Quad 303 blew up

Interesting. Thanks very much for the explanation. If I do this single channel idea I'd like to make it reversible. Rather than removing a board, can that switch on the unit be redeployed to cut the power supply to one of the cards? Or does the input stage to the card also need to be disconnected? Cheers, Iain

 

All seems to be going well. Spoke with the technician and he said he found the fault. He said one of the very old capacitors blew on one of the channels along with a few resistors. I explained the idea of using only one channel and he said he could modify the switch wiring to do the disengagement of the card. He'll call later with a final quote. He said it won't be expensive. Epcos capacitors are manufactured here in Brazil so it'll wind up much cheaper using these than importing the Dada or NetAudio kits.

 

That small switch in your picture is not suitable for connecting / disconnecting the power to one board, it needs to handle a fair amount of current.

Get him to put some terminal block or crimp connectors in the power wires going to one channel so you can connect or disconnect them easily.

 

Is this something inside the unit?

 

I'd leave connectors in the wires to one board inside the unit. I doubt you will want to switch it very often, will you?

 

My amp is nearly fixed with the capacitors changed, however the technician just sent me a message saying there`s a transistor blown for which he can`t find an exact replacement. There are two of them I believe, one for each channel. The original is a "38496" . Possible substitutes from Farnel are the BC641 and the 2N5322. Would either of these do the job or should I source a part from elsewhere?
Thanks!

 

I'm sure that Quad Service Dept. themselves were supplying new boards for the 303 not very long ago, so after the holidays, it may be a good idea to ask them. Loads of sites supplying 303 circuits (Richard Bryce comes to mind)

Thing is, the 303 in standard but updated form is a charming little amp with an endearingly musical velvet-glove sound. Why severely change it?

 

I'm sure Rob can answer your question when he returns from his holiday in the North Pole

 

Thanks. Came across this page: http://www.dadaelectronics.eu/News.htm where the Dada Electronics people suggest the BC461 as a replacement for the 38496. That`s good, since it`s available.

 

Hello, I'm resurrecting my old thread because unfortunately, this little saga is still running!

Despite the valiant efforts of the technician, who now is trying to complete job more as favour I think, one of the channels remains unstable. From what I understood, he was attempting to adjust the bias setting when the card "burnt out". He said it's now very tricky to fix because the board is very fragile.

I wrote to the Dada engineering forum about this and they suggested one of their upgrade cards - however, since my ultimate aim is to have a pair of 303s working side-by-side - i'd need to buy 4 cards to have a matched system (ok - to do this I'll only be using one channel on each - but I'd like to be able to use the amps separately when necessary). At 87 euros a pop and given our dismal exchange rate and 100% state and federal import duties - it amounts to a small fortune and more than I paid for both the amps in the first place. A quick calculation gives R$2336 for the 4 cards excluding postage which is also taxed at the same rate - ouch!

The tech said he doesn't need any parts - but that new circuit boards would be a big help.

I found these Chinese ones on ebay that are more affordable. I wonder what forum members think?

http://www.ebay.com/itm/one-set-Qua...889?pt=LH_DefaultDomain_0&hash=item5b11ef1821

I've attached a photo of the burnt card.

All the best and congrats on the new forum format

 

It's a pretty simple circuit. Why can't he just repair it like in the above picture?

I imagine the chinese ones are okay. Have a close look and see if it's the same as your original ones.

 

I don't know. Anyway, he just confirmed that the boards are the same - and i just bought a kit on ebay. Will report back if and when it all goes well! Thanks.

 

The quads are reunited after just over a year of corrective surgery and waiting for parts to arrive. The modification implemented Rob's suggestion of using just one channel of each amp, disconnecting the power supply to the second channel. This is reversible with a switch on each amp. It's sounding good. Thanks everyone for your advice.