Phono stage gain setting to match preamp and power amp capabilities

Hi Mark,

First, kudos for stating your question so thoroughly and well.

Clearly the hiss is being caused by something upstream (ahead of) the volume control mechanism in the preamp. Looking at the preamp schematic at arcdb.ws I see that the volume control devices are located not far in the signal path from its input connectors, with only the input select switches and a few resistors and associated switches (which provide the gain select function) in between.

Noise performance for vinyl sources will often be limited by circuitry in the phono stage that is at or near its input, since a given amount of noise generated by that circuitry will be greater in relation to the signal amplitude than a similar amount of noise generated further downstream. But without knowing the details of the Whest’s design it’s hard to predict how such noise will vary as a function of its gain setting. If I were to guess, though, my suspicion would be that lowering its gain to 55 db would be more likely to help than raising it to 65 db. Despite the somewhat low sensitivity of your power amp (1.9 volts; 23.5 db gain into 8 ohms) and your speakers, the 18 db gain setting you are using on the preamp coupled with the 0.6 mv rating of the cartridge should enable you to do that while still being able to drive the amp to full power on high volume musical peaks, without running out of range on the volume control.

In addition to the phono stage’s intrinsic noise performance, though, there are some other things that might be causing or contributing to the issue:

1)I see that you have the power amp located close to and in between the phono stage and the preamp. It seems conceivable that the power amp is coupling noise into either or both of them. As an experiment, at least, you might try relocating those components such that the power amp is as far away as possible from the other two components, especially the phono stage (and also the cable connecting the phono stage to the preamp).

2)A ground loop issue between the phono stage and the preamp could conceivably be contributing, even if there is no perceptible hum. You might try temporarily using a cheater plug (a 3-prong to 2-prong adapter, with the safety ground not connected to the outlet) on the power plug of one or both of those components. That would break any ground loop that may exist between them.

Good luck. Regards,
-- Al

I don't think there's a perfect answer to your situation, but based on the cartridge's output I would set the Whest at 50 or 55dB gain and then adjust the preamp accordingly.  I wouldn't be worried about the position of the volume control as long as it still has some extra adjustment range.  If you are trying to achieve concert hall levels (95dB+), then you probably need a larger amp with your current loudspeakers.

Let's us know how your listening goes.

More gain on the Whest less gain on LS-25 since the Whest is solid state it will be quieter when turned up 100k is best for me with Transfiguration Proteus but it depends on the cartridge.Good luck enjoy!!

Is there a way to listen and measure the noise properly?  As in, can I turn the volume up, have the input selector on phono, and just listen with nothing playing?  Or is that not a way to isolate and listen to noise only? If I could do something in that ballpark, I think it would be easier to hear the changes that you all are suggesting.  Either that, or perhaps play a track on the turntable that is extremely sparse and allows one to hear the background noise.  Suggestions?

To recap, some say lower the phono stage gain, and some say raise the phono stage gain.  Does anyone want to back up their argument with some supporting evidence?

Almarg, As for amplifier interference, I take it you saw my system photo. Is there anyplace on the rack where the amp would not interfere?  I ask this because the speaker cables are not long enough to have the amp anywhere other than in the center position.  The only option would be to put the amp on top of the rack, next to the turntable, or, reconfigure the shelf heights and put the amp on the bottom, with the preamps on the raised up center section.  If you think this is not adequate, then unfortunately, I don't have much of an option.  Of course, if I am looking for the source of the hiss, and that is it, I can put the amp on the floor in the middle of the room as I have some longer interconnect, but I think I will save that for the last test.

As for the ground loop, just so I understand properly, I disconnect my power conditioner from the wall outlet, plug in the cheater plug, and replug into the wall, and listen for a hiss change/reduction?  Is there any danger to my equipment for this test?

Thanks!