High-Gain JCM800/2204 Build

novosibir":1nn5uibd said:
FourT6and2":1nn5uibd said:
What's up with the EROs that are wrapped in green?

m4XtpRUbQx5KWDiUQv6tcYw.jpg
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The former Greenies still are sounding a tad more vintage with a pronounced mid range, compared to the later Yellowies...
... but they do have sometimes a leaking problem quite like the orig. Astron's in old Fender amps
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This is good stuff. Thanks for taking the time to post!
 
Tested a few more bright caps. Mallory 150, new Murata 2kV of some sort—no idea what class or rating—and the Philips and BC. My fav of the bunch is actually some sort of third-world ceramic disk cap I got in a Ceriatone kit years ago. No idea what brand it is. Second fav is the BC I started with. But it has a bit too much hash noise sometimes. The Ceriatone cap is the winner.

Will test a few more tone stack treble caps and then the last two things to test before buttoning it up are the zeners and the first dropping resistor (currently 12K with V1a plate at 150v).

Then clips!
 
OK I'm an idiot. I've had the PT wired for low voltage this whole time haha.

The wiring diagram for the Merren transformer isn't really labeled clearly. I'm getting 330v on the PT secondaries and the amp sounds awesome, but I was scratching my head as to why my B+ is only 440v. Turns out the outer lugs on the PT are the high-voltage taps. And I'm getting 375v there. That should bring my B+ up to where it belongs. Will rewire it for that and see how it sounds. Getting 490v on the plates now.
 
Just don't run it without tubes; you may blow your 500V filter caps if you do (assuming you are running two in series for increased voltage capacity)...
 
V2a":1344vv2h said:
Just don't run it without tubes; you may blow your 500V filter caps if you do (assuming you are running two in series for increased voltage capacity)...
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Usually the 500V types 'eat' a +5%, when they haven't to work hard, but after an expected B+ of almost 500V w/o tubes it might creep up to 530V or more.
Btw JJ is offering cap cans w/ 50+50/560V with the same size as the 50+50/500V ;)
 
FourT6and2":f6nu4qdq said:
OK I'm an idiot. I've had the PT wired for low voltage this whole time haha.

The wiring diagram for the Merren transformer isn't really labeled clearly. I'm getting 330v on the PT secondaries and the amp sounds awesome, but I was scratching my head as to why my B+ is only 440v. Turns out the outer lugs on the PT are the high-voltage taps. And I'm getting 375v there. That should bring my B+ up to where it belongs. Will rewire it for that and see how it sounds. Getting 490v on the plates now.
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Great thread! Fwiw, Merren's color code follows earlier Marshalls
 
glip22":u7q0d7kk said:
FourT6and2":u7q0d7kk said:
OK I'm an idiot. I've had the PT wired for low voltage this whole time haha.

The wiring diagram for the Merren transformer isn't really labeled clearly. I'm getting 330v on the PT secondaries and the amp sounds awesome, but I was scratching my head as to why my B+ is only 440v. Turns out the outer lugs on the PT are the high-voltage taps. And I'm getting 375v there. That should bring my B+ up to where it belongs. Will rewire it for that and see how it sounds. Getting 490v on the plates now.
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Great thread! Fwiw, Merren's color code follows earlier Marshalls
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No colors to follow. The PT uses solder tags. Merren provided a little diagram showing what each tag/tap is for. But some are just unlabeled. So I assumed they were dummy tags and not used. Turns out the secondaries are tapped for high and low voltage.

I think 490v is cutting it too close for comfort. Will see how the amp sounds wired up this way, but the amp really did sound amazing with 440v on the plates, even though it's a bit low.
Merren did tell me that I can also try wiring it up using one high voltage tap and one low voltage tap to get something between 440v and 490v. But I don't know if there's an issue hitting the rectifier with an imbalance so one side is seeing 330v AC and the other is seeing 375v AC.
 
Yeah, just a passive/insert loop. One day maybe I'll focus on a good buffered loop. But passive seems to be ok with the single delay pedal I use lol.
 
Interesting thread, and I'm sure we'd all love to hear the amp and the different clipping voicings. I don't build amps myself, but I would like to try to clear up some things about the effect of different capacitor types. AFAIK and ICBW, caps are not amplifying components, so I'm not sure they can generate harmonics unless maybe when driven beyond their voltage value...no?

I have read from several reputable sources that ceramic caps are more prone to resonant in an active circuit. It should also be noted that metalized-film caps have a smoother transition into the operating range (for lack of a better description), which may go hand in hand with less resonance. Therefore, if the "Treble" cap in a tone stack resonates, it will simply drive the amp section harder around it's resonance peak. That will generate more of some balance of even or odd harmonics from that peak depending on the amp section configuration.

Pentodes are said to generate more 3rd harmonics than tetrodes, and class AB amps cancel the generated even harmonics unless biased hot so 2nd harmonics are introduced. Therefore, a hot-biased AB tetrode power section will generate some 2nd, but less 3rd harmonics than a pentode power section, and a cold-biased AB pentode section won't generate any even harmonics, but more 3rd. The generated harmonics (of whichever mixture) will of course be stronger around the resonant peak of the "offending" cap. Is not that what is actually happening via different cap types rather than the caps themselves generating harmonics?
 
GCKelloch":3i63l6b2 said:
Interesting thread, and I'm sure we'd all love to hear the amp and the different clipping voicings. I don't build amps myself, but I would like to try to clear up some things about the effect of different capacitor types. AFAIK and ICBW, caps are not amplifying components, so I'm not sure they can generate harmonics unless maybe when driven beyond their voltage value...no?

I have read from several reputable sources that ceramic caps are more prone to resonant in an active circuit. It should also be noted that metalized-film caps have a smoother transition into the operating range (for lack of a better description), which may go hand in hand with less resonance. Therefore, if the "Treble" cap in a tone stack resonates, it will simply drive the amp section harder around it's resonance peak. That will generate more of some balance of even or odd harmonics from that peak depending on the amp section configuration.

Pentodes are said to generate more 3rd harmonics than tetrodes, and class AB amps cancel the generated even harmonics unless biased hot so 2nd harmonics are introduced. Therefore, a hot-biased AB tetrode power section will generate some 2nd, but less 3rd harmonics than a pentode power section, and a cold-biased AB pentode section won't generate any even harmonics, but more 3rd. The generated harmonics (of whichever mixture) will of course be stronger around the resonant peak of the "offending" cap. Is not that what is actually happening via different cap types rather than the caps themselves generating harmonics?
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You can talk theory until your eyes pop out of your skull lol. But in the end, I'm sitting here and swapping caps as I play and there is a definite audible and tactile difference that even non-guitar players can hear. I'm only talking about the bright cap across the gain pot and the treble cap in the tone stack. However, I've found the same to be true of all the caps in the amp, including cathode bypass caps, plate coupling caps, and filter caps.

As far as clipping goes, I can certainly record a video of the different clipping levels. Tonally, they are all similar. Just more levels of clipping and compression as you progress from 24v zeners down to 9v and then the transistors. Personally, with this amp, I prefer 18v zeners. Anything less than that and it's just too much clipping and sounds too compressed. 18v zeners in this amp will get you some brutal high gain sounds. I'm not talking about Van Halen tones either. More like modern metal, prog rock, djent, hard rock, etc. 16v could work too. Maybe 17v is the sweet spot but I don't have any 17v zeners. After playing around with all of them, I decided to take out the zener rotary switch and just hardwire the 18s in. But I can clip the switch back in for some vids.
 
Oh yeah, I'm not saying cap types don't affect the sound. It's whether they generate harmonics themselves that I question. If we aren't sure what's happening and where, perhaps it's better not to speculate? No need to make any changes to the amp again. Maybe just let us hear it when you get a chance.

An FX loop eliminates the impedance affect of the PI tube on the tube b4 it, thereby changing the preamp overdrive dynamics, no? I assume that's why "purists" don't use an FX loop. I don't know just how it works, but perhaps a parallel FX loop can avoid that?
 
Tested a few more caps, including an old Panasonic Dave sent me. I like that one the most. The Ceriatone mystery cap in second. Played with PT voltages as well and I actually prefer the amp on the low-voltage taps for 440v on the plates. My guitars are very tight and bright, though. With something like a Les Paul, maybe higher voltages would be better. But I like the bounce the lower voltages have. Then I can raise the preamp voltages for a tighter response. Just need to tweak the first dropping resistor and it'll be good to go. Need to fly out of town for a week or two. So it will be after I get back.

But this thing is awesome. Best sounding amp I've built.
 
FourT6and2":u8010ds7 said:
Tested a few more caps, including an old Panasonic Dave sent me. I like that one the most. The Ceriatone mystery cap in second. Played with PT voltages as well and I actually prefer the amp on the low-voltage taps for 440v on the plates. My guitars are very tight and bright, though. With something like a Les Paul, maybe higher voltages would be better. But I like the bounce the lower voltages have. Then I can raise the preamp voltages for a tighter response. Just need to tweak the first dropping resistor and it'll be good to go. Need to fly out of town for a week or two. So it will be after I get back.

But this thing is awesome. Best sounding amp I've built.
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Awesome, glad this turned out well. It's a cool build :thumbsup:
 
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