A more "gainy" sound

[pjd3]

This is more of a "getting picky" thing since I'm getting great results with the single channel Vibroverb I just built with the aid of a pedal board I also have built up over the years but I wanted to hear what some of you say about this:

If I could say that there is one thing missing from my sound now, its the tone/response one gets from a "3 gain stage" blackface Fender, like the normal channel on a super reverb, twin reverb, deluxe reverb, the usual AB736 preamp.

My amp is really the normal channel of a Vibroverb with no reverb or tremelo so, that really makes it a 2 stage I believe - a first preamp stage, a second EQ recovery stage, and an 12AT7 LTP phase inverter.

I'm curious to what you might suggest for getting an amp like this a little close to the sound of a 3 gain stage amp. I find there is just a little more excitement to that sound, just a little more nice grease and texture.

What would you do (besides get an amp with 3-gain stages), is there a pedal that works really well to emulate this? Would a variable NFB bring some of the harmonic excitement missing from 2 gain stages? Is there a known working switchable gain stage that others have included to accomplish this?

I get nice compliments on my range of tones all the time but, feel that this is one little sonic place that could be filled at some point

Thanks for your time!

Phil D.

[Roe]

first add a 150pf cap over the 220k mixer resistor at the phase inverter grid/input. or remove the 220k completely. adding a presence control to the power amp might help somewhat or increasing the 10k mid pot or 6.8k mid resistor perhaps. still 2 gainstages will never become 3 gainstages. try a high-gain tube though and keep the plate voltage at 250-260v

[pompeiisneaks]

If Roe's specifics don't help, I've used two pedals myself to get great tone and gain,

I've got the Electro Harmonix Soul Food which is the cheapest and one of the best rated Klon Centaur Clones out there. It just boosts the signal with the right kind of grit at the front end to push the first tube a lot harder.

If you want more deep heavy gain, I love my Way Huge Sound Green Rhino, it's got a great tone, and a 100Hz boost/dip pot as well as a curve shaping pot. Lets you dial in that right amount of meat.

My 2c

~Phil

[sluckey]

The normal channel on any AB763 amp such as deluxe, super, or twin is only two gain stages. The easiest way to get a more gainy sound from the normal channel of any AB763 amp is to replace the mid control with a 250KA RAW control. If you only have two tone knobs then replace the 6.8K tail resistor in the tone stack with a 250KA RAW control. The pot functions as a normal MID control for the first part of rotation but begins to lift the tone stack for the rest of the rotation. This gives a lot more gain with some hair on it.

[Tony Bones]

Rob's Blackvibe has 220k/270k resistors forming a voltage divider to mimic the reduced gain of the AB763 normal channel (he calls them "mixing" and "Vib Ch load".) You can remove them for more gain. It won't necessarily add the flavor of the third stage in the trem channel, but it's easy to try. You might as well remove the 0.047uF coupling cap before them as well.

[pjd3]

Thats right Tony, and that is the amp I built, Rob Robinettes Blackvibe with the 6L6's. I wanted to start with a 2 gain stage clean amp to render my pedals more clearly and it does just that. Those Run-off-Groove Tube to FET pedals have been a really great thing for getting in the ballpark of the classic amp overdrive responses but they can get a tad bit harsh and greatly benefit from a clean tube path. That, plus cranking up the mid raw control give those pedals a nice thick and meaty sound without rendering the highs too harshly. Now its just getting back that intermediate gain thing that the 3 tube pre stages make, that Blackface reverb channel level gain/grit area. I think its time to build some more pedals, something that might get that in there.

Thanks,
Phil D.

[JD0x0]

If your single channel vibroverb has reverb as the name would entail, you already have a 3 triode clean.. You can adjust the voltage divider network in the mixer stage if you want more gain, and/or use a large value mid pot like 100k-250kA as suggested. You can hit the PI a bit harder if you completely bypass the tremolo when it's disengaged. The loading from it reduces gain a bit, but the increase is a different sound than a 2 vs 3 triode amp, it's more like turning the (Pre-PI) 'Master' volume up to '10' when before it was stuck on 8 or 9 with the tremolo loading things down.

[pjd3]

Hi JD, thanks for stopping by

This is an amp with just the Vibroverb normal channel with no reverb or tremolo driver. I believe that makes it kind of a 2 stage amp, if you don't include the 12AT7 for the LTP phase inverter. I'm pretty sure that in typical blackface vibrato channels the reverb driver is adding gain apart from the input stage and post EQ stage. Its a really clean amp, and that is what I wanted. I don't want to lose that because its a huge benefit to the tone of the overdrive and distortion pedals I use. The one sound I'm sorta missing is that blackface vibrato channel Deluxe Reverb turned up to 4-5 sound, where its still not breaking up too much but, there is a good dose of sting and grit in the sound, good for some bluesy leads and slicey rhythms. I did listen to some clips of the Soul Food and Klon Centaur and a couple others and when the drive control is turned way down, its getting to the missing tone I'm looking for.

I'll just keep listening and see it something stands out. I continue to be open to suggestions.

Thanks!
Phil D

[Tony Bones]

Have you tried removing (or changing) the voltage divider?

[pdf64]

The fx channel’s 3rd stage only adds ~3dB gain; getting rid of the 220k mixer resistors will give you more than that.
Be aware that BF SF RI thereof Fenders have vol and treble pots with a ~30% audio taper; unless you carefully sourced them, your pots will just be the regular audio taper of 10% (Bourne, CTS) or 15% (Alpha USA), so other than maxxed, it’s invalid to attempt to compare settings.
As mentioned, typical mods to increase the grunt of such an amp are a higher value mid control (I prefer a 47k 10% taper pot, as even when it’s set high, all 3 tone controls still work as expected), and a decreased / variable power amp negative feedback ratio. Note that the Super Reverb and Princeton Reverb have the lowest stock ratios, so perhaps try those first, or just put it on a pot.

I agree that the EHX Soul Food is handy to have; it’s replaced my Tube Screamer for a boost on some songs, but I’m actually looking for a second one that I can mostly leave on at min gain. Their downside is hiss.

[Roe]

the reverb channel is not just more gainy but also more compressed noisy and bright sounding than the normal channel. A bright sounding compressor, e.g. suhr koji, into the normal channel might work. or the solodallas storm pedal might work, since it compresses and boosts, although it may lack some treble for this particular application