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Help with a pre-amp
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Graham Slee View Drop Down
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 04 Apr 2011 at 8:34pm
I remember pre-amplification was a lot more flexible with an audio mixer - any views?
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Graham Slee View Drop Down
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Points: 16298 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 06 Apr 2011 at 8:54pm
No takers to last comment then?

Actually, I would definitely find the flexibility of some audio mixer properties of value. I suppose it's OK to have level matching adjustment on each input of a preamp, but a mixer does that for you already. It could be argued that the user would have to turn down an unused input whilst using another to get rid of any residual noise from an unused input, but there is the possibility of using PFL or "booth" buttons which send unused inputs to another mixer bus which achieves the same end.

Maybe I'm getting too technical again or most people don't understand audio mixers?

All you need do is ask - you know that most of the time I'm happy to explain/expand on a subject.

Graham
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BAK View Drop Down
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Points: 1744 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2011 at 3:02am
Originally posted by Graham Slee Graham Slee wrote:

No takers to last comment then?

Actually, I would definitely find the flexibility of some audio mixer properties of value. I suppose it's OK to have level matching adjustment on each input of a preamp, but a mixer does that for you already. It could be argued that the user would have to turn down an unused input whilst using another to get rid of any residual noise from an unused input, but there is the possibility of using PFL or "booth" buttons which send unused inputs to another mixer bus which achieves the same end.

Maybe I'm getting too technical again or most people don't understand audio mixers?
I like the features of some high end mixers but I would not use all of them in a home sound system. That fact makes the really good mixers too expensive.
An input shorting switch used for those inputs not in use would be good. I have seen FETs used for this purpose. I can imagine a set of FETs used for input selection and another set of FETs used for muting unused inputs, all controlled by the same control voltage. One brand used CD4016 quad switches for input selectors having only 100 ohms in series with the signal path when "on" (I am not sure of the musicallity of such CMOS use). Another uses special contact relays to select inputs. Relays add the muting very easily using NC contacts when at rest.
 
 The individual input level controls could be set screw type next to the respective input. I would think 3 inputs would be enough for a small preamp with input selector.
 
The master gain I mentioned before would be an added plus for 2 reasons: first
to keep others from turning up the system too loud or into overload,
and second to set the gain so normal listening is at 12 o'clock on the volume control.
To keep it safe, the master gain setting would be best located on the rear or some how hidden. It could be switched, one position for "normal" and another for "maximum without distortion"; each position with it's own set screw level.
 
All of these set screw levels could be hidden behind a removable panel so as not to overpopulate the rear or front panels. Front would have: POWER sw, Volume, ON LED, INPUT selector, and NORMAL/MAX gain switch.
 
These are my ideas from years past and I have never put them into solder.
Bruce
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BAK View Drop Down
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Points: 1744 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2011 at 3:16am
Graham, what are your thoughts on voltage controled amplifiers?
 
Can a low noise op-amp be voltage controled via a FET in the feedback loop and not detract from the sound quality?
If so, one could make a remotely controled amplifier stage very close to the input selector and have the control anywhere on a chasis.Wink
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BAK View Drop Down
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Points: 1744 		Post Options Post Options   Thanks (0) Thanks(0)   Quote BAK Quote  Post ReplyReply Direct Link To This Post Posted: 07 Apr 2011 at 3:27am
Originally posted by BAK BAK wrote:

All of these set screw levels could be hidden behind a removable panel so as not to overpopulate the rear or front panels.
 
The selector and input level controls could be on a separate PCB very close to the input connectors
OR
housed in a separate box to facillitate a FET or RELAY switch circuit with it's own power supply regulator for the FET bias or RELAY control.
The separate housing would keep noise to a minimum.
 
Just some ideas...
 
Anybody else interested?
Bruce
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Points: 124 		Post Options Post Options   Thanks (0) Thanks(0)   Quote frimmers3 Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2016 at 1:59pm
I wonder if anyone could help....I use an AR Legend turntable with a Goldring G1042 cartridge, a Graham Slee Amp2se through an Arcam Delta 290 integrated amp,feeding a pair of Wharfedale Diamond 220's stand mounts,with Chord interconnects/speakers throughout...Not "high end",but very pleasing to these old ears:)....cut to the chase....I have sourced a mint Arcam Delta 290P (power amp),and intend to bi-amp my system,with the integrated amp providing the high frequencies,the power amp the low frequencies..What (if any) advantages could(should) this measure provide? Thanks for any constructive criticism!
Rega P8, Exact m.m, Accession m. phono stage, Graham Slee /Chord interconnects, Dali Oberon floor standers.
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Chris Firth View Drop Down
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Points: 1533 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Chris Firth Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2016 at 2:41pm
Originally posted by frimmers3 frimmers3 wrote:

What (if any) advantages could(should) this measure provide? Thanks for any constructive criticism!


I've never heard a passively biamped system, so I don't what difference there will be, if any.
You do end up with a power amp driving each speaker driver, but the filtering is passive (ie subractive of the signal).
At best you might hear an improvement, at worst you'll hear no improvement
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