Turntable Cartridge Output Voltage with Vintage Receivers

[LTig]

Linn doesi

I've sometimes wondered why more "perfectionist" turntables don't offer on-board preamplifier as an option, because that's easiest way to achieve the lowest possible cable capacitance

Linn does it, but at very high costs.

 

[Chrispy]

The relevant part of the schematic in an ARC SP-8 (left channel shown).

View attachment 237806

Not shown, 390V hybrid SS/tube regulated power supply and heater supplies

Thanks, but how does such spec out?

 

[rongon]

So if the source is same and the loudest you want to play is 50% of volume knob with that fixed source, the amp will distort or clip just as much as at 90% volume knob?

FYI I'm an ME, not an EE, and sorry if my rule of thumb is bunk.

It just means that the position of the volume control, all by itself, in isolation, has nothing to do with distortion or likelihood of clipping.

The volume control itself is just a voltage divider. It does not amplify. It can only attenuate.

If you apply a small signal to the volume control input and adjust the control to 50%, the output from the volume control is going to be made smaller.

If you apply a monstrously large signal to that same volume control (feeding the same amplifier stage as above) and adjust the control to that same 50%, the output from the volume control is going to be smaller than it was at its input, but still could be much larger than in the previous example, and perhaps enough to overload or clip the following stage.

Here's an example.

If the volume control is set to attenuate an incoming voltage by 10X (-20dB) then:
1) an incoming 100mV signal will be attenuated to 10mV.
2) an incoming 10V signal will be attenuated to 1V.

Let's say the amplifier following the volume control reaches full power with a 500mV (0.5V) input level.

So, with the volume control at the same exact physical setting:

The example in 1) will not come close to clipping or overloading the following amplifying stage, but
The example in 2) will drive the amplifier far into overload and clipping, with high distortion at its output.

Does that make sense?

____________________________________________________

In example 1) above, if the incoming signal is 100mV, and the amplifier after the volume control can accept up to a 500mV signal without clipping, that means you could turn up the volume control all the way to 10 (100%) and it would pass 100mV to the amplifier input. Since the amplifier can accept up to 5 times that signal level without clipping, turning the volume control up all the way will not cause the amplifier to clip/overload.

In this case turning the volume control up to maximum does not cause gross distortion at all.

Which is all a long winded way of saying that the volume control only adjusts *relative* signal level. It's the amplifiers that distort. If you keep signal levels below overload thresholds, there will be no distortion.

It all depends...

 

[restorer-john]

It just means that the position of the volume control, all by itself, in isolation, has nothing to do with distortion or likelihood of clipping.

The volume control itself is just a voltage divider. It does not amplify. It can only attenuate.

If you apply a small signal to the volume control input and adjust the control to 50%, the output from the volume control is going to be made smaller.

If you apply a monstrously large signal to that same volume control (feeding the same amplifier stage as above) and adjust the control to that same 50%, the output from the volume control is going to be smaller than it was at its input, but still could be much larger than in the previous example, and perhaps enough to overload or clip the following stage.

Here's an example.

If the volume control is set to attenuate an incoming voltage by 10X (-20dB) then:
1) an incoming 100mV signal will be attenuated to 10mV.
2) an incoming 10V signal will be attenuated to 1V.

Let's say the amplifier following the volume control reaches full power with a 500mV (0.5V) input level.

So, with the volume control at the same exact physical setting:

The example in 1) will not come close to clipping or overloading the following amplifying stage, but
The example in 2) will drive the amplifier far into overload and clipping, with high distortion at its output.

Does that make sense?

____________________________________________________

In example 1) above, if the incoming signal is 100mV, and the amplifier after the volume control can accept up to a 500mV signal without clipping, that means you could turn up the volume control all the way to 10 (100%) and it would pass 100mV to the amplifier input. Since the amplifier can accept up to 5 times that signal level without clipping, turning the volume control up all the way will not cause the amplifier to clip/overload.

In this case turning the volume control up to maximum does not cause gross distortion at all.

Which is all a long winded way of saying that the volume control only adjusts *relative* signal level. It's the amplifiers that distort. If you keep signal levels below overload thresholds, there will be no distortion.

It all depends...

All that may have been true in the past, but now we have conventional volume volume pots on amplifiers having a single track read by an A/D converter and translated to digitally controlled VCAs (or switched att) in silicon.

What that means is overload often is unpredictable, or fixed, regardless of the volume pot position. Take the Yamaha A-Sxx series for example. They will overload with a little over 4.3V into a line input, regardless of the position of the analogue volume pot.

Depending on where in the signal path the traditional volume pot is, whether a buffer/gain stage is up front also determines overload characteristics. It's not a one-size fits all simple voltage divider type deal.

 

[Timcognito]

Learning as I go. Thanks for the info. Sounds like I got wrong but it seems like it could often be true looking at Amirs graphs especially tube and some SS amps but not by design. Your patience is much appreciated. Last EE class was at UC Berkeley in 1976 at dawn of the digital age.

 

[rongon]

That's interesting.

Is the Yamaha A-S801 representative of the A-Sxx series?

I wonder if these amps take all incoming analog signals and digitize them, then perform volume control by DSP. If so, that could explain why they would overload on a 4.3V signal no matter what the volume control position happens to be, because the line input is still seeing 4.3V no matter what the position of the volume control.

What I don't understand is how an amplifier could overload with 4.3V present at the input of an 'analogue' volume pot. If that volume control is a resistive potentiometer, and you set that pot to -20dB attenuation, that 4.3V input should be knocked down to 0.43V -- correct? How does the amplifier input sense the voltage level before the pot has attenuated it? What is the purpose of the pot in that situation? I suspect it's a digital thing and I just don't know enough about that stuff.

When would a consumer see a 4.3V signal source? (Also, is that peak-to-peak, peak, or rms?)

@Timcognito - We're all learning! It's an endless process. restorer-john's points are teaching me, for sure. Thanks!

 

[restorer-john]

That's interesting.

Is the Yamaha A-S801 representative of the A-Sxx series?

I wonder if these amps take all incoming analog signals and digitize them, then perform volume control by DSP. If so, that could explain why they would overload on a 4.3V signal no matter what the volume control position happens to be, because the line input is still seeing 4.3V no matter what the position of the volume control.

What I don't understand is how an amplifier could overload with 4.3V present at the input of an 'analogue' volume pot. If that volume control is a resistive potentiometer, and you set that pot to -20dB attenuation, that 4.3V input should be knocked down to 0.43V -- correct? How does the amplifier input sense the voltage level before the pot has attenuated it? What is the purpose of the pot in that situation? I suspect it's a digital thing and I just don't know enough about that stuff.

When would a consumer see a 4.3V signal source? (Also, is that peak-to-peak, peak, or rms?)

@Timcognito - We're all learning! It's an endless process. restorer-john's points are teaching me, for sure. Thanks!

The A-Sxx example is just one I used. But no, the signal is not digitized. The limitations and subsequent overloads are constrained by the supply rails and the operation of the input selector/volume/tone IC itself.

This might sound weird, but the analogue volume pot in these Yamahas do not 'see' the audio signal at all. It is merely a rotational position input to an analogue to digital converter line on the micro, which translates that to direct control of the various types of attenuators used in the front end. Kind of 'fly-by-wire' like a modern electronic pedal/accelerator position sensor in your car.

A balanced output DAC or line level mixer can easily swing a little over 4V, a traditional preamplifier can swing 10-12V or more and an out board phono stage can output much greater than 4V.

 

[restorer-john]

Here's a basic A-S701 block diagram.

See how the Analogue Volume pot is merely an input to the micro?

Also see how the front end is routed. The constraints are the supply limits of the IC and the consequent swings it can process without distortion. With +/-7V rails, we are very limited. Basically around the limits I measured at 4.3V.

(Basically 7V divided by root 2 minus a typical junction drop of 0.6V gives ~4.3V RMS)

 

[rongon]

Thanks! I appreciate the explanation.

EDIT: I just now saw your explanation of the control circuitry and the motor-driven pot controlling the IC502 microprocessor. Thanks very much for that. Yes, I see now.

_)__________________

I have to wonder at Yamaha's design decision to go to all the trouble of making an amplifier that's guaranteed to overload on all those sources.

I can see that Yamaha didn't envision anyone connecting a traditional preamp or mixing board into the line input on one of their high-tech 21st century integrated amps. Besides, traditional preamplifiers are almost completely useless nowadays with signal sources routinely delivering 2V or more, and traditional power amplifiers all having input sensitivity of somewhere around 200mV to 500mV rms to full power.

Oh well. I feel hopelessly left behind now. I guess I'm something of a Luddite. I prefer to use a standalone DAC fed by some kind of computer holding my music and an LP playing system that's all analog (opamp preamp in my case), into a passive selector switch/volume control box, connecting to a pair of powered speakers with analog inputs. I suppose I could remove a couple of A-D conversions by switching to a pair of powered speakers with digital inputs and selector switching in the speakers, so my music computer could connect in the digital domain straight to that. But then what to do about the LP playback chain? Maybe a phono preamp with an ADC on its outputs. This is sounding expensive.

And now I see the purpose of these digital integrated amplifiers like that Yamaha. But how does it sound? Does it sound like those Yamaha Natural Sound amplifiers from 30 years ago?