So it continues...
A brace of good quality OPA134 op-amps to replace the not so hot (though state of the 'fet input' op amp art of the time) TL071s in the pre and power amp - a starter for ten. Also some decent speaker connectors to replace the woeful original spring push ones. A mod also done by Quad to later 405's.
Got the pre-hooked up to my 'phones this eve. Bass is super tuneful, treble nice and sweet and easy - bass definitely easier to follow than the Arcam. Mid... jury out. Slightly 'thick' sounding maybe? Maybe lacking in detail? I know the op-amps will reduce the noise level, but detail? Who knows... one step at a time.
Pleased with the effort that's gone into the power supplies on the pre, will leave that alone aside from faster rectifiers. Still not convinced that I need a buffer on the CD input - may add a 'straight through' switch to the 'Aux' card, with a bit of attenuation - one less active stage must be a good thing. Input switching, uses CMOS 4066's from eons ago, which apparently add 0.01% distortion all by themselves. (I designed a pre back in about '85 and thought about using them, but gut feeling led me to abandon the idea and I used CMOS latches to drive telecoms relays instead) Yes, 0.01% is low, very low, but it can be bettered by later versions of the 4066 so I will probably look there. Torn though as ideally I would fit reed relays rather than relay on CMOS (spit!) to do my switching but I dont want to make it less 'Quad' so I'll try Maxim's versons of the 4066 which have huge bandwidth an should be almost an order of magnitude better THD-wise in a low signal level switching application, which generally means other aspects of performance will be better also.
It's never going to be the most transparent of pre's, but it is a lovely piece of design work. A joy to work on and to use. The power amp however, that has the potential to be truly phenomenal. A very clever design, and something I'm sure will respond to reworking with a few modern ideas and components applied sensitively. Arise FrankenQuad! :twisted:
<edit> listening to some old Rage Against the Machine - bass guitar is about as 'real' as I've heard on anything. Yes, the low end certainly does have some serious dynamics!
A brace of good quality OPA134 op-amps to replace the not so hot (though state of the 'fet input' op amp art of the time) TL071s in the pre and power amp - a starter for ten. Also some decent speaker connectors to replace the woeful original spring push ones. A mod also done by Quad to later 405's.
Got the pre-hooked up to my 'phones this eve. Bass is super tuneful, treble nice and sweet and easy - bass definitely easier to follow than the Arcam. Mid... jury out. Slightly 'thick' sounding maybe? Maybe lacking in detail? I know the op-amps will reduce the noise level, but detail? Who knows... one step at a time.
Pleased with the effort that's gone into the power supplies on the pre, will leave that alone aside from faster rectifiers. Still not convinced that I need a buffer on the CD input - may add a 'straight through' switch to the 'Aux' card, with a bit of attenuation - one less active stage must be a good thing. Input switching, uses CMOS 4066's from eons ago, which apparently add 0.01% distortion all by themselves. (I designed a pre back in about '85 and thought about using them, but gut feeling led me to abandon the idea and I used CMOS latches to drive telecoms relays instead) Yes, 0.01% is low, very low, but it can be bettered by later versions of the 4066 so I will probably look there. Torn though as ideally I would fit reed relays rather than relay on CMOS (spit!) to do my switching but I dont want to make it less 'Quad' so I'll try Maxim's versons of the 4066 which have huge bandwidth an should be almost an order of magnitude better THD-wise in a low signal level switching application, which generally means other aspects of performance will be better also.
It's never going to be the most transparent of pre's, but it is a lovely piece of design work. A joy to work on and to use. The power amp however, that has the potential to be truly phenomenal. A very clever design, and something I'm sure will respond to reworking with a few modern ideas and components applied sensitively. Arise FrankenQuad! :twisted:
<edit> listening to some old Rage Against the Machine - bass guitar is about as 'real' as I've heard on anything. Yes, the low end certainly does have some serious dynamics!
