Rocket Issues

[Blackburn]

I'm curious why my Rocket build is exhibiting some strange behavior. Nothing is wired incorrectly and all my voltages are in spec with the Rocket document. Thing is....

I'm getting some weird undertones on certain notes that are like an octave below. Not a whole lot of them but some. Almost like it's the speaker's fault, but I'm damn near sure it's not. It's an ASW Elegante. There is also a scattered nature of the tone when clipping. It's like it's under filtered or something. I didn't use an 80uf cap. I used a 47uf at 500v for the reservoir and another 47uf for the screens. The rest are standard as on the schem. Also, I remember reading somewhere that a quirk about the AC30 was some chords sounding out of tune. Maybe I'm mistaken but I think I heard that with it. Maybe I just need new strings?!

That's pretty much it. I absolutely adore the cleans but the grit is leaving some tweaking to be desired. Anyone? Bueller??

David

[Colossal]

Ghost noting? Hmmm though...I've built a couple of Rockets with no more than 40uF for the reservoir cap and 20uF down the rest of the rail and didn't get any ghosting. Are you using a choke?

[Blackburn]

Yeah a 20 henry.

And I see it's the end of an era. You got a new avatar.

[M Fowler]

Try a different speaker cab and if you have the same issue it has to be the filter cap/caps or solder problem.

Nice avatar Dave

[Blackburn]

Will do. I've got a Crossroads by ASW in my V4 so we'll see what up. What brand of filters did you use, Dave? And Mark, have you had issues like this before?

[Colossal]

And I see it's the end of an era. You got a new avatar.

Nice avatar Dave

Haha, yes, thought it was time for a change. Crazy Homer seemed appropriate

20H. That's fine and the ripple should be pretty low. I suppose this isn't an issue of motor boating (OT primary leads, flipped) but just only on specific notes? You might try bypassing that choke (in front) with 47n to ground.

p.s. Mark I got a chuckle out of your avatar too

[Blackburn]

Okay it does it even more so with a ceramic it seems.

Yeah this is a very small issue and nothing indicating large problem. Just a minor one. I consider motor boating quite a problem and I've only had that happen to two amps. And what's this about bypassing the choke? You're talking .047 to ground at the reservoir? I know this problem very likely resides in the filter section, but they're new caps. I'll check the wires coming of them in a sec. Hopefully it's just something minor on my part. Usually is.

[Blackburn]

Alright, I jumpered in a 30uf in parallel with the 47uf for essentially an 80uf input capacitance. Unfortunately, with family complaining about the volume, (It was at noon) it was difficult, but I still kinda heard it. That cap 'seemed' to help a little, though I couldn't really give the notes hell like I do with no one around. I haven't tried the cap to ground that Dave suggested because I want to eliminate all possibilities before doing something like that. I use top notch stuff, so it is a curious scenario. Never had a ghosting problem before.

Any other ideas?

[M Fowler]

Mark, have you had issues like this before?

Only with an old Fender Tremolux head it was bad filter caps.

Power supply filter caps but yours are news so that should be OK.
Choke can cause ghosting.
Over biasing but this is Cathode bias, what are you at 10-11 mV?

[Blackburn]

I'm biased pretty hot right now with what's in there. I've got 9.5v across the 50R and roughly 305 plate volts. I'm dissipating over 14 watts, but I do have a quad of NOS Mullards so I'm not real worried. Old ACs were much more destructive to their tubes. I have JJs in there now to suffer the abuse of turning this thing on five times a day to fiddle with what the problem may be. The choke idea intrigues me, Mark. I don't really use them and I was just talking with an experienced friend yesterday about the issue and he referenced choke's occasionally resonating, I think. I can't recall exactly, but it too sounded strange. I'll give this thing a go again today and see if that extra cap helped.

[M Fowler]

You can also add a poly cap such as .22/600v parallel to the preamp filter caps to help with resonating frequencies. Not suppose to be critical in guitar amps but worth a try.

Also, take a look at Merlin's Designing Power Supplies for info about chokes.

[Blackburn]

Okay, finally got to dime this mofo today and think I've come to a conclusion... Although the issue still persists, I don't think there is any problem at all. Most of my builds prior to this one have been smaller and I've never built anything with this much gain, as well as harmonic complexity. I assume there is no problem, and attribute what I was hearing to an outside source that resonates while I'm playing because when I dimed her, the 'problem' was drowned out by the volume. If this were an oscillation, I'd assume it would be intermittent at any volume. When I went back to noon on the volume, I could hear it again. I tried notes on the D string in sequence, 10,9,8,7,6,5,4 etc and all of them cause it. I'm also playing a Les Paul so there is much more girth to the notes that may lead to things resonating than something like a Strat or Tele. It's much, much more prevalent with the neck pup than the bridge. This is just my theory, because there is SO much bass response in this amp and when coupled with my LP...

Think this holds water?

[LeftyStrat]

Can you post a clip of the effect?

[Blackburn]

You know, while I was playing this thing at full tilt today, despite my ghastly headache, I was thinking of a way of making some kind of recording, either audio or video. The camera is no good... I tried recording my Princeton's fabulous trem whilst the volume was quite low and I still got the damn thing clipping. My friend has a studio and we've been meaning to record, but haven't found the time. I may snag one of those Zoom Q3s in next couple days and if I do, I'll definitely do a clip or two. I want something that's easy to use spontaneously and good quality, rather than a phone. At least, the clips I've heard with the Zoom sound pretty good to me.

[keewee]

I think this is the true nature of the vox, cold biased v1, coupled with the long tailed pair phase inverter, also cold biased leads to a rather icey sound ( many odd harmonics ) while sounding chimey at slight breakup, when overdriven harmonics start summing and subtacting alot ( modulating) thus sounding out of tune hence: The Power Cord, two may be three notes max. one notes sounds best. Example Beatles "Tax Man" George uses less than four note chords the whole song. Nature of the beast.