Tightening bass in Fender blackface

[SixStringBender]

WOW, WOW, WOW!

I can not believe the difference with R12 clipped. This was it. The amp tightened up. It was like there was a parasite sucking the tone out of the thing and we cut it's head off. The piano tones I was searching for are here now. Next I have to try jumpering R35.

I don't know if it is possible, but it is like the frequency of the amp moved up or something. The bass isn't as farty and the mids are amazing. I can get that Tin Pan Alley tone from Montreux 1985 now. It sounds so good now I almost don't want to touch it anymore. lol

I was in no way expecting this positive of a change. So it certainly is not a placebo effect if anyone has doubts.

Just to note. I pulled V1 long ago. And I have many of the 64 Vibroverb Custom mods already. I haven't checked to see if switching R12 in and out is one of the Vibroverb Custom mods.

[Tone Lover]

Ok so after following along over a long period. Im confused about everything that was done. Any chance of a schematic being done or should I just re-read everything again. Man it sucks being old and forgetfull. (LOL). Im not after this tone myself but I do love a good study and comparison of the differant schematics on my wall.
Bill

[SixStringBender]

Hey Bill, sorry a schematic would be very difficult for us to do. I think I can list everything we've done here. Most of the following was already done before this thread. I think I have a list in the first post. I believe C18 to .022uF from .1uF, the dwell/send reverb control and the R12 removal is the only things since the beginning of the thread. Each made an improvement though. The bass cut in the Strat wasn't worthwhile.

The first thing I ever did was to pull V1. It made a noticeable difference, but it certainly was not a WOW that is SRV tone moment. A nice improvement though.

I changed the PI for a 12AX7. Why would I want a terrible wimpy sounding 12AT7 as a voltage amplifier reducing signal to the output? I tried a 12AT7 again the other day. It just neuters the amp. A 5751 would be a better choice if less gain is desired.

Then I disconnected the tremolo at the intensity pot. Again a nice improvement, but even more mud in the bass.

Then the OT. I currently have a Classic Tone Vibroverb size OT, but I just ordered a Twin Reverb size M6 steel Classic Tone OT with 4, 8 and 16 ohm taps. The 40-18013 is the one in the mail. With either OT I can use the 4 ohm tap with JJ 6V6S and an 8 ohm speaker load to get a 8K primary for the JJ 6V6S. When I want to put 5881's or 6L6GC's in I can change the tap to the 8 ohm tap to get a 4K primary. I have it wired to a 13A jack, so all I have to do is insert a dumby plug to change the taps. That will prevent an accidental switch throw. It takes a lot more intelligent thought to plug a plug into a jack to select impedance than to throw a switch. It can't be done by accident.

Edit: Installed a plug in yellow jacket SS rectifier. A must with the power supply stiffening below.

I removed the series wired main filters (C31 and C32 and I wired two 50uF 600V caps in parallel. I removed R65 and R66 and trashed them. These were the bleeder resistors for the series wired pair. No longer needed with the parallel pair. The Diaz mod is to put two 220uF 285V-350V caps in series with 100K resistors across each cap, but I didn't really have room for those huge caps and I decided two 50uF caps in parallel at 600V is a better idea anyway. 110uF Diaz vs 100uF with two 50uF caps in parallel is very minor in difference.

I replaced R67 with a 1K 1W flame proof metal film and R68 with a 4.7K 1W FP metal film. The DRRI has 10K for both. The 1K and 4.7K are the Vibroverb and Super Reverb values. The result was more clean headroom. The OT, main filters and this resistor swap changed the amp a lot. I was amazed how much I liked the R67 and R68 resistor swap.

Next was the preamp changes and the 100R resistor in the NFB.

Replaced R13 and R14 with 100K 1/4W metal film.
Replaced R15 with 1M 1/4W metal film.
replaced the mid cap, C9, with a .022uF Orange Drops 225P
Replaced the bass cap, C8, with a .1uF Orange Drops PS. I had to relocate the bass cap to the back of the control board. This is also why the new 225P mid cap fit on the other side.
Replaced the bright cap, C10, with a 120pF silver mica. A must for SRV's tone. It is impossible to get his mid 80's tone without the bright cap.
Replaced C7, C13 and C14 with equal value as stock silver mica caps.
Replaced C12 with an Orange Drops .022uF 225P. Same as stock value.
C11 to .68uF 250V radial polyester. The lead spacing of that voltage in a radial is what fit nicely.
R24 and R17 to 2.7K
Replaced R53 100R 1/4W with a metal film.

Then C18 to .022uF Orange Drops 225P.
R26 replaced with a 1M audio taper pot for dwell/send control for the reverb. I cut the reverb wire and tremolo wire to the footswitch at the PCB so I could use the footswitch hole for the dwell control. I used shielded wire from R26 to the pot. I used the ground location at R26 to ground the right lug of the pot using the shield of the RCA wire I used and the point of R26 that goes to C14 as the center conductor to the left lug of the pot. We cut the wire from the PCB to the grids of V3 at the PCB and wired it to the wiper of the pot. Cutting the wire is necessary to break the connection to C14 as well.

Then we cut R12 at the side that connects to R35. We didn't try to put R12 in parallel with R35 as pdf64 suggested. I decided I will try jumpering R35 when I get a chance.

I think that is everything. Just put that in the DRRI schematic and you have it.

This amp will get the Mosfet source followers post PI. Heyboer is going to wind a custom PT with a 230V center tap secondary for me to do it. I'm also thinking of using V1 as a cathode follower for the tone stack. I will make it switchable if I do it. I just need a good switch that can handle the high DCV. I need a DPDT toggle. I think pdf64 was looking for a switch for me.

I have a diagram for using V1 as a cathode follower for the reverb channels tone stack if you want a link to it. I was going to use the PCB for the normal channel as much as possible if I do it.

It requires cutting the trace to the normal channel tone stack, among some other things, to use the PCB and supplied wiring to V1. V1B would be completely disconnected and grounded.

I may still tighten the amp more by shedding bass in the preamp. I don't know yet. I kind of want to see what the even larger OT and buffer after the PI will do.

[vibratoking]

Your changes are interesting and I'm glad you are satisfied. I just wish you wouldn't try to pass off your opinion as concrete fact.

I, for one, dislike pulling V1. It is an old approach that takes away more headroom than I like and trashes the clean chime.

Orange drops in a BF amp are not my preference.

Glad you like your changes.

[SixStringBender]

Bill, I made an edit in the post. I forgot about the SS rectifier. A must with 100uF main filtering.

vibratoking, I didn't post anything as fact other than the things that are fact. I didn't say poly caps must be used. The only thing one could say I said that is opinionated that I may have made it seem fact is the bit about the 12AT7 in the PI. However, why would anyone want to put a current amplifier in a voltage amplification stage? Especially since there is the 5751, with similar gain as the 12AT7, for the job.

Most of the mods I listed are straight from the Fender 64 Vibroverb Custom schematic. That is factual information that these mods will take a DRRI closer to SRV's tone. SRV's tone changed over the years, so whatever tone is being saught after will vary with the mods. If I were after his early 80's tone I would leave out the C11, R24 and R17 changes. I'd also leave C18 alone. Those are my opinions, but his tone had more extended bass in the early 80's. Even honky with the Super Reverbs at times. I believe these mods by Diaz took place over a period of time through the 80's. I believe the PI changes I've read about, when the Vibroverb had the silverface PI, were done in the late 80's. That would fit with his even cleaner thinner clean tone. IMO, his mid 80's tone was his best tone. From 84-87, or so. However, I've heard late 80's and 1990 tone that was great. Who knows how often Diaz was tweaking his amps?

I would have to disagree about the pulling V1. It does increase gain, but it increases volume too. I don't know the measurement of the clipping, but I believe the clipping would be at a higher volume level than with the tube.

The R12 removal was dramatic. If you think about it the signal from the reverb channel was going back through the normal channel circuit. Even though V1 tube was pulled there is still the path to V1B's plate resistor that goes to DCV. Imagine what that is doing to the signal. I'm not much of a tech, but it is parasitic. I believe it is like the signal is going to ground through the 220K mixer resistor and the 100K V1B plate resistor. From my understanding the AC signal from the reverb channel basically sees the DCV on the other side of V1B's plate resistor the same as it does as if it were ground.

My amp has way more headroom and chime now than it did stock. The R67 and R68 resistor changes increased the preamp voltage and increased headroom a lot. A stock DRRI has a lot lower headroom and more drive with the 10K resistors.

My BillM modded Blues Junior sounded better than my DRRI when it was stock. By a bit even. Now my modded DRRI sounds amazing. Both amps sound good, but the DRRI is now my favorite amp.

And in the words of Uncle Si, that's a fact jack! lol jokin' of course.

[Colossal]

Here is a marked up DRRI schematic for anyone trying to wrap their head around this.

[John_P_WI]

Here is a marked up DRRI schematic for anyone trying to wrap their head around this.

Thank you kind sir, this damn head cold and hopped up on NyQuil made it nearly impossible to follow without a schematic. Ahhh, I see now, R12 was partially shunting the signal through the power rail - snipping it allowed full drive to the PI.

Thank you again Colossal.

[Reeltarded]

https://m.youtube.com/watch?v=Pvxzg9y3HkE

[SixStringBender]

Here is more detail on the cathode follower for the reverb channel tone stack by using the V1 socket and normal channel PCB layout in the DRRI. The diagram may have a mistake, so it will be best to follow my text description with the DRRI schematic in hand. The diagram was drawn by my wife with me explaining what to draw. So there could be a misunderstanding between her and I there. Again, for anyone just tuning in I am blind so I can not draw a schematic.

The DPDT switch is to have the ability to switch between the stock plate fed tone stack and the cathode follower fed tone stack.

I would use a 12AU7 for this. Or maybe even scrap the use of V1 socket and use a MOSFET.

The plate of the first gain stage of the reverb channel (V2A) will feed the grid of the cathode follower tube (V1A), going through the DPDT. I would run a wire directly from pin 1 of V2A to the DPDT (leaving the wire from R16 in pin 1 of V2A as well).

The cathode of the cathode follower, V1A pin 3, will then feed the tonestack of the reverb channel (through the DPDT). The trace between R16/V2A pin 1 and the reverb channel tone stack must be cut to be able to do this. I would drill a #60 hole through the trace that goes to the reverb channel tone stack (on the tone stack side of the cut) on the main PCB and feed the tone stack there. The plate fed mode would feed the tone stack through this same wire as well when the DPDT switch is in the plate fed throw mode.

I would cut the trace from R4 to the normal channel tone stack. Making sure there is no connection to the tone stack anymore. Then remove and jumper R4 to get power to the plate of V1A.

I then need the cathode follower's bias resistor to ground. I can remove a component for the normal channel for this (the stock cathode bypass cap for V1A, C1). I will install a 100K 1/2W resistor in place of C1 and I have to remove R5 as well so it won't parallel the new 100K cathode bias resistor. The lead spacing of R5 is too narrow for a 1/2W resistor, so C1 is a better location for the new 100K resistor. This location is convenient because it goes directly to pin 3 of V1A already.

I'll remove the wires from the plate, grid and cathode of V1B pins six, seven and eight) jumper them and run them to ground where R5's lead was going to ground. Since that half of the tube will be unused the elements need to be grounded.

V1A's grid, pin 2, has to be disconnected from the input of the normal channel. I'll just remove that wire and use it somewhere when wiring the switch. We certainly do not want high voltage on the normal channel input jacks.

Then wire the DPDT, like in the diagram to V1A and it is done. We'll have to unsolder pin 3 on V1A to put the shared wires for the cathode bias resistor and the cathode follower wire to the DPDT in it. We'll also have to unsolder pin 1 on V2A to put the wire that feeds signal to the DPDT in with the wire from R16.

I would put a 12V 0.5W zener diode, not shown, across the grid and the cathode at the DPDT. Anode side to the grid and cathode side to the cathode.

That does it utilizing supplied traces and wiring as much as possible so there shouldn't be any problems with unwanted noise. Wire runs will be short, several using the stock wiring, and only a single wire going over the board to feed the tone stack of the reverb channel. I would mount the DPDT switch on the back panel between V1 and V2.

With a flip of a switch I should have CF mode and another flip should give me stock sounding plate mode. The difference in tone should be slight, but the idea isn't to change it radically. Only to try to improve signal through the tone stack and increase second order harmonics.

Now, the only hold back is the best switch I have found is an 80 DCV DPDT. I need a DPDT that can handle more DC voltage. Or maybe switch to standby before flipping the switch, however, I may flip it by accident when not on standby.

[SixStringBender]

I discovered the 12AT7 I had tried in the PI was bad. That is why it sounded horrible. I tried another one I found and it sounded good. I found a 5751 in my stash and there isn't much difference between the too in the PI. The 5751 is what I decided to leave in.

I would have left the 12AX7 in, but we jumpered R35 and it increased volume so I wanted to try to shed some with the 5751. The amp has more gain now when cranked too.

It is loud. A variable resistor here may be nice to dial in a level and desired drive to the PI.

I've never rolled tubes in this amp, so I decided to try it. I tried the following in the first preamp stage. An EI Elite, a Sovtek 12AX7/LPS and the stock JJ ECC83S. The EI was the loudest and cleanest, but not as dynamic as the JJ. The Sovtek LPS sounded good, but it was noisy and the JJ sounded everybit as good with no noise. It went back in.

Gonna put the Twin Reverb sized Classic Tone OT in tonight.

[Teleguy61]

https://m.youtube.com/watch?v=Pvxzg9y3HkE

Reel, I'm a little concerned not only that you could find this clip, but that you might have listened to it.

[Reeltarded]

I have been looping it for three days, this time.

[Teleguy61]

I have been looping it for three days, this time.

Much is explained.
I think it's genius anyway, that singer.

[pdf64]

The Carling 110 series are quick make/break, suitable for higher voltage dc, several are rated at 250Vdc http://www.carlingtech.com/sites/defaul ... Series.pdf
An SPST item from that line is traditionally used for standby I think, eg maybe up to 500Vdc.
So this DPDT may be suitable for the switchable cathode follower idea http://www.newark.com/carling-technolog ... 0000005412
It's out of stock but should be available elsewhere.
Or this Eaton one looks a similar spec http://www.newark.com/eaton/8373k122c/s ... /dp/23F502

[SixStringBender]

pdf64, thank you very much for the links! I'll check them out.

I put the Twin Reverb Classic Tone OT with multiple taps in.

Big Edit:
So I did have the secondary taps wrong. Classic Tone changed the tap colors from my last Classic Tone OT to the Twin Reverb OT. I had checked the specs sheet, but forgot it was the green wire I should be using with JJ 6V6S. So I changed the tap and the tone improved greatly, but it still is not as sweet as the Vibroverb size Classic Tone OT. It is too stiff in the bass for my likeing and it has too much treble. It is ice pick. No more grit with the proper tap though. It sounds like a lower volume Twin. The Twin's tone has a LOT to do with the OT.

I read where Diaz said he didn't mind an impedance mismatch and he said he put the larger Super Reverb OT in SRV's Vibroverb for more headroom. Well I put a Twin Reverb OT in my DRRI for what I thought would be better tone. No way. With the correct tap there may be the slightest more headroom, if any at all, however, with the wrong tap there was much less headroom. I had a 4K primary with the tap I was using with JJ 6V6S and the tone was gritty as could be. It was horrible. May be why SRV's tone went worse in the late 80's. May be why Diaz put the silver face PI resistors on the grids of the PI. A vintage Fender Super Reverb OT in a Vibroverb would be an even worse mismatch than I had going on.