Meat Plow wrote:

Eeyorewrote:
Gareth Magennis wrote:
"Gareth Magennis" wrote
"Meat Plow" wrote in message
"Gareth Magennis" wrote:

IIRC, the C-Audio RA series commonly used BUZ Mosfets, both T03 and
T0247, which are still easily available.

http://uk.farnell.com/jsp/search/bro...estid=48642 0

Good to know when the old J50's and K135's decide to check out.


Well, I didn't say the BUZ were replacements for those, but C-audio did
use a selection of different devices throughout the years they were in
production.

Some of the amps were rather prone to RF oscillations, burning out their
Zobel networks - attributed to various things like heatsink/ground
bonding or layout design, depending on who you talked to and what opinion
they had, or how much bull**** they liked to talk.

I replaced quite a few BUZ's, and they were expensive back then, about the
same as Farnell charge now. Can't remember changing many, if any,
reservoir capacitors though.

Surprised at that. C-Audio's stance was they were a 'service item'. Like the mosfets presumably !


Oh, and the worst problem they suffered from was (allegedly) smoke fluid (in
club installs) being deposited on the PCB behind the fan intake. This would
eventually corrode lots of fine tracks running along the board, the most
common victim being part of the Protect/Speaker Relay circuit, so the amp
would stay in Protect forever.

Annoyingly, the corrosive substance would creep under the Speaker relays and
eat the tracks under them as well, so repairing these amps properly was
either very time consuming and expensive, or just plain uneconomical.

And, the 47 ohm 10 Watt ceramic Soft Start resistors would very often need
replacing.

These had their fair share of design problems, that's for sure.

Which is why I didn't approve them to be sold under the Studiomaster badge and went on to design the much loved D Series.
http://cgi.ebay.co.uk/ws/eBayISAPI.d...MEWA:IT&ih=011

Siemens ODM'd the RA3001 though IIRC.

I own a Studiomaster 700D and would like to replace the quad set of
mains filters. These are low profile, I know there is a specific name
for them. The tops of these all seem to bubble upwards but when I
picked that part off it was just a cover of sorts for the real
container both overshod with heat shrink. I don't think they are bad,
haven't removed them but the amp works however I'm worried about it
being in service as my bass guitar amp.

NEVER seen that myself but those amps are getting old now. Original spec parts were Samwha (forget which series but the plastic film was dark
green) 3300uF/63V (yes they're overvolted off load @ 67V but we checked that for reliability with Samwha and they sent us detailed info to say
it's basically OK, the leakage current just increases very marginally at ~ 5% overvoltage and no load).

The alternative part was IIRC, Panasonic (again forget which series). Dumpy little black cans. Looked absurdly small. I expect that's what
you've got.

I specced the ripple current per cap at ~ 2.7-3A IIRC. You'll find something in Farnell that'll do fine. Use 105C caps if you want to continue
using it forever.

I assume you're driving a 4 ohm load btw ?

Want some more Oomph ? Fit 4700s. It'll reduce the dynamic headroom though.

What do you think of the amp btw ?

Graham