Cartridge gain overload - please explain

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

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

01-18-13: Lewm
There seems to be an underlying assumption that the Whest phono stage is a truly balanced device. It may have XLR input or output jacks, but I find no evidence anywhere to say it is balanced. For that matter, the same holds true for the ARC, altho in the latter case one can probably find out.

Hi Lew,

I don't think those assumptions are being made. What is being assumed, which seems to be consistent with both the OP's findings and the specs on the various components, is that changing from an unbalanced connection between an ARC PH3SE phono stage (which only provides unbalanced outputs) and an ARC LS25 line stage, to a balanced connection between the Whest phono stage and the same ARC LS25 line stage, results in a 6 db increase.

Given the LS25's gain spec, which (quoted verbatim) is ...

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

... that would seem to be within reason, regardless of whether or not any of the components have internally balanced signal paths.

Also, looking at the schematic for the LS25 (which is shown at the ARCDB link that John provided earlier), it does appear that it has a balanced internal signal path.

Best regards,
-- Al

01-18-13: Dover
I think somebody is confused here.
Using the balanced OUTPUT of the LS25 increases the gain by 6db.
I presume you plug the phono stage into the INPUT, at least I hope so.
There is nothing to suggest that using the balanced INPUT on the LS25 increases the gain.

Hi Dover,

What is confused is the wording of the spec, which is what led me to say that it was being "quoted verbatim." In one of my posts above, dated 1-14-13, I had said the following with regard to the interpretation of that spec:

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.

If you study the first page of the schematic, I think you will conclude that what I have said is correct.

Best regards,
-- Al

Note: The schematic link provided in my previous post appears to work some of the time but not others, perhaps depending on whether it has been previously cached in the browser after being accessed from the main LS25 page. If the link doesn't work, go to http://www.arcdb.ws/LS25/LS25.html, scroll down to near the bottom of the page, and click on the thumbnail for page 1 of the schematic, which is at the left side of the page.

When the schematic opens, in its upper right corner click on the symbol that looks something like an "X." That will expand the drawing, so that it can be more easily viewed.

Best regards,
-- Al