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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
dover
2,250 posts
 
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.
almarg's avatar
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almarg
9,670 posts
 
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
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almarg
9,670 posts
 
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
zd542
5,339 posts
 
Mark,

Just wondering if you made any progress with your system? If so, what did you do?
marktomaras OP
544 posts
 
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?
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