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

Can I turn the volume up, have the input selector on phono, and just listen with nothing playing?

Absolutely. In fact, that is what you should be doing. Additional noise that occurs just while a record is being played would be a function of some combination of the turntable, tonearm, cartridge, cartridge and tonearm adjustments, and the recording. And for a given playback volume would not be affected by the gain settings.

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?

As I said, it’s hard to predict without detailed knowledge of the Whest’s design, and perhaps also without published measurements being available. But FWIW my instinct is that more often than not lower phono stage gain will correlate with better noise performance, **everything else being equal.**

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.

Yes, I was just suggesting moving things for experimental purposes, to see if it makes a difference. So this sounds like a plan!

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?

No to both questions. Regarding the first question, as I indicated the cheater plug(s) should be placed on the power plugs of the phono stage and/or the preamp, to eliminate the possibility that a ground loop between those two components may be contributing. (Putting a cheater plug on the preamp’s power plug would also break a ground loop between the preamp and the power amp, although it doesn’t seem as if that is an issue here, since the noise is volume control sensitive).

Regards,
-- Al

P.S: Regarding the phono stage gain question, you may find the following thread to be of interest:

Gain vs. Volume

The bottom line, as stated in that thread by Atmasphere:

A simple way to look at it is to use the least amount of gain that you can to get the job done, as the more gain, the more can go wrong.

I am citing this in regard only to the phono stage in this case, however. Not in regard to the preamp, due in part to the examination of its schematic that I mentioned.

Regards,
-- Al

Al, would you mind a brief phone chat with me?

Thanks, Mark, but my preference is to participate just via the forum.  Hope you'll understand.

Also, I'm not sure that I can add anything at this point beyond what I've posted above.

Regards,
-- Al
 

Sounds like good progress!

If the remaining hiss varies with the setting of the volume control, as it did previously, the fact that the volume control mechanism is located not far from the "front end" of the preamp’s internal signal path would seem to suggest that the hiss is probably being introduced primarily by either the phono stage or by a ground loop between the phono stage and the preamp.

A quick experiment that may be useful would be to disconnect the XLR cable that connects the phono stage to the preamp, and assessing the hiss under that condition. As well as trying the cheater plug experiment I had suggested.

Also, try disconnecting power from the DAC and the Mac Mini, to verify that they are not radiating or coupling digital noise into the phono stage or the preamp.

Good luck. Regards,
-- Al