TL072CP Op Amp Differences

Ginsly said:
but I think any Ge diode would do
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Not true.

Circuits that use the Ge diodes as hard clippers (Distortion+, Klon, Cornish SS-3) can tolerate a large amount of leakage. I have Russian D9E diodes installed in my VFE Merman (PPCB Sea Monk) and they are très leaky.

Circuits that use the Ge diodes as soft clippers (Cornish G-2 & NG-2) must use low-leakage Ge or the diodes will kill the gain. Good luck finding low-leakage GE diodes. small Bear has 1N695 which might be low enough leakage for soft clipping.

Jubal81 has pointed out that a pair of back-to-back BAT41s with a 68Ω resistor in series is a pretty accurate sub for a pair of Ge diodes. Schottky diodes are also fairly leaky, so testing them is a good idea.
 
Chuck D. Bones said:
Not true.

Circuits that use the Ge diodes as hard clippers (Distortion+, Klon, Cornish SS-3) can tolerate a large amount of leakage. I have Russian D9E diodes installed in my VFE Merman (PPCB Sea Monk) and they are très leaky.

Circuits that use the Ge diodes as soft clippers (Cornish G-2 & NG-2) must use low-leakage Ge or the diodes will kill the gain. Good luck finding low-leakage GE diodes. small Bear has 1N695 which might be low enough leakage for soft clipping.

Jubal81 has pointed out that a pair of back-to-back BAT41s with a 68Ω resistor in series is a pretty accurate sub for a pair of Ge diodes. Schottky diodes are also fairly leaky, so testing them is a good idea.
Click to expand...
This is great to know, and is counter to some of the things (I thought) I learned around here. Many said that the difference between Ge and silicon was far diminished when using them in pairs as hard clippers. In a Klon circuit it seemed like a different story. Thanks for the correction!

I also didn’t realize Schottky diodes were leaky! Huh…
 
@Chuck D. Bones what would you say is too leaky for non-hard-clipping when it comes to Ge diodes (or Schottky apparently)? Is there a leakage that is too high for anything at all?

As an aside, anyone hoping to get 1N34As from Tubes N More might want to exercise caution. Just saw this review from just a couple weeks ago (below). Given the price of these and the questionable availability, I think I'll hold off until a build absolutely needs this particular part; even then, I'm not sure what I'll be getting is usable (or actually a 1N34A). Some of my upcoming builds call very generally for a pair of "Ge diodes". In that case, I'll just have to try some and see what works. I have a few- need to test their leakage, sounds like. Tubes N More also has 1N60s for a buck, and I need to order from them anyways at some point... 🤷‍♂️

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Ginsly said:
@Chuck D. Bones what would you say is too leaky for non-hard-clipping when it comes to Ge diodes (or Schottky apparently)? Is there a leakage that is too high for anything at all?
Click to expand...

Depends on the circuit. specifically, if the diodes are in parallel with a resistor (as they invariably are in a soft clipper), then the leakage resistance of both diodes in parallel should be greater than the resistor that parallels them. Example: the diodes are in parallel with a 470K resistor in the Cornish G2. I have yet to measure any Ge diodes with resistance that high, so in the case of the G2, get the highest leakage resistance you can and hope that it's enough to not reduce the gain too much. Pete Cornish is a smart guy so he must expect the Ge diodes to limit the gain somewhat.
 
Chuck D. Bones said:
Depends on the circuit. specifically, if the diodes are in parallel with a resistor (as they invariably are in a soft clipper), then the leakage resistance of both diodes in parallel should be greater than the resistor that parallels them. Example: the diodes are in parallel with a 470K resistor in the Cornish G2. I have yet to measure any Ge diodes with resistance that high, so in the case of the G2, get the highest leakage resistance you can and hope that it's enough to not reduce the gain too much. Pete Cornish is a smart guy so he must expect the Ge diodes to limit the gain somewhat.
Click to expand...
Gotcha. I'll have to cross that bridge eventually, and this is good info.

What I SHOULD have asked, is - how best to measure diode leakage, whether Ge or Schottky? Does a DCA55 give you that info like it would for a transistor?
 
Ginsly said:
As an aside, anyone hoping to get 1N34As from Tubes N More might want to exercise caution. Just saw this review from just a couple weeks ago (below). Given the price of these and the questionable availability, I think I'll hold off until a build absolutely needs this particular part; even then, I'm not sure what I'll be getting is usable (or actually a 1N34A). Some of my upcoming builds call very generally for a pair of "Ge diodes". In that case, I'll just have to try some and see what works. I have a few- need to test their leakage, sounds like. Tubes N More also has 1N60s for a buck, and I need to order from them anyways at some point... 🤷‍♂️

View attachment 72671
Click to expand...
There were dozens, if not hundreds, of different legit 1N34A diodes manufactured over the years. Their marking and transfer functions varied considerably from one manufacturer to the next. Therefore, it's hard to know if this review is correct. I bought some "1N270" and "1N34A" diodes from Tayda a few years ago. They look identical, glass diodes with two black bands. Their curves lay on top of each other up to 2mA. They diverge from there, indicating that the "1N34A" has a higher bulk resistance. They are clearly Ge diodes. whether they are actually 1N34A or 1N270 is anyone's guess. The original parts have been out of production for decades. It appears that there are new Ge parts being manufactured in China. That could very well be what those are.
Unless we're buying from a manufacturer-authorized vendor, the parts will most likely have no traceability back to the manufacturer. In that case, we have to trust the vendor and everyone else in the supply chain. Who knows if everyone in the supply chain is knowledgeable and honest.
 
To the best of our knowledge, our current stock is the Unizon 1N34A as seen on this page. Keep in mind that the brands we carry (and our sister company AES/tubesandmore carries) for NOS products can change unless stated otherwise as we work to maintain stock of an item that is only getting more and more scarce.

The same team that is responsible for our new products also finds and/or approves our surplus and new old stock items, and we always conduct exhaustive research and electrical tests when possible to ensure we're getting legitimate NOS products.
 
Amplified Parts said:
To the best of our knowledge, our current stock is the Unizon 1N34A as seen on this page. Keep in mind that the brands we carry (and our sister company AES/tubesandmore carries) for NOS products can change unless stated otherwise as we work to maintain stock of an item that is only getting more and more scarce.

The same team that is responsible for our new products also finds and/or approves our surplus and new old stock items, and we always conduct exhaustive research and electrical tests when possible to ensure we're getting legitimate NOS products.
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Good to know, thanks for the clarification. About to place my first AES order, just wanted to check in about that. Certainly wasn't insinuating "fakes" or anything, my apologies.

I actually messaged you last week about AES! :)
 
Chuck D. Bones said:
Depends on the circuit. specifically, if the diodes are in parallel with a resistor (as they invariably are in a soft clipper), then the leakage resistance of both diodes in parallel should be greater than the resistor that parallels them. Example: the diodes are in parallel with a 470K resistor in the Cornish G2. I have yet to measure any Ge diodes with resistance that high, so in the case of the G2, get the highest leakage resistance you can and hope that it's enough to not reduce the gain too much. Pete Cornish is a smart guy so he must expect the Ge diodes to limit the gain somewhat.
Click to expand...
Not to go too far off topic, but I'm not convinced that the G2 actually uses germanium diodes:
PedalBuilder said:
Wild idea, but what if the G-2 doesn't use germanium diodes after all? I went back and looked at the original tracing thread for the Cornish G-2, and now I'm wondering if the original G-2 actually used germanium diodes rather than a glass package Schottky diode like the HP2835. The tracers were not able to determine what model of diode was used, but they saw a glass package like a germanium diode and measured a forward voltage of ~.22 volts using a multimeter. A Vf of .22 volts is on the low side for a germanium diode, but it's well in spec for a Schottky diode. Using a Schottky would also eliminate the leakage issue that seemingly every germanium diode has. Although Cornish has described the pedal as having "warm Germanium qualities," he also has a track record of exaggerating and making misleading statements about what is inside of his pedals.
Click to expand...
If Cornish really is using germanium diodes, then he's either found a particular manufacturer/model of germanium diodes that consistently has leakage that's an order of magnitude lower than anything I've ever encountered or he's spending a long time testing diodes every time he builds a G2.
 
Chuck D. Bones said:
Can you tell us about the electrical tests you perform on Germanium diodes & transistors?
Click to expand...
It varies a bit depending on what we’re inspecting and the source, but we start with a visual inspection. We're fortunate enough to have access to a lot of desirable semiconductor types from various manufacturers from the work we do here and from the personal collections of the builders we have on staff, so we have a good eye for spotting any visual inconsistencies or concerns at this point. If everything looks good, we’ll run a sample amount through meters/testers. The Peak DCA75 and its accompanying software DCA Pro get a lot of use here. Those measurements are then checked against datasheets and/or measurements of known legitimate examples to make sure everything lines up and that the batch has not been previously cherry-picked. Finally, in-circuit tests are performed whenever possible. A lot of those tests turn into the builds you see on our instagram.

We also have custom proprietary hardware built here for testing the transistors in known germanium circuits which is used for all of the Fuzz Face transistor sets we sell.

And no problem, Ginsly! Nothing to apologize for. It's an understandable concern to raise.
 
Thanks for the reply.
Is it fair to say that for transistors, you measure HFE, Vbe, Iceo and Ices?
For diodes you measure Vbe and Ir?
Do you measure 100% of the parts in a batch, or do you sample them? If sampling, what % do you sample?

I have experience working in the Aerospace industry and worked closely with component engineering, so I know all the right questions to ask. I don't expect vintage commercial parts to be treated with the same rigor as Hi-Rel space electronics. But it is nice to understand what you're doing.
 
That tracks with our testing although so far I don't believe we've had cause to test Ices directly, but we do have the means to if needed. When leakage parameters are given in the datasheets we are comparing against we typically see Icbo or Iceo values which is always part of our tests.

The % we test is really going to depend on the size of the lot and what state the components are in. We've received lots that are in original manufacturer packaging, sealed packaging from an old electronics vendor dated from when the transistors were ordered, open packaging, loose, etc. If it's a large amount and the spot testing is very consistent it could be a small percentage but we've had smaller batches of more expensive transistors where we've tested each individual part.
 
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