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Cartridge gain overload - please explain

I am using a Lyra Delos on a JA Michell tecnodec, a Whest .30R phono stage,
an ARC LS25 linestage, ARC VT100 amp, and Rockport Mira Monitors.

I recently added the Whest to get more gain because the ARC PH3SE with 54dB was not enough, especially because the LS25 gives just 12dB of gain to single ended sources. By switching to the Whest, I was able to get more gain right from the phono stage, and also an additional 6dB from running balanced into the LS25.

Because I was coming in from a under-gain situation, I started with the Whest set to 66dB, thinking a bit more is good, and I could just turn the volume knob lower on the LS25. But there was that record pop / loud static discharge sound which was actually cartridge gain overload. When I changed the gain settings to 60dB, the problem ceased.

My question is, why does this happen? Whats wrong with an extra 6dB from the phonostage and just a little less output from the linestage to compensate? In my mind, that seems like it would work fine.

I would like to know more about this. Perhaps there will be even a benefit if I switch down to 55dB? But that seems counter intuitive, because I was getting too little gain before and I had to really ramp up the volume on the line stage, which caused a lot of noise.

thanks,
Mark
marktomaras
almarg's avatar
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almarg
9,670 posts
 
I basically agree with you, Zd, with the slight qualification that if the overload is not occurring in the phono stage, but is occurring in the LS25 in circuitry that is ahead of the volume control, it is possible that a different preamp would not overload under the same conditions. Per my earlier post, we don't have enough information to be able to say whether the overloading is occurring in the phono stage, in circuitry that is at or "after" the point where the gain adjustment is located, or in the preamp, in circuitry that is at or before the point where the volume control is located.

Also, I would note that while the distortion may remain constant relative to signal level as the volume setting is reduced, depending on its frequency components and on how severe it is it might be harder to perceive at lower volumes, as a result of the Fletcher-Munson Effect.

Best regards,
-- Al
jmcgrogan2's avatar
jmcgrogan2
6,346 posts
 
Thank you for the clarification Zd, you are correct, it does seem like the problem lies within the the phono stage. Thank you too Al, your acute awareness of minute details is simply amazing. You are a beam of light for the rest of us taking stabs in the dark. Keep up the good work. :)
marktomaras OP
544 posts
 
Hello All,

Just a point of clarification. The ARC LS25 has variable gain, and had more gain available to balanced inputs. Selectable for each input: 18db, 12dB, 6dB Balanced output. (12dB, 6dB, 0dB SE output)

So, that is why I get more gain with the Whest, running balanced, before I even boost up the gain on the phono stage.

I agree with many of you, I think the distortion is in the phono stage when the gain is set too high, as I experienced at 66dB. Now i am at 60dB, and it seems fine. I also am pleased with where my volume knob is at 60dB.

The other night, my wife and a couple of friends were having an epic listening session, and the music was definitely loud. At the loudest point, the volume was getting very close to 3 o'clock. I'd imagine that I will very rarely ever go louder.

So, do you think I should be trying 55dB to get less distortion, and risk the need to push the volume knob higher, or stick with 60 dB? If I switch from 60 to 55, what should I be looking for sonically?

thanks!
Mark
zd542
5,339 posts
 
Mark,

The one thing I see in your last post that gives me pause is your reference the position of your volume knob. I think you may be focusing too much on that. Given that you can adjust the gain on your phono pre and the LS25, your volume knob can be almost anywhere and not, necessarily be a problem.

If it were me, I would get the phono preamp dialed in first. You ask what you should be looking for sonically. The first thing, of course, is to get your gain set low enough to where there is no distortion. From that point, its up to you. Most people like to try a verity of settings and just pick what sounds best to you.

Once you find a gain setting on your phono that you like, then set the LS25. Just pick a setting that gives you the best control for how you like to listen to music. I wouldn't worry too much about the actual position of the volume knob. Once you take care of the gain issue with the phono, I don't see you having any problems with your LS25. Your phono preamp is a line level source. You can expect the same type of performance you are getting from any of your other sources.
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