Preamp levels versus Amp input attenuation

Na, that's that bunch of Guardian Angels, warming up theirt voices.....
 
Ok, so I hears yas about the suggestions, but what I found is that the gain attenuators (at least in my case) should be used to adjust the overall gain for two reasons.

The first is to balance the channels - The left is slightly higher, so using a voltmeter and a generated 1K signal I have adjusted the balance within about 2mV of each other.

The second is that it does make a difference in the overall S/N ratio, at least in my case. If I allow for a higher output from the preamp by dialing the gains on the amp back a bit, the ambient noise is definitely much less than if I leave the gain pots wide open. Granted I have to have ears a few inches from the tweeters to hear, but in balancing the preamp's output with the 75 percent rule (turn it 75 percent... adjust the gains on amp until ears bleed) I can't hear anything at all.

Ya know what they say (who the heck IS "they" anyway? I think "they" are the "Van Pattens" :cyclops:)... YMMV! But that's what I've observed so far...
 
Jer
Have you tried the same with no cables on the input of the amp and both inputs directly grounded using RCA grounding plugs? You might find that it is external to the amp that you are tuning the SNR for. If that is the case, you should go about finding what the external noise sources are.
 
Gepetto said:
Jer
Have you tried the same with no cables on the input of the amp and both inputs directly grounded using RCA grounding plugs? You might find that it is external to the amp that you are tuning the SNR for. If that is the case, you should go about finding what the external noise sources are.
Click to expand...

Hi Joe,

I'm confused on what that is going to tell me. If I ground the inputs, then effectively it's well.. grounding the inputs which would obviously kill any residual noise.

Here's how I'm thinking - If the gains are turned back, then effectively the gain of the amp has decreased. Therefore for the same output, more input... and more input "over" the residual hiss/noise which can't be a bad thing - whether it's the source or the amp, it's still "present".

Heh.. like I said, I'm a tweaker at heart so I'll always be experimenting like this for the "best" sound. I'm also going to (for grins... let's see how it changes the sound characteristics?) get 4 of the MJ15024's for drivers, again just to experiment a little bit. It's all good stuff... the PLWO kicks the crap out of my M80 as it is!
 
Hi Jer
What Lee and I have been writing is that the gain of the power amp remains exactly the same regardless of whether the pot is up or down. It does nothing to affect the 26dB of gain that is always there in the power amp. The pot is an input attenuator. That's pretty much it (within the audible band that is).

If you turn down the input pot and your noise goes down, what that is telling you is that their is a noise source external to the RCA jacks that you are attenuating before it is presented to the fixed gain power amp.

The pot is not adjusting the electronic gain of the PL700 amp.

Hope this better explains what I wrote earlier
 
Joe,

I think we're in agreement. My point is that if the input signal is forced "upwards" since the attenuator is now only allowing so much into the amp's circuit for the same output level, then it would have the effect of driving the signal input higher than the residual noise floor.
 
Yes, agree Jer. You are attempting to improve the input SNR to the maximum by adjusting as you are.
 
But improving the INPUT SNR, not the amps SNR---THE pre-amps SNR.
 
Lee, because this thread has become a very interesting topic area - have you ever tried to wrap a toroid in foil to reduce the AC hum? I have a little computer amp with a particularly nasty 120Hz sawtooth. Even though it is barely audible, I would like to send it to ground. The inputs are shielded and the AC power wires are as short as I can get them.

Thoughts?
 
mlucitt said:
Lee, because this thread has become a very interesting topic area - have you ever tried to wrap a toroid in foil to reduce the AC hum? I have a little computer amp with a particularly nasty 120Hz sawtooth. Even though it is barely audible, I would like to send it to ground. The inputs are shielded and the AC power wires are as short as I can get them.

Thoughts?
Click to expand...


My luck with hum would indicate---a 60% Gelodyn Longhole Powder stick with a .05 delay electric cap.
 
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