BLACK FOREST High Gain Preamp - Based on the Bogner Uberschall

[pakrat]

Nice! It's like Xmas visiting this thread 

[Cap]

Like this?
http://www.diystompboxes.com/smfforum/index.php?topic=36392.msg751853#msg751853

[J0K3RX]

This is the fix for the constant hum/noise problem for any of you who might have built it or were thinking of building...

Replace R15 and R16 both with 1.8k resistors. You can probably use 2.2k also but I used 1.8k so I know they work. Then remove R2 and replace with jumper and put a 470pF cap across R1. Replace C2 with a 220nF or 470nF cap. For the boost resistors (R22 and R5) I use 10k and 18k. If you replaced C22 with a 220uF cap you can leave that in there, it's fine... If you have 100uF that's fine, I don't notice any real difference between the two... Also, I removed the presence knob because it was causing weird problems with the tone stack mainly in the treble pot. Has plenty of presence anyway. The two main changes are R15 and R16 to 1.8k, all the rest is just fine tuned stuff...  Bias all of the transistors at half the voltage, mine are 4.3v for Q1, Q2 and Q3 then 4.5v for Q4 and Q5.  That's it, you shouldn't have any hum with the volume rolled all the way down on your guitar and just the expected noise you get with high gain when the volume is turned up.. And btw, I have the noise gate working perfectly which removes almost all of the "normal high gain noise" without killing the sound at all!

[haveyouseenhim]

I really want to make one but it keeps changing

I etched a board early in this thread but it was kinda bad so I'm going to wait till the definitive layout.

[pakrat]

I built one Mike, and it's a monster. It seems the latest changes don't require a new pcb, so you might be safe now. Maybe socket the entire board? 
Thanks for posting the improvements JOK3RX!

[J0K3RX]

High gain circuits are a real bitch!!! I am pretty much done with this now... The low level hummmmm was a real problem, it was present even with the volume all the way off on the guitar or the pedal but the fix I posted will take care of that! After hours of sh!t trouble shooting I finally figured it out... The 4th jfet and the added gain stage were screaming with the audio probe and I couldn't figure out why... Turns out that both of the source resistors were way off causing the whole circuit to become a massive sh!t storm of hum and noise... Bumped those resistors up and bingo! So, I think you are safe now Mike I am moving on to the ENGL and then I will finish the Soldano Avenger...

Pakrat - Let me know if this fixes yours?

[pakrat]

I'm glad you got it worked out Jim, I thought you might give up on this    I have to see if I have those caps laying around, I hope I do!

[J0K3RX]

I'm glad you got it worked out Jim, I thought you might give up on this    I have to see if I have those caps laying around, I hope I do!

The caps are not a big deal... the two resistors and a good re-bias will pretty much do the trick!!

[haveyouseenhim]

Thanks Jim. I'm going to wait for pakrat's approval to start.

@pakat let me know if you don't have those caps

[pakrat]

It's 2:30 am..... do I need to do this now??? I think so....... Gimme 10 min 

[pakrat]

Testing.......

[pakrat]

Ok, I replaced R15 and R16 with 1.8k, and removed R2 and it's dead quiet! Do I need to make the cap changes?

[J0K3RX]

Ok, I replaced R15 and R16 with 1.8k, and removed R2 and it's dead quiet! Do I need to make the cap changes?

dead quiet as in not working or dead quiet as in no more hummmm? You don't need to make the cap changes.. optional.  C2 tightens up the bottom end a bit... You need to re-bias...

[pakrat]

It is dead quiet, without the gate even. I can't remember which resistor I have for boost, but it's higher than 18k and it's still quiet! I still have a bit of an issue with a little static in the decay, but it might just be that I'm using a bugera 333xl to test. Tomorrow I'll try it in a better rig. Good job Jim, this thing really smokes!

[J0K3RX]

If you remove the noise gate and put it back to normal before the gate was added the static will probably go away.. I think your gate is whacky

[pakrat]

I dunno what happened with the gate, but I'll try original boost value and see. At this point, the gate isn't needed and it is super high gain, go figure. Oh, one last thing.... to remove the presence pot, just take it out? I had tried removing the ground from the presence pot but it didn't make a difference with my tone pot.

[pakrat]

If you remove the noise gate and put it back to normal before the gate was added the static will probably go away.. I think your gate is whacky

My gate is removed already

[haveyouseenhim]

Awesome. I will re etch and populate tomorrow!  I have to make a trip to the music shop to use their(better than my dumpsterjet) laserjet   

[pakrat]

Maybe we should inform Riccardo of the changes here. He put a lot of work into his layout with the onboard pots. Now if we could only get him to add in the gate......

[pakrat]

Yeah Mike, I doubt you will be disappointed in this one. It sounds pretty sick with cab impulses on it too.