Fender Deluxe Reverb - Muddy and Overtone when Distorted

[davegardner0]

Last year I converted a Fender DRRI amp with issues to turret board wiring, using a kit from Hoffman amps, as described in this thread:
Fender Deluxe Reverb Reissue Hoffman Board Conversion - The Basics

The amp works great! It seems to only have two anomalies, one of which I'd like to try to fix. The first is a tiny issue, the vibrato channel's volume doesn't come on until "2", then gets loud kind of quickly. No big deal really. The second issue, though, is that the amp sounds too "bassy" to my ears. For instance, I have a strat that's extremely icepicky shrill - it sounds balanced and great though this amp while it's terrible on my other amps (Marshall JVM210, Traynor YBA1mod1, Peavey Red Stripe Bandit). Of course the rest of my guitars sound like they have too much bass/low mids through the amp...

I suspect this excess bass is also causing the amp to have a weird overtone when cranked up. See the video below... The amp makes this overtone when picking hard, and it does it when played loud AND with an attenuator. It also still does it when using an external speaker cab only so I think it's coming from the amp itself.

So, is there a capacitor or set of capacitors I can change in the amp to brighten things up some / remove some bass? Or, could the strange distortion overtone be coming from something else wrong with the amp?

Amp's strange overtone with distortion:

Thanks for the help!!!!!!!!!!!

[davegardner0]

Here's a link to the kit I used:
http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf

Here's what it sounded like cranked up when it still had the PCBs:

[Justin Thomas]

I'm not hearing an "overtone" as much as I'm hearing a frequency- and volume-dependent crackle. My two main suspects are a bad wiring connection or mechanical vibration, or a parasitic oscillation at certain signal strengths. How's the wiring look compared to an original Fender? The routing of wiring can have a HUGE impact on these kinds of issues. Do any of the knobs have any effect on the weirdness - as in, an effect that wouldn't be EXPECTED - volume or frequencies drop in and then out again as knobs are twiddled?

Of course, I also heard a possible microphonic tube in the old video, and maybe it's a tube issue in the new one, too...

Justin

[Enzo]

It is a reissue model, which had a printed circuit board. he has replaced that board with an eyelet board kit. SO ther is no way to compare wiring. However, you are right that lead dress is still important in his build.

Is your Strat a single coil pickup? And are the other guitars humbuckers?

The first way to brighten an amp is to install brighter speakers. You have other amps that sound different, so unplug the speakers from the Deluxe chassis, and connect them to one of your other heads. Do they sound bright now? Or are they still dark and bassy?

And likewise, play one of your other guitars that sound too bassy here. Play one into this amp, but connected to some other speaker cab.

This way we have tried the two halves of your system - speakers and amp chassis - individually, and that shows us which half is the major contributor to your bassy tone.

[Justin Thomas]

Sorry, let me clarify - how close does the wiring match the included layout diagram supplied with the kit? I would think'after all these years, that layout would have had any major bugs worked out... failing that, is it as close as possible to an original 60s DR? I know it'll be a little different, but I was thinking more dramatic changes or deviations.

No, definitely won't compare to the PCB layout!

Justin

[Chuck H]

The first thing I notice is that the amp is set up for clean and then only the volume knob is increased. Something to be aware of regarding the BF topology is that the tone controls are IN FRONT OF any clipping stages. That means that once the amp is clipping the tone controls are no longer tone controls. They are clipping character controls. Most BF type amp players already know that if you set up the right bass level for clean tones it will absolutely be too much bass for clipped tones. Most BF amps (that I've played) sound like yours with the bass above 5 when clipping. Most of the time a setting of 2 or 3 is about max bass for heavy clipping. The thing to do is set the amp up for clipping and advance the bass control until it just starts sounding too flubby or you have too much "beating" (sum/difference overtones). Then back the bass off a tad. That's it. Because of the gain in the preamp that is all the good sounding bass the amp can make. Turning up the bass beyond that doesn't actually make more bass volume. Just more mush and LF overtones.

EDIT: Oh, hey, my bad. I only watched the second video and thought it was the reference for the problem. Still, all of the above applies. I just watched the first vid where you're adjusting the bass control and heard the crackle. It's probable you have a lead dress issue as Justin said. I don't think it's a mechanical issue, but I've been fooled before. Compare your work to the vintage layout for the original Fender design (available on line everywhere). And if you could post a vid of the trem channel volume weirdness that might be good too. It could be related since the two channels are actually out of phase at the PI input.

[Randall]

I tore the guts out of a DRRI and built it up once on fiber board, and again on a glass turret board. I didn't use a kit, I had a real 65 AB763 SR sitting behind me that I referenced for lead dress. I don't know what they supplied you with for coupling caps, but I used all the stock schematic values. I wouldn't say mine sounds dark and muddy at all. Are you using the stock speaker that it came with? It's a Jensen C12K 100 watt, and IMO Fender knew what they were doing by pairing the amp with that speaker. I messed around with different speakers, but came back to that one, because it just sounded the best, not muddy at all,

Please recheck your work, that circuit has been well vetted. Doubt you need to change any components unless a new cap is out of spec, which does sometimes happen.

[TimmyP1955]

I've had something similar in several RI Fenders right out of the box. It could be cured by disconnecting the reverb tank or by removing the reverb driver tube. A tube swap did not help. Never did sort it - as they were new, we just sent them back. I suspect faulty reverb driver transformers.

[davegardner0]

Guys, REALLY SORRY, for some reason the "notify me by email when someone replies to this thread" didn't work at all so I didn't see any of your messages until now. Sorry about that!!!! Thanks for the great ideas though. Let me answer some of your questions.

I'm not hearing an "overtone" as much as I'm hearing a frequency- and volume-dependent crackle. My two main suspects are a bad wiring connection or mechanical vibration, or a parasitic oscillation at certain signal strengths. How's the wiring look compared to an original Fender? The routing of wiring can have a HUGE impact on these kinds of issues. Do any of the knobs have any effect on the weirdness - as in, an effect that wouldn't be EXPECTED - volume or frequencies drop in and then out again as knobs are twiddled?

Of course, I also heard a possible microphonic tube in the old video, and maybe it's a tube issue in the new one, too...

Justin

I *think* my lead dress is pretty solid. I have some photos in the original thread I linked above. I did triple-check for any potential bad connections but of course it's always possible. I don't think it's any sort of mechanical vibration though, because I get the exact same issue when playing the amp through an external speaker cab only. Also I don't think it's the tubes, as I replaced them all with new JJ tubes.

I think this link should take you to the post where I showed the completed wiring: Fender Deluxe Reverb Reissue Hoffman Board Conversion - The Basics

It is a reissue model, which had a printed circuit board. he has replaced that board with an eyelet board kit. SO ther is no way to compare wiring. However, you are right that lead dress is still important in his build.

Is your Strat a single coil pickup? And are the other guitars humbuckers?

The first way to brighten an amp is to install brighter speakers. You have other amps that sound different, so unplug the speakers from the Deluxe chassis, and connect them to one of your other heads. Do they sound bright now? Or are they still dark and bassy?

And likewise, play one of your other guitars that sound too bassy here. Play one into this amp, but connected to some other speaker cab.

This way we have tried the two halves of your system - speakers and amp chassis - individually, and that shows us which half is the major contributor to your bassy tone.

I don't think it's guitar or speaker-related, as I've swapped guitars, and I've also swapped speakers, both playing the DR through an external cab and playing other amps through the DR's speaker. I do think the issue is within the DR's circuitry itself. I only brought up the other guitars to illustrate the fact that this amp is a lot more bassy than other amps I have, and that holds true with a couple different guitars plugged in.

The first thing I notice is that the amp is set up for clean and then only the volume knob is increased. Something to be aware of regarding the BF topology is that the tone controls are IN FRONT OF any clipping stages. That means that once the amp is clipping the tone controls are no longer tone controls. They are clipping character controls. Most BF type amp players already know that if you set up the right bass level for clean tones it will absolutely be too much bass for clipped tones. Most BF amps (that I've played) sound like yours with the bass above 5 when clipping. Most of the time a setting of 2 or 3 is about max bass for heavy clipping. The thing to do is set the amp up for clipping and advance the bass control until it just starts sounding too flubby or you have too much "beating" (sum/difference overtones). Then back the bass off a tad. That's it. Because of the gain in the preamp that is all the good sounding bass the amp can make. Turning up the bass beyond that doesn't actually make more bass volume. Just more mush and LF overtones.

EDIT: Oh, hey, my bad. I only watched the second video and thought it was the reference for the problem. Still, all of the above applies. I just watched the first vid where you're adjusting the bass control and heard the crackle. It's probable you have a lead dress issue as Justin said. I don't think it's a mechanical issue, but I've been fooled before. Compare your work to the vintage layout for the original Fender design (available on line everywhere). And if you could post a vid of the trem channel volume weirdness that might be good too. It could be related since the two channels are actually out of phase at the PI input.

This is really good info, thanks! One issue I have here is that I haven't played other BF amps so I don't know what's normal and what is an issue. Your info on how the tone controls work is really really helpful. As a matter of fact, I can get the farty overtone to go away if I back the bass control down to 0. What I'd like though is to modify the amp's voicing a bit so I get (a) a little more treble when played clean, and (b) a little less mud when playing distorted. Maybe my amp is just on the bassy side of normal for BF amps?

I should mention as well that the amp is MUCH more bassy and farty when turned up on the vibrato channel, whereas the normal channel doesn't have the weird overtone and muddiness. Is this only because the normal channel has 1 less gain stage? And/or is the normal channel usually brighter?


On a final sidenote I'm now suspecting that the vibrato channel's volume knob issue could be related to using the wrong taper on the volume pot. The schematic I followed here: http://el34world.com/Hoffman/files/Hoffman_AB763_2.pdf doesn't specify the taper, and I bought a random CTS 1 meg pot with a SPST switch so I could have a switchable bright cap.

[Randall]

Actually that schematic does specify the taper 1Ma. The a is for audio taper.

[davegardner0]

I still have a list of "simple stuff" to go through and check on the amp as described above BUT I was reading today about similar issues and I found this article on blocking distortion, which I think sounds like what's happening in my amp:
What Is "Blocking" Distortion?

Do you guys think this is the issue I'm having? Of course if it is blocking distortion it could be caused by an error during assembly or just by too much bass due to capacitors being on the edge of tolerance, etc...

[davegardner0]

Actually that schematic does specify the taper 1Ma. The a is for audio taper.

Thanks for that clarification, I've got the notation down now...

[waspclothes]

Hi Dave, I'd try this with a different speaker/cab just to rule that out. If speakers have small tears, it's the high bass that really gets them buzzin'.. so I'd rule that out first.

After that, it sounds like some sort of "mostly-good-but-kinda-bad" connection, I'd then shot-gun resolder everything.

Then if you have a scope, I'd see what that weird distortion looks like on the scope at the output and work my way back. Scope the input going to the PI, is the weird distortion still visible there, etc. Once you can find a section of the circuit where it isn't happening, you've narrowed down your problem to only a few associated components.

[davegardner0]

Hi Dave, I'd try this with a different speaker/cab just to rule that out. If speakers have small tears, it's the high bass that really gets them buzzin'.. so I'd rule that out first.

After that, it sounds like some sort of "mostly-good-but-kinda-bad" connection, I'd then shot-gun resolder everything.

Then if you have a scope, I'd see what that weird distortion looks like on the scope at the output and work my way back. Scope the input going to the PI, is the weird distortion still visible there, etc. Once you can find a section of the circuit where it isn't happening, you've narrowed down your problem to only a few associated components.

I have tried the speaker swap using an external cab and the issue was still present. Good thought though! Reflowing my connections is on the to do list for sure. Unfortunately i don't have an oscilloscope. I wonder if there is a smartphone version using the headphone/mic input though? Audio signals aren't particularly high speed as scopes go.

[davegardner0]

I've had something similar in several RI Fenders right out of the box. It could be cured by disconnecting the reverb tank or by removing the reverb driver tube. A tube swap did not help. Never did sort it - as they were new, we just sent them back. I suspect faulty reverb driver transformers.

I just tried disconnecting the reverb tank - the bad distortion is slightly quieter but still present unfortunately.