Fender Super Reverb (AB763) distortion quality?

[VintageCharlie]

Hi folks,

How would you describe the distortion quality of a properly maintained Black Face Super Reverb?

I have an old original, which is stock and in good condition. It has fantastic clean tone, but i am not too crazy about it's distortion quality. Adding a boost in front does make it sound actually worse, when it is cranked. I record amps direct into my DAW through a reactive load. My experience is that this way, after applying a good Impulse response to the signal, it sounds pretty much identical to how the recording through a mic would sound. I like the overdrive of my 45/100 and of my ac30, but the Super just sounds quite thin, a bit harsh and, well, scooped. Instead of getting a nice smooth overdrive like here (which is pretty much the tone i would hope to get from my Super Reverb):

https://www.youtube.com/watch?v=eQeudZPm3Qg

There are small mods done to the Super in this link, but nothing drastic - stuff that increases headroom and slightly also the gain. But the main difference i notice is the smoothenss of the drive. Mine seems harsh/a bit ratty. Sounds great with a Tubescreamer or a Bluesbreaker though, but that is the only way to get smooth drive from it.
A big part of the tone above are certainly the EV speakers, i base my comparison on Impulse Responses of EVM 12L speakers, which should be fairly similar in regard to smoothenss.

Also this one sounds great - it is a 79 "70w" master volume Super Reverb: https://youtu.be/0fDVI939BKw?t=1005

These are to me good examples of the Super Reverb distortion, that sounds almost like a "clean" tone - that is what i like so much about it.

Both of these sound like i would like mine to sound, but it seems harshar / splattier / "uglier" in the drive department. Wondering which way to look (do not want to mod it, if possible to avoid that).

[pdf64]

Are you sure it's actually working right? Have the values of all parts been checked? What does the scoped waveform look like, as is transitions into overdrive? What's the idle anode / cathode current of the 6L6s? Too high and there will be more bias shift and the negative feedback's action will be stronger.

[Stevem]

If both channels sound the same and have the same level of punch when the amp is open to 5 ,even when you swap the first two 12AX7s ( V1 and V2) then I would check to see if all 4 of the speakers are working and that they are still wired to provide a 2 ohm load to the output transformer .

Also a weak rectifier tube can cause a issue like this, so how does this tube test?
Do you have another you can swap into the amp?
If you do not have another known good 5U4GB then a known good 5AR4 will work for a quick test session.

One of the best things you can do to determine how fit the amp is, is test for how much clean RMS wattage the amp can output even if you only have a 4 or 8 ohm resistor to test with.

If the amp has ok preamp tubes and good output tubes, rectifer tube and power supply filters then it should output 31 watts RMS into a 4 ohm load and 18 watts RMS into a 8 ohm load.

Another really important thing to test is the negative bias voltage on pin 5 of each output tube with the 2 tubes out of the socket.
If it’s over -52 volts the amp will sound thin, lack punch and have very unpleasant distortion when cranked and maybe even bad clean tones if this voltage is set too high.

You should only read a negative voltage on pins 5, if it’s positive then one or both of the coupling caps feeding pin 5 off of that last 12AX7 is going bad.

In fact the FIRST thing I would do is to make this bias voltage test and make sure that there is at least a -48 volts on each pin 5, if not then do not put the output tubes back in until you have adjusted the bias pot to have at least - 51 volts on each pin 5.
Another major reason for lack of power is one open side of the primary of the output transformer.
To check this test that you have over 400 volts on pin 3 of each output tube.

You can test this with the tubes in the sockets and if one pin 3 reads a low negative voltage then that side of the transformer ( brown or blue wire) is open.

[VintageCharlie]

Thanks for the suggestions guys, i will start to look into it more systematically, starting with tubes and bias check.
I played around with the settings some more and did find some that sounded good. It is sounding still thin and brash compared to the AC30, but maybe it is the way it is supposed to sound. I think that a lot of the Super Reverb tones that sound excellent benefit a lot from the effects of the room. The AC30 has the unique quality of sounding excellent without the room masking anything - it has spoiled me i think.

[Colossal]

VintageCharlie,

I know exactly what you mean about that ratty quality some Fender amps have when they are driven to distortion. It is sort of a hard, blatting, skidding sound, with a strident edge in the upper mids and not smooth. Most offensive to my ears. Some Fenders are magical though and have more of a clear, singing quality. Those are the ones I like.

Here is some reading which may be of interest, if you have not seen it already.

http://fenderguru.com/amps/super-reverb/

[VintageCharlie]

VintageCharlie,

I know exactly what you mean about that ratty quality some Fender amps have when they are driven to distortion. It is sort of a hard, blatting, skidding sound, with a strident edge in the upper mids and not smooth. Most offensive to my ears. Some Fenders are magical though and have more of a clear, singing quality. Those are the ones I like.

Here is some reading which may be of interest, if you have not seen it already.

http://fenderguru.com/amps/super-reverb/

Yes, that is exactly what i mean with the distortion. I have the feeling there are good sounds in there, but it needs some dialing in to get there. And that clear, sustainy, singing quality is exactly what i am looking for. There is some of it there and it sounds quite good in the room. Just looking to improve its sound through the reactive loads DI.

[Roe]

Most of the ab763 amps can distort nicely if you control the low bass and blocking distortion.

[Reeltarded]

Check all grounds, especially tone stack..

[deuce42]

Coming late to the party with this thread but my experience is that huge change can come from changing the first cathode bypass. To confirm this point, the link you provided is from Tyler Grund who made the same change (amongst others he did) based on Caeser Diaz's recommendation. Somewhere on the web is a quote form Caeser Diaz himself saying he changed the first cathode bypass on the super reverb's SRV used to tour with.

The standard Marshall 2.7k/0.68Uf can really make a the amp smooth out the overly bass heavy "splat" in my humble opinion.

Others will have much more knowledge than my novice info but out of all the Caeser Diaz mods, this one I really liked.

Cheers

[VintageCharlie]

Thanks for the input guys! I checked the amp and compared it more to my other amps with a real cab at gig volumes. Sounds fantastic in the room. I think that is an amp that just does not sound as good (to my ear) as an ac30 or a JTM into the close-miked situation that i am simulating with a reactive load and an IR.

[VintageCharlie]

Coming late to the party with this thread but my experience is that huge change can come from changing the first cathode bypass. To confirm this point, the link you provided is from Tyler Grund who made the same change (amongst others he did) based on Caeser Diaz's recommendation. Somewhere on the web is a quote form Caeser Diaz himself saying he changed the first cathode bypass on the super reverb's SRV used to tour with.

The standard Marshall 2.7k/0.68Uf can really make a the amp smooth out the overly bass heavy "splat" in my humble opinion.

Others will have much more knowledge than my novice info but out of all the Caeser Diaz mods, this one I really liked.

Cheers

Thanks for the hint about the cathode bypass mod. I will keep that in mind for a build I might do in the future - do not want to mod the original.

[TUBEDUDE]

Try dropping the feedback.

[JD0x0]

What Phase inverter tube are you using? 12AX7 or 12AT7?

If the blocking distortion is an issue, you could drop the PI output couplers somewhere around 22nF-33nF to reduce it, without shaving off much audible bass.

[andyhardy]

Keep an open mind with IR'S try tons of different ones 4x10 4x12 2x12 etc
Whats sounds great with one amp can sound complete crap on another

The super reverb is looking for a 2 ohm load not sure what your reactive load is rated at
Always add a bit of room effect on the IR and cut some highs with eq

Here is a link on using IR's

https://www.youtube.com/watch?v=i770M9pM0_k

Here's a link to amazing super reverb tone

https://www.youtube.com/watch?v=4h_iujpSUqA

Bob

[pottedplant]

I record amps direct into my DAW through a reactive load. My experience is that this way, after applying a good Impulse response to the signal, it sounds pretty much identical to how the recording through a mic would sound.

but the Super just sounds quite thin, a bit harsh and, well, scooped. Instead of getting a nice smooth overdrive like here (which is pretty much the tone i would hope to get from my Super Reverb):

So here's something no one talks about, what reactive load are you using? A LOT of the reactive loads on the market have very inaccurate impedance curve simulations that don't really resemble the impedance behavior of most speakers on the market. Two of the biggest offenders that are SUPER common on the marketplace are the UA OX and Two Notes Captor line of products.

The simulated impedance curves of these two devices are extremely scooped and "bathtub shaped". To my understanding, amps with more negative feedback will succumb less to this inaccuracy (as is the main purpose of applying negative feedback to a power section) but those without negative feedback in theory would sound wildly different than if they were mic'd up and connected to a real speaker because of the curve they're being shown from the reactive load.

Here are some impedance graphs that someone made of a real marshall cabinet, a suhr load and the two products mentioned above.

real cabinet and suhr.PNG

ox and captor curves.PNG

I highlighted the impedance curves and you can see just how not realistic the OX and Two Notes curves are. These curves from what I understand represent the behavior of an amp with negative feedback, thus making any amp that runs through this load box more like an amp with negative feedback. I imagine an AC-30 will sound awful through one of these boxes.

It could be that this is what you're experiencing. The problem being, the suhr box is fixed at 8 ohms so you can't test it on your Super