My first build - AB763 Deluxe Reverb clone - opinions please

[The Dude]

FWIW, the amp I'm working on ('68 Custom Deluxe Reverb) exhibits the symptom more on a "D" than any other note (if that helps). Not to say that the amp in this thread has the identical symptom.

[Greg_L]

I bet if you sweep through some freqs with a dial type sig gen, you will see the kink get more or less severe. I just consider it an artifact of the reverb circuit?

I'll try it. I'm really starting to think that it's just the way it is. As I've said, the amp is fine. It doesn't do anything weird at all except for the little bit of brittle that started this whole thread, and even that seems to be getting marginally better and better as I play it more and more. No weird noises, hums, pops, buzzes, nothing. It works perfectly. I've had amps go into real serious oscillation and this one does none of that. So I'm thinking I'm just gonna live with it, play the hell out of it, and go back in later and see what's up.

FWIW, the amp I'm working on ('68 Custom Deluxe Reverb) exhibits the symptom more on a "D" than any other note (if that helps). Not to say that the amp in this thread has the identical symptom.

Which issue are you having? The brittle sound?

I've heard my brittle sound in other Fender amps. Mine just seems a little crispier, so I wanted to try and figure it out.

[The Dude]

The customer described it as a "tinny distortion mostly when I play a 'D'". He is right. I hear it and it's not something typical. I've just started on the amp and also have other projects going, so it may be a bit. I haven't scoped it yet, but I'll update as to what I find.

Edit: I've also found that it's unaffected by tone controls. Even if you turn the treble down, the high frequency distortion is still present.

[Jazz P Bass]

Note: Reply to the Dudes post:

Cabinet vibration?

And don't forget to look for foreign metal objects stuck to the speaker magnet.

[Greg_L]

The customer described it as a "tinny distortion mostly when I play a 'D'". He is right. I hear it and it's not something typical. I've just started on the amp and also have other projects going, so it may be a bit. I haven't scoped it yet, but I'll update as to what I find.

Edit: I've also found that it's unaffected by tone controls. Even if you turn the treble down, the high frequency distortion is still present.

Yes that sounds similar to mine.

I haven't narrowed mine down to "D". When sweeping a recorded track with an EQ, it seems to me that it "pops" the most around 3200hz....which is like a G or something.

[Greg_L]

Cabinet vibration?

And don't forget to look for foreign metal objects stuck to the speaker magnet.

No, I wish, but that's not it. I've tried it through three different cabs, five speakers, six mics, several preamps....it's always the same. It's in the amp. And these cabs get loud Marshalls blasted through them regularly and they don't have this same sound issue.

[galaxiex]

FWIW, the amp I'm working on ('68 Custom Deluxe Reverb) exhibits the symptom more on a "D" than any other note (if that helps). Not to say that the amp in this thread has the identical symptom.

Hmmmm, I didn't hear the symptom on this until I turned up the bass control on my computer speakers.

(I have a Logitech THX speaker system with sub)

At first I was worried that my old guy hearing was going...
which is very worrying to me, since I have surprisingly excellent hearing for someone my age... 60.

But with the bass turned up I clearly hear a distinct "buzz".

Sorry for the slight O/T.

back to our regular program...

[The Dude]

FWIW: That "video" is just a generic test tone from YouTube. It's not a recording of the amp I'm working on. Sorry for the confusion. I simply linked it as a courtesy to the OP.

[Greg_L]

FWIW: That "video" is just a generic test tone from YouTube. It's not a recording of the amp I'm working on. Sorry for the confusion. I simply linked it as a courtesy to the OP.

Thanks. My phone generator app will do sweeps. I'll try that frequency and see what happens.

[Chuck H]

Have you grounded the reverb circuit away from the preamp yet???

[Greg_L]

Have you grounded the reverb circuit away from the preamp yet???

Not yet. That's on my to-do list. I started to get after it this afternoon and got sidetracked.

My RCA jacks are grounded to the chassis via contact. The transformer is grounded with the preamp buss. Should I just run it to the RCA jacks? Does it matter which one?

[Greg_L]

Have you grounded the reverb circuit away from the preamp yet???

I just thought of something that might be an issue....

As you all probably know, this circuit has four B+ "nodes".

The filter cap node (B) that powers the reverb transformer is grounded with the power supply/center taps/output section (A,B,C). But I have the transformer itself grounded with the preamp node (D) which is separate from the other grounds. My thinking on this was to keep the preamp stuff totally separated from the output/power stuff. What I didn't consider at the time was having the transformer grounding with the preamps while the reverb's power supply is grounded elsewhere.

It would be simple to alter this arrangement and have the A node isolated with the power supply and B, C, and D ground together at the buss bar, which would put my reverb power and ground on the same plane....like an original stock Deluxe Reverb.

Is this something I should explore?

[Chuck H]

Having B, C and D on the same ground away from the main filter is STILL less than ideal. At face value it doesn't look as though "Fender" considered grounding, but they did. A little. Their reverb circuit hums like it doesn't know the words. But this is WRT the signal path, not the power supply. Their power supply has all the filters grounded in the same place. For low gain applications this is probably acceptible, sort of. Where Fender did occasionally make concessions is with chassis grounds. I think there was clearly some alteration to what is grounded on the chassis where to achieve the lower noise option. Still not ideal, but ok as long as the amp isn't pressed into maximum output all the time (as todays amps are judged).

Each filter should be grounded with it's circuit at the chassis or on the buss as they occur in the circuit. If that makes sense.?. Short of trying to sort that out, just ground the reverb circuit at the RCA jacks for the tank and see if that doesn't help. It shouldn't matter which jack since they're only an inch apart on the chassis! There may still be a bunch of hum introduced when the reverb is turned up. We can deal with that as a different issue. Right now we just want the amp to behave.

[tubeswell]

I just thought of something that might be an issue....

As you all probably know, this circuit has four B+ "nodes".

The filter cap node (B) that powers the reverb transformer is grounded with the power supply/center taps/output section (A,B,C). But I have the transformer itself grounded with the preamp node (D) which is separate from the other grounds. My thinking on this was to keep the preamp stuff totally separated from the output/power stuff. What I didn't consider at the time was having the transformer grounding with the preamps while the reverb's power supply is grounded elsewhere.

It would be simple to alter this arrangement and have the A node isolated with the power supply and B, C, and D ground together at the buss bar, which would put my reverb power and ground on the same plane....like an original stock Deluxe Reverb.

Is this something I should explore?

I would ground the 12AT7 reverb driver cathode, grid leak and RT secondary at the same filter cap that you are taking the reverb transformer primary from. The other ground returns for teh reverb recovery etc can be with the filter cap node that you are taking the reverb recovery stage from. YMMV

[Greg_L]

Having B, C and D on the same ground away from the main filter is STILL less than ideal. At face value it doesn't look as though "Fender" considered grounding, but they did. A little. Their reverb circuit hums like it doesn't know the words. But this is WRT the signal path, not the power supply. Their power supply has all the filters grounded in the same place. For low gain applications this is probably acceptible, sort of. Where Fender did occasionally make concessions is with chassis grounds. I think there was clearly some alteration to what is grounded on the chassis where to achieve the lower noise option. Still not ideal, but ok as long as the amp isn't pressed into maximum output all the time (as todays amps are judged).

Each filter should be grounded with it's circuit at the chassis or on the buss as they occur in the circuit. If that makes sense.?. Short of trying to sort that out, just ground the reverb circuit at the RCA jacks for the tank and see if that doesn't help. It shouldn't matter which jack since they're only an inch apart on the chassis! There may still be a bunch of hum introduced when the reverb is turned up. We can deal with that as a different issue. Right now we just want the amp to behave.

I would ground the 12AT7 reverb driver cathode, grid leak and RT secondary at the same filter cap that you are taking the reverb transformer primary from. The other ground returns for teh reverb recovery etc can be with the filter cap node that you are taking the reverb recovery stage from. YMMV

I see. Thanks. Well my amp definitely does not hum. I don't know if you heard my sound examples, but noise is not one of the issues I'm fighting. The only unwanted noise in my clips is the occasional noise of a single coil. I'm not fighting a hum issue, I'm just trying to make sure everything is working optimally.

If each filter should be grounded with it's circuit, if I'm understanding you correctly, then I should alter my filter cap grounding...putting B, C and D together at the buss bar to input jack corner ground - like Fender intended. The reverb transformer gets power from "B", and the preamp circuit, reverb circuit, and all the related pots and cathodes go to ground via the buss bar to chassis, so they'll all be grouped together and far far away from the mains/power supply/center taps ground. Moving the reverb transformer's ground to the RCA jacks (which are chassis grounded) will put it grounded in close proximity with the tank. So that will leave me with three grounding points - like a triangle - all pretty far from each other. But keep in mind I'm only trying to smooth out that kink that happens on the scope with the reverb circuit. It's not a hum issue.

Basically it would just be this:


I'd remove the X'd ground wire and put one between the C and D nodes. That would leave A node grounded all by itself at the PT, and the rest grounded via buss bar to input jack location.