Wonder if the brains trust has any advice for me.
Just taken delivery of a lovely Quad 303, restored by Rob at AmpLabs (who's been a perfect gent throughout) to match the original design but with old components swapped for new.
I'm almost completely delighted with the results warmth, intimacy, believability, it really draws you into the music. For the most part it lives up to the praise it's received in these quarters.
However, the treble has its peculiarities. There's the odd touch of aerosol can sibilance on female vocals, and it has an issue with hi-hats in particular, which somehow sound slightly slurred and a bit tin-foily. Not good on the likes of Chic, where accurate reproduction of the hi-hats is a must
Never had these issues in the system before. Other links in the chain include a Cary SLP50A valve preamp and Rogers Studio 7 speakers. Rob suggested that I'd simply reached the limitations of the original Quad design, and that off-axis treble response was the issue.
Toeing-in the speakers a bit (they're about 2m apart with the listening position about 2.5m away) did take some of the edge off, and it is recording-dependent but the problem is still there.
Rob says he tested it with B&W and it sounded very impressive...Anyone had experience with the 303 not liking particular speakers and favouring others? Or indeed any words of wisdom in terms of diagnosing and dealing with this sort of treble issue?
Exact replacements for the output transistors are not that easily available (possible though).
If modern transistors are used (with a lower junction capacitance), oscillation can occur that might affect the treble performance. The exact old stock RCA transistors are available on ebay. If interest, I’ll have a look and provide a link. I have four 303’s, none have problems with the treble.