BLACK FOREST High Gain Preamp - Based on the Bogner Uberschall

[J0K3RX]

ok, I settled at 18k from input to ground... not muffled or anything at lower volumes on the guitar, not muffled at lower gain on the pedal, no background hum with the volume off, no loss of highs (muffled), no hum at full volume etc... "NO HUM!!!" sounds perfect to me! Really sounds like 100%!!! I think I am gonna box this F#$ker up and call it a day! Really, just totally fixed it for me and I even still have the noise gate on a switch just for super silent mode... Damn, this thing sounds unbelievable!!! Also built the Hotline 2 cab simulator and WOW!!!! It's going in there too along with a tube screamer for that razor edge!  

Need to make a clean channel for a total preamp?

[J0K3RX]

jymaze - what about paralleled J201's or 2N5457's for the 1st stage? Wampler does this... less noise?

Ah well, I'll just try it and see what happens....

[bluesdevil]

I'm trying to keep up with the changes still.
So what did the correct value of C2 end up being?
Any resistor changes?
Is changing r24 to a trimmer an outdated fix now?
Sorry for all the questions.

I tried the latest fix with 18k tacked at front end, but didn't like it with passive pickups and still hums. Maybe just give in and strong arm it with a permanent buffer at front end?

[J0K3RX]

I'm trying to keep up with the changes still.
So what did the correct value of C2 end up being?
Any resistor changes?
Is changing r24 to a trimmer an outdated fix now?
Sorry for all the questions.

I tried the latest fix with 18k tacked at front end, but didn't like it with passive pickups and still hums. Maybe just give in and strong arm it with a permanent buffer at front end?

Did you install the gate, yet?

18k might not work for all different pickups... experiment with different values

Quick sh!tty sample, no noise gate... How does the hotline cabsim sound?
http://dl.dropbox.com/u/11178619/New%20Preamps/ENGL_HL_CABSIM.mp3

[bluesdevil]

Hey Jim - I'll hack in the gate tonight and will report back with results. I was putting off doing it in fear I would make a mess of everything and cause more problems.
So was 220nf the wrong value for C2?

Ah, I wanna check out your Hotline cabsim, but no sound for computer right now..... everything is tore apart waiting to recarpet the room my stereo is in, damit!!!

[J0K3RX]

Hey Jim - I'll hack in the gate tonight and will report back with results. I was putting off doing it in fear I would make a mess of everything and cause more problems.
So was 220nf the wrong value for C2?

Ah, I wanna check out your Hotline cabsim, but no sound for computer right now..... everything is tore apart waiting to recarpet the room my stereo is in, damit!!!

I will do up a diagram of all the changes I made... As for C2, not sure if I would say it was wrong at 220n but I have mine @ 47n right now and C3 is 2.2uF instead of 22uF... R8 is now 2k and R19 is 100k. C17 and C18 are 10uF surface mount tant caps. I think that's about it.. but I will go back over it and make sure.

[bluesdevil]

Alright, spliced in the noise gate circuit between C14 and the R19/R18 junction.
Definitely kills the high end buzz when used with active pickup, but the low end buzz is still there.... could be because I've got the circuit board wired to breadboard.
The noise gate does cause a good bit of sustain loss with gated sound unless I turn gain all the way up..

I'm gonna try the r24 trimmer thing next and then reduce the two cap values you mentioned before.
Damn, I really wanted to box this one up, so I'm hoping something will work out the buzzing without compromising the sound.... ain't quitting yet!!

[Maik]

Tested today hooked to F1 channel send/return without gate,

Hey, where to find that F1 pcb?

[fretzburner]

@Maik the F1 i'm talking about is original AMT pedal.Small mod to my  build R19 to 100k same as Jok3rx's.Careful with soldering because i busted one 2N7000 by changing R19 too much heat makes the V4 dead.

[J0K3RX]

Alright, spliced in the noise gate circuit between C14 and the R19/R18 junction.
Definitely kills the high end buzz when used with active pickup, but the low end buzz is still there.... could be because I've got the circuit board wired to breadboard.
The noise gate does cause a good bit of sustain loss with gated sound unless I turn gain all the way up..

I'm gonna try the r24 trimmer thing next and then reduce the two cap values you mentioned before.
Damn, I really wanted to box this one up, so I'm hoping something will work out the buzzing without compromising the sound.... ain't quitting yet!!

hmmm... Not sure man? I have mine dialed in like a dream now even with the gate at lower gain I get little to no sustain loss. But, whatever I have done has completely eliminated the noise/hum so I really don't need the gate... By the way you can adjust the gating effect by replacing the 1M resistor with a 1M/B pot so you can fine tune the gate that way. Anyway,  I tried mine with three different guitars, all with different pickups and one has EMG actives and no hum with any of them.  In any case we need to find a way to get the noise level/gain down a lot more on the 1st stage... It probably would be acceptable if we were using J201's for every stage but with those following mofets it really kicks it up in to smokin ultra high gain...

Just some thoughts I had: Lower the voltage going to the 1st stage by changing R8 to 2k. Also, maybe raise R3 to 1.8k or 2.2k or 2.7k like the Krankenstein?

These are the changes I have done to date:
Added 18k on the input to ground
Changed C2 to 47n
Changed C3 to 2.2u
Added 22pF from source to drain on V1 - J201
Changed R8 to 2k
Changed R19 to 100k
Changed C17 to 10u tantalum
Changed C18 to 10u tantalum

After thinking long and hard about this I thought, why would these Russian schematics be made this way if there is so much noise? The answer is simple, they were not, and we are not following the Russian schematics! These were originaly designed using KP303A for stage 1 and KP303E for stages 5 and 6 for a reason I am guessing. I have heard many sound samples of these preamps using the correct jfets and I can't hear any noise! So, either they are hiding the noise really really well or, we are doing something wrong or, they are simply not getting the noise in the first place. Also, from listening to their sound clips from what I can tell I think they are getting slightly less gain than what we are getting using the J201, 2N5457 or whatever! This thing produces "ultra mega gain" and therein lies the problem... These were not designed with J201's in mind! J201's are noisy as hell! Even using the lower noise 2N5457 or 2N5458 something is not right!  


This preamp has "A LOT" more gain than any of my retail AMT pedals so, I am not at all surprised that there is a lot of noise! In fact, these have too much gain which got me thinking and looking at some of the AMT schematics. Personally I consider AMT to be "THE BEST" at reproducing jfet pedal versions of these different famous preamps! One thing I noticed is that they are similar in design in that they both use some formula to scale these down rather than just copying the actual tube schematic value for value... i.e. Dr.Boogie, 7theaven, Black Forest etc... So, after looking at the AMT schematics I noticed a few things. One is that Victor K has found a great jfet in the 2SK208A-R, very good for these high gainers but very hard to get! Another thing I noticed is that he is scaling these down very precisely to produce an almost indistinguishable difference between the real thing and the pedal version! Also, I notice he does not go "over the top" with the gain which is more like the actual tube preamp and also seems to better capture/reproduce the tone! Most guitarists I know and have heard (myself included) use some sort of tube screamer variant in front of them to give them that extra bite and low end tightness! This is also commonly done with the real tube versions to overdrive the input and give the same effect.

I think we are snipe hunting here (meaning we are hunting for something magical we are not gonna find)
I just think we are going in the wrong direction and looking at the wrong things... Maybe we just need to redesign the whole 1st stage?

I noticed with these jfet/mosfet based preamps that the whole thing is scaled except for the 1 stage on all of the schematics... If you look at the Engl, VHT or Krank tube amp schematics the 1st stages are almost the same as the tube version! If you look at AMT they are totally different than the amp they are made after...

Maybe we should incorporate the AMT design or close variant into this Russian ENGL to accommodate the noisy @ss J201??? Anybody got any other ideas?

Here is the ENGL 1st stage and I am fairly sure this is correct as far as I could tell from tracing it... Should fit into this jfet/mosfet design with little or no modifications... Also take notice of the 50k gain pot.
 

[J0K3RX]

@Maik the F1 i'm talking about is original AMT pedal.Small mod to my  build R19 to 100k same as Jok3rx's.Careful with soldering because i busted one 2N7000 by changing R19 too much heat makes the V4 dead.

Sockets!!! Use them

[bluesdevil]

Hey Jim - First of all, thanks for all your patience! I'm beginning to think you are on to something by changing the 1st stage over to the 1st ENGL version and I think I may go that route.
Something weird I just noticed, but maybe I'm wrong thinking this:
On the ENGL3 drive pot, lug 1 goes to +4.5v rail per schematic and not to ground... could that be the problem?
Thanks for everything, we'll get it worked out!

[J0K3RX]

Something weird I just noticed, but maybe I'm wrong thinking this:
On the ENGL3 drive pot, lug 1 goes to +4.5v rail per schematic and not to ground... could that be the problem?

Nope... makes no difference, tried that a long time ago, ran it to ground and sounds exactly the same and the hum lives on. Nice try

Might not be a bad idea - permanent buffer at front end as you stated in a earlier post... Question now is which buffer? Maybe build it on a small daughter board or piece of perf board? There is no way I can cram it into the current layout!

[bluesdevil]

AAAARRRGH!!!!

[jymaze]

Yep Jok3rx, too much gain... That is the diagnosis.

Basically I think this circuit has one too many stage for 9-18 volts of power supply. Think about it:

1) Real Engl/Ubershall: 4 stages  with clipping at 330+ volts

2) Pedals based on these: 4 stages with clipping at 9 volts

Incidentally the gain of one stage is probably 15-20 for a jfet and 30-40 for a MOS. SO in order to get the same clipping effect with the pedal you need about one less stage in term of gain.

Clipping 30 times earlier means 30 times worse signal-to-noise ratio or about 30 dB more noise than the same circuit built with tubes.

If I ever get around to building it (still have to find time) I may just suppress V4.

[J0K3RX]

Yep Jok3rx, too much gain... That is the diagnosis.

Basically I think this circuit has one too many stage for 9-18 volts of power supply. Think about it:

1) Real Engl/Ubershall: 4 stages  with clipping at 330+ volts

2) Pedals based on these: 4 stages with clipping at 9 volts

Incidentally the gain of one stage is probably 15-20 for a jfet and 30-40 for a MOS. SO in order to get the same clipping effect with the pedal you need about one less stage in term of gain.

Clipping 30 times earlier means 30 times worse signal-to-noise ratio or about 30 dB more noise than the same circuit built with tubes.

If I ever get around to building it (still have to find time) I may just suppress V4.

Easy enough to do... I can just jumper bypass V4 and and connect V3 to V5 and see.

Like I said earlier in this post I got this thing working like dream now... I hate tearing into this now but for the sake of all I will sacrifice...

[jymaze]

Do that on your Black Forest instead!

[fretzburner]

Just tested today i changed V1 to 2SK152 and biased to 4v drain and the noise goes down to normal.Loose some gain too but still sounds okay,anyway my previous V1 was 2SK117 and lots of gain where i only dial to around 2oclock.This time i can set the gain to 10.

[J0K3RX]

Do that on your Black Forest instead!

Black Forest is coming back this time with all on-board pots like Engl... all of them will be like this but hopefully without the hum from hell

Like I said before... My AMT pedals E1, P1, SS-30 and just got a B1... none of them have this much gain!!!

[deadastronaut]

jim....have you tried a 2 fet 1st stage config like the bsiab...may be quieter noise wise....just thinking aloud as the spitty is very quiet...