C-Audio Power Amp Head ...

Probably cheaper to remove all the Hitachis (and sell them ?) and replace all with Exicon or Semelab.

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You need the 'BUZ' parts.

Oh yeah.

It 'might' be something else. You'll only tell by removing the output devices (thankfully easy enough) and testing them but C-Audio have a reputation for eating them. And will do so again if driven hard into 4 ohms.

Graham

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 bullshit 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.

Gareth.

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.

Gareth.

Not originally.

But best not to mix them I imagine.

Graham

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

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.

Siemens ODM'd the RA3001 though IIRC.

Graham

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You are right. One whole bank of FETs is o/c - hence the very asymmetric output. There has been a further development. I rang the shop to tell him the bad news that a set of twelve devices was going to set him back 100 quid, with the possibility of there being some o/c on the other channel (a couple of them seem very cool under drive conditions, compared to their neighbours, so a good indication that they may well be open as well) and then the possibility of some smoothers as well. Turns out that when he sold the guy this one as a s/h unit, he picked up the wrong one. This example was sitting waiting to come to me for checking, so he has now given the customer the right one, and is writing this one off, for the time being at least. Thanks for the useful pointer to the FETs, anyway.

Arfa

This one that I had on the bench used BUZ's, and the soldering on them looks original

Arfa

I looked through the BUZ lists at Farnell and the specs for the BUZ pairs compliment or exceed the original specs.

mosfets presumably !

went on to design the much loved D Series.

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. I'm also looking for a new speaker binder set as one is broken off. Currently I'm using Spec-on connectors. I bought this amp used at a thieves price.

Is there a place here in the US for factory parts or do i have to get them from GB?

reputation

That's what happens. The weakest or hottest fail first (open) and the relatively large ON resistance for these devices causes assymmetry in the delevered peak voltage to the load.

Graham

mosfets presumably !

and went on to design > the much loved D Series.

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

You must have a US model. Those weren't sourced in the UK. That means you have an Indian built one. Can't tell you what they used sadly.

price.

They go on ebay for 'reasonable' prices. I just bought one on behalf on my local music pub client for £72. 10 years old and looked almost new inside. Just had some 'rack rash'.

Not at all. I gave data in my other post. Don't scrimp on the ripple current btw. Use good brand caps. I found Samwha to be excellent btw at a reasonable price. My second preference is Panasonic.

Graham

I'm fairly certain the original spec is the Samwha HC series 3300uF 63V.

Yes, this pdf includes the data sheet. The ripple current is in fact > 3A.

Now ask me how I remember that after over 15 years ago.

You'll easily find replacements.

Graham

Often C Audio would put little pink or green dots on the transistors, presumably after testing them prior to production. Not the kind of thing a repairshop would do, so this may indicate if they are the originals or not.

I often used to find only one or two devices not working or clamping at high voltages, you may not have to replace the lot at all.

Gareth.

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I order just about all my stuff from Farnell. They don't tend to have much in the way of unusual or older transistors, these I can usually find at Cricklewood Electronics.

I get my stuff next day without fail from both Farnell and Cricklewood, nothing is usually out of stock or comes from Belgium.

I'm in Leeds, so is Farnell, so maybe that might have something to do with it, but shouldn't really. What kind of stuff is coming from Belgium? Chocolate screwdrivers? ;)

Cheers,

Gareth.

I've seem multiple deliveries from them. Simple explanation. They don't hold all stock in a single place.

Graham

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Seems like just about anything I order now can come from the Belgian warehouse. To be fair, it usually comes the next day, as the stuff from Leeds does, but how much must it be costing them to process, pack and ship from Belgium, just one item out of an order of perhaps 10 items ? They also seem to employ no rhyme or reason with determining how exactly the orders are shipped by default. One day, they will deliver a transformer weighing a couple of pounds, in a Jiffy bag, by regular post. The next day, a packet of transistors will arrive in a box a foot square, conveyed by UPS, who don't usually get to me until late afternoon. One thing about UPS *really* irritates me (must be my age). After having got it to the right address, and asked me to sign for it, and after the same bloke delivering the same sorts of packets to me from the same company, for a long time, he still says every time after I finish signing "What's the surname, please ?" Aaaaarrghhh !!!

I haven't used Cricklewood for a while. I also hadn't used Grandata for a while until a few weeks ago. They have really gone down the toilet compared to what they were. I needed an STK, and a couple of power transistors for an amp, as well as a few other bits and pieces - fuses and so on. All items showed as in stock on the website, so I went ahead and placed the order, credit card payment and all that. The next day, I was extremely annoyed to get an e-mail informing me that half the stuff was on 3 to 10 day back order. It has actually taken a total of about 5 weeks to finally get everything that was on the order, the last transistor arriving just yesterday ...

Arfa

Why do you think they charge the price they do ?

The use of 'satellite warehouses' is well established. Someone must have done the sums. You can bet UPS don't get their standard fee for such an operation.

Graham