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System Gain, Volume, and component matching?

I'm facing a bit of an unknown regarding proper gain matching of components and could really use some help in understanding this. First, with my current setup I typically listen at ~60 out of 99 on my Rowland Pre (maybe 90db or so). Here is what I believe my component gain structure is right now:
APL3910 4V output
Rowland 20db overall gain
JC1 amps 1V=28.3V out (56.6V max power)
Magnepan MG3.6 85db at 2.83V (4ohm load)

Am I correct in saying that to reach 85db at 1m on a continuous test tone, my pre would need to feed the JC1's 100mV?

If this is true, it seems that my pre would have to attenuate that 4V output from the APL a huge amount? But given the Rowland Pre's 20db overall gain, doesn't that suggest that: 1.) at max vol setting, Vout/Vin = 100? 2.) With APL outputting 4V, at max vol setting, the pre would be outputting 400V (no chance). 3.) If the volume knob is linearly calibrated, that would suggest that 4V per vol point (0-99) (no chance).

Could someone help me understand this? As I said earlier, I usually listen at ~60 out of 99 on the Rowland. I'm replacing the Rowland with another Pre that has 8db of gain (Rowland has 20db), and I'm sending my APL back to have a linear power supply upgrade which will drop output from 4V to around 1.5 to 2V. If I used the mathematical approach above, I wouldn't be worried about a thing. However, from a practical point, I currently listen at 60 out 99 on the Rowland, will be decreasing Pre gain from 20db to 8db, and will be reducing APL CD Player output from 4V to possibly 1.5V.

So, with those changes, am I going to be craving a pre that will "go to 11"? Will I run out of gain? And finally, I've heard people mentioning problems with too high of gain in a system causing certain distortions and very little (e.g. 7 to 9o'clock) control of volume, but is it possible to have too little gain when source is only a line level source with outputs in the 1+V range (No phono in system)?

Lots of questions in there I'm sure. I really appreciate any help in understanding this matter.

Thanks!!!

Jordan
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Showing 4 responses by germanboxers

germanboxers's avatar
germanboxers OP
241 posts
 
Bob, looks like you're right...dB=10log(Po/Pi) and since P is proportional to V^2, it becomes dB=2*10log(Vo/Vi). Thanks for the correction! Ok, that's an order of magnitude difference: 400V to 40V. This makes much more sense, though 40V is still way too high to feed an amp with 29dB of gain. Can you think of any reason why I'm using so much pre Vol control for such modest listening levels?

Thanks!

Jordan
germanboxers's avatar
germanboxers OP
241 posts
 
Thanks for the responses so far!

Bob, I think the conversion is Bel=log(Vo/Vi), so dB=10log(Vo/Vi), right? So, 20db gain with Vi = 4V from APL should be: 20=10log(Vo/4) => Vo=400V. Isn't this right? I love the Rowland BTW, it is very smooth, clean, and articulate...even dimensional. I'm replacing it with a Cary SLP-05, a vacuum tube preamp.

NgJockey, my room is 19'x21'x8', so it's not huge. The maggies are ~85db, BUT, that's a 4ohm load @2.83V, not 1w. I also use balanced cables from the Pre to Amp.

I just got out my radio shack spl meter and measured an average loudness (c-weighted, slow) around 83-85dB at the listening position (11' from speakers) while listening to "Turn me on" by Norah Jones at "60" on my Rowland Pre. For this CD, that's about normal listening for me. This means that at 60/99 the Rowland must be putting out something over 100mV, right? I don't the relationship between distance and loudness for a dipole.

Eldartford, I thought when they say it outputs 2V rms that it means that is the average output, not the max, right? Maybe that's where I'm confused?

Thanks for the help, guys...is the general consenus that I should be fine with a 1.5-2V output player and only an 8dB gain preamp?

Regards,

Jordan
germanboxers's avatar
germanboxers OP
241 posts
 
Hi Drubin...how to you like your APL Marantz with the AKM DACS and new upsampler? Also, are the Rowland 201's and Primaluna amps competitive in quality? I'm going to take your advice and hold on to the Rowland until I'm sure I have enough gain...although on paper, I have plenty. ugh!

I think there might be something wrong with Rowland's specs, or they have a highly non-linear volume control. For example, to drive the JC1's (~14.5dB gain) to full power (~800w into 4ohm) would take: 14.5=10log(56.6/Vin) => Vin =~2V. So, technically, I could drive my amps to full power with a unity gain preamp and a 2V output player? And given my amp and speakers...that would be around 110dB!! I haven't even had peaks that get close to that number!

Anyone?

Thanks!!

Jordan
germanboxers's avatar
germanboxers OP
241 posts
 
Thanks Bob, since the maggies are dipoles, they do not follow the same inverse law of decay that a point source would, but I'm not sure what relationship applies? I have a Rives test disc and I agree that 80dB is VERY loud with a continuous tone, but with normal music, it's not continuous and with slow response, C-Weighted on the RadioShack SPL, I don't think it's super high. If I listen for more than 30min, I'm listening at slightly lower volumes, but on some songs, I'll turn it up to around 85dB.

I am using a 7m balanced pair of Purist Audio Museaus IC's between pre and amp. Room is carpeted and I have two 16" tube traps, and two 11" tube traps, plus bookcases, etc to diffuse the sound.

Thanks for all the help!

Jordan
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