Cartridge gain overload - please explain

Zd542, they are seperate issues, but they can be worked on together. His ARC PH3SE had a gain of 54 db which he said is not enough for the Delos with his LS 25 set to 12 dB of gain. Then he got a Whest with 66 db of gain and set it to max out, and found out that 66 dB of gain overloaded the LS25 input. When he reduced it to 60 dB of gain the overload problem went away.

I'm saying that it doesn't matter whether he uses his ARC PH3SE at 54 dB of gain and changes his LS25 to 18 dB of gain OR he has his Whest set to 60 DB of gain and his LS 25 set to 12 dB of gain. Either way he is getting 72 dB of gain, which should be more than enough gain for a 0.6 mV output cartridge.

Thanks very much for the nice words, ActusReus.

I can't offer any particularly definitive comments, though, because overload specs and/or measurements for the PS.30R don't seem to be available. In general, for a given cartridge and a given phono stage, increasing the gain setting will bring the circuits closer to the overload point, whatever it may be. Also, distortion can be expected to increase to some degree as that point is approached. By "circuits" I am referring both to those in the phono stage and to those in the preamp that are "ahead of" (i.e., upstream of) the volume control.

01-14-13: Jmcgrogan2
Then he got a Whest with 66 db of gain and set it to max out, and found out that 66 dB of gain overloaded the LS25 input.

Based on the info that was provided, I don't think we can say that, John. The overload could very conceivably have been occurring in some circuit stage within the Whest, rather than at the LS25 input.

The LS25 has a maximum input spec of 28 volts for the balanced input, with gain set to 6 db. At the 18 db gain setting (more on that below), as a worst case I would expect that to be reduced by a factor of 4, to 7 volts. 66 db of phono stage gain would increase a 0.6 mv cartridge output to 1.2 volts. Occasional notes that are particularly loud would probably cause the 0.6 mv and 1.2 volt figures to be exceeded several-fold, so conceivably the LS25 input could occasionally get overloaded at those settings, but I don't think we can rule out the possibility that the phono stage itself would overload first, at lower signal levels.

I'm saying that it doesn't matter whether he uses his ARC PH3SE at 54 dB of gain and changes his LS25 to 18 dB of gain OR he has his Whest set to 60 DB of gain and his LS 25 set to 12 dB of gain. Either way he is getting 72 dB of gain, which should be more than enough gain for a 0.6 mV output cartridge.

Assuming the specs are accurate, it wouldn't matter with respect to avoiding running out of range at the top end of the volume control, but it certainly could matter with respect to noise levels. Mark's other thread appears to indicate that both issues were being faced. Equal overall gains are by no means necessarily equal in terms of the amount of noise that will result.

According to the specs at ARCDB your LS 25 has selectable gain for each input with settings of 6, 12 or 18 db. So it seems like you could still run your PH3SE and just increase the gain in your LS 25 from 12 to 18 db of gain.

Could be, but the specs leave me uncertain. From the link you provided:

Gain -- Main Output: Selectable for each input: 18db, 12dB, 6dB Balanced output. (12dB, 6dB, 0dB SE output)

My guess, and it is just a guess, is that the 18 db figure applies to the gain between a balanced input and a balanced output. If so, single-ended in to balanced out would be only 12 db at that setting.

Marktomaras 01-13-13
Perhaps there will be even a benefit if I switch down to 55dB?

Seems to me to be worth trying, and comparing sonics, given all of the uncertainties about the specs, and also the possibility that they may not be entirely accurate.

Best regards,
-- Al

Sorry if I wasn't clear on my first post. I typed it out really fast this morning as not to be late for work. Its no excuse, of course, but its true. All I really meant to say was that if the phono stage was being overloaded, whatever the cause, and there was audible distortion, you would hear that distortion whatever volume the line stage (LS25) was set to; low or high.

If we look at this piece of the OP:

"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. "

Thats the question I was trying to answer. When I read that, it seems to me that the OP didn't understand why the distortion didn't go away when he turned down the volume on his LS25. Whatever is causing the excess gain issue with his phono preamp, has to be dealt with there. The LS25 has nothing to do with the problem. Actually, any preamp you insert into that system should show the same results. (That is if I'm reading the problem correctly. If not, have no fear. I'm sure Al will chime in and post me back into place.)

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

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. :)