Tonestack on BF/SF fenders.What value/comp do you guys like?

[sidehatch]

Got a question for the builders/modders here. Im thinking about fiddling with the 3 cap tonestack on my pro reverb on the vibrato channel.

Now it has the .1 , .047 and .047 setup and its those dark blue caps
These:
[IMG:799:599]http://img.photobucket.com/albums/v334/ ... G_8603.jpg[/img]

I'm thinking of trying another configuration and I'd like to know what you amp buiders/modders like. I have read that 3 of the same type(say orange drop) don't sound as good as mixed but that may be internet garbage.

The amp has a lot of bottom end. As it is I run the bass at 2 and the treble at 8. On my other fenders the treble gets ran at 3 or so. The amp is Dark and fat by nature. I like the midrange content and really dont want to add a mid pot or anything or mess with the mid resistor because I've been down that road before and didnt like it.

So basically, which 3 caps would you use and which brands/compositions

I already have 1 of those .022 paper in oil russian military caps I bought from a guy on the gear page. I put one in my strat and was shocked how much better it sounded when I used the tone control so it got me thinking about the amp.

My desired goal is better classic fender amp tone and maybe open up the sound a tad without making it brittle. I like its basic sound,breakup,volume ability. Lets see if we can get some mojo happening. I do hate the bright cab. Maybe I could put a different cap value in there? Is that a .002? I'd have to go look.

Oh Yeah, Speakers I have in there are Emi's red,white and blues and a C rex. I have the original oxfords put away which I think are terrible .

I also have some jensens and a celestion G12H30. Im willing to swap one of those out but for now just want to mess with caps. I like the amp as is but think it can be better and want to learn about cap selection and tone.

The amp has had fresh service, New tubes,bias, Sprague atoms, grouded power cord etc. In case anyone is worried about the amp or its condition. Its gig ready now. Its quiet,buzz free,has rev & vibrato on both channels.

I'm thinking of this as a chance to see what changing 3 simple caps can do on an amp.

Thanks!

Here's a few more view of the amp so you can see what we are dealing with.
[IMG:599:799]http://img.photobucket.com/albums/v334/ ... G_8589.jpg[/img]
[IMG:599:799]http://img.photobucket.com/albums/v334/ ... G_8590.jpg[/img]
[IMG:599:799]http://img.photobucket.com/albums/v334/ ... G_8591.jpg[/img]
[IMG:799:599]http://img.photobucket.com/albums/v334/ ... G_8593.jpg[/img]
[IMG:799:599]http://img.photobucket.com/albums/v334/ ... G_8594.jpg[/img]
[IMG:599:799]http://img.photobucket.com/albums/v334/ ... G_8595.jpg[/img]
[IMG:599:799]http://img.photobucket.com/albums/v334/ ... G_8596.jpg[/img]
[IMG:599:799]http://img.photobucket.com/albums/v334/ ... G_8597.jpg[/img]
[IMG:799:599]http://img.photobucket.com/albums/v334/ ... G_8601.jpg[/img]

[solderstain]

Got a question for the builders/modders here. Im thinking about fiddling with the 3 cap tonestack on my pro reverb on the vibrato channel.

Now it has the .1 , .047 and .047 setup and its those dark blue caps
These:
[IMG:799:599]http://img.photobucket.com/albums/v334/ ... G_8603.jpg[/img]

Hi -

First things first: Just to make sure we're all on the same wave length, I'll assume that you know that the picture you posted showing the caps (above) isn't the Trem channel, right? That's the Normal channel we're looking at in that picture.

Also, the tone caps aren't .1, .047, and .047. The treble cap is the tiny ceramic disk cap (250pf) at the other end of the 100k resistor. The other blue .047 cap is output coupling cap that runs to the mix resistors on the other end of the board. And that .047 coupling cap is for the Normal channel. The coupling cap for the Trem channel is .02uf.

Here's what I'd suggest as a starting point: Blueprint the original tone stack before you mod it. Meaning, I'd bet that the existing caps were on the outer limits of their manufacturing tolerance when new, and have drifted well away from that by now. Start be replacing all three caps with new caps that you've measured to be sure they're close (if not dead-on) with the original spec. Replace the 100k resistor with a good carbon film (or better) that you've measured to be closest to spec.

Getting the tone stack working at its designed parameters, you MIGHT find that it doesn't need to altered at all. But get it 'right' before you go shooting off in another direction.

Just my $.02

[sidehatch]

Thanks for the reply and advice. Yes, I know thats tjhe normal channel in the 1st photo. I just took many pics and thats the best one that illustrates the caps Im talking about.

I understand the treble cap is the small 250pf cap. One my super reverb its a Tantalum. I wonder if its been replaced?

On my super reverb it has a .1 and a .022 and a .047 and the pro has (2) .047's which I guess maybe works with the 12" speaker better?

I am just getting into working on amps myself. Got a bias probe and have a cap discharge device( alligater clip system I read about and made)

I definitely don't want to just start replacing things becasue i would hate to loose what I already like about the amp.

I'm wondering a few things now:

a. Should I start with the cathode bypass caps and switch them to 10uf instead of 25uf and see if that opens up the amp before I even mess with the tonestack?

b. I have a super reverb that I just love and it has been gone thru by a great tech and I can see a lot of things have been replaced. I wonder if I should post photo's of that amp and see what things I should tackle on the pro?

The pro has been gone thru,new atoms,tubes etc. Its probably in the top 5 fender amps I've owned but doesnt sound as good as the super even thru the supers speakers(I know there is a mismatching of ohms too)

Im just thinking if I can get this pro as great sounding as the super I'll be really setup on a stereo clean sound for big gigs and use my redplate for leads:)

Thanks for the help!

[dehughes]

My recommendation (huge grain of salt here):

Use the original values...these amps are classics for a reason, and we (r.e., I) have a tendency to tinker needlessly with a good thing. If it ain't broke...

That said, I do enjoy the 6PS caps in Fender-y amps, though Mallory M-150s or Sozo caps are great as well. Small value caps are usually silver mica (in Voxy amps only, usually) or ceramic (Fender, Marshall, rarely Vox) or polystyrene (Marshall, Vox, rarely Fender). YMMV, of course...

But do stick with the original values at first...

[billyz]

You could try changing the treble cap to a Polystrene . Change the treble value to 330pf or even 500pf or 120pf. The mid and bass try .02, .02 or try .03, .03 , like very early blackface circuits did. You can also change the slope resistor, try 56k like a marshall or other values. If no middle control try upping the middle resistor to 10K or even 25K. Just examples.

[solderstain]

First, I apologize that I didn't word my previous post clearly enough... I'll try again with some visual aids:

I understand the treble cap is the small 250pf cap...
...On my super reverb it has a .1 and a .022 and a .047 and the pro has (2) .047's.

It seems from your typing that you're still confused about what the tone stack actually includes. Below are two images - the top one is from the Pro Reverb schemo, and the one below it is from the Super Reverb schemo.

As you can see, the tone stack consists of the 250pf Treble cap (on both), the 0.1uf Bass cap (on both) and on the Pro, a .047uf Mid cap, and on the Super, a .033uf Mid cap.

Unless it's been modified, your Super doesn't have a .1, a .022 and .047 in the tone stack. Likewise, unless the Pro has been modified, it doesn't have two .047s. And from your photos, it looks like it's still stock.

I think you're mistaking the .047uf coupling caps for being part of the tone stack. The in both of these pictures, you can see the .047 cap at the output of the second gain stage in the upper-right of the picture. They sit relatively close to the tone caps on the board, but they're not part of the tone stack.

[img:274:203]http://www.doctorvintage.com/misc/pro_r ... estack.jpg[/img]

[img:245:173]http://www.doctorvintage.com/misc/super ... estack.jpg[/img]

Now... since we're talking about the coupling caps, that is an area that you can fiddle with very easily on a Fender amp. When you look at the schemos for this style Fender amp, you'll see that the two different channels have different values for the coupling cap in that position. The Normal channel uses a .047uf cap, as shown in those pictures. The Trem channel uses a .02uf cap. You can change those caps around to change what each channels sends on to the PI. Easy. Easy.

I have a Pro myself (well, it USED to be a Pro...). One of the mods I did to the Trem channel is to have TWO different coupling caps - the original .02uf cap, and another which I have switchable, which brings the coupling cap up to roughly the .047uf value of the normal channel. The bigger cap makes a 'bigger' sound. I flip the switch around to 'tune' that channel depending on whether I'm playing humbuckers or single-coils.

GREAT STUFF!

I stand by my original recommendation - blue print the tone stacks (the real tone stacks...)

And add this one - play with the value(s) of the coupling caps following the second gain stage, particularly the .02uf cap on the output of the Trem channel. Big results for very little work...

[sidehatch]

Thanks for all your help!!

I need to order some caps to play with on this but for tonight because I had the .022 russian military cap( I bought 2, put one in a guitar and saved the other for a guitar but I cant believe how much difference that cap made a difference in a guitar-a strat too. This is what got me thinking about trying different comps and values in amps.)

I decided to put the .02 in place of the mid cap in my pro.

Its is GOBS better with just that one change!. before I liked the normal channel best on that amp for some reson-maybe less gain?

Anyway its night and day better sounding on the vibrato channel. My wife kept saying "that is much much nicer sounding" Not as boomy. before , She said "you could walka bass line thru it"

well I am so pleased that I would like to hear what someone who really likes tweaking fender amps could make the amp sound.

Im going to order the other caps and such but If I do something it will be one cap at a time with full documentation.


This lower mid cap really calmed things down. Im thining a low cap that isnt so bassy? IN a PM, Heisthl recommended a 330pf cap for highs, a .02 orange drop mid and a .01 bas cap in a sola if I didnt mind springing the dough. He aslo said I might change the caps at the entrance to the PI stage and the 2 PI output caps that feed the output tubes. "I would try a .0027 entrance and .05 for the outputs".

Thanks to the hep I got on here Im 90% more pleased.

Thanks