Semenov Boogie

[Kipper4]

Calling Jim
I don't suppose you can dig out your VHT mod5 and share the voltages please
Mine seems unbiased some where.
I'll follow up with my voltages and a copy of the schematic later thanks
Rich
Link to schematic
https://imageshack.com/i/idrfp5xXj

Also here

http://www.guitarristas.info/foros/muestras-sonido-messa-soldano-krank-engl-vht/88517/pagina2

[Kipper4]

Im getting output but not like i expected


eg Q1 fet j201
D 2.1
G 0.41
S  00


Q2 mos 2n7000
D 4.23
G 4.48
S 3.27

Q3 j201
D 3.26
G 00
S 0.58

Q4 2n7000
D 4.75
G 4.31
S 3.29

Q5 j201
D 9.09 same as wall wart
G 4.75
S 5.43

Q6 j201
D 9.1    same as wall wart
G 00
S 0.72

All my pots are wired back to front but still function (just backwards)

Is there a reason theres an asterix (*) next to R3 22k.
according to the schematic I should be getting +4v at the drain of Q1

thanks for the help
Rich

[Kipper4]

Just remembered I subbed R14 (2k in schematic) with  1k8 brain fart, good job i made a note of it
back in a tick, strikes up the iron gonna try a 2k2

[Kipper4]

I'm off to bed now. wasnt much better. Its 2 am and I'm done in. It'll l wait till morning now.
Any ideas leave em here.
Smoke me a kipper. I'll be back fo breakfast.

[J0K3RX]

Maybe this will help you...? Here is the one I made, maybe you can cross reference yours with this one... or, you can just download these files and build this one.. s'up to you  

BTW - I called it "FIGHT BR33D" because it kinda reminds me of the VHT Pitbull and pitbulls are also a breed of dog that is bred to fight... make sense? 

Here is the zip with the pdf transfer file.
https://dl.dropboxusercontent.com/u/11178619/VHT%20JFET-MOSFET%20Verified/VHT%20JFET-MOSFET%20PREAMP.zip

[Kipper4]

Nice one man.
Had to go with keens 2nd and use a 12k+10k lin trimmer for Q1 and 100k lin trimmer for Q3.
Time to rehash the layout to accomdate these changes.
I'll probably do the B100k sweep pot mod later when i have it biased satifactorily.
Thanks for the layout too. mightrjust base mt new layout on that and try to use 9mm pots from tayda that arrived today.
More tweeking to do I might even be able to find a close enough value R to replace those trimmers at some point hopefully.
Good work
cheers

[J0K3RX]

Nice one man.
Had to go with keens 2nd and use a 12k+10k lin trimmer for Q1 and 100k lin trimmer for Q3.
Time to rehash the layout to accomdate these changes.
I'll probably do the B100k sweep pot mod later when i have it biased satifactorily.
Thanks for the layout too. mightrjust base mt new layout on that and try to use 9mm pots from tayda that arrived today.
More tweeking to do I might even be able to find a close enough value R to replace those trimmers at some point hopefully.
Good work
cheers

"Had to go with keens 2nd and use a 12k+10k lin trimmer for Q1"?... lost me on that one? I am guessing you mean a 12k fixed resistor in series with a 10k trimmer? I guess that would work alright but not sure why you would do it that way unless maybe you only had 10k trimmers on hand... I always replace the trimmers after I get them biased where I like them anyway and I use metal film for those. I do everything I can to reduce the noise on these FET preamps, every little bit helps... 

I use the "sweep" pot on nearly everything now that has a Marshall tone stack... Every time you turn it affects the entire tone stack so you can really get more control over a much wider range of frequencies. Notch filters before or after the stack or even between the 3rd and 4th stages are also something to play around with! Another thing you may want to try is diode clipping between V5 and the tone stack   

One thing I will say is that the VHT was not my favorite and probably my least favorite of the bunch! It was good at low gain stuff and cleaned up well... sounds good with the neck pickup, might make a decent lower gain bluesy kinda thing..

[Kipper4]

You got it. No 20 k trimmers. I'm gonna build another recommendation pls I want more bottom end the vht is lacking.

[Kipper4]

tested at more than bedroom level now and its got plenty of low end.
I like the sweep function bags of tones available
my finding for biasing Q1  R3 14.2k
                        "     Q3  R15 13.4k measured in circuit
couple of subs  treble in tonestack 220k in schematic used a 250k.
                     mids in tonestack 22k   "        "          used a 20k
i might swap out the 470p in the stack for a 220pf might not make enough differance  but it has to be done
and when i get em i'll try the BAV21s
This is turning into an experimental pcb
I'm using a 50k for the gain too instaed of schematic 100k plenty of dirt on tap still

Edit make R15 68k when measure out of circuit
replaced and works a treat if a little lower than unity depending on tonestack settings. hhhmmm

[Kipper4]

Quick question
What are the diodes from gate to source doing here?
Thanks
Rich

[Kipper4]

Of course I mean the BAV21s

[mac]

Rich,
Those BAV21 have more reverse current (leakage) than 1N4148. I wonder if for a given Mosfet you'll get different drain voltages.

http://www.nxp.com/documents/data_sheet/BAV20.pdf

http://www.nxp.com/documents/data_sheet/1N4148_1N4448.pdf

mac

[Kipper4]

Cheers Mac old buddy.
I'll do some measuring and see.

[Kipper4]

Ive been messing with the seventheaven schematic and this is where im at.
Of course it sounds Assome.
I'll do a tube in the morning.


http://imagizer.imageshack.com/img661/2366/2GoOsJ.jpg

[mac]

Rich, what happens if you put another diode in the opposite direction?
I ask because Mosfets need tiny currents to bias, and since there is almost no current through the forward biased diode you *might* have a kind of darlington Bazz Fuss. I mean, BF tuning condition is Vc=Vb, Vd=Vg in this case. That's why darlington BF sounds better than single silicons.

mac

[Kipper4]

I've no idea Mac. I'll give it a go on the amt B1 and let you know. All good information there.
Cheers

[Kipper4]

Here you go

https://www.youtube.com/watch?v=DQy-A_bKWPU

[steveyraff]

Here you go

https://www.youtube.com/watch?v=DQy-A_bKWPU

Sounds great Kipper

[J0K3RX]

Rich, doesn't sound like there is nearly as much dirty gain as mine had? It sounds like the volume is up really high but the gain is down really low..? Has a clangy sound to it kinda like just the clean sound of the amp with maybe a FET boost or something... Is that what you were shooting for? Mine had a blistering amount of high gain especially on the input jack of an amp!

[mac]

LTSpice simulation of a similar mosfet stage, with/without diode.

http://imgur.com/a/drFvX





mac