[Cumtax]

I live in Europe, for me it is out of the question to order delicate stuff and the very high customs taxes nullify the idea of being able to order an SMS Sarno preamp (to which I would then have to add power amp, rack mount = $$$$$$$$) . However, I found the head of an old BF Twin that was transformed into one and I would have the possibility to have it modded by a capable friend, but what should I tell him to do?

It's not easy to find information about it, I found a list of things here that seemed a little confusing or in any case didn't seem very precise (would that really be all there is to it?), I even stumbled across some drama. Many links have been eliminated therefore many Dead ends. I think I understand that until a few years ago there was information on Jerry Mod available, is there nothing left? I also scraped Healey's information but as usual, there is no comprehensive guide or list.

[Slewfoot2000]

Here are a few previous threads about it…hope that helps!

viewtopic.php?t=12321

viewtopic.php?t=20644

[Chocol8]

First off, you do not need to change anything to get the Jerry tone except maybe speakers. The other stuff has a very small impact, and will not help much if you don't have the playing down.

The main mod starting in late 1973 is the pre-amp out mod that allowed Jerry to use the McIntosh power amps. http://www.dozin.com/gear/preamp/mod.html

The tone stack mods were replacing the mid and bass capacitors with lower value .022 uf caps. With Jerry's setting of treble 10, mids 5.5 and bass 0, the impact of this mod is minimal and basically just a slight extra rolloff of bass. You really don't need to do this, especially if not playing at stadium volumes with a full band. The normal tone stack rolls off more than enough bass for lower volume playing.

Finally, the electrolytic cathode bypass caps were supposedly replaced with military spec axial lead tantalums. Be super careful with this mod as 1) you very likely can't get the caps they used, and 2) Tants can explode on you. The argument for this mod is increased high frequencies and long-term reliability, but with the tantalum caps available today, you very well may see the opposite for both!

My advice would be to use the Twin stock but with JBL D-120/K-120/E-120 or clone speakers. If you can't get the tone with that, (which is actually what Jerry used until the early 70's) the problem is not the amp.

[Cumtax]

First off, you do not need to change anything to get the Jerry tone except maybe speakers. The other stuff has a very small impact, and will not help much if you don't have the playing down.

The main mod starting in late 1973 is the pre-amp out mod that allowed Jerry to use the McIntosh power amps. http://www.dozin.com/gear/preamp/mod.html

The tone stack mods were replacing the mid and bass capacitors with lower value .022 uf caps. With Jerry's setting of treble 10, mids 5.5 and bass 0, the impact of this mod is minimal and basically just a slight extra rolloff of bass. You really don't need to do this, especially if not playing at stadium volumes with a full band. The normal tone stack rolls off more than enough bass for lower volume playing.

Finally, the electrolytic cathode bypass caps were supposedly replaced with military spec axial lead tantalums. Be super careful with this mod as 1) you very likely can't get the caps they used, and 2) Tants can explode on you. The argument for this mod is increased high frequencies and long-term reliability, but with the tantalum caps available today, you very well may see the opposite for both!

My advice would be to use the Twin stock but with JBL D-120/K-120/E-120 or clone speakers. If you can't get the tone with that, (which is actually what Jerry used until the early 70's) the problem is not the amp.

Regarding the tonestack, wouldn't boosting the mids a bit and making the bass tighter make the "jerry mod" a bit like a Dumble?

If I'm not mistaken, the ODS (yeah, ok, it's suitable for those who want more gain but let's assume it's clean) focuses precisely on these characteristics. Mayer uses a Two Rock which according to him, unlike the Twin, is less "spongy" (yeah I know, guitar-lingo), so I think he means less mid-scooped and more centered on the mids while still retaining the characteristic of a Fenderish amp.

[Chocol8]

No, the Jerry mods are almost the opposite of a Dumble ODS type amp. Jerry didn't really boost the mids at all. With the cap changes and his mid setting of 5.5, his mids were in the same range as a blackface fender without a mid control, if not a touch less. Turning up the mid control on a stock Twin Reverb will get you significantly more mids (and gain!).

Jerry's tone involved cutting out the bass to leave that frequency range to Phil and keyboards. He ran the amps and signal chain very bright, with max treble and moderate mids, but controlled that somewhat with the guitar tone controls.

[Slewfoot2000]

Jerry's tone involved cutting out the bass to leave that frequency range to Phil and keyboards. He ran the amps and signal chain very bright, with max treble and moderate mids, but controlled that somewhat with the guitar tone controls.

Yep! And that is why it often sounds kinda odd and sterile to play at home with the bass on zero.

Just a wee bit of a difference playing solo at home and rocking it out in an arena with a band!

[Chocol8]

Yep! And that is why it often sounds kinda odd and sterile to play at home with the bass on zero.

Just a a wee bit of a difference playing solo at home and rocking it out in an arena with a band!

Yes, this is why I would not recommend the amp mods beyond maybe the pre-amp out. With the controls set the way Jerry did, there is little tonal difference from the cap changes, other than a bit of extra bass rolloff. Most of us probably don't need or want any more bass rolloff than a stock Fender, and even if we did, you can get there with an EQ more easily.

Another thing to keep in mind is what era tones are you after. All of this discussion applies to Spring 73-1974 and 1977-1992 years. In between he was using the Mesa Boogie MkI amps (still sounded like Jerry!).

From 1965 to Spring 1973, he was using stock Fender Twin Reverbs and at some points, there was also a Dual Showman head. He started with just one BF twin. Sometime in late 66 or maybe January 67, he got new amps funded by Bear and the Twin or Twins (up to 3, or 2 plus a showman head) also had Fender Dual Showman 2x15 cabs loaded with JBL D-130's or later 4x12's with D120's. This is important because when a Twin is driving its two D-120's plus an external cab, the load seen by the amp is 2 ohms instead of 4 ohms and this contributes to the distorted tones you hear in the late 60's. This is a big part of the creamy distorted lead tones he was getting out of the Gibson P90's and hum buckers. He did not have any dirt pedals in the live rig until late 1976 I believe.

The big drivers of his tone changes from 1965 to 1992/3 are really in the guitars and the effects. All of those tones are accessible with a stock Twin Reverb driving JBL speakers. The main benefit to going with something like the SMS pre-amp is weight savings and volume control, but at the cost of not being able to get the late 60's distorted tones. BTW, a trick to get the 60's distorted tones with the load mismatch is to pull two power tubes (inner pair or outer pair, leave one on each side). This makes the amp expect to see an 8 ohm load instead of 4, so driving the 4 ohm load of the internal speakers gives the same effect as the 4 power tubes driving a 2 ohm load with an external cab, but with half the output power, which is still really loud.

Finally, if you want to incorporate a McIntosh or other power amp, an alternative to the pre-amp out mod is to get something like a Suhr RL. A reactive load makes the amp think it is driving speakers, but gives you a line level output to feed a power amp. The Suhr is an 8 ohm load, so again, you can pull 2 power tubes to make the load match the amp for the clean 70's-90's tones with no other amp mods needed.

[caspersvapors]

First off, you do not need to change anything to get the Jerry tone except maybe speakers. The other stuff has a very small impact, and will not help much if you don't have the playing down.

The main mod starting in late 1973 is the pre-amp out mod that allowed Jerry to use the McIntosh power amps. http://www.dozin.com/gear/preamp/mod.html

The tone stack mods were replacing the mid and bass capacitors with lower value .022 uf caps. With Jerry's setting of treble 10, mids 5.5 and bass 0, the impact of this mod is minimal and basically just a slight extra rolloff of bass. You really don't need to do this, especially if not playing at stadium volumes with a full band. The normal tone stack rolls off more than enough bass for lower volume playing.

Finally, the electrolytic cathode bypass caps were supposedly replaced with military spec axial lead tantalums. Be super careful with this mod as 1) you very likely can't get the caps they used, and 2) Tants can explode on you. The argument for this mod is increased high frequencies and long-term reliability, but with the tantalum caps available today, you very well may see the opposite for both!

My advice would be to use the Twin stock but with JBL D-120/K-120/E-120 or clone speakers. If you can't get the tone with that, (which is actually what Jerry used until the early 70's) the problem is not the amp.

Regarding the tonestack, wouldn't boosting the mids a bit and making the bass tighter make the "jerry mod" a bit like a Dumble?

If I'm not mistaken, the ODS (yeah, ok, it's suitable for those who want more gain but let's assume it's clean) focuses precisely on these characteristics. Mayer uses a Two Rock which according to him, unlike the Twin, is less "spongy" (yeah I know, guitar-lingo), so I think he means less mid-scooped and more centered on the mids while still retaining the characteristic of a Fenderish amp.

I think Mayer in this regard is referring moreso to the "stiffness" of an amp feel which could relate to the power section and rectification or sag.

and to extend it further, a Fender twin will feel a lot more stiff than say a Tweed Deluxe or even Princeton. Perceived stiffness could also be changed via speakers. A high wattage JBL will feel less spongy than a small magnet alnico.

[Searing75]

I agree fully with the posts above recommending JBL K120’s for the Twin. Also, good tubes, properly biased, make a big difference as well. If you are going to have your buddy do mods, mind as well do the tone stack mod.

[Cumtax]

damn guys, thank you for the quality posts. Your deep-dives really made things clear. You are the best

[TI4-1009]

http://www.dozin.com/gear/preamp/mod.html

[Cumtax]

http://www.dozin.com/gear/preamp/mod.html

is this the jerry mod?

[Chocol8]

http://www.dozin.com/gear/preamp/mod.html

is this the jerry mod?

This is only the pre-amp out mod.