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tvrgeek 17th October 2012 10:28 PM

Creek 4330 died
One channel of my nice little Creek just quit. With visions of obsolete transistors, no schematics, and all the other fun of vintage amps, I swapped in my old trusty RA-840 Rotel and carried the Creek to the bench. A quick check and, well, I must have been living right today! Over on the side where the optional phono board would plug in are a pair of jumbers. Seems the years have allowed a tad of oxide. Re-seat ( and a bit of Carmoline) was all it took.

So, if yo are lucky enough to have one of these, and have issues, check the jumpers before yo get worked up. :)

sajti 18th October 2012 07:43 AM


try to ask "x-pro" directly. He was the planner of the 4330. He has the schematic, and all the necessary knowledge. He is very helpful


sajti 18th October 2012 07:45 AM

And "search" is Your friend :)


gtmcgar1 17th February 2013 06:18 AM

4330 also died
My 4330 died this week so I changed the output mosfets for IR540n everything looked good except i could get the bias above 15mv, 4A fuseS blew again. After replacing and variac power up, main led is now red, i know this indicates mute but i think i may have blown the outputs again any ideas. thx

Ian Finch 17th February 2013 07:45 AM

Well, for starters, original mosfets specified on the schematic referred to above are BUK555-100A which are logic-level voltage switching. IRF540 have a different switching threshold.

Perhaps that will give you a clue on more suitable replacement Mosfets.

The other point is that the Mosfets may have failed due to other faults, or even caused further damage. Check also ZD1 voltage, D2 etc. and Q8,9,10.

Whenever powering a repair up, until it proves satisfactory, use a bulb tester to prevent further damage. That's a 60-75W incandescent bulb in series with the active power lead to the device. It's not rocket science but it works, indicates excess idle current and if you take care and use appropriate wiring practice, is a safe means of testing. Search it in this forum.

gtmcgar1 17th February 2013 09:11 PM

Thanks for the reply. much appreciated. Would the following parts work, the 540n was recommended in another post, i guess i should have checked the specs.
huf75639p3 $1.74
stp40nf10l $2.28
buk9540-100a $1.61
I should also change zd1,2,3 and q1-q10 on both sides. Should the bias be 35mv or 11mV I've seen both quoted. This is a 4330R not the SE. Thanks again.

Ian Finch 17th February 2013 10:48 PM

Before tossing everything, first a question as we need to be sure about the original parts. ie the output Mosfets: Were they BUK 555? A brief check shows the specs. for CAS4330 and 43330R are identical but there is no freely available separate schematic for the R or SE versions. From reviews, I gather that the difference with the later versions is the protection circuitry.

There is a cheap source for the original Mosfets: items in BUK555-100 store on eBay!
These are usually reputable traders and the cases at least look correctly different for A & B Philips types.
BUK9540 is certainly logic-level but it is a TRENCHFET. Actually, I know little about them but I read here that they are not suitable for audio. The other two also seem to be unsuitable, based on their high conductance alone.

Don't replace everything as a shotgun measure. If you don't find the culprit, it will likely just fail all over again and start to fill the bin with $$$. Test the transistors with the output Mosfets removed and the bulb tester in place. All bipolar transistors should then show around 0.6V between Base and collector and that is a good, quick check on their health. Obviously, you need a better than junk quality but not necessarily expensive DMM. It should also have a transistor test socket feature for proper, out of circuit testing small parts.

Take care not to slip or lose concentration with testing powered circuits. It usually kills transistors in a tiny flash. I suggest IC clip leads when you need a third hand but a few short jumper leads (small crocodile clip each end) work as well and are a great help.
All testing is done without any signal input or output to the amplifier. If the preamp. can be isolated or muted, do so or least turn the volume right down.

You will need to test your work - simply replacing parts is hit or miss at the best. If you can't test or think it might get too expensive, stop now and get pro. repair as this may be more difficult than you bargained for.

gtmcgar1 18th February 2013 01:05 AM

ok the original mosfets were buk555s. I have a variac/dim bulb tester and a fluke so can test the transistors with the mosfets removed, i guess thats my next move. thanks

Ian Finch 18th February 2013 05:55 AM

Sorry about post #7. I should have said "0.6V between base and emitter" . Late nights do strange things to thinking. I note that the parts equivalents you quote come from no less than Winfield Hill (of Horowitz & Hill?) back in 2005, when this same query was raised on another forum:- RRe: transistor equivalent . Who am I to disagree?

OK, let's assume the transistors read OK and the zener reads 15V, other diodes show expected 0.6-7 voltage drop where applicable. It should then be safe to fit correct Mosfets and bring up voltage slowly.

Variacs are tricky to use because there is no inherent current limiting or low-level indication and thus safety. The circuit won't function immediately - perhaps around 8-12V parts of it will become operational but zener voltages have to be exceeded for the output stage to turn on. In that situation, I would fit 100R resistors in place of the power rail fuses, so that I could protect it and monitor current as the rails rose. That actually makes the variac redundant, but it's how I go about repairing small amps. Perhaps you have experience already and this is superfluous advice but others who have no clue or experience with electronics are usually the ones who search these threads to attempt DIY repairs when their gear breaks down.

If current exceeds ~130mA when reassembled or 60mA without the Mosfets, there is something still amiss. Before applying power when the output Mosfets are fitted, set the quiescent or idle current (PP1) to minimum as measured across R22 (large 0.1R resistor) If the output mosfets have failed, this is also in series, so it could be open-circuit. Check.

According to the schematic, the correct idle, bias or quiescent current is measured as 7mv across this resistor or ~70mA. That is believable for Mosfets. Don't set that level until all is functional and any faults are cleared up.

gtmcgar1 18th February 2013 09:57 PM

I think I will order the buk555 parts just to eliminate the question of substitute parts. I usually build/mod tube amps but I would like to give this repair a 'go' I appreciate your help and inputs will let you know once I have some basic tests done.


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