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
Mark,

There are quite a few A-gon members like Almarg with a tremendous wealth of technical knowledge who will hopefully respond with an in-depth explanation to your query. From my experience and understanding, the voltage gain on the phono pre should "match" the voltage output of the cartridge for optimal performance. Tools like the KAB calculator http://www.kabusa.com/frameset.htm?/ are useful to determining the gain your cart needs to perform well. It's just an approximation, but from my experience it's actually quite accurate. According to the calculation, the Delos needs 55 dB of gain. It has certainly worked in my systems.

As I wrote in the thread you referred to, too much gain results in a sound that's shrill, harsh, and overall unpleasant. I'd think it's the excessive voltage that amplifies the signal and generates spikes in amplitude that is responsible for the harshness and edgy sound I get with excessive gain on my phono pre. It's not distortion, but edginess that is immediately audible and unbearable. I've never experienced pops or static discharge as a result of excessive gain, but it certainly does not surprise me. For what it's worth, I've also found that increasing the gain on the line stage (if it allows it) to compensate for insufficient volume works better than increasing the gain on the phono preamp. Might be a bit noisier, especially if it's a tube line stage, but does not make the sound edgy or shrill.

Mark, 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. That should be plenty of gain.
The reason for the problem is that you are talking about 2 separate things. The volume/gain on your linestage has nothing to do with your phono stage. If you have a gain problem with your phono stage, it exists at all volumes, it really doesn't matter what setting the volume is on the LS. Until you reduce the gain on your phono, the problem will remain; at at whatever volume you have your LS set to.
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. :)
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
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.
Volume knob comment. Actually many preamps do best with the volume control somewhere near the 1 to 2 oclock position. So 12 to 3 is fine.
Usually really low volume control position should be avoided like 9 oclock...

I would comment on the overload in a stage of a component, but i am too fuzzy (at the moment) to be sure it would be correct. Though the previous comments are pretty good..
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. Whest are so mysterious about their products that one can only go on the absence of a claim on their website, rather than on any real circuit description. Well, they do not claim that any of their products are balanced, so I am tending to think they are not. Ergo, subtract some db from your estimates.
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
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.
Changing to a balanced INPUT on the LS25 does however increase maximum input from 14Volts to 28Volts which could give more headroom.

Funny thing is my old Quicksilver preamp could take 60volts up its jacksie on single ended before overload, and my 1960 Marantz 7 can take 30volts up its jacksie without overloading. I guess they dont make preamps like they use to.

The other thing I dont understand is that my Marantz 7 has 60db of TOTAL GAIN INCLUDING LINE STAGE and I can use a Koetsu with 0.4mV output with no noise and gain to spare. What has happened to modern tube preamp design - more noise, less gain and lower overload margins.
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
Mark,

Just wondering if you made any progress with your system? If so, what did you do?
Progress. Yes I did indeed. The whest allows me to get 6 more dB out of the LS25, so off the bat, it's a help. I then tried 60 and 66 dB on the whest. 66 gave me distortion/overload, so I dropped to 60. Then, to see if I was still getting some less obvious distortion at 60, I dropped it to 55. This setting may not give as much gain as 60, obviously, but it is still a jump in output over the ARC's 54 single ended. I may go back up to 60 eventually. Right now I am playing with loading. 100 seemed a wee bit flabby, so I am now listening to it at 200. Actually, I am having a tough time hearing the loading differences. I have an ear doctor appt soon for reasons other than ohm load sonic difference detection, but I will sure test loading again after I get back from the doc! Any advice on loading?