SRV Vibroverb - Cesar Diaz Mods

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Bombacaototal
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SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

SixStringBender and I have been exchanging some of the SRV Vibroverb Cesar Diaz Mods and I decided to put it here for benefit of the forum members. The funny thing is that the reliable sources are very contradictory and there is really no conclusive answer as to what was really going on in his amp


Cesar Diaz interview where he speaks about the mods he did (non of which are in the custom vibroverb) http://forum.licklibrary.com/chat/cesar ... est-report

He says the following: "I'd change the 68K input resistor to 100K so that we wouldn't have so much input signal going into the tubes. The coupling capacitors would be changed to adjust the tone. I'd use a .047 or a .1 in place of a .042 cap. That's where the tone is in the preamp." "Vibroverbs we used output transformers from a Bassman."

SRV stolen amp: http://www.valcoamp.com/stevie-ray-vaug ... nal-notes/

The article also says the amp was very trebly and that amp was being used between February 20, 1989 and March 18, 1990

Mods: Sprague caps in tone section were changed in Channel Two to Orange Drops along with caps in the reverb return and the three main caps in the phase inverter to Orange Drops, bypass caps on both channels were changed to 33uf, The original grid resistors were changed to 2 watt carbon comp, the 1 meg resistors in the phase inverter circuit were changed to a later ‘70s value (silverface?), 1 watt plate load resistors were added on Channel Two and in the reverb, output transformer is a larger 2 ohm from a Concert or Super Reverb, Groove Tubes plug-in solid state rectifier with 220uf filter caps in place of the normal 70 mfd caps

I attach the schematic of the 64 Custom Vibroverb Diaz which was released by Fender. Mods follow:
R13, R14 to 100K
No V1: Remove R12
R17 to 2.7K
R24 to 2.7K and C11 to .68
No Trem: Remove R48 and maybe a jumper on C18 and R35
R53 to 100R
R67 to 1K and R68 to 4.7K
Solid State rectifier with 220mfd
R65, R66 to Fr 100K / 2W

I am wondering what is everyone's opinions about these sources and mods and why you think they are so different and contradictory
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Last edited by Bombacaototal on Mon Nov 07, 2016 10:28 am, edited 3 times in total.
Stevem
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Post by Stevem »

It takes a lot of input signal to clip that first gain stage unless you use a stomp box in front of the amp, in which case a 68K to 100k swap makes no sence to me as you have control of the signal level by means of the stomp box.
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by frankdrebin »

my opinion?
the more i look to forum statements about amplifiers of any kind,the more i am convinced that the so called techs of the stars don't have any clue of what they're doing,90% of them are still copying mistakes from the past and can't really advance in any field for many reasons.
Big pile of BS.
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by martin manning »

Hard to tell. No doubt a lot of misinformation (perhaps deliberate) and speculation are spread around, especially on the less-technical forums. Actual examples, when seen, do make you wonder if the originator knows much about what he is doing. Others, like HAD, seem to be legit. I'm often surprised at the audacity of someone offering their services in this field having little or no formal training.
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Roe »

diaz also modded the PI plate resistors to 47k
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Bombacaototal
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

Roe wrote:diaz also modded the PI plate resistors to 47k
Hi Roe, thanks for the input. May I ask what is the source of this info. I've seen so many wrong info on forums over the years that I just want to make sure this comes from a reliable source :)
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Roe »

The info is old, so it is a little difficult to remember. But I do think it was an interview with Diaz published in a guitar mag
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by SixStringBender »

Just to be clear, the R12 220K mix resistor cut, R48 cut, C18 jumper and R35 jumper are things I did in my own Deluxe Reverb Reissue amp. These are what I feel are a common sense approach as R12, C18 and R35 are no longer needed if V1 is pulled and the tremolo intensity pot (R48) is disconnected.

You can send the signal from the plate of V4B directly to the C25 PI input cap if the normal channel and tremolo intensity pot are permanently disconnected. This is a better impedance match.

And for future readers, who may be brought here by a search engine, and who may not be educated about a DC blocking coupling cap. You should not remove and jumper C18 unless you permanently cut R12 and R48. If those two things are cut there is no longer any need for C18 or R35. If you don't cut R12 and R48 you must leave C18. And be warned your amp can kill you, even with the amp unplugged.

Again, this is just my own approach to completely remove the normal channel and the tremolo circuit, to make the blackface a single channel amp. I also do the Diaz 2.7K cathode resistors for V2 A and B too.

I believe these are mods Diaz most likely did to SRV's Vibroverbs. I have no proof. Just a common sense approach since it is well known Diaz pulled V1 and he disconnected the tremolo intensity pot.

With R12 cut and R48 cut a lot more signal hits the phase inverter. Remove and jumper R35 and even more signal hits the phase inverter.

This increased signal hitting the phase inverter is why I believe Diaz installed the silverface phase inverter resistors. To clean up the amp a bit.

And I think these mods took place over time. It certainly wasn't done the first time Diaz poked around in SRV's amps. His blackface amps sounded stock in the very early years. In the early 80's they had more of a single channel blackface amp tone, with a stock sounding extended bass and a blackface sounding phase inverter. In the mid 80's his tone got tighter and cleaner. I'm sure the SSS had a huge role in that, but the Vibroverbs were there and they were not adding an extended bass or grit to the sound like a stock blackface amp sounds like. They were sounding cleaner and tighter than before. So I think this is the time period the silverface PI resistors were installed, as well as the .68uF V2B cathode bypass cap and 2.7K V2 A and B cathode resistors.

I would not do the other mods in the interviews.

A larger output tranny with an impedance mismatch, no.
A larger C12 coupling cap, no. Who ever heard of a .042 cap anyway? I think Diaz was blowing smoke or someone made a typo and meant .022.
33uF cathode bypass caps, no.

Something I like that has never been mentioned as being done on SRV's amps. Install a reverb dwell with a 1M audio pot. Helps get the reverb under control.

These are just my thoughts and opinions. I'm certainly not even close to the most educated tech here.
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by 67plexi »

I have not played a SRV song since 1982 what I used then was two
Blackface Twin's and a Kittyhawk M1 it was close enough at that time.

In the last month I was told that the SSS-150 SRV amps were high gain
preamps. So I built a EF86 TMB 18 Watt amp. On the EF86 channel volume
with a 7 position treble switch the .0022uf nails SRV spot on.
I was going to put a bass cut switch just didn't have room.

Take it how ever you want.

Steve.
Bombacaototal
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

I found this older post about same topic which has interesting discussions
http://ampgarage.com/forum/viewtopic.ph ... light=diaz
Bombacaototal
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

Some of SRV amps. I mapped the following:
1980s: 2 Vibroverbs
1982 Montreux: 2 Musicman Twin Blackface (2nd pic below)
1983 Mocambo: 1 Vibroverb, 1 Super Reverb
1985 Montreux: 2 Vibroverbs, 1 Dumble SSS, 1 Super
1985 Tokyo: 2 Vibroverbs, 1 Super, 2 Twins (late 70's silver and mid 80's bf) (last pic below).
1987: Nashville: 1 JCM800, 1 Super, 1 Dumble SSS, 1 Twin
1988 UK Interview: 1 Marshall Major, 1 Dumble SSS
1989 Austin City: 1 Vibro to drive the Vibratone, 1 Marshall Major, Blackface SSS and the 2 Super as a speaker cabinet
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Bombacaototal
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

A couple more pics, one of 1989 austin city limits, one of mocambo and the other of 1985 montreux
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Bombacaototal
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

On V2B the Diaz mod has a 0.68/250V cap. Is there any reason for such a high rated (250V) cap? Is it fine to have it as a 2V instead?

I am thinking Vishay MKT1813 (160V). Any recommendation?
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Roe »

10v or 16v is fine.
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Re: SRV Vibroverb - Cesar Diaz Mods

Post by Bombacaototal »

Roe wrote:10v or 16v is fine.
Noted with thanks
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