Too much gain?

jfmerk61

Member
2018-05-01 1:22 am
Hello,
I don’t post often and hope I’ve chosen the right forum. First, my system for music listening is a Transcendent Sound GG Preamp, Odyssey Khartago amp,
Blussound Node 2i, Rega Dac r and recently acquired Kef R11 speakers.
My original speaker were the Jim Holtz Mini Statements.

My question or concern is that with the R11s, my sound level with the volume on the GG at say 23% of pot rotation is about 90 decibels at 15’ from the speakers. I’d never go past 30% where sound level is 95-98 decibels. I recently installed a 100K Alps motorized remote volume control I picked up on eBay.
Do I have the wrong volume control or is there nothing to be concerned about?
The R11s are more sensitive at 90dB.
This is the volume control I installed:

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/372638880007

Any comments are much appreciated!

Jeff
 
That preamp can put out 20Vrms, so its not surprizing at all. 2Vrms is enough for most power amps.
Sure, but in what way is that relevant to the OP's question?

The main determining factors in how touchy the volume control is are:
1. DAC output level
2. The sum of preamp and power amp voltage gain.

Preamp gain is a nominal 12 dB.
Power amp gain is not stated anywhere (neither on the website nor any reviews) but let's assume it to be a typical 26-29.5 dB.

In sum, certainly nothing too excessive. Speakers are a few dB above average though, so in sum gain may be fairly typical.

How much is 23% of the volume pot? Like 10 o'clock? It is not an uncommon occurrence for people to run into channel imbalance issues below 9 o'clock at normal volumes these days if they are running straight CD player levels into their integrated amps.

If you are doubting the pot, see whether it still gets a lot louder after the 30% mark - if so, it's a proper log (and there is no reason why it shouldn't be, really).

Possibly fixes for Touchy Volume Pot Syndrome:
1. Turn down source amplitude. (Using ReplayGain with settings adequate for all but a few CDs ever made typically accounts for about 10 dB here.)
2. Add a passive attenuator between preamp output and power amp input, with values chosen so that neither is too unhappy. Maybe 12 dB perhaps? Transformerless tube preamps don't tend to be the last word on noise anyway, even if this one is supposed to be better than average. (Tubes just have a whole lot of voltage noise even in the best of cases.) Unless, of course, the volume pot is cleverly placed at the output - in which case I would rather place said attenuator just ahead of the pot (values maybe 56k/22k?). Using a 100k pot ahead of a 22k power amp input is not ideal in various respects and a buffer stage would be good, but it is what it is.
 
Sure, but in what way is that relevant to the OP's question?


Its relevant because the post said "Any comments are much appreciated!", and because that preamp clearly has lots of unwanted headroom, given that spec and the described behaviour. 20Vrms is extremely high and able to blow up power amp input stages, note.



Yes, attenuation after the preamp might be sensible - it will no doubt affect distortion levels and have an effect on noise too.
 
Oh, yes, definitely anti-audio_phool_, but I'm not being silly. 20Vrms is about 6dB above a mixing desk max output for instance, and 20dB above most high level sources. That amount of headroom gives a real chance of accidentally blowing up an input section or launching voice-coil assemblies across the room if you forget to turn it down. Something with that output voltage capability would be much safer with a configurable soft-clipping circuit on the output for these reasons. Its always preferable to clip at low power than in the main power amp...
 
If the volume pot is in fact at the output as I suspect (which would be the easiest way of getting the pre as quiet as advertised), it shouldn't be an issue at all at normal volume settings. Plus you can drive a moderate gain (e.g. 13.5 dB) tube power amp if you want - at a total 25.5 dB, noise definitely won't be an issue, and when using high sensitivity speakers on top you wouldn't have to run that much level into the whole shebang either.

A 12 dB preamp built like that would have to output at least 8 Vrms just for input clipping at 2 Vrms, let alone any headroom above that. If we say we want 2.5 or even 3 Vrms in, that's 10-12 Vrms, and suddenly 20 Vrms isn't looking quite so outlandish any more... still overdressed, yes, but you know how it is, big numbers = moar bettah. ;)

Remember we're talking transformerless hollow state tech here. That stuff is good for dozens or even hundreds of Vpp while audio frequency input noise rarely makes it much below the 40 nV/√(Hz) mark. Assuming you can get your linearity straight, having your gain in front of the volume pot makes all the sense in the world. In fact, linearity considerations may have resulted in the high maximum output in the first place - after all, distortion would depend on input level and input level only.
 
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