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Icarus
2009-04-05, 06:32
Hi

I have a Quad 405-2 poweramp, 44 preamp, Dacmagic & SB3.
I wish to do away with the 44 preamp. This would mean using the SBs volume control. Can someone please tell me how this works. Does it use any form of compression, ie will it degrade the sound at all as this would defeat the object.

Thanks Icarus

SenorCitizen
2009-04-05, 07:10
It's not a good idea. The SB3 has a digital volume control, which will degrade sound quality when large amounts of attenuation are used. Additionally, the input on the Quad 405 is very very sensitive, so you would have to use very large amounts of attenuation.

Just stick with the good old 44, it's not bad - especially if you're handy enough to do some mods. On mine, the relay is cut out of the signal path and all opamps have been replaced with Burr-Brown OPA601s.

.sc

Icarus
2009-04-05, 07:46
SenorCitizen thanks for your thoughts.

I use the SB3 through a Dacmagic DAC which inturn feeds the 44.
I have tried removing the 44 & connecting the Dacmagic directly to the 405-2. The sound does not change any amount. This would suggest to me that the 'old' opamps in the 44 do not affect the end sound. ie the 44 is transparent.

The 405-2 has been modified with opa627, On Semiconductor MJE15031 power transistors, Motorola MJE15031 driver transistors, 2 Epcos x 22000uf psu caps & complete internal rewire using quality PTFE insulated Silver plated stranded OFC cable from Missing Link.
It now sounds great.

mudlark
2009-04-05, 09:50
I use my SB3 straight to my Quad 405, but I have reduced the input sensitivity of the Quad by quite a bit using a kit bought from Ebay. It does make me nervous though as I have two SB3s and if I change the output to 100% on the wrong one....!!!!!

pippin
2009-04-05, 10:04
I use my SB3 straight to my Quad 405, but I have reduced the input sensitivity of the Quad by quite a bit using a kit bought from Ebay. It does make me nervous though as I have two SB3s and if I change the output to 100% on the wrong one....!!!!!

Why didn't you use external attenuators?

SenorCitizen
2009-04-06, 03:54
I use the SB3 through a Dacmagic DAC which inturn feeds the 44.
I have tried removing the 44 & connecting the Dacmagic directly to the 405-2. The sound does not change any amount. This would suggest to me that the 'old' opamps in the 44 do not affect the end sound. ie the 44 is transparent.


If you can't hear a difference, you might as well have the 44 in the signal path to keep from having to resort to digital attenuation.

That said, I don't think the 44 is exactly transparent. I did measurement runs before and after my mods, which also included beefier PSU caps. The change that had the biggest impact was bypassing the relay, it induced some noticeable ripple noise. The newer op-amps are a bit cleaner than the TL071/072, but there are design choices made with the 44 that can't be helped with mods. The biggest of these is the poor-ish channel separation especially at higher frequencies. The unit was designed in the vinyl era, and does exceed the separation you can get with any cartridge in high frequencies, but with digital sources it might be a different thing. Whether it is really audible is another matter, of course.

My 405 has about the same modifications as yours. I think they're nice little classics...

.sc

Edit: Just to add, the downside to bypassing the output relay is that I now get a thump through the speakers when powering the 44 on or off. Still, I think the improvement was audible - obviously not blind tested since I've only got one unit. YMMV.