2. amps-preamps
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Bypassing A Preamp With Volume Pot In Amp

I see preamps as a convenient tool to control the volume of multiple sources. It only adds another link in the chain. It also adds to the cost of your system because you will need other pairs of interconnects and a power cable.

I was thinking about completely bypassing a preamp by adding a volume pot or a resistor based stepped attenuator into the amp, greatly reducing the signal path from the source to the amp.

The only detriment I can think of, is switching the interconnects from each source which is as troublesome as switching out a disk from the CD player.

Please chime in with your opinions and especially your experiences with this "issue".

The volume control I have in mind is the Khozmo stepped attenuator using 2 Vishay TX2575 resistors in a hybrid tubed/ss amp.
c_avila1
c_avila1 OP
71 posts
 
I would like to add that this upgrade also removed an "electronic glare" that was plaguing my system. This upgrade made a huge difference as much as my Hidiamond D9 ICs and bypassing the amp's PS electrolytics with .22uf V-Cap CuTF caps.

One point of concern: The attenuator is placed on the side panel, towards the rear of the amp, about 3 inches from the heat sinks. I noticed that the volume pot and knob does adsorb heat. I highly doubt that the sound quality will be affected do to the low temperature coefficient of the resistors (TX2575 TC is at 1ppm). I'm concerned for the attenuator's ability to stand the test of time with continuous heating and cooling.
c_avila1 OP
71 posts
 
Yesterday, I replaced the Kimber TCSS wire that connect the female GRFA RCA jacks in the amp to the Khozmo attenuator. The results: major improvement in tonality. The Kimber TCSS wires use teflon insulation that obviously colors the signal. This is my second test with teflon insulated wires. Both tests resulted in unfavorable opinions of teflon insulated wires within the signal and incoming A/C power. If I ever need another leap in tonal transparency, I'll switch the remaining Kimber teflon wires that connect the Khozmo to the amp. For now, I am content with the current tonality.

Revisit to my previous post: Currently, there are no issues regarding absorbed heat into the attenuator.
atmasphere's avatar
atmasphere
7,068 posts
 
Teflon is a pretty good dielectric. There may be more to this than meets the eye as to why you heard a difference/improvement.
c_avila1 OP
71 posts
 
I forgot to mention the wire I used to replace the Kimber TCSS is the Neotech solid core, UP-OCC, 20 AWG wire with PVC jacket.
salectric
683 posts
 
When you switched wires, there was more involved than just the dielectric. I agree that the Neotech copper wire sounds very good, better than TCSS, but this relates to the metal as well as dielectric. Incidentally, the Neotech copper wire is also available with Teflon.

Recently I have been using Neotech silver 20 g. with Teflon insulation. The silver sounds even better than the copper Neotech.
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