BLACK FOREST High Gain Preamp - Based on the Bogner Uberschall

[fretzburner]

Build update as of today


photo sharing

image sharing

[J0K3RX]

fretzburner - Gettin close! 

[fretzburner]

Now it's burning hahaha,i like it i like it i like it!!!Used 2SK117 on V1,while V5 and V6 2N5457 and 58.Will try later with 2SK117.Will house this on 1590B to match the size of my F1.

[jymaze]

So you used some Jfets and no MOSfets...

It will work anyway, just a little less gain. It has so much gain anyway that you won't miss it...

I think what makes the russian version different tonally from the Engl-like version is mainly the fact that there is a little more treble boost in the eq so it may make it tighter and more razor sharp, but decreases the low end growl (you can't have everything...).

Maybe there is a tonal difference between Jfets and MOSfets, but it is at best subtle a such a high gain I bet. The polarization certainly makes a difference by making the clipping more symmetrical in he russian version. It should be more aggressive and defined, but less organic, which should be more noticeable for crunch sounds. In theory the crunch sounds of the Engl-like should be a little better to get that bluesy sound.

It is all theoretical, but maybe Jok3r can confirm/infirm...

[fretzburner]

jymaze i'm using 2N7000 on V2,V3,and V4 as per schematic.I don't have J201 right now but liked the sound as i first fire it up.Maybe i will permanently use 2SK117 on V1 and reroute my pins config which was configured to J201.

Edited my previous post to make it clear.In a hurry posting,so excited what i just created.

[J0K3RX]

The way I interpreted what fretzburner said was that he used (2SK117 on V1 and V5) or (stage 1 and stage 5) and on V6 he used or tried both a 2N5457 and a 2N5458. He then went on to say that he was going to try the 2SK117's for V1 - V5 and V6.... But I could be totally reading it wrong here...? Do that a lot

Nevermind -  fretzburner beat me to it

I would be inclined to go with the 2SK117's if it sounds good! I only use the J201's because that is what I have and is a kind of a multi purpose component... Keep in mind that the original Russian schematic calls for KP303A for V1 and KP303E for V5 and V6... The 2SK117 maybe be a more suitable match?

[J0K3RX]

jymaze i'm using 2N7000 on V2,V3,and V4 as per schematic.I don't have J201 right now but liked the sound as i first fire it up.Maybe i will permanently use 2SK117 on V1 and reroute my pins config which was configured to J201.

Edited my previous post to make it clear.In a hurry posting,so excited what i just created.

Whatever you used if you don't get that hum noise then by all means keep using them!!! The J201's are noisy! I hope that is what it is, let me know cause I got my mouse finger ready to click on an order of 2SK117's right now!  

Do you know which classification your 2SK117's are? Y: 1.2~3.0 mA, GR: 2.6~6.5 mA or BL: 6~14 mA

Please verify and you will be honored greatly!!!

[jymaze]

I probably just misread your post, sorry... But the rest of my post about pre-eq and polarization still stands at least...

[fretzburner]

JOK3RX i still get the usual hum but the enclosure is still open no cover at the bottom.We can finalize this as i boxed it.About the transistor it's K117GR

[J0K3RX]

JOK3RX i still get the usual hum but the enclosure is still open no cover at the bottom.We can finalize this as i boxed it.About the transistor it's K117GR

Balls! Balls! Balls!... Ok, can you try a tube screamer or some sort of pedal with a buffer or bypass buffer? Just so I am not the only one who find this to work, kills the hum. I doubt if it's boxed up is gonna make maybe a minimal difference, In this case anyway... But who knows?

[fretzburner]

How about 2SK30A? shall we consider using this?

[J0K3RX]

How about 2SK30A? shall we consider using this?

2SK30A-R would be the best possible choice from what I know... But very Rare! I can get the 2SK30A-Y all day long but the R's are really hard to find!

I am noticing the hum is there even when the gain is dialed all the way back... Seems to be a power related!?

[fretzburner]

I closed the enclosure and there still hum and whistling at full gain.whistle gone at around 75 percent gain.Maybe i will use shielded wires.Yes 2SK30A-Y,dont have R.But i liked the sound very much.Lots of experiment should be done to lessen the hum.will try noise gate later.

[J0K3RX]

I closed the enclosure and there still hum and whistling at full gain.whistle gone at around 75 percent gain.Maybe i will use shielded wires.Yes 2SK30A-Y,dont have R.But i liked the sound very much.Lots of experiment should be done to lessen the hum.will try noise gate later.

Well the whistle is a new one... I haven't had any whistle. Hum yes, whistle no..

maybe jymaze call pull this one out of the crapper!?

Like I said a buffered pedal in front on the engl cures it for me and the noise gate also pretty much puts a lid on it but I still want to fix it! Also if you temporarily remove R24 and install a trim pot you can dial out a lot of the hum, it's a delicate balance...

[fretzburner]

My diy noise gate makes this acceptable.Anyway the hum is comparable to my original DT-2 and GT2.These 2 pedals are noisy too.

[jymaze]

This whistle/hum stuff must be some oscillation on the first stage : If a buffer solves it is very much in favor of oscillations.

Make sure you try a 22pF between drain and gate and put a 100pF in parallel with the 1M pull-down resistor. It may not work, but it is easy to try.

[J0K3RX]

This is a good informative thread that was started back in early 2011 by brymus (Bryan G) who got the Russian Krank from GTlabs working. The Krankenstien is almost the same as the Engl so whatever applies to that most likely will apply to the Engl as well. A lot of notes taken and good rundown... He has not been active in quite a long time so I doubt we will get any answers from him, but who knows? And By the way, I also built the Krank and it has the same hum as the Engl so maybe this is it???

http://www.diystompboxes.com/smfforum/index.php?topic=89399.0

Read post #6... Is this what we are experiencing with the Engl maybe? If so, then he said that fixed it...

Edit: jymaze - I will try your suggestions. In any case I really think these need the quietest cleanest power possible!? Like I said I can hear the hum or hiss with the gain all the way down and the volume down so I am not sure about the oscillation?  

[jymaze]

Volume of the pedal all the way down you mean?

Is the noise the same with guitar plugged or unplugged?

Maybe the ESR of these 100uf is just too much for a circuit with such poor PSRR. The post you refer to is right: Using 10uF caps is enough decoupling and the lower ESR is beneficial. I would put a 22nF poly cap across the first stage's electrolytic too.

[fretzburner]

I just tried to power this with the original adaptor from my F1 which is 12v and it is really good no noise gain 0-25 and guitar vol full,while gain max and guitar volume zero no hum except the whistle which started as i closed the enclosure cover.When i first fire this build(the pcb is still halfway out of the enclosure)i did not experience the whistle.Will check my wiring as experienced in my past build with mercury box.
Note: i did not re-bias V1 for 12v use,i just test it randomly to check if it tames the hum and it really improve.Maybe a lot better if biased to 4v.

[J0K3RX]

I just tried to power this with the original adaptor from my F1 which is 12v and it is really good no noise gain 0-25 and guitar vol full,while gain max and guitar volume zero no hum except the whistle which started as i closed the enclosure cover.When i first fire this build(the pcb is still halfway out of the enclosure)i did not experience the whistle.Will check my wiring as experienced in my past build with mercury box.
Note: i did not re-bias V1 for 12v use,i just test it randomly to check if it tames the hum and it really improve.Maybe a lot better if biased to 4v.

Interesting! I will try mine @ 18v since I don't have a 12v adapter at the moment... I have gotten the high pitched whistle before with other high gainers.. usually something to do with the wiring.. Make sure the output wires and the input wires are not crossing over each other and make sure the wires aren't under or over the board anywhere... Shielded wire of course, and the wires going to the gain pot can be noisy/squeal

Edit: I have the schematic for the AMT V1 by the way... Some interesting stuff under the hood, I like the FX loop! Don't really understand all the auxiliary power outputs but whatever...?

How do you like the mercury box? I have the VST emulation of that in TH2 and I really like it! Would love to know what's inside the Burning Box and maybe even the Taxi Drive!! The Brunetti amp models are awesome!!!