High Voltage Hijinks

Had a rehersal today and ditched double chain setup, but used both amp inputs parallel with 1to2 jack mono cable. Adjusted brite channel volume on top of normal and it was better suited to get the tone I want. Two separate chains with different pedals was too much a hassle. One chain to both inputs is better and easier to setup for now.

Also I finally found LM308/opamp sag people talk about! I had Brutalist going into Rat variant and hitting big chords gave pleasantly brutal sounding bandwidth drop. Turned Rat off and for my surprised it was Brutalist doing the sag.
 
Damn thou my problem child Simms-Watts! Went through almost 4 months problem free, but last sunday tube cutoff came in when chugging power chords, but there wasn’t problems on long sustaining notes.

A dying preamp tube? Bias drifted too high on big bottles? Faulty supply cap somewhere? Just too much gain and grid clamping in action? Or is it just some faulty contact on pedalboard? Dunno lol……

FFS I really need to gather some motivation to do the troubleshooting. Maybe I could raise LTP-PI tail resistor value up from 10k when Im there and remove v2a cathode bypass cap…damn.
 
Asdrael said:
Ouch. Check your voltages of course but maybe look into the NFB? And scope the B+ caps…
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No more cutoffs as I changed some values on V1-2&PI, but changing PI cathode resistors from 470r/10K to 1.2K/22K made a difference in low freq hum this amps been making. Now the amp has less gain and tone with fuzz was all right, but getting into really saturated chuggahs didn’t work so well now. Maybe I’ll solder 500p silver mica back to second stage volume and tweak V1 and V2b cathode values. Maybe V1a-b to 1-4.7uF and V2b to 20-22uF?
 
Been reading about preamp design and started thinking maybe I need some blocking distortion in preamp to get into that filthy pre amp drive zone with fuzz/dirt pedals. This is against usual guidelines and manuals about a tube circuit design so is there anything else to dive into I haven’t crossed apart from experimenting with different component values and testing how it plays?
 
JohnnyCreepy said:
Been reading about preamp design and started thinking maybe I need some blocking distortion in preamp to get into that filthy pre amp drive zone with fuzz/dirt pedals. This is against usual guidelines and manuals about a tube circuit design so is there anything else to dive into I haven’t crossed apart from experimenting with different component values and testing how it plays?
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Frequency manipulation before and after your dirt is a big part of it.

For example the Mesa Mark series is all about pushing extreme mids in the gain stages, and then cutting the mids and bringing back the highs and lows after the pre with the graphic EQ.

VH4 CH3 cuts away all the fatty meat with that 1N coupler after the first stage, and then after the gain stages it dumps the highs to ground so it's all not fizz.

As far as the dirt itself, normal gain stages shaped by bypass caps selection and cutting the gain between stages with finesse. You also have the Soldano cold clipper, and Jose style diode clipping to play around with.

I want to experiment with 2 or 3 frequency separated parallel paths in the dirt section. Smash the lows with compression via local negative feedback, and then treat the low-mids and high-mids to different tortures.
 
Hal Harvey said:
Frequency manipulation before and after your dirt is a big part of it.

….

As far as the dirt itself, normal gain stages shaped by bypass caps selection and cutting the gain between stages with finesse. You also have the Soldano cold clipper, and Jose style diode clipping to play around with.
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Yeah, I made the amp play pristine cleans now and unruly but articulate fuzz driven fire is gone. Harder to find fine point balance there between stability and abuse.
Recent cathode bypass cap adjust and
more PI headroom/balance/stability just tamed the beast too much

Stuck with 2 preamp tubes with 3 or 4 stages to play with before PI. Now the topology resembles two channels both having plate driven treble-bass tonestack before two gain stages driving the PI.

I was wondering if I’d just turn whole preamp to resemble bassman/super bass. I’d have less wire and fewer pots to run wires back and forth on front panel. It would change the while sound of preamp. Can’t say if it is worth a try. Maybe I’d get rid of rest of the hum in second tube revisiting lead dress and layout with fewer wire runs.
 
Yeah, bassman with a few Robinette mods? 3 way NFB, tone stack bypass, maybe a cold clipper 3 way on the second stage. Two or three toggles will give you lots of options.
 
Asdrael said:
Of option paralysis you mean 😁
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I have a couple of similar mods on my Matamp GT120 build. Three way local NFB on 1st and 2nd gain stage - "none/some on 2nd gain stage/some on 1st gain stage and even more on gain stage two". Also a tone stack lift.

I mostly leave it on some local NFB on 2nd gain stage and almost never lift the tone stack. It's nice to have the other options though :)
 
Well after a bit I decided my VH4 variant clone was feeling and sounding a bit... congested? So I switched the NFB tap from the 8 Ohm to 4 Ohm output. Kind of an interesting change: seems like I am getting a more open sound, a bit more dynamic too. I like it. Then again, holy shit is the NFB stock a najor clamb. 8 Ohm tap with only a 22k resistor.
 
Just about to have my first listen to my long delayed bass amp project. Only running in 60 watt mode for now until my new Heyboer 100watt OT arrives. Looked good on my test bench yesterday and I've already work up some new tone control tweaks I just thought of a few days ago. I just can't resist highly interactive formats! :cool:

My big beef with tubes for bass is how unfriendly they often are to active basses, IME. I don't even own a passive bass either, so it's going to be all or nothing here. And I'm trying a 12SL7 front end for the first time, among the many other unusual design aspects. First one out of the box shows no microphonics on the test bench...yay! Finding good 6SL7s for bass was fairly challenging a decade ago, at least old 12SL7s are still relatively inexpensive. The youngest one I bought is around 60 years old, I think one may even be WWII vintage.
 
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pbrommer said:
Full send, passinwind. Hopefully it works out.
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Seems good so far, I think the EQ scheme complements my more normal active bass really well. On to the wacky one that’s optimized for slide bass with a “filter preamp” for the bridge pickup next.

It’s working well enough that I’ll probably put together the rest of the case later today, and maybe the place holder wood control plate as well. I think the first Sylvania 12SL7 I grabbed for testing is mid 50s vintage, dead quiet and not a hint of microphonic ring at all. IIRC it cost me less than ten bucks including shipping, the most expensive older (40s probably) National Union one I took a flyer on was like $20.

PW100B.jpg
 
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"slide bass" 😻

I wonder what these tubes cost back in the day when they were brand new, relative to income of the day adjusted for inflation to today!

Are they cheaper now, relative to today's income, or still would've been cheaper way back when.
 
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