Posted: Fri May 11, 2018 6:17 pm Post subject: Randall Modern to Orange Rockerverb - Help
I bought a Modern and it turned out to be faulty. I got it very cheap so I wasn't worried and figured i'd use it as a doner module for a home project.
I traced out the board and discovered there was a break in the trace between V2 cathode 1 and it's pin connection. I put a jumper wire across believing it would solve the problem. In hindsight I should have checked if this would fix the issue before proceeding with the rest of the mod. Too late now!
I believe I have done an almost exact copy of the pre-amp of the Rockerverb schematic posted on orangefieldguide. The only change is replacing the VR4-A with resistors to get rid of the stereo pot.
Once I finished, I reassembled the module and ran it in the amp. To no surprise, it didn't work.
When I play a note it makes a clipping like buzz sound and dissipates quickly. I think I can also hear a very faint clean sound coming through.
The main board is Brit module A, Rev 2.0 2-27-02
The tube board is Brit tube Rev 2.0 2-27-02
Here is a list of the changes I made:
.R9 to 1M
.R15 to 68k
.C6 to 10uF
.R16 to 1k5
.C7 to 10uF
.R17 to 1k
.R21 to 220k
.R12 to 220k (after R21, grounded to R7)
.R7 to 470pF
.C13 to 10uF
.R29 to 2k2
.R30 to 1k5
.R27 to 220k (with 1M+470k grounded to C18)(pot replacement)
.R31 to 39k
.C14 to 560pF
.R36 to 220k
.R34 to 470k
The major change i made was breaking the trace between V2 plate 2 and V2 grid 1. I added a 470pF and a 470k in series between V2 plate 2 and V2 grid 1. I added a 220k between the 470k and V2 grid 1 and grounded this to R14.
The only issue i can see is that the 470pF cap i used has a small hole in it and it's exposing the metal inside... could this be the problem? i have gone through all my soldered joints and they are fine.
If i have missed some fundamental rule for modding the Randall modules please tell me! any help will be appreciated! (...silently hoping for Rob to chime in..)
I'm terribly visual, so unfortunately the parts and positions do little for me. I often repair DIY work and almost always the issue has to do with damage to the module from a heavy solder hand or something done that takes out the switching circuitry. I'd love to help, but I'm not sure what can be done with the info provided. _________________ www.jadedfaithmods.com https://www.facebook.com/JadedFaithMods
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