A tale of Gain.

[DonH50]

Analyzing and optimizing the signal gain chain of an RF system can be complicated and I have no reason to believe it is different in audio. Choosing the optimum gain to maximize dynamic range and minimize distortion can be tricky. However, audio components seem to have relatively standard gains and very wide dynamic range so we get away with a lot...

 

[garylkoh]

This may not be applicable to the systems of many of the members here, but you'll almost always want to have the preamp operating at -40dB or more of its maximum gain due to the volume potentiometer. The exception are those preamps with discrete volume pots. This is because most volume pots don't track well at below -40dB.

So, dropping the gain on the power amp, and operating the preamp at it's "sweet spot" may be very beneficial for the majority of preamps available.

The other consideration is how the power amp gain is switched. A couple of the power amps I've seen with this gain switch achieves this by negative feedback in the input buffer stage to drop the open loop gain. A lower gain implies higher negative feedback (note I'm not one of the "all feedback is bad" brigade), and this can change the characteristics of the sound.

 

[DaveyF]

Gary, that's very interesting about the change in negative feedback. I'm not one who generally likes negative feedback designs. Do you know which amps utilize this feature in this manner?

 

[Steve Williams]

Gary, that's very interesting about the change in negative feedback. I'm not one who generally likes negative feedback designs. Do you know which amps utilize this feature in this manner?

My amp does. I've never used it

 

[garylkoh]

Gary, that's very interesting about the change in negative feedback. I'm not one who generally likes negative feedback designs. Do you know which amps utilize this feature in this manner?

Davey, you might mean "global negative feedback". There are exceedingly few amplifiers that have no feedback at all. I won't name names, but there's usually always some local feedback.

 

[garylkoh]

I should add that even the very best volume pots don't track well at -60dB.

 

[Steve Williams]

A description of my amp.......

The ML3 has no overall feedback loop, however the amplifier features an option that allows the user to introduce a small amount of local feedback in the output stage. Furthermore, there is a choice of two amounts of such feedback: NFB1 and NFB2, which differ in their levels. Therefore, there are three options regarding feedback use in the amplifier: no feedback, NFB1 or NFB2.

 

[JackD201]

Often times I would wonder why I read so many posts about impedance matching but hardly ever any posts about gain matching aside from in carts-phonostages. Not just gain but voltage drive as well especially for many of us who bi-amp (including those using subs fed from the pre's secondary outputs). We also tend to use long runs of interconnects.

I use one preamp that deals with this is a bit different way. The Valvet Soulshine has two knobs in the middle. What they do is control the input sensitivity for the sources. When you play with them the first thought is that the can be used as balanced controls. The more you listen though it becomes obvious that they shouldn't. Every mismatch between L and R show different distortion spectra which are clearly audible as notes sound...... wait for it .....a tad hirsute.

I suppose this also cuts the usage of the available peak gain thereby indirectly rendering it adjustable. I have found that there is indeed a sweetspot and these vary according to the amps they are used to drive. Same goes albeit more directly for the input stage.

@Steve

I don't see at all why there would be an adjustable gain option for the LL1 when it was designed specifically for the ML3. Specs show it would also do well with the greater majority of amps out there. Still, personally, I can't even think of the LL1 without thinking of the ML3. I suspect that an overwhelming majority of LL1 buyers are buying them to complete the Signature set.

 

[Steve Williams]

Often times I would wonder why I read so many posts about impedance matching but hardly ever any posts about gain matching aside from in carts-phonostages. Not just gain but voltage drive as well especially for many of us who bi-amp (including those using subs fed from the pre's secondary outputs). We also tend to use long runs of interconnects.

I use one preamp that deals with this is a bit different way. The Valvet Soulshine has two knobs in the middle. What they do is control the input sensitivity for the sources. When you play with them the first thought is that the can be used as balanced controls. The more you listen though it becomes obvious that they shouldn't. Every mismatch between L and R show different distortion spectra which are clearly audible as notes sound...... wait for it .....a tad hirsute.

I suppose this also cuts the usage of the available peak gain thereby indirectly rendering it adjustable. I have found that there is indeed a sweetspot and these vary according to the amps they are used to drive. Same goes albeit more directly for the input stage.

@Steve

I don't see at all why there would be an adjustable gain option for the LL1 when it was designed specifically for the ML3. Specs show it would also do well with the greater majority of amps out there. Still, personally, I can't even think of the LL1 without thinking of the ML3. I suspect that an overwhelming majority of LL1 buyers are buying them to complete the Signature set.

Best amp/preamp combo I've ever owned and now comes Vlad's Signature Phonostage to complete his Signature line

 

[DaveyF]

A description of my amp.......

The ML3 has no overall feedback loop, however the amplifier features an option that allows the user to introduce a small amount of local feedback in the output stage. Furthermore, there is a choice of two amounts of such feedback: NFB1 and NFB2, which differ in their levels. Therefore, there are three options regarding feedback use in the amplifier: no feedback, NFB1 or NFB2.

Steve, have you ever experimented with the feedback adjustment? I had left my gain setting alone assuming that was the right one based on my dealer's suggestion. However, as I posted, that turned out not to be the case with my particular preamp/amp combo. If the ML3 has an ability to easily change the feedback, may be worth an experiment? BTW, if I'm not mistaken, HD of Dartzeel dislikes global feedback so much that he has made it a point of removing it from his designs. I presume that you have your amps set up with no feedback, vs. NFB1 or NFB2. Is that how Vladimir delivers them?

 

[Steve Williams]

That is how he delivers them. I asked him when I should use NFB1 and/or NFB2. He said "forget about it"

 

[DaveyF]

That is how he delivers them. I asked him when I should use NFB1 and/or NFB2. He said "forget about it"

So why offer that option

 

[Steve Williams]

Because people asked him about it and he added it. I don't use it.

 

[DaveyF]

Would be interesting to know why people would want that option. It's not something that I would think would be an asset either. The ability to change gain settings is another matter though.

 

[microstrip]

A description of my amp.......

The ML3 has no overall feedback loop, however the amplifier features an option that allows the user to introduce a small amount of local feedback in the output stage. Furthermore, there is a choice of two amounts of such feedback: NFB1 and NFB2, which differ in their levels. Therefore, there are three options regarding feedback use in the amplifier: no feedback, NFB1 or NFB2.

Several other tube designs have this feature. It will change gain, but the main measured effect will come from changing the damping factor of the amplifier, as feedback will reduce the output amplifier impedance. A small reduction in distortion is also expected. However most users will prefer the non-feedback position.