Asteroid unpleasing distortion

[Coyotesgator]

unfortunately, that didn't solve anything. The scope still shows the same. I reconnected the tonestack to check the sound, and the buzz is still there.
Here's the scoping - I put the two waves together for close comparison;

DS1Z_QuickPrint1.png

Where exactly was your probe for this?

[romberg]

Back on page one of this thread you posted a spreadsheet with voltages for three amps. Which one is is the amp we are currently talking about? The one with the title Barry's seems to have way too high of voltages on the PI plates. It looks like the PI might be connected up to B+1 or B+2 instead of B+3. If that is this amp, then that may be what is going on with the PI.

As far as what is going on with stage one, the options are getting more thin. I assume you have tried different tubes in V1 to see if it may just be a bad tube? Otherwise, I'd measure each and every component associated with stage one. At this point there is only four resistors (grid stopper, grid leak, bias and plate) and one cap involved.

Mike

[arjepsen]

uhhg.. anyone have photoshop.. maybe we could fix it with image editing..

Is there any possible way a single strand of shield is touching positive.. or a preamp tube is loopy.. or you are near a gamma emission source.. or someone has a horse tranquilizer I could mix with liquor?

Heh, thanks for the humor

Where exactly was your probe for this?

The yellow line is from the probe connected to the grid pin of V1a - right after the initial 33k grid stopper.
I had desoldered the 100k+500pf to the tonestack, so that's out of the picture - then I soldered a 100nf to the plate pin with the 100k plate resistor, and the blue line is the probe connected to the other end of that cap. After making the trace, I reconnected the tonestack, removed the 100nf cap and the probes, and tried listening again - still same buzz.

Back on page one of this thread you posted a spreadsheet with voltages for three amps.

Mine is the bottom one "Anders' Asteroid". (mind you, I'm using both triodes of V2, leaving one triode on V1 unused).
(hmm.. I wonder if I should try to ground the three unused pins on V1?)

As far as what is going on with stage one, the options are getting more thin. I assume you have tried different tubes in V1 to see if it may just be a bad tube? Otherwise, I'd measure each and every component associated with stage one. At this point there is only four resistors (grid stopper, grid leak, bias and plate) and one cap involved.

Mike

Yeah, I tried various tubes, still same.
Actually, for the fun of it, I tried doing the same trace on the first triode of my Rocket build (same type of ptp layout - also just one triode used on V1).
Here I actually get the same kind of trace, with the bump on the blue line.
I wonder if it really is something wrong, or just the way it should look?
Could somebody else with a scope try to do a similar single shot trace of grid and output of their first stage in one of their amps?? Just to compare?

And once again: Thanks so much for your continued help guys!

[thejaf]

Just to be persistent, did you ensure that the grid loads on 6L6 were reduced to 100K total from pin5 to the bias supply? That's the total of load and stopper resistors. I'd ensure that your power amp values are within published tolerances, and working correctly before modifying to match a particular schematic.

[arjepsen]

well, thanks a lot for being persistent!
Anyway, since I'd read that a komet 60 were meant to accomodate both el34 and 6l6 among others, I assumed that I could plug the 6l6's in with no modification to the circuit.
Seems other people do that - and I think I read that the guy who made the demos used 6l6's in there for those demos.
Also, looking at old fender schematics, it seems they use 220k's.

I actually originally tried various el34's but since they also had the buzziness, I tried various others - with the 6l6's seemingly sounding the best.

Anyways, I can try out using 100k's instead of the 220k's in the schematic.

[thejaf]

Totally understand, and I have a modified 1987 circuit with 6L6s running 220K (LARMAR PPIMV). That waveform you posted looks like cutoff distortion, IMHO. Thus, you're getting cutoff in the power amp -or- just before and getting it amplified. Usually generated from tubes operating well outside designed range, so trying to put everything back to within "official" working range then slowly moving into modified land would make sense.

I noticed on the pencil Komet schematic, there's almost 400V getting dropped across the 12AX7 (plate to cathode) in the final preamp stage. Is that correct? Does your amp do this as well?

[arjepsen]

Yeah, the final stage does drop that.
You can see my voltages in the excel file I linked in page 1

[Mant]

Man I read this entire thread thinking there was an ending.
This has been a real page turner.
It’s like a classic noir

[Mant]

Any updates?

[arjepsen]

Sorry - hadn't seen your post.
My current assumptions:

I believe the first stage works fine. I looked through the internet, and found other images of a single string plucked on an oscilloscope.
It looks quite similar to mine - WITH - the added bumps that doesn't seem to be there on mine.
I do wonder if anyone could thoroughly describe/decipher why the guitar signal looks this way.

Also, I don't think the buzziness I hear in the distortion is caused by the first stage - I've used a headphone amp to track the audible signal through the amp, and it's clean, all the way up to the phase inverter.

However, I'm still not sure whether the bad sounds are from the pi or the power tubes, but I do hear it around the pi when using the headphone amp.

I do wonder if this is simply the way this amp sounds, but I don't hear these sounds in the demo I linked.

[statorvane]

Since you have pretty much isolated the buzz to the PI, check Mile's first post - blocking distortion. At this point I'd certainly try bypassing the PPIMV and re-evaluate.

Keep at it, you'll get it solved.

[arjepsen]

yeah, my very first thought was about blocking distortion.
However, I've tried large grid stoppers pretty much throughout the amp, which didn't do all that much.
And I also bypassed the ppimv a few posts back
I keep coming back to wondering whether it simply is the way it sounds - which is why I keep trying to pester others to make a short clip plucking their a-string, to see if I hear the same from their k60's.

[stephenl]

I've built Express and K50 clones (1 each) and I didn't really love the sound of the distorted PI, which is part of their design. This is just my opinion/experience. Many others here have built wonderful sounding clones of these - no disrespect for the Fisher designs.

I spent time tube rolling and trying different "fizz caps" and stopper values but I couldn't get them quite right for my taste. So maybe it just isn't right for you as well.

Maybe try experimenting with increasing the B+ for the PI to increase the headroom? If you really want to try something a bit more extreme, change the LTPI to a Gain Stage > Cathodyne

[Mant]

What about split plat load feeding into PI?
Won’t drive the the PI as hot?

[Reeltarded]

The signature thing is the distortion with your pots wide open and hard to believe clean tones when you moderate those volumes.

The wiggle in the pi.. no idea, really. I know what the amps sound like WFO and it's crazy with sustain.. then it's all about the volume control on the guitar..

Unintuitive and in a way too much for me to deal with after playing the other end of the spectrum for so long. I hate single amp setups because 100 reasons and 101 is I don't have to relearn how to converse with the gear. I click a button. My 80s rig sounded like the bottom of Niagra. whhhhsssssssshhhhhhhhhhhhhh (bold 128pt font)