High gain jfet/mosfet preamps - Tone stack issues.

[J0K3RX]

One thing to keep in mind with both of these real amps is that the pre amps filter out most all of the low end. The negative feedback loop around the power amp is used to restore the low frequencies filtered out before the distortion in the preamp. If you are only building the pre amp, there is no way you are going to achieve the real amps sound. There are ways to emulate this negative feedback filtering though. Quite possibly using opamps or the like. Have a look at the resonance circuits in the real amps for a clue as to where to start.

Lawrence - There is plenty of low end, not sure what you are getting at?

I had some tone stack problems in the beginning but that has been resolved as far as I am concerned...

Ian - Google ENGL Schematics and select "images" for your search, you should fine hundreds if not thousands of them... I believe this is the E530

[Groovenut]

One thing to keep in mind with both of these real amps is that the pre amps filter out most all of the low end. The negative feedback loop around the power amp is used to restore the low frequencies filtered out before the distortion in the preamp. If you are only building the pre amp, there is no way you are going to achieve the real amps sound. There are ways to emulate this negative feedback filtering though. Quite possibly using opamps or the like. Have a look at the resonance circuits in the real amps for a clue as to where to start.

Lawrence - There is plenty of low end, not sure what you are getting at?

I had some tone stack problems in the beginning but that has been resolved as far as I am concerned...

Oh ok, I had read most of the thread but may have missed the resolution. Glad there is plenty of bass for you with the existing config. Nothing to see here carry on...

[J0K3RX]

Lawrence - That's ok man.. I still am not real happy with the TS but it's as good as can be expected. I am still gonna experiment with some other designs like the Blackstar ISF controls with the values divided by 10..? Friend has a Blackstar and I like the tone controls a lot! 

[JebemMajke]

How does this fare to that Amt-like design of yours, aka "Like E1"


?

[J0K3RX]

How does this fare to that Amt-like design of yours, aka "Like E1"

?

This one sounds way better! Just one problem, It has noise when I roll the volume pot back/down on the guitar.. a lot of noise! The AMT clone is silent and volume and tone stack work great but lacks the true "ENGL" tone that this one (the E3) has! It also has much less gain! I traced the AMT engl from picks that somebody posted on FSB but I don't think I got it exactly right? Had to guess at a lot of the parts... It sounds really good but not really like an engl like the jfet/mosfet design... It's probably because of mistakes in my trace job? If I could get this f__king volume problem sorted this thing would be golden! I tried a 2N5457 for Q1 and the noise on the volume pot disappeared but so did the tone and mojo so.......?

Weird thing is that when I put a tube screamer in front of it and turn the level on about 3 and the drive all the way off it's perfect? The volume rolls back and no noise and the pedal is pretty much silent, well quiet anyway for a high gainer! I can even turn the level on the tube screamer past 5 and the drive on 1 or 2 and still quiet? Then if I hit the bypass on the tube screamer, there it is, the noise on the volume pot on the guitar is back again??? I have a hard time believing it's because of all the high gain since the tube screamer actually even boosts the already massive gain even higher and the noise disappears?? like I said earlier the noise only happens when the volume pot on the guitar is turned back to around 3/4 of the way and peaks @ mid range, if it's turned fully up there is no noise...?

Look at this post « Reply #35 on: December 28, 2004, 01:36:02 AM »
http://www.diystompboxes.com/smfforum/index.php?topic=27925.20

He wrote:
Hellow to all.

It is not necessary very carefully to select details.
This device will work after installation of any properly functioning builders.
Versions of possible substitution are reduced below.
Russin KII303A,X-->J201
KII303I' -->2N5457,2N5458

Russian KII303A and KII303I ' have a low noise and allow to receive fine result.
The application J201 and 2N5457,58 will give hardly the greater noise probably (but it will be noticeably only in a position "MIN" of a level regulator on a guitar)
In speakersim circuit:
Russian p-channel KII103 -->J2N5020
KII303X-->J201
I hope, that this information will be useful.
I wish success to all.
Xbananov

This is a really old post from 2004 as you can see and xbananoff is Victor Kampf from AMT... Is he saying what I am experiencing by using the J201's in place of the KP303A's??? Anybody know?

Edit: I tried a 2N5458 and a 2N5457 and I like them, no noise and plenty of gain!! I tried the 5457 before and didn't like it but it actually works good now, probably because I  am getting 8.5v right before the trimmer now..? Not sure but sounds real good! The 5458 has a little less gain but completely silent. Mensur suggested I try a 2N5484 medium gain and low noise but I haven't got any, yet. Now we are gettin somewhere!!!  

[deadastronaut]

^ cool, glad you solved your vol problem, so its fet sensitive then....

[J0K3RX]

^ cool, glad you solved your vol problem, so its fet sensitive then....

Well, I am definitely on to something and making headway with this!  Seems to be a noticeable loss of gain when using the 5457 for the first stage and even more so when using the 5458 but this preamp can stand to lose a little gain... The 2N7000's really kick these into high gear! I tried the BS170's also and they are about the same as the 7000's but maybe a little darker sounding. I wonder what the Dr.Boogie and others would sound like now with 7000's or BS170's?? There are a couple Russian designs like the Krank that have this combination in order (J201 - 2N7000 - J201 - 2N7000 - J201) and the buffer after the tone stack is J201. Interesting and a great alternative to using J201's plus the 2N7000's are real cheap still and builders don't seem to be scarfing them all up like the J201's

I still gotta try the 2N5484.

[deadastronaut]

interesting, yeah i suppose why not mix em up a bit...

[J0K3RX]

Ok, I am torn between the AMT Engl clone that I traced from some pics in a forum and the Russian Engl 3 by AZG...?

I think I like the E3 better but the AMT clone sounds extremely good also and has no noise what so ever..

Here is some noodling with the "Like E1" AMT clone... What do ya'll think? Listen to the tone, ignore my playing  

http://dl.dropbox.com/u/11178619/E1-%20Impulse2.mp3

[JebemMajke]

Amt clone sounds better. It doesn't have as much gain as E3 does, but it does sound like the real thing. Have you tried pushing it with tubescreamer or something similar?

[J0K3RX]

Amt clone sounds better. It doesn't have as much gain as E3 does, but it does sound like the real thing. Have you tried pushing it with tubescreamer or something similar?

Yeah, I normally use a TS in front of all of these however, I was not in that clip. One thing about both of these preamps is that they are extremely touch and pick attack sensitive. So, if you pick lightly it sort of cleans up and you don't seem to have as much gain but if you really cut into it and chug it opens up.. I like that, very tube like! I am sure I can get almost the same tone from the E3 if not better if I mess with it a bit! Thing is I can play easier with the E3 and really opens up on the neck pickup.. The AMT does well but the neck pickup doesn't sound as bluesy and round. I like them both damn-it!