Quad 303 any good?

[honmanm]

Re 4 ohm loads, with the NA PSU board the 303 is coping pretty well with a pair of 4 ohm small maggies. That's with standard output transistors but an increased current limit of 8.6A (as per Net Audio mods page) and 6A output inductors. Changing the current limiter did not have much effect on the sound prior to the PSU board swap. NB the amp is no longer short circuit proof!

For my taste, going fully complementary is a mod too far - just about everything else is easily reversible. If quasi comp is good enough for the Naimees and Avophiles around here, who am I to disagree? (I'm just another Quadlodyte)...

 

[John_73]

Interesting all this talk about reversed phase on some of Quad's components.

Just reversed phase on my DIY GB150D power amp, with my Quad 34 as pre, and it sounded quite 'dull' and uninvolving. Restoring phase back to 'normal' everything sounded fine again. So perhaps the 34 doesn't invert, or certain revisions only reverse phase? Mine is serial number 7328. Should add that all the op-amps have been chaged to a mixture of OPA627s and OPA227s and all caps replaced. Wouldn't have thought any of that would 'revert' phase though.

 

[honmanm]

A couple more thoughts... I can remember the 34 being sold with 306 (non-inverting) and before that I believe it was sold with the 405-2 (inverting). So there could be different 34 variants (was there ever a brown 34?) - or perhaps even a non-inverting "late 405-2" ??

Due to an error in the child-speaker interface one of the dipole radiating Maggies is out of action for a while - a friend has lent me a pair of Harbeth P3s and with the P3s the absolute phase makes very little difference - at this point I can't even say which way round I prefer, let alone which is "better".

 

[mudlark]

how does the phase being 180 degrees out change the sound?

 

[Robert]

I use a 34/306 and assumed that the combo had correct absolute phase.
Will have a listen tonight having reversed the speaker connections.

 

[John_73]

A couple more thoughts... I can remember the 34 being sold with 306 (non-inverting) and before that I believe it was sold with the 405-2 (inverting). So there could be different 34 variants (was there ever a brown 34?)

Yep mine's an early brown unit with the DIN sockets - looks very 70s!! Love it (though I have changed the LEDs to amber to better suit it - got this idea from Keith Snooks super Quad pages).

 

[honmanm]

how does the phase being 180 degrees out change the sound?

Using the 303 with no pre and speaker connections "as marked", it sounds relatively dull and uninvolving. With reversed connection, the sound is more peppy with well defined transients and better imaging and presence. Brighter too.

This effect is speaker-dependent - very little with the very well damped Harbeth P3s, but hugely different with the small Maggies where the following effect come into play

a) forward transients are better defined - the panel is pulled into a stronger magnetic field.
b) the rear wave reflects from the surface behind the speakers, is inverted, and interacts with the forward wave. High frequencies are absorbed by the curtains.

I haven't been able to test with more common speakers, although the experiments were triggered by reading this thread after taking the 303 to the home of a NAP250 owning friend - I'd expected the 303 to sound flat in comparison, but not *that* flat!

 

[Tony L]

I finally have my 303 up and running in my second system! I bought a nice little Audio Synthesis PAS 02 passive preamp off eBay about 8 months ago, but ended up lending it to a friend who wanted to try it with his big ugly active Spendors (sounded very good). I've just got it back and have now set it up with the, now Quad serviced, 303 in my second system (TV / Sky / Airport Express and Klipsch Heresys). It's sounding really nice and seems to suit the Heresys very well indeed, certainly better than any solid state amp I've tried to date. It's a very clean clear sound, remarkably free of grain or glare, quite tube-like - perhaps not the most dynamic or exiting sound, but very free of vices. I'll need to buy a phono stage to get my TD-124 back into the equation, I may head out to Richer tomorrow and grab a 640p as it's cheap and I already know I like it as a couple of friends have them.

Tony.

 

[Tony L]

I've just been googling around a little to try and establish for certain which Quad amps invert absolute phase, and which don't, and I've found the Gradient Sub site. In the manual for their ESL63 sub here it states that the Quad II, 306 and 606 are non-inverting, and the 303, 405 and 405 II are all inverting. Nice to have the information from a known source. Why Quad did this is anyone's guess!

Tony.

 

[barrymidd]

Perhaps they were made in Australia?

 

[honmanm]

the 303, 405 and 405 II are all inverting. Nice to have the information from a known source. Why Quad did this is anyone's guess!
Tony.

Probably because the 33/303 were designed to work together, as as long as the preamp and power amplifier were both inverting, no problem... I guess the 405s are inverting because IIRC early 405s were sold with the 33 as pre.

It probably makes most sense to reverse the speaker + and - when using a non-inverting pre, polarity inversion is audible (but not necesarily right or wrong) and re-inverting the output make comparison with other amps easier.

BTW polarity inversion was much more audible with Maggies than normal box speakers, this could be due to the asymmetric construction of the Maggies.

So Tony, have you got the Net Audio PSU board in there?

 

[Tony L]

So Tony, have you got the Net Audio PSU board in there?

No, it's completely stock and freshly Quad serviced at present so it should be bang on it's original spec. I'm running it with the Audio Synthesis passive connected with a Gotham 4 pin DIN to RCA lead from eBay and it's sounding very nice through the Heresys, so I'll almost certainly leave it alone for a good while. Especially given I don't have the knowledge to do any of the upgrading myself even though I have the parts - they may be useful in the future. I have a feeling the 303 really suits the Heresys - they like a tube amp, and the PAS-02 / 303 is smooth, rather warm and remarkably non-grainy sounding. I swapped the speaker polarity to correct 'red to black' phase yesterday and I'm sure it sounds better, just a little crisper and cleaner. I bought a Cambridge 640p so I've got the turntable sorted now too.

Tony.

 

[DSJR]

I recently bought a late 33 as a line buffer/tone control for the headphone amp and fitted the Dada update kit, together with some 1uF output caps as suggested on Richard Bryce's site. I think it sounds far better now - the lovely midrange quality has extended into the bass and treble, although it's still a touch "soft" I think, compared to a now re-worked MF X10-D (now fully "Rock-Grotto'd with new caps, diodes and valves). Maybe the absolute phase inversion is more audible on headphones, but the MF is if anything too clean and clear in its new upgraded guise.

Now looking out for a good late 303. I don't need it tbh, but I'd like to have one to complete the set and I always very much liked the sonics if the speakers were an easy load..

 

[Martyn Miles]

I have just bought a Quad 303 and I'm using it with a passive pre-amp. I am staggered how good it is. I borrowed a 33/303 about a year ago. It was an old one and it had been unused for years. It sounded dull & lifeless, and lacking in any sort of 'get up and go'. To my mind the 303 power amplifier is the star of the Quad combination. Mine ( recently used and looked after ) is giving me a great deal of musical pleasure. I wonder what a 405 would sound like... MGM

 

[Tony L]

I dragged my 303 through and gave it a run between my new Croft Micro 25R pre and the Tannoys a few days ago and it sounded lovely; a relaxed slightly mid-centric open and detailed sound, quite tube-like in a way. I could very happily live with that amp / speaker combo.

 

[Robert]

I have just bought a Quad 303 and I'm using it with a passive pre-amp. I am staggered how good it is. I borrowed a 33/303 about a year ago. It was an old one and it had been unused for years. It sounded dull & lifeless, and lacking in any sort of 'get up and go'. To my mind the 303 power amplifier is the star of the Quad combination. Mine ( recently used and looked after ) is giving me a great deal of musical pleasure. I wonder what a 405 would sound like... MGM

Where are you based Martyn?

I can play you 303 v 306 v 405/2 if you can get to East London.

 

[Martyn Miles]

That's kind of you. I'm in Oxfordshire, Nr. Oxford ( about 12 miles away) Travelling to East London is not on at the moment, but I would like to hear your combination. I'll contact if/when I can make it. MGM