BLACK FOREST High Gain Preamp - Based on the Bogner Uberschall

[chromesphere]

No worries Jim, ill work it out, thanks again!
Paul

[bluesdevil]

Hell yeah, got my parts in today for the ENGL 3 build.... will report back in a few days with results!!

[chromesphere]

The ENGL 3 layout really needs to be verified (visually).  Interested to see your results bluedevil!
Paul

[J0K3RX]

Interested to see your results bluedevil!
Paul

+1 Bill (bluedevil)

Where in FL? I live in New Port Richey.

~ Jim

[bluesdevil]

You're right , Paul. I better at least take a quick look before soldering!
Not feeling well today..... catching the flu or allergies are kicking my butt. I'll do my best to get a report up over the weekend.

Hey J0K3RX, I'm in Zephyrhills... hell, we're in the same county!

[J0K3RX]

You're right , Paul. I better at least take a quick look before soldering!
Not feeling well today..... catching the flu or allergies are kicking my butt. I'll do my best to get a report up over the weekend.

Hey J0K3RX, I'm in Zephyrhills... hell, we're in the same county!

Yup, about 40 miles away in-land... Howdie neighbor!

I have had a couple flu's already this year... still have the after affects of the last one draggin me down

Check the pot configuration! I am notorious for backward pots 

I have another layout that doesn't have on-board pots, that's what I recorded the sound clips with.

There is one minor bug with this preamp but I am slowly figuring it out. Keep in mind I pulled this from the Russian forums so the original was designed for those cold war KP303A and KP303E transistors.. The 2N7000's are the only things that stayed the same. The bug is when you turn the volume pot on your guitar down there is an increase in noise At least with my guitars it does this.. Anyway, you can remedy it by putting a tube screamer or any pedal with a bypass buffer in front of it. Totally eliminates that problem 100%! So, I need to make a small buffer board of some sort to throw in front of this thing. Other than that it works excellent, well, my other layout anyway. The noise gate also works great and you can actually built it right on the switch!

For myself I was just going to build this E3 preamp, a TS-808 and the cabsim all in one box.. I like flipping on the TS anyway to tighten up the low end although it's already really tight! The TS gives it a little more scream ya know... I turn the gain all the way down on the TS and turn the level up to about 3 or 4 and it just rips! Most dudes who have Engl amps who play metal use a TS or a varaint in front of the amp anyway, same difference here. I may just make the tube screamer with a level switch and fixed resistors for the tone and gain? I don't really feel like having all those pots and once I find the sweat spot on the TS I hardly ever change the settings again, if ever....Just connect it to a stomp switch and call it "tight boost" or something? And when it's bypassed leave the buffer inline, then totally remove it from the path for true bypass. I have like 10 or more 1790ns enclosures so I may even build a crunch and clean channel? Seems kinda a logical on a preamp to have more than one channel anyway, no? blah blah blah...     

[deadastronaut]

The bug is when you turn the volume pot on your guitar down there is an increase in noise

hmmmm...thats weird, so it doesn't like ''nothing'' going into it?...not sure what causes that, or the remedy....strange.

[J0K3RX]

The bug is when you turn the volume pot on your guitar down there is an increase in noise

hmmmm...thats weird, so it doesn't like ''nothing'' going into it?...not sure what causes that, or the remedy....strange.

Well it like to eat tube screamers... 

[jymaze]

Jok3rx,

For your noise problem, I think it is worth a shot trying a 10n cap at the input, just to make sure there is no DC across your 1M resistor.

I am really not sure it will work, but it is worth a shot...

[J0K3RX]

ok, I tried all possible fixes mentioned here and no cigar... The only thing that works so far is the buffer/TS in front of the preamp.

I did audio probe this and all of the noise is coming from the 4th stage mosfet. No surprise to me! That's kinda what the BF was doing as well... So, I stuck trim pots on the source and drain and tried to even it up but no matter where I biased it I still gets the noise. Every one of these f&$#kin preamps does this same thing! There has got to be something that will fix them besides the buffer thing??? This one problem is the only thing keeping these from being really great pedals! Damn-it!!!

[bluesdevil]

BUILD UPDATE:
All components and sockets for jfets soldered in, just gotta get the pots installed and then hope for sonic mayhem!! Unfortunately I didn't get pcb mount pots so lots of wires to deal with... and I'm dreading it, ha!

[J0K3RX]

BUILD UPDATE:
All components and sockets for jfets soldered in, just gotta get the pots installed and then hope for sonic mayhem!! Unfortunately I didn't get pcb mount pots so lots of wires to deal with... and I'm dreading it, ha!

Looking forward... I want to see if yours does what mine does.

[jymaze]

I just don't understand how a TS in front is fixing noise from the 4th stage... Does not make any sense to me. Is it random noise or more like high gain background noise? Does it vary with the gain knob?

[J0K3RX]

I just don't understand how a TS in front is fixing noise from the 4th stage... Does not make any sense to me. Is it random noise or more like high gain background noise? Does it vary with the gain knob?

Yeah, I really don't understand it either   It seems like everything I build other than a Dr.Boogie and the AMT B1 clone has this similar issue!? The BF had it and the Engl has it or something similar..?

I started another topic about the noise here. Tried all the suggestions but if anything made things worse...  
http://www.diystompboxes.com/smfforum/index.php?topic=101250.0

Returning it to it's original state and then I will record the noise only and roll the volume on the guitar back so you can hear it. Everything on this is just as the schematic except for the substitution of KP303's with the J201's. I listen to the sound demos in the Russian forums and I don't hear any noise but they don't roll the vol knob up and down..? I think J201's are not suited for this maybe?  

Found this mod in the forum with somebody using J201's, might give it a try. The browser translation from Russian to English doesn't work so well but this is what I could make of it...
R9 - 27k / drain = 6.45v
R16 - 33k / drain = 6.5v
V4 change to BS170
R20 - 47k / drain = 5.8v

I think the noise on stage 4 is coming from the increase in gain from the previous stages... By the time it reaches the 4th stage it's already got too much gain/noise (mostly noise) so the 4th stage just gets too noisy and hums? I think it all starts from the noise produced in the first stage by the J201 and basically builds to a hum on the 4th stage? While the noise is not noticeable to the human ear in the first stage, it becomes multiplied as it goes through the following stages and becomes a problem at the 4th stage.. I think the the buffer on the first stage quiets the noise produced by the J201 a bit? Just my uneducated theory anyway....

The tube screamer or buffer doesn't completely eradicate the noise but with some minor tweaking does bring it down to a acceptable level... The down side is that it affects the over all tone as well, not very noticeable when using full high gain but if you roll the volume back on the guitar it doesn't clean up very well. Hard to explain but it doesn't sound like it's operating at it's full potential, kinda wimps out no sustain etc..  

Keep in mind - I am "VERY PICKY" and it has to be perfect or I am not happy!!! Others might not find this to be a big deal but I WANT PERFECTION!!!

[jymaze]

You know my usual answer: Too much gain kills a pedal! It makes it noisy and sometimes unstable.

Also, the first stage is the one that is critical for noise (Frii's formula) so I would use a device with less noise. For reference a 2N5457 has about 5 times less noise density than a J201.

[J0K3RX]

You know my usual answer: Too much gain kills a pedal! It makes it noisy and sometimes unstable.

Also, the first stage is the one that is critical for noise (Frii's formula) so I would use a device with less noise. For reference a 2N5457 has about 5 times less noise density than a J201.

You are absolutely right about too much gain killing a pedal! The question is, when is it too much? I guess when it starts to sound like sh!t? I have tried the 2N5457 and it does help, a lot... but still get the noise but greatly reduced! Probably wouldn't hurt to make the 3rd stage a 2N5457 also. Like on the SLO and VHT schematics it's a J201 but same idea...

[jymaze]

About too much gain kills a pedal:

I have a Rocktron SilverDragon. It is not too bad (not spectacular) at high gain without the boost, but with the boost on it becomes a messy noisy thing, impossible to tame and it sounds pretty bad...

[jymaze]

Ok, you tried a 10nf cap added in series at the input right?

I have another idea, to address potential instabilities of the first stage: Try adding a 10pF between drain and gate of the first jfet.

[bluesdevil]

Okay, just finished the ENGL3 and have it hooked up to my breadboard jig (power and I/O jacks). It fired right up..... yippee, no debugging!!!!!!!
With Chromesphere's corrections, it works. I am getting a hum, probably due to such a high gain circuit exposed without any shielding.
The only difference is I changed out the J201 in Q1 for a 2n5457. Also the pots are laid out correctly... no worries there.
Only question I have is what are those two empty pad holes on power rails near bottom right corner supposed to be for.... a missing component?
    Compared to Dr. Boogey, I say this is a tighter, higher quality high gain sound. Just need to box up and put shielded wires for in/out to see if that kills that hum.
       Thanks to Jim for the great project and to Paul for the BOM and finding mistakes on the layout.

 

[J0K3RX]

Ok, you tried a 10nf cap added in series at the input right?

I have another idea, to address potential instabilities of the first stage: Try adding a 10pF between drain and gate of the first jfet.

I'll try that tonight, didn't think of that one, yet... Thanks! I have to get my board back to a somewhat normal state, starting to look like a battle field like my black forest did at the end of it's life Hoping bluesdevil reports back with some better news with his? I want to etch that layout but kinda holding off until I hear from him. It really isn't a death sentence for this more like one of those little imperfections that just bugs the living hell out of me and ends up driving me totally insane! I could just build something like a Dr.Boogie that has stood the test of time but, I want to make new stuff! I can't just keep building the same old stuff over and over again ya know... booooring