Bogner Seventheaven

[demym]

Hi to all,

i'm building the Bogner Ecstacy jfet emulation, basing on the Seventheaven pedal by GoosoniqueWorx:



I have some problem with the STRUCTURE switch; in fact, when i switch it on (bringing to GND R10 - 4.75k and C4 - 2.2uF) it also changes the bias of the associated J201... now, i have the bias trimmable; but it will not surely be trimmable once i close the enclosure.

As the scheme is practically the same as the real Ecstasy amp, maybe the tubes don't suffer about this issue ?

I think i will make only the 2.2uF cap switchable, are there other alternative solutions ?

I also have a big squeal right after Q4 (tried both J201 and 2N5457).. That squeal is not there at gate of Q4 (i mean, it's introduced in that fourth stage..)..

I triple-checked values of components between Q3 and Q4, and all seems to be correct...

Any suggestions ? I've seen a lot of videos of this pedal on YT, and it sounds fine.

Thanks in advance !

[anchovie]

As the scheme is practically the same as the real Ecstasy amp, maybe the tubes don't suffer about this issue ?

Yes, along with the tubes having a voltage supply about 40 times higher and not requiring adjustment of a trimpot to bias them due to massive variance of components.

I think i will make only the 2.2uF cap switchable

This is the easiest way to deal with it in this pedal.

I also have a big squeal right after Q4 (tried both J201 and 2N5457).. That squeal is not there at gate of Q4 (i mean, it's introduced in that fourth stage..)

This is the last signal amplification stage, so gain is getting pretty huge at this point. The circuit will be very sensitive to wiring arrangement (you might even need to use shielded wire). Quite a few people had squeal problems with the Dr Boogey, so you could search for some threads on that.

Getting rid of C8 might provide a benefit, and putting the cap in parallel with R17 instead might help even more.

[demym]

Thanks very much.

What value should a cap in parallel with R17 should have ? i tried till 10n, but no cure (it only changed the pitch, toward lower frequencies, of the squeal).

I also tried to breadboard apart the last stage, and having source resistor at at least 47k (tried 10, 20, 22 with no success) eliminates the squeal (but also, obviously, reduces a bit gain and moves Q4 trimmer spot point away).

Did not yet try to get rid of C8 (470pF), though.

Thanks anyway, i'll try some more.

[anchovie]

What value should a cap in parallel with R17 should have ?

If 10n isn't fixing it then I don't think that's the solution.

[demym]

Ok,

so, before making my Q4 source resistor a 47k, how can i reduce signal entering Q4 from the previous stage ? Could this be done making R19 bigger ? (although i tried with 1meg, but still squeals...)..

If it's not possible, i'll simply make Q4 source resistor a 47k; this leaves me some delusion, as the original stage is not like that, and as i'll loose some of the juicy gain that would come with the original values (squeal apart, obviously !)..

Also, i have not yet put Q5 and the tone stack... Q5, i tried it on the breadboard, and i'm sure it doesn't cure the problem... can it be that the tonestack is organized to cut those squealing frequencies ?...

Generally speaking, in all high gain pedals i have done till now (dr.boogey, carvinlegacy jfet, bsiab..), i usually always have this kind of problem on the fourth and beyond jfet (and i don't think, sincerely, that's only a matter of shielded wire and so on) ... Does this happen to you guys also ? I use to do my circuits stage for stage (don't love much breadboarding all of a circuit, so i use to breadboard one stage at a time, and when it works correctly i 'print' it on perfboard or veroboard, preferring this last one, and the breadboard the next stage.. This helps me to debug better problems that can arise...)..

Thanx anyway, have a nice time


UPDATE: as in one of my past posts, putting a tillman preamp in front of the bogner cures the squeal !!... really confused.... i'm using and Ibanez guitar with DiMarzio Evolution neck & bridge pickups....  i thank it was an useful info for fixing ipothesis...

[defaced]

Looking at the Dr Boogie schem (http://gaussmarkov.net/layouts/drboo/drboo-schem.png), the placement of C19 in the boogie schem relative to the placement of C8 in yoru schem seems like it would affect high frequencies differently (attenuate them maybe?) before entering Q4.  This might be worth playing with.

[demym]

Hi, another update: i found an error between Q3 and Q4: R19 was before (and not after, as per schematic) R18, thus invalidating the voltage divider before entering Q4... now the squeal has almost completely gone (there's a little bit yet, indeed, but i think it's caused by the effect not yet enclosured; in fact, it's sufficient to shield it nearing my hand to input/output to make it silent).

thanks for your help...

one more question: what is technically called Q5 ? i've notice that it's output is from the source, different from all the others ? is it a buffer or something similar ? what is its function ?

Thanx

[anchovie]

is it a buffer or something similar ?

Yes. When implemented using a tube it's a cathode follower, in this case it's a source follower. It ensures that a low impedance is driving the tonestack.

[Maik]

any pcb?