggle room on a low voltage supply. Overheating isn’t the only thing that can happen.
If you have the devices and want to make a preamp (power amp or whatever) go for it. Just don’t expect miracles. Spending undue amounts of money sourcing Ge parts, and then obsessing over detail in circuits that were never very good to begin with, is a fool’s errand.
If you have the devices and want to make a preamp (power amp or whatever) go for it. Just don’t expect miracles. Spending undue amounts of money sourcing Ge parts, and then obsessing over detail in circuits that were never very good to begin with, is a fool’s errand.
Unlike small signal silicon transistors, germanium ones are placed inside huge metalic cans that can beneffit from better cooling if needed so there's compensation.Besides there are a lot of germanium preemps in old reel to reel or phono preamps still in service.
There are a very few cases where the lower bandgap is important enough to warrant considering germanium transistors, but I have modified circuits to be rid of them when practical to do so. They are a bit like selenium rectifiers, a nasty old technology that we dumped as soon as something better was available. Germanium transistors were noisy, leaky, very sensitive to heat, and slow. If you have a lot of germanium transistors, they may contain useful silicon grease, otherwise recycle them for the copper.
There are now transistors/chips that combine germanium and silicon:
https://en.wikipedia.org/wiki/Silicon–germanium
There are now transistors/chips that combine germanium and silicon:
https://en.wikipedia.org/wiki/Silicon–germanium
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If you have a lot of Ge transistors then why not go ahead and use them, I think you'll enjoy the challenges of designing and building with these devices which may not be the case with some off-the-shelf Si project. Almost every example of hype in Audio is just that, hype, but when you make it yourself all that is immaterial as you will get a lot of pleasure from the designing and building and then the debugging and listening and all the follow on ideas it will give you. Jump in and get going - far the better use of your time than chasing approval on here 🙂
So what?
🙂))
Can you give an useful example for an audio preamplifier?
Germanium is also used on space telescope to detect far infrared spectrum of the very far stars and that is because its current dependence to temperature allows for very faint radiation to be picked up, but that's telling me that germanium is also a very responsive material to heat in a very predictable manner which means that you can use it also to compensate the thermal runaway of other similar device by sensing it.Molly used germanium transistors in a vbe refferenced ccs in his class A headphones amplifier and it showed pretty good behavior , I took a step further by making an output stage out of two complementary vbe ref ccs with simmetrical bootstrap and i didn't even need to include that buffer in a feedback loop because of its very low thd while the output dc offset was below 10mv...I found that pretty cool honestly.
If we're going to talk up the benefits of germanium, let's stick with the OP's guitar preamp application, which, like most guitar devices, is really all about creating and preserving desirable types of distortion. Low noise and distortion is the main game in this "solid state" forum here but guitar effects and other music production gear are usually confined to the "Live Sound" > "instruments and amps" forum, so I guess it's not surprising that some replies have completely missed the point of using germanium transistors here. It's twofold though. First copy the gear that the early guitar heroes used to make their original, impressive and popular sounds, then make your own, even more impressive effects according to what you and your audience prefer to hear now.
Nobody? Except for the very highly regarded Abbas dacs and their imitators SWiX. Ge in both the i/v stages and in series/shunt regulators.
Apart from this tiny omission, thanks for all the usefully condensed info.
Thanks! I never knew about that work, but i might come back one day on my own project using some ac187 instead of the ztx1055 transistors : https://www.diyaudio.com/community/...static-headphones-output.350325/#post-6099803
Low bandgap semiconductors do indeed have applications for infra-red sensing, but I suspect what you are refering to here is the use of Ge as a lens material for IR optics as its transparent in the far infra-red. This is absolutely nothing to do with commercially produced BJTs using Ge from the 60's.