mbz

Probably a good time to buy, would allow you to run some extra test cases like connecting the PC directly to the power amp... Hums can be caused by bad GND connections, perhaps some damage was done removing the XLR (from the DAC?). Would also explain why there is no problem when the PC is off. Do you have a multimeter, maybe poke around checking the GND path from PC to DAC to ,,,

Service manual available on hifiengine. Checked power supply to display? Expect about 2.2/3.2VAC, test at connector W801, pins 1,2 on display board or CH801 on supply board. Also check solder joints on these connectors. Supply should be ok as it comes off a transformer winding so measure, if not ok check solder joints etc...

Did noise disappear? Are you using the Rotel as a pre or power amp. This "breaks" the connection to the PC so can rule out pc I wouldn't assume no damage. Do you have RCA's on the Holton, ie, go RCA's from DAC to power amp. I'm more worried about the crackle, often relates to dc voltage which can damage spkrs however protection circuit should take care of it. Very unclear what you have done and the corresponding results. Reads like a power amp issue possibly when you removed the XLR's. If possible, test with RCA input. Do you have a multimeter, maybe test the XLR pins(male) on the amp, work through every pin combination and compare with other channel, amp needs to be powered off/unplugged. Confirm hum/whistle/crackle 1) occurs on both channels? 2)occurs on both channels at same time?

Tell him his dreaming... Looks like an international purchase, probably Japan with the 4A fuses which he hasn't changed to 2A(?) Note 240V "sticker". Amp hasn't been recapped. Lettering missing on front face. Working normal, maybe $200-$350 then allow maybe $300 for a refurb. You can pick up the "legendary" CA-1000, refurb'd for about $1k...

I have an early(?) epitome with square tweeter plate, and consonance cyber 800, cdp, cvt,,, Packed the valve gear away, prefer SS, running Yamaha CX-1000, vintage electrocompanient preampliwire(?) and a range of integrateds like Yamaha CA-2010/1010/1000... Pioneer SA-8500II, Luxman L410, 480,, still looking for a sansui alpha or 919 or... This is another vote for vintage SS, if you can haggle you could get a CA-2010 for $1000-. I'd suggest getting the 555A refurbished, but if you need the extra Watts...

The NE5532 supports a max supply voltage of +/-22Vdc and a nominal supply of +/-15Vdc. However some manufactures (eg, NAD 3150) went for +/-18.5Vdc. Many opamps have a max supply of +/-18Vdc, so simply rolling opamp into such amps would cause them to smoke. Bottom line, check the supply voltages, pin 4 and 8. Don't probe the IC, find a connected cap, resistor... Also check that the current draw of the replacement IC is about the same as the NE5532, lower current draw means low volt drop in R's and higher supply voltage. Knock yourself out, try OPA2134, NJM2068DD, LM4562,,,

Soory, I don't consider the car place as a reliable source of silicon. Also their Serv**ol "Clean and Lube" does very little cleaning, reasonable as a lube. Both Mouser and Digikey have free shipping to AU for orders over AUD60-, delivery in 3 days max(!) For small orders RS. I'm undecided about ele14 though did buy a power supply from them, seems to be of suitable quality.

Generally the transistors don't conduct when incorrectly inserted so you might be lucky. You can try testing in circuit, looking for a short between b-e or c-e or.. using either resistance/ohms function but the diode test feature is better. Attached graphic shows the 6 combinations to be tested with expected results OL (open loop) or 650mV(or there abouts), red/black give meter probe orientation. Graphic curtesy markthefixer from audiokarma. EDIT: I should add that some faulty transistors need a few "amps" before they fail, bottom line, a transistor that passess diode test may still be faulty since your MM does not deliver the necessary mA. Conversely anything that fails diode test is certainly faulty. EDIT 2:If you find a suspect transistor then you need to remove and test out of circuit in which case you might as well replace as per aussievintage

Welcome. Another vote for vintage gear. Read too many posts of people pondering buying this new $10K amp or that $20k amp... All the main players made some great vintage gear that can be had cheaply. Learn the diy skills and do a refurb and you end up with a great amp. Service manuals available on hifiengine and other sites...

Nice work. Keep in mind that you don't need boutique caps in the "bypass" positions, ie, caps that connect to spkr GND. Budget polyprop is fine for these positions. Electrolytic is also fine but I'd spring for the extra dollars and go pp.

Consider vintage gear or should I call it bling? Sure they prefer vinyl but do ok on the digital.

Those top boards are just "mechanical stays", unsolder away. Maybe the solder joints provide easy access to some test points??? You now mention that the problem is a diode. As a punt, I hope you are not talking about either D549,D444,D699,D649 on the SP-A or SP-B boards. These are for relay flyback, they are connected across the relay. If you try and test the diode your MM will test the relay since it's an easier path and will show a low ohm/near short.

Exactly which transistor is suspect faulty, eg TRnnn, Qnnn and on which board. I will check schematic for low resistance paths that may screw up your in circuit testing. If you are 100% sure then no other way but to unsolder the boards, need a reasonable quality solder pump/sucker. I would also melt some solder on the iron tip and then apply that melted blob to the pin to be unsoldered (distributes the heat) and use solder pump.

Need to work out if problem is with HF or MF, your measurements suggests HF is ok but MF not OK. Some things to consider trying... Problem with crossover??? Run a connection/wire from speaker posts directly to the HF+ and HF-, play audio at minimal volume. Repeat for MF+ and MF-. Alternatively you can connect a junk speaker driver to HF+/HF- and test for audio, again minimal volume as this changes the overall spkr impedance.

My post was pure b.s