Another mod success here!
Howdy folks, I received my order from Mouser last weekend and did the preamp mod too.
I'm by no means a professional solder jockey, but do have years of experience in building fx pedals and a tube amp head.
So, with a little bit of knowledge, experience in soldering and patience, the mod was painless and relatively easy to do.
I used three
OPA1604AIDR SMD ICs + adapter as suggested by
@Lysander to replace the original TL084s.
(Preparing/soldering the adapters and the SMD ICs was the hardest part to be honest...)
For replacing the RC4558s I had found two older
OPA2134s in my parts stash so I socketed and used these:
It's a bit tight with the adapters over the existing parts, but if you carefully bow the ceramic and film caps down a bit, the adapter pins fit in just snuggly:
Along with the IC replacements I also did some updates to the input stage as proposed by
@WKSmith :
CMF55 metal film resistors:
Box film cap changes:
- C12, C13 use .22uf
- Output coupling caps (C14, C2) use 1uf
I used Wima MKP 2 caps, which are great, and red, but also a tad bit large... ;-)
I had no problem fitting them on the board though, the spacing is large enough to accomodate the "not so little buggers"...
So, what's the result of a few hours of work?
The hiss definitely is a lot quieter than before, but it's still there and audible when you are standing close to the amp.
I have no weird phasing or oscillating issues with my replacements too.
One thing I noticed on my amp is that not the loudness, but the "sound" or "tone" of the hiss changes when using the mid and treble controls on the preamp: They both add more pronounced hiss in their respective frequency range, which further goes to show that the hiss definitely is a product of the preamp (design).
I had initially hoped for even more hiss reduction from reading
@Lysander 's initial post on the Gearforum, but take a few steps back and you can't really hear it anymore. And it's a total non-issue once you start playing anyways! This thing sounds really great!
Overall I'm happy with the result, so massive thank you m8s to
@Lysander and
@WKSmith , you guys rock!
I will still follow WKSmith and his preamp update(s) and see what he will eventually come up with to maybe further better this already awesome product!
Cheers folks!