Is it possible for new caps to have a different dynamic?

[justonwo]

I just completed my second Weber 5E3x2 build. Instead of using the supplied Chinese 450 volt electrolytics, I used 500 volt Sprague Atoms instead.

After powering up the amp and playing for a minute or so, I cranked the volume just to check things out. I can only describe the resulting sound as having EXTREME sag. The volume dropped, the tone became very thin, and it generally sounded like the circuit was not keeping up. If I turned the volume down to 12 o'clock this problem went away.

After 5 minutes or so of playing, the extreme sag problem went away with the volume cranked. Is it possible that the electrolytic caps were undergoing some "forming" process during that time that prevented them from keeping up? Does it matter that I used 500 VDC electrolytics instead of the supplied 450 VDC (I have to assume no). The amp seems to be operating perfectly now.

[Old Tele man]

...yes, ESR could be different which affects AC-signal amplitude, phase, and delays.

[justonwo]

Esr?

[Blue Strat]

Are you aware that the volume controls on that amp are interactive and could relate to the volume setting effects?

[justonwo]

Are you aware that the volume controls on that amp are interactive and could relate to the volume setting effects?

Good point and, yes, I am aware of that. Looking back over what I wrote, I guess I wasn't clear. At the highest volume setting, the sound would change severely only after hitting a couple of chords. If you waited about 2 seconds, you could actually hear the amp recover its volume, and it would oscillate slightly (louder quieter louder). After playing the amp for several minutes, I no longer observed this problem.

[da-boogieman]

Esr?

Equivalent Series Resistance - google should be able to fill in your info voids.

[Blue Strat]

Good point and, yes, I am aware of that. Looking back over what I wrote, I guess I wasn't clear. At the highest volume setting, the sound would change severely only after hitting a couple of chords. If you waited about 2 seconds, you could actually hear the amp recover its volume, and it would oscillate slightly (louder quieter louder). After playing the amp for several minutes, I no longer observed this problem.

Interesting. If it hadn't "corrected itself" I would have thought that the problem could be almost anything. Hopefully it will stay problem free.

[justonwo]

We'll see. I plan on selling the amp, so I need to make sure it works properly before sending it out into the rocking world.

I don't remember the last double deluxe I built having any problems like this.

[justonwo]

Well, I played through the amp for about 1/2 hour last night and observed no issues. I guess I'll be forming caps prior to use in the future.

[vibroverbus]

Well, I played through the amp for about 1/2 hour last night and observed no issues. I guess I'll be forming caps prior to use in the future.

Aside from specifically cap forming issues, which may or may not be the case here, I'd suggest you think of it more as "burn in" time, which is standard practice for lots of manufacturer and retailers of electrical (and mechanical stuff).

[justonwo]

Hmmm . . . volume knob goes up to 12. It sounds great with my SG up until 10 - it retains its bottom end and definition. Between 10 and 12, the volume drops somewhat, the sound gets really compressed, and it gets pretty buzzy and farty. Sounds terrible.

I assume this is because I'm using a humbucker guitar into the high gain input on the amp? These things don't hold together too well with humbuckers when dimed, right?

[bob-i]

Hmmm . . . volume knob goes up to 12. It sounds great with my SG up until 10 - it retains its bottom end and definition. Between 10 and 12, the volume drops somewhat, the sound gets really compressed, and it gets pretty buzzy and farty. Sounds terrible.

Sounds like it could be a high frequency oscillation. It can really suck up the power and cause this type of issue. Put it on the scope and look for any high frequency wave forms when the amp is cranked up with no input.

I assume this is because I'm using a humbucker guitar into the high gain input on the amp? These things don't hold together too well with humbuckers when dimed, right?

Possible, have you tried a 12AY7 in V1?

[vibroverbus]

Hmmm . . . volume knob goes up to 12. It sounds great with my SG up until 10 - it retains its bottom end and definition. Between 10 and 12, the volume drops somewhat, the sound gets really compressed, and it gets pretty buzzy and farty. Sounds terrible.


hmmm... is this a new symptom, Justo? sounds a little different to before... i'd say blocking distortion maybe, but seems odd that the symptoms keep changing or aren't consistent (+1 to oscillation for inconsistency)

[justonwo]

No, not a new symptom. After the amp settled in, this kinda became the norm. However, as I discovered tonight, it's only with humbuckers in the high gain input. It gets better when I use the low gain input, and it goes away completely on both inputs when I use my Tele. I think it's just too much for the little amp to handle.

[vibroverbus]

then I'd say blocking distortion. another good use of the 'scope - check the output at each gain stage and see where it's occurring, and if at extreme signal peaks it causes more than just 'flat top' clipping, it's probably that... attenuate the signal at that point just a wee bit and you're there...

[justonwo]

When you say "attenuate the signal at that point," what is the best method of doing that vibroverbus?

[vibroverbus]

When you say "attenuate the signal at that point," what is the best method of doing that vibroverbus?
depends on the circuit and the stage that's the problem. hopefully it's just adding a grid stopper or tweaking an existing voltage divider (like it your case it might be a different volume pot value for instance if that was were the problem was).

again Randall Aiken has some nice notes on this, particularly the last paragraph
here: http://www.aikenamps.com/BlockingDistortion.html
and more on grid stoppers: http://www.aikenamps.com/InputRes.htm