Lowest listening level

[currentflow]

The twist on the AU 717 is that the potentiometer has a DUAL function while the one will be a voltage divider in the input of the gain stage to attenuate incoming signals and the second gang of the pot is another divider obviously working in parallel to set the gain of the gain stage .

This is done before, some used a pot not as a volume control but as an actual gain control of the circuit but since the value of the pot was too big had tracking issues and failed to produce real 0 volume .

Now as we learned from audio sun to noise in the output of a gain stage is constant so in very low listening power there will be a danger of S/N ratio drop .

So from that we have to assume that the Sansui designer controls the the level of the source with the passive pot in the input of the gain stage while at the same controls the actual gain of the stage to reduce noise in the output .

Here is a very simple question:

Why any manufacturer should bother to ask Alps to construct for him a very sophisticated pot in the black line of Alps advanced beyond known standards involving a danger of tracking issues twice as much than any normal pot while instead he could simply use any quality pot of a standard value use it :

On the output of the gain stage control the level of the next stage while preserving the highest available S/N ratio possible .

Answer this solve my problem too ....

The Sansui AU717 you referred to uses a quad-gang potentiometer for controlling the volume level. For each L/R channel, the first gang pair (VR701a/b=150K) at the input to the gain/tone stage and uses a tapped taper to act as a variable loudness control, when enabled by S02a/b. The second gang pair (VR701c/d=5K) at the output of the gain/tone stage acts as a standard voltage divider which connects to the power amplifier input.

Both the input and output potentiometer gangs behave as voltage dividers. In this design, the overall gain of the 'active' stage is constant between these controls. Placing a level control at the output of the gain stage would help preserve the S/N ratio.

Sansui have chosen to control the loudness on the input potentiometer, which would explain the need for a specialised tapped control.

In your example, the "real 0 volume" you describe would be fulfilled by the loudness control, where the lower frequencies are amplified more at lower volume settings.

 

[east electronics]

I will have to verify with the schematic... I might as well be wrong . If so i stand corrected here also

Thanks for the pointer current flow will check it again an let you know

Kind regards
Sakis

 

[currentflow]

Correction: I meant to say that the loudness control boosts both high and low frequencies at low volume settings.

A good explanation may be found here

 

[sgrossklass]

A two-stage volume control as explained above basically solves one dilemma:

If you place all of your gain after the volume pot, the input is virtually impossible to overload but output noise levels will be relatively high.
With part or all of the gain in front of the volume pot, output noise is reduced accordingly (making for very low-noise preamps), but input overload levels may become rather tight, and levels in the input stage become rather high --> distortion.

The two-stage volume control keeps output noise low, but at the same time levels in the tone/preamp are much reduced, potentially much improving distortion performance. Keep in mind that preamp circuits in the '70s could be pretty basic and would often dominate the "sound" of an integrated amp.

BTW, even an input buffer can already increase dynamics in the sense of reducing output noise - you can use it to drive lower-impedance volume pots. Though that has its limits, as channel tracking commonly appears to suffer when going below 50-100k.

Preamp voltage gain is dictated by power amp gain, power amp rated output and desired input sensitivity (the latter two determine total voltage gain).

Electrolytic coupling caps may degrade the sound, but in the one example I encountered they were 30-year-old standard quality polar types that had never seen any appreciable DC voltage for about as long - IOW, "all bets are off" territory. These probably were leaky as hell, and don't even ask about DA. That's what you get if the designer forgets to take the pecularities of his parts into account - garbage in, garbage out, no surprises there.