Studio Preamp IIC+ mod and reverb replacement outcome

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crduval

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Hi all;

New member and first post... Nice to be among Boogie-philes.

I have owned a studio preamp (along with a 50/50 power amp) since the late 80's, and have always loved the smooth, singing lead tone. I was less happy with the somewhat loose, fuzzy lower end in the lead channel, but it was an OK compromise for what I was doing, and the presence knob on the 50/50 helped somewhat...

I had some problems with the rig recently, and upon opening up the preamp discovered that the spring reverb was in bad shape, one loose spring rolling around (hence the problems I was having), and another that was broken. After verifying that everything else was working properly, I ordered a replacement reverb tank, and whiled away the time for delivery looking into doing the IIc+ mod. I finally decided to give it a try, because I had read that the low end tightened up somewhat.

Well, I just completed the work, and in testing the result, I have to say the difference is pretty striking. The low end is much bigger, and the tone is more reminiscent of an older Marshall's kind of grunty quality. The gain at the same settings is lower, and I will need to re-work some settings to regain that singing lead tone (which I believe is still there), but its a lot weightier tone. I never really used the EQ before, but it might be necessary now to re-balance the spectrum more towards the way I like it.

One thing is that I think this amp will record better - It always sounded great, but a little thin mic'ed up, but this default tone should really sound full. I'm looking forward to experimenting with it in the coming weeks.

The new reverb tank sounded OK, a little tinny I thought, but I am not a big spring reverb guy, so I am probably not the best judge. After all, I didn't know the old tank was broken until the loose spring started shorting things out so that should tell you how often I used it :)

FYI for reference, I run the rig into a Boogie Road-Ready 4x12 loaded with old greenback Celestions I salvaged out of an old Marshall cabinet I used to have. The prominent low end I got was a surprise given those greenbacks I have to say, they are not the heaviest sounding things around - think late 60's early 70's rock guitar tones. I love 'em though...

All this to say, if you are considering doing this modification, or having it done by someone else, be prepared for a big change in default tone. If you love that out of the box singing lead tone, I would think twice before having this done. Of course, its pretty easy to reverse the rework, but I hate to do too much desoldering / resoldering etc - it just leads to damaged PC boards, melted wiring and broken feedthroughs!

I may have inadvertently switched a couple of the tubes around (V3 and 5), and that could also be contributing to the big difference - I can check that out tomorrow...

Anyway, thought I would try to describe the difference with and without the mod in some detail in case anyone was thinking of doing it. UNfortunately, I did not record before / after :(
 
That's good info; thanks for sharing it. I've considered trying this mod on my Studio Preamp in the past, but the fact that I really, really like the out-of-the-box tone has always held me back. This tells me that I'm better off keeping it stock.
 
Yep, thanks for the interesting post. It also makes me reconsider modding my Studio Preamp.
 
I have a non modded and a modded studio pre which was modded by a member here, then sold to another member, then I bought it.
I'd also have to agree with your review of the sound change.
I've also find mine is quieter(less noisy) than the non modded studio.
The modded amp I bought according to the person who modded it has also had the bass shift mod, but it doesn't have a push pull knob, so I don't know if it really has been done, or if he just never added the knob(so maybe that may add to the quietness?).
Looking at the 2 amps opened up,there are alot of changes, but I haven't taken out the schems(which are pretty crappy) to check.
I've gone back and forth between the 2, I've found that I'm using the modded amp more, but do enjoy going back to the non modded amp too.
There's just a thickness or sound that I cant seem to get out of the non modded amp that the modded one gets easily, but you do loose some of the higher gain treble sound that the non modded amp puts out.
 
Just to follow up on my experience with the mod; after a week or so of playing around with the EQ, I found that a little cut at 80Hz, plus a small boost at 2.2K and a little more at 6.6K brings my high end back to where I like it, and playing around with the settings of the lead gain and volume got me back to the level of saturation I like, so now I'm ready to try some recording to see how it all comes together. Its still thicker than the old tone but now I've got some bite and articulation back so I'm happy.
 
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