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Old 3rd November 2003, 09:03 AM   #1
Boris29 is offline Boris29  Germany
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Question Volume Control between pre and power amp?

Where to place volume control in an integrated amplifier??

"Between pre amp and power amp, of course" you would say.
However, in many integrated amplifiers (Pioneer, for instance), volume control is in front of the tone control section! In practice, this worsens the signal to noise ratio of the tone section.

Can somebody explain me, why they do this???

I checked with several amplifiers, and only an old Fisher had volume control in the "right place". You can easily check, what yours does: turn volume low, play with the treble knob and listen if it influences the remaining noise coming out of your speakers.

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Boris
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Old 3rd November 2003, 01:00 PM   #2
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In Yamaha preamp, C80, the volume control consists of four deck, custom Alps pot and the volume is controlled both befor and after tone control. The traces on plastic elements of the pot are made in such a way that when first attenuator works the other is only conducting and when first goes into pure conduction (around half turn) the second starts its work. They don't make equipment like this anymore

BTW, the preamp sounded very badly.
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Old 3rd November 2003, 01:21 PM   #3
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Default Power Active Filter Stage..........

"In practice, this worsens the signal to noise ratio of the tone section."
It also helps to keep the tone section out of overload condition.

In many consumer integrated amplifiers the tone controls are part of the power amp negative feedback network - ie modifying negative feedback to modify overall frequency response.
This brings another set of problems, especially during power amp overload, and is typically sonically bad in this condition.

Eric.
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Old 3rd November 2003, 02:43 PM   #4
Boris29 is offline Boris29  Germany
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Default Thank you, Eric.

Aha, so this is why.

I did not know, that tone control is integrated into the power amp, nowadays. I mean, the idea is good, since a separate tone control stage works exactly with the same principle but would cost extra parts.
Probably, in my modern (mid price) Pioneer amp they chose this cheaper solution, and this explains why activating tone control increases the noise level, even with volume control set to zero.

Still I am wondering, why in my old Marantz Receiver (having a conventional tone control stage) the Volume control is in front of the tone control. "keep the tone section out of overload condition" might be a reason, but is unlikely, I beleive, since nominally we have 1V, and overload may occur at more than 5V.
May be they just did not care at that time?

Thanks again

Boris
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Old 3rd November 2003, 04:22 PM   #5
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Default Impedence Buffering Also.......

The tone control stage after the volume control also acts as buffering between the volume control wiper (variable source impedence) and the power amp input stage (often relatively low impedence).

Eric.
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Old 4th November 2003, 12:46 AM   #6
owdeo is offline owdeo  Australia
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But if it's a standard Baxandall tone control it needs to be driven from a low output impedance - ie not a volume pot.

IMHO you'd have to be trying pretty hard to overload a tone stage placed after the preamp volume pot and gain stages, as most power amps need <2V to drive them into clipping, while a typical opamp stage can swing 10V. So for me this is the best place for a tone stage.

Based on my experience with this kind of configuration, I would still put the pot in an integrated amp before the preamp gain stage, as to me power amps never sound dynamic enough driven from a pot.

Cheers.
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Old 4th November 2003, 04:02 PM   #7
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"Based on my experience with this kind of configuration, I would still put the pot in an integrated amp before the preamp gain stage, as to me power amps never sound dynamic enough driven from a pot."
I've heard plenty of nicely dynamic sounding power amps with volume pots on the front panel.

Eric.
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