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I was asked to work on one of these reissue Quad preamps, the client says that the line level inputs have a wonderful "shimmer" to the sounds, whereas the phono inputs sound muddy and loses vitality. Upon opening this up I see it is an op amp front end for the phono, with one of those miniature tubes soldered in for use as a ?? (dual triode, maybe as a cathode follower or a line level voltage amp, don't have the schematic with this one). Any ideas what is going on with this? The client says that using a cheap phono preamp plugged into the line level inputs gives that nice "shimmer", but not through the on-board phono stage. Thanks
Better opamp(s) might help, but don't count on it. Jim Hagerman's Bugle2 is 100% opamp, but it employs passive EQ and (no surprise) sounds pretty darned good. From an expense point of view, it might make sense to convert the Quad to line level I/Ps only and buy a Bugle2. Another possibility is to completely rework the phono section to use better opamp(s) and passive EQ.
It seems that the OEM phono section is totally inadequate. :> (( Methinks "digititis" and "bean counting" were at work.
Thanks, Eli, unfortunately that is not an option as it is not mine and I doubt the owner will want to wholesale change the preamp and destroy any "value". It really is a POS, Chinese-made hunk of crap that is travesty to the name of Quad. I have yet to see a review of the preamp, so I don't know if this is SOP for the phono stage or if there is something wrong with the set.
Can't he just used an external phono stage into an auxiliary input without modification?
Yes, and he has done so, but I am guessing he wants to use the built-in since he paid for it! The big question is whether the built-in phono stage is operating correctly or if it is not, I don't know anything about this unit so its hard to evaluate its phono stage performance and let him know his options. Thanks!
You could check the curve with a revers RIAA equalizer, signal generator and a scope. I suspect you already knew that!
Thanks, Dave, I was thinking about doing that but I don't have a reverse RIAA sig gen, any ideas where I would get one?
Hagerman makes on and it cost $49. See link.
Getting a schematic, one way or another, is essential.
The owner is worried about value, but it has very little, lacking a decent phono section. :> (( Chinese guano!
What opamp IC(s) are in the "box"? Please provide the soldered in sub-mini tube type. A look at a data sheet might be informative.
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