Enzo bravo mod instructions?

[UJN]

does anyone have step by step instructions to activate the pulled gain knob on a Peavey Bravo via a footswitch?

[Enzo]

To tell the truth I don't even have that. I see what is needed and make it up as I go.

Here is the entire collection of documentation on this. It really is not a complex thing.


You might also look over at Blue Guitar, I could have uploaded something on it there, but I doubt it. I think they only have some Classic 30 notes from me.

[tats_dragon]

Thank you for the detailed instructions. I just completed the mod.
The lowend is lacking, below what seems like 300hz, when the pull gain is engaged are R102 and C250 the culprits?

[tedmich]

Howdy TatsD!

Enzo's Mod just makes the footswitch "pull" the boost switch on pot VR6; there is no tone change over the stock amp.I believe R102 and C250 are just to smooth out the voltage going to the K3 relay coil, they shouldn't effect the tone of the switched cathode bypass boost at C11 (on V1B). That switched boost is a bit "nasal" in many peoples minds. The "pull boost" cathode bypass cap C11, creates a boost above ~450hz, switching to 1.0 uF will lower the boost to ~200hz, some go even bigger (lower, 2.2uF) but I like 1uF.

On the "tone mod" front , the Bravo is one of the earliest Ultra type preamp design that PV made; the somewhat nasal cocked wah tone is a major concern to many players, and is GREATLY exacerbated by the poor quality speaker, reverb circuit and to some degree the sonic character of the EL84 output section. Many of the mods to the (closely related) Rockmaster preamp work well on the Bravo.

The 1nF coupling cap (C2) is also a popular site for modding with 2.2nF/630vdc being the most loved value. Others like boosting the preamp voltages (lowering values of R63 R64), lowering plate resistors R1 R2 to 100k etc etc but I haven't tried these.

On any mods on a Bravo, go slow and be careful, you can electrocute yourself even if unplugged and the Bravo's PCB traces are very delicate; heat lightly and be gentle with the solder sucker (or use a wick).

Merlin's WEB site and book have good info on cathode bypass caps and guitar preamps in general.

[Enzo]

Keep in mind that the mod we did was intended ONLY as a way to shift the control from the panel down to a footswitch. We were not altering the tone of the amp. That is a separate issue.

[tats_dragon]

Tedmich,
I agree with your original Bravo's speaker assessment, a Celestion blue sounds very nice in the combo now. As most Bravo owners know, closed back cabs sound great with these tube amps. As far as the EL84 section, compared only to a Mesa 20/20 stereo El84 amp, I preferred the Bravo by a large margin.

So C11 is a boost above 450hz? It sure sounds like the lows are cut at the same time. I will try those values once I learn how to properly drain the large caps.

[tedmich]

+1 on the speaker (also the reverb needs bagging!) There was a guy with a Bravo/Mesa Thiele on youtube a while back and it sounded godly.

to avoid HV shock you can just attach a ~220k "bleeder resistor" from the end of the big PS caps
kinda like this
DSL100 | Bleeding Filter Caps
although I like a nice fully insulated resistor with sheathed alligator clips
RG's safety guide at Geofex
http://www.geofex.com/tubeampfaq/tube_amp.htm#Section0
Aiken amps safety page
SafetyTips

The Bravo is a great amp to learn on, even with the confusing way the schematic is drawn! The boost circuit and Merlin's chapter on tube gain stages are how I understood what cathode bypass caps did.
His book is great and well worth its cost, and his chapter is still free on his web site
http://www.freewebs.co.uk/valvewizard/index.html
although this mirror site with the gain stage chapter appears to be down currently

[stoneattic]

I know this is an old thread, but does anyone happen to have the files that Enzo (who is sadly no longer with us) had posted? The links don't appear to work for me.
TIA!

[tedmich]

Those files appear long gone sadly. From memory I think Enzo used the reverb switching in the TSR foot switch to activate the coil on K3 . This puts C11 (0.47uF) to ground where it acts as the cathode bypass for V1B producing the boost. A slightly larger value of C11 would be expected to make the boost lower.

Ive always wondered what adding another cathode bypass cap to V2A in this boost circuit would do, theres even a pad for it right next to R7 undrilled.

Good luck!!

[stoneattic]

Thank you for the response tedmich. I'm going to give it a try,but I'm thinking about adding a separate jack for the boost just so I can keep the reverb switchable, although I may not....