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Studio Preamp LDR

Posted: Sat Dec 02, 2017 11:25 am
by Electricsun
Hi, I think this is my first thread here, but my account is not new.

Can you please help me identify these LDR models?

The preamp is a Studio Preamp, Serial Number SP1060

I’ve been reading a lot about a problem I have with the drive channel leaking sound into the clean channel, and I’m almost certain that the problem could be the LDR, as also confirmed by Mesa/Boogie staff by email.

I thought about sending to repairman, but here in Japan is just so expensive to have a repair, even if I just need them to do an specific job (changing LDR) the repair shop won’t receive the preamp unless I do overhaul first (about $150)

So, putting all the fees altogether is almost the price I paid for the unit, so I just want to try repair myself :mrgreen:

Are these the rights equivalents?

Photos inside link

https://imgur.com/a/5G5oc


I’ll go soon to the electronic shop (in akihabara!) hoping they have the parts.


On a second note, are these too difficult to take from the PCB?

It’s not easy access, but I’m guessing I just need to desolder from the top and just replace, right?

Thanks for your time, any help is appreciated!

Re: Studio Preamp LDR

Posted: Sat Dec 02, 2017 11:32 am
by Electricsun
Sorry I forgot to add, I think it’s

LDR1 and LDR2 is 21L883
LDR3 is 21L884
LDR4 is the Vactec Vactrol

21L884 = VTL5C4
21L883 = VTL5C1
Vactec Vactrol = VTL5C1

Re: Studio Preamp LDR

Posted: Fri Dec 15, 2017 7:41 pm
by MesaMad1378
Hi there,

Does it look like they have been replaced before? I'd like to know if someone has used these in a 2:90 as well?

They have different current and voltages to the VTL5C9 that the 2:90 has in it.

Re: Studio Preamp LDR

Posted: Tue Jan 02, 2018 7:31 pm
by Electricsun
MesaMad1378 wrote:Hi there,

Does it look like they have been replaced before? I'd like to know if someone has used these in a 2:90 as well?

They have different current and voltages to the VTL5C9 that the 2:90 has in it.
Thanks for your reply!

When I looked into it it didn’t seem they had been replaced. I got this unit from a friend for about $200, and he got it used from another person, so I can’t really tell how it was used.

Do you think I could be making a mistake trying to replace them with similar values of LDR?

I thought about buying from Cabin Tech website

Re: Studio Preamp LDR

Posted: Wed Jan 03, 2018 7:57 am
by MesaMad1378
Those numbers you have would probably be right, I’ve seen other vactrols used in other Mesa Amps, such as the Triaxis, I haven’t seen other brands, though I haven’t had the please of playing around in all Mesa Amps yet. Definitely would not mind though.