Hoffman AB763 with robrob reverb mod?

[mresistor]

Anybody ever mod a Hoffman Ab763 turret board with robrob's reverb on both channels mod?  One of the cool things it does is put the two channels in phase and I hear also boosts gain on the Norm chan.


https://robrobinette.com/AB763_Modifications.htm#robrob_Normal_Channel_Reverb_Mod

[2deaf]

I haven't tried it but I was looking at Fender's '64 Custom Hand-Wired DeLuxe Reverb-Amp and it looks like they just made V1-B and V2-B into a garden variety common anode mixer and ran that into the reverb and beyond.  If I were inclined to try it with a Hoffman board, I might do this:

1.  Eliminate C5 (.047)

2.  Eliminate the long under board wire from C5 to R16 (220K).

3.  Eliminate R15 (1.5K) and C6 (22uF) and the wire connecting them to V1-B pin 8.

4.  Connect V1-B pin 8 to V2-B pin 8 .

5.  Change R25 (1.5K) to 820r.

6.  Connect the plate of V1-B to the plate of V2-B leaving both plates connected to their 100K plate resistors (R14 and R24).

7.  Eliminate R16 (220K)

Fender appears to have eliminated R16, but I would have used it to make a 220K/220K voltage divider by connecting the end of R16 that used to go to C5 to ground.  That would be closer to what happens with a 220K/220K mixer. 

[Apexelectric]

Sounds good in theory. Let us know if it’s worthwhile when and if you try it.

[mresistor]

Thanks 2deaf..   interesting.. I just got the amp fired up for the first time.   I will let you know if I try this Apex.  I made the normal channel with more gain though, marshall-esque so don't know yet if I'll try it.  Seems like if one were to do this mod on a hoffman board it should be planned out before the board is made so turrets could be installed to facilitate the mod

[2deaf]

Seems like if one were to do this mod on a hoffman board it should be planned out before the board is made so turrets could be installed to facilitate the mod

  Maybe for the Torres mod that robrob is showing, but the '64 Custom mod can use the stock Hoffman board and is fully reversible if that long under board wire is left in place. 

[2deaf]

Fender also changed Hoffman's R37 (470K) to a 1.5M.  They wired the '68 Custom DeLuxe Reverb the same way.

[DummyLoad]

2deaf, is this what you mean?  please review attached.

you could also increase gain of V4b to get some more grit by eliminating R30 (47K). i'd probably do that anyway... 

 --pete

[2deaf]

2deaf, is this what you mean?

Yes, except C19 is .0033uF.  Attached (hopefully) is a '68 Custom schematic.  I don't have a '64 Custom schematic, but the gut shot they have looks like they wired it like the '68 Custom. 

[DummyLoad]

2deaf, is this what you mean?

Yes, except C19 is .0033uF.  Attached (hopefully) is a '68 Custom schematic.  I don't have a '64 Custom schematic, but the gut shot they have looks like they wired it like the '68 Custom.

thanks for sharing that schema.


--pete