deluxe reverb amp with extra gain stage on chanel 1 to make it more like channel 2

[mikepukmel]

Hi All,
Curious if any of the amp tinkerers out there added an extra gain stage on channel 1 of a Fender Reverb amp (most schematics are fairly close), to get the gain of channel 1 up closer to channel 2 (reverb channel). When I switch between the two channels, on my deluxe reverb clone, they both sounds good, but with reverb off (or set to 1 anyway), channel 2 sounds better, a little more 'gainy', don't know how to word it.
I read that channel 2 has an extra gain stage to make up for the losses in the reverb portion of the circuit but that it more than makes up for the loss, which is what I experienced as well.
I spent a few days searching for a schematic, but couldn't find one. Some discussions here and there, but more like guitarists asking how to add a gain stage on channel1, and less technical discussions that get into the design parameters.
Going through Merlin's book as well.
Thanks

[Leo_Gnardo]

Don't forget about that "loss" stage, at the dry/reverb mix point. Consider the mix circuit together with the following triode as a total gain block. You can dial the gain up or down by selecting different resistors in the voltage divider formed by 3M3 resistor in series with 220K. As well as the brightness by leaving out the 10pF cap bypassing the 3M3, or selecting different brightness caps across whichever resistor you may select in this leg. Lots of choices available here. You can leave the 3M3/10pF alone, the 470K from reverb pot too, but increase the 220K to 470K or 1M for more overall gain - actually less loss. You're certainly not stuck with the values Fender selected. Take a look at some early Traynor schematics like YGL3, you'll see variations on this circuit. And back to Fender, they leave out the 220K ground leg in Princeton Reverbs to conserve overall gain so the amp doesn't get wimpy. Plenty of room to tinker here, and find the combination that suits your ear. Have fun!

[mikepukmel]

Thanks Leo!

[Justin Thomas]

Or, you can mod the amp to habe the third gain stage shared between both channels, sp you dont HAVE to add a stage. Also, I think that would put the channels in phase, which is another bonus!

Justin

[Raybob]

I spent a few days searching for a schematic, but couldn't find one.

http://el34world.com/charts/TubeAmpSchematics.htm

[mikepukmel]

Or, you can mod the amp to have the third gain stage shared between both channels, sp you dont HAVE to add a stage. Also, I think that would put the channels in phase, which is another bonus!

Justin

Thanks Justin, there's a big space where tremolo would normally go, that I did not drill out the turrets, and there's the unused tremolo socket.

I haven't tried Leo's suggestion out yet, do have the parts, have vacation time, will try adjusting the gain and 'bright cap' on the reverb channel tomorrow.

Over the weekend, curiosity got the better of me, I tried out wiring in 1/2 a 12AX7 setup just like the reverb ch has (820R resistor + 25uf 25v, 100k plate resistor) right before the 220k mixing resistor (after the dc filter cap) on channel 1. As you gurus would expect, it did add quite a bit of gain. Lots of gain. Wayy plenty gain. And a huge amount of noise. It was pretty late, and I could only get the volume for ch1 on about 2, but I could only hit 2 notes, it was too loud. i think some more resistors haveta be put in there someplace. Ain't fer sure where, jest yet.

Shut the amp off, and disconnected the experiment for now. No sparks or smoke.

At the drawing board now, going through pertinent parts of Merlin's book, and some other amp schematics looking for how they shoehorned in a gain stage. Think the final thing will be a combination of an extra 1/2 tube on ch1, and the gain/tone mod's Leo suggested.

[mikepukmel]

Cool, thanks for the link Raybob.

[galaxiex]

Robrob's channel mod...

https://robrobinette.com/Silverface_...nel_Reverb_Mod

[soundmasterg]

I vote for modding to have channel 1 share the third stage as noted above. Did this on my brother's Pro Reverb among quite a few other BF Fenders and everyone I did that mod for loves it now. You can voice Channel 1 to be slightly different or lots different and since they are now in phase it makes for a more versatile amp. On some SF amps it can get noisy due to layout issues but you can mod that too and have a great and versatile amp. no need to add another gain stage either.

Greg

[pdf64]

Robrob's channel mod...

https://robrobinette.com/Silverface_...nel_Reverb_Mod

Though his site is a fantastic achievement, be aware that Rob doesn't seem to have any EE training, and as a consequence there's a fair amount of nonsense there.
Lot's of great ideas but take any explanations / analysis with a pinch of salt.

[Dave H]

Over the weekend, curiosity got the better of me, I tried out wiring in 1/2 a 12AX7 setup just like the reverb ch has (820R resistor + 25uf 25v, 100k plate resistor) right before the 220k mixing resistor (after the dc filter cap) on channel 1. As you gurus would expect, it did add quite a bit of gain. Lots of gain. Wayy plenty gain. And a huge amount of noise. It was pretty late, and I could only get the volume for ch1 on about 2, but I could only hit 2 notes, it was too loud. i think some more resistors haveta be put in there someplace. Ain't fer sure where, jest yet.

Shut the amp off, and disconnected the experiment for now. No sparks or smoke.

At the drawing board now, going through pertinent parts of Merlin's book, and some other amp schematics looking for how they shoehorned in a gain stage. Think the final thing will be a combination of an extra 1/2 tube on ch1, and the gain/tone mod's Leo suggested.

Have you tried mixing the channels at the input of the third gain stage as suggested in posts 4 and 9?

The gain of the two channels would then be the same as Channel 2 (as required) with no extra gain and noise to deal with. It only needs one extra R an C. I've marked up the schematic below.

[mikepukmel]

Thanks everyone, reading . . .

[Zouto]

Here‘s a link to a typical 80s style channel cascading mod for SF Fender amps, but you get only one „gainier“ channel.
https://www.premierguitar.com/articl...a-super-reverb
Have fun
Zouto

[mikepukmel]

Have you tried mixing the channels at the input of the third gain stage as suggested in posts 4 and 9?

The gain of the two channels would then be the same as Channel 2 (as required) with no extra gain and noise to deal with. It only needs one extra R an C. I've marked up the schematic below.

[ATTACH=CONFIG]50880[/ATTACH]

Oh very cool idea, thanks, will try that as well. Finally got a space cleared out in the basement, and some old kitchen cabinets and a piece of old kitchen counter for a workbench. Now no one complains about solder burning odor I can tinker more!!

I pulled the parts out from the mostly failed attempt to use both sides of the spare 12AX7 that would have been the tremolo tube. Will try all 3 suggestions. Dang this is fun stuff, thanks everyone!

[tubeswell]

Or, you can mod the amp to habe the third gain stage shared between both channels, sp you dont HAVE to add a stage. Also, I think that would put the channels in phase, which is another bonus!

Justin

yes, one could replace one or more of the 100k plate resistors on the first two stages with between 150k to 470k (depending on whim), or reduce the cathode resistance (to get hotter bias and more tube current through the load)