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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
germanboxers
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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
eldartford
4,262 posts
 
SPL vs Distance for Maggies vs point source is something I just recently looked at. From anpther thread...

Here are some SPL measurements.
Planar is a MG1.6. PS is a Dynaudio Gemini (small MTM).
Signal is pink noise generated by Prepro (intended for setting levels).
Distance is feet.

Distance..Planar...PS.....PS
........0........100.....100
........1.........98......90.....108
........2.........96......88.....102
........3.........96......85......99
........4.........95......83......97
........5.........94......81......96
........6.........93......80......94
........7.........92......79......93
........8.........91......77......93
........9.........91......77......92
.......10.........90......77......92
.......11.........90......77......92
.......12.........90......77......90
.......13.........88
.......14.........88
.......15.........87
.......16.........87
.......17.........86

The first PS column shows the SPL leveling out at 77 dB. I think this reflects room effect. For the second PS column I increased the volume so that the SPL at 12 feet was the same as the planar, 90dB. This required the near field SPL to be a lot higher, 108 dB at 1 foot.

I don't think anyone listens at a distance of 3 feet, although that is close to the 1 meter distance used for the spec. At a more reasonable listening distance, between 8 and 12 feet, the Planar SPL falls off by 1 dB over this distance range, while the PS falls off by 3 dB. To produce equal SPL at 12 feet the PS speaker would need to be about 3dB more efficient at 1 meter. I think that these results are generally in agreement with theory.
ngjockey
1,042 posts
 
Can't comment on the Rowland. Never been fortunate enough to own one. It could be nonlinear for obvious reasons. I can think of a few, that I know of, like that. However, standard practice for actives is to amplify and then attenuate. There would be some loss going from 20 db to 8 but mostly at the end of the scale.

Volume is directly related to voltage. For example; on resistor based passives, the selected resistor will reduce voltage but current remains the same. Reducing the output of the CDP will reduce volume significantly, all other things being equal.

Eldartford - There are many CDPs/DACs that have higher than standard output stages. Consider the AA Capitole or many of those with volume controls that max out at 6V. Wadia has settings to tailor the output. Many preamps such the SFL-2 specifically state not to use more than 2V supplied to RCA inputs (4V XLR) to avoid damage.
eldartford
4,262 posts
 
Ngjockey...Having a standard, like 2 vrms max, assures compatability. Good thing for the industry. When standards are not observed problems may arise. In this case a high signal level problem can be dealt with quite easily using a fixed attenuator, so that the preamp volume control range is better. I understand why a CDP with a volume control might have outputs with extra gain (so that you can drive a power amp directly) but I think that it ought to include a second set of outputs, fixed at the standard level.
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