Before I start - HELP!!! but PLEASE be gentle with me here
I recently inherited a Crown IC150 preamp and (expensively) wrecked the volume control pot while trying to correct a drop-out in it's rotation. Hopefully sorted, BUT, while it's in pieces, the component upgrade bug has bitten..
This sample appears to be a mid-period one - full manuals available here -
The mother board, what there is of it, is type 7923 and if any of you look at the circuit, most of the components are actually power supply and tone/loudness associated, the supply to the IC's, which do all the work, being simple? +/- 18V rails. Having heard HiFi Dave's sample, I was surprised his didn't take my fillings out - quite the opposite in fact..
Anyway, possible bodges/tweaks? The first thing is that this brand used the best available components back then in critical parts and these bits, caps, 1% resistors etc., really do seem to stand the test of time and thrashing.
The IC's originally supplied were LM301's, judged dreadful by today's standards (and even when the thing was new it seems). Whats in there is summat like 3532's. Works well if the preamp is run nearly flat out, but noise and distortion, together with a overly-crisp sound, develops at low volume levels. I have some 833N's I could drop straight in, the OPA604's seem popular and I'm tempted by the LME49710N, although this may be too "wide open" for the design.
The supply caps - four in main supply and one on phono board are tiny (by modern standards) 250uF 30V ones. I've earmarked some 1000uF long life/high ripple Panasonics which I'm hoping will be ok. The four 1uF tants on the main board have already gone, replaced by some Wima 1uF I had left over from the Quad 33. There are four bead tants of 4.7uF on the phono board, which I have no idea what to put in place (I've seen some bead-electrolytics the same size).
The main thing is, there are some odd value electrolytics there - 500Uf 3V and 25Uf 15V NP and a 5uF 30V in the power supply. Assuming I ought to replace them either now while the thing is in bits, or later, what do you suggest?
PLEASE chaps, before suggesting I either bin the internals and put a valve buffer in there, could you technically inclined glance over the schematics linked to and suggest modern values and types that should work, hopefully better.
Thanks in advance. I'm going to need some of the facilities on offer here up in the office system, so it would be nice to get the best out of this old timer if at all possible, with modern caps and IC's at least..