5 or 10 k is not 'silly' George. Any decent op amp (and there are dozens) will drive 2 k happily at single digit ppm. My amps are generally 10k. 100k output z on a tube output in my view is extremely high. It should be buffered. I always wonder why in tube preamps a transformer is not used . . . but that's just my opinion.
I would think that almost any pot can be driven from a low source impedance source directly without buffering. If you are going to have a long cable run from the pot to the amplifier, buffering is probably s good idea - when the pot is set to mid point, the output z is significant and that can result in response anomalies and noise pickup susceptibility.
However, if your output z is high, like that from a tube stage, then buffering before the pot makes sense. Without it, you are forced to use high track resistance pots and that results in noise - and especially so at the pot midpoint. In my experience, 10k pot resistance is about as high as you want to go if feeding a bipolar stage, and perhaps 50 k feeding a JFET stage.
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Sometimes input stage will have loads of capacitance at the input. ESP's P3A circuit, for example has a 220pF cap across the input, and a 2k2 resistor in series with it. At very high level of attenuation it is possible to have frequency rolloff within the audio band and thus create subjective perceptions about passive attenuators, when in fact the problem lies elsewhere.
For example when a 10k pot is at 2k/8k ratio, the -3dB point is at 18k after adding the 2k2 series resistor. For higher pot values the situation is considerably worse.
For example when a 10k pot is at 2k/8k ratio, the -3dB point is at 18k after adding the 2k2 series resistor. For higher pot values the situation is considerably worse.
Yep as Andrew says use low capacitance cable
<100pf per ft and you can have 1mt on a 10kohm passive which is at worst around 7k out and the hf roll off will approximately be only be -3db @ 80khz
Cheers George
<100pf per ft and you can have 1mt on a 10kohm passive which is at worst around 7k out and the hf roll off will approximately be only be -3db @ 80khz
Cheers George
What are you driving if the source is <200ohm, the pot is 10kohm, the cable is 1mt at 300pf, and the input of the amp is say 50kohms?
Cheers George
Cheers George
The source has an output impedance of <200ohms.
The load seen by that Source is 1m @ 300pF/m in parallel to the 10k of the vol pot and that is in parallel to the next cable capacitance and that too is in parallel to the Rin of the Receiver. If the second cable is also 1m @ 300pF/m and the Receiver is 300r feeding a 1nF RF filter capacitor then the load seen by the Source is:
300pF||10k||300pF||50k||(300r+1nF)
Source sees a complex load of 600pF & 8k3 & (300r+1nF)
The high frequencies in the signal load the source, due to load capacitance, much more than the 8k3 does.
But with a low source impedance the treble roll-off is not too bad.
Change the Source to
That's why I posted:
The load seen by that Source is 1m @ 300pF/m in parallel to the 10k of the vol pot and that is in parallel to the next cable capacitance and that too is in parallel to the Rin of the Receiver. If the second cable is also 1m @ 300pF/m and the Receiver is 300r feeding a 1nF RF filter capacitor then the load seen by the Source is:
300pF||10k||300pF||50k||(300r+1nF)
Source sees a complex load of 600pF & 8k3 & (300r+1nF)
The high frequencies in the signal load the source, due to load capacitance, much more than the 8k3 does.
But with a low source impedance the treble roll-off is not too bad.
Change the Source to
and the consequences for the treble output are VERY DIFFERENT.
That's why I posted:
But in my scenario there is no problem. With dynamics or HF filtering, or loading.
And 7kohm can happily drive 1mt of interconnect that is <100pf per ft, which most good quality ones are even lower.
And there is no added cable load impedance to worry about. So scaring people off passives is not right Andrew with your statement "without a buffer".
Only if the amps input load gets stupid low then is this statement correct.
Cheers George
And 7kohm can happily drive 1mt of interconnect that is <100pf per ft, which most good quality ones are even lower.
And there is no added cable load impedance to worry about. So scaring people off passives is not right Andrew with your statement "without a buffer".
Only if the amps input load gets stupid low then is this statement correct.
Cheers George
Yes it is, as there are many commercial tube preamps out there that can't drive these silly low input impedance amps, then add an active sub with plate amps that are just as low and then those tube preamps have no chance at all.
I believe all amps should be standardized to 100kohm then everything would drive them.
Cheers George
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Then sort the source.
Easy by adding a buffer at the output of the source.
Then one can drive any cables, even 75ohm transmission lines.
1) Reminder : My comments have to do with behavior in low listening level .
2) In consumer audio manufacturers know that amplifier will spent most of its life playing in casual listening level . So they want the amplifier to be able to play well joyful and colorful even in this low level .That is the reason why loudness exist , active loudness from Yamaha and others and at 95% of the cases the input of the amp is buffered and the pot is before that .
To enhance this Japanese went a step ahead and supply a 2 transistor amplifier way over SOA which should no more than 35+35often with rail voltage 45-55 Volts ...Obviously they gained headroom give the amp a wide spread for dynamic peaks and when things get rough VI limmiter will kick in and introduce all the known problems but still keep the amp safe and alive .Target was to make it play well in low listening level .
Farther more there was manufacturers that try to control the gain of the preamp ( gain means gain not level attenuation often people get confused about that ) in order to solve the specific problem ....Using a pot of that range they failed to produce real 0 volume and lost tracking of channels on the way but drive ability was unique !Target here was also the same ..
Comes in mind the legendary SANSUI AU 717 that has a unique potentiometer and configuration that controls input level and gain of the preamp at the same time Where target there was exactly the same .
3) Can i call the above a standard practice ? You can call it anything you like Point is that this is given approach for specific targets and we can argue after that as much as you like .
Here is list of amplifiers from my schematics library that work like that . Please notice that in 95% of the main amp has a reasonable impedance between 22-100K so it can be driven the other way around like you say but actually it doesn't and seems that none of you is able to explain me why .
Accuphase E202
acoustic research A06
Adcom gtp 500
Aiwa mx-z300
Aiwa AA8700
Aiwa ZD3300
Akai Am2850
Akai AA1020
Akai AA1040
Akai AA1050
Akai AmU210
Akai Am59
Akai AM69
Akai AM75
Akai AM95
Akai AM 2200
Akai Am 2250
Akai AM2350
Akai AM2400
Akai AM 2450
Akai Am 2950
Akai AM A3
Akai Am U1
Akai AM U 2
Akai Am U 4
Akai Am U 11
Akaia AMU 33
Akai AM U 55
Arcam Delta 290
Audiolab 8000A
B& O beocenter 2000
Benytone M2600A
Brown regie 450
Brown regie 510
Brown regie 520
Cambridge audio A100
Cambridge Audio c70
Denon PMA 530
Dual CV6050
Fisher CA873
Fisher CA2320
Goodmans Maxamp
Grundig SV 2000
Grundig sv 210
Grindig sv 3100
Grundig V8100
Hafler DH101
Hafler 915 preamp
HArman Kardon 655 VXI
Harman Kardon A402
HArman kardon pm 645
Harman kardon pm 655
Harman Kardon 6550
Kenwood kr 3070
I could go on and on and on with many more schematics if you like while the rate between them will be 1-5 that is made the other way around
Searching also through my schematics i realized that from the devices i have listed as preamplifiers the 100% feature the pot before the output stage
Anybody cares to explain why ?
2) In consumer audio manufacturers know that amplifier will spent most of its life playing in casual listening level . So they want the amplifier to be able to play well joyful and colorful even in this low level .That is the reason why loudness exist , active loudness from Yamaha and others and at 95% of the cases the input of the amp is buffered and the pot is before that .
To enhance this Japanese went a step ahead and supply a 2 transistor amplifier way over SOA which should no more than 35+35often with rail voltage 45-55 Volts ...Obviously they gained headroom give the amp a wide spread for dynamic peaks and when things get rough VI limmiter will kick in and introduce all the known problems but still keep the amp safe and alive .Target was to make it play well in low listening level .
Farther more there was manufacturers that try to control the gain of the preamp ( gain means gain not level attenuation often people get confused about that ) in order to solve the specific problem ....Using a pot of that range they failed to produce real 0 volume and lost tracking of channels on the way but drive ability was unique !Target here was also the same ..
Comes in mind the legendary SANSUI AU 717 that has a unique potentiometer and configuration that controls input level and gain of the preamp at the same time Where target there was exactly the same .
3) Can i call the above a standard practice ? You can call it anything you like Point is that this is given approach for specific targets and we can argue after that as much as you like .
Here is list of amplifiers from my schematics library that work like that . Please notice that in 95% of the main amp has a reasonable impedance between 22-100K so it can be driven the other way around like you say but actually it doesn't and seems that none of you is able to explain me why .
Accuphase E202
acoustic research A06
Adcom gtp 500
Aiwa mx-z300
Aiwa AA8700
Aiwa ZD3300
Akai Am2850
Akai AA1020
Akai AA1040
Akai AA1050
Akai AmU210
Akai Am59
Akai AM69
Akai AM75
Akai AM95
Akai AM 2200
Akai Am 2250
Akai AM2350
Akai AM2400
Akai AM 2450
Akai Am 2950
Akai AM A3
Akai Am U1
Akai AM U 2
Akai Am U 4
Akai Am U 11
Akaia AMU 33
Akai AM U 55
Arcam Delta 290
Audiolab 8000A
B& O beocenter 2000
Benytone M2600A
Brown regie 450
Brown regie 510
Brown regie 520
Cambridge audio A100
Cambridge Audio c70
Denon PMA 530
Dual CV6050
Fisher CA873
Fisher CA2320
Goodmans Maxamp
Grundig SV 2000
Grundig sv 210
Grindig sv 3100
Grundig V8100
Hafler DH101
Hafler 915 preamp
HArman Kardon 655 VXI
Harman Kardon A402
HArman kardon pm 645
Harman kardon pm 655
Harman Kardon 6550
Kenwood kr 3070
I could go on and on and on with many more schematics if you like while the rate between them will be 1-5 that is made the other way around
Searching also through my schematics i realized that from the devices i have listed as preamplifiers the 100% feature the pot before the output stage
Anybody cares to explain why ?
I said commercial tube preamps Andrew and you want to put buffers on them, would'nt the right thing to do is to have poweramps standardized to 100kohm input, this also lets cap coupled preamps go down low in frequency without "monster plastic caps on their outputs.
And remember gods quote on passive preamps.
Nelson Pass,
"We’ve got lots of gain in our electronics. More gain than some of us need or want. At least 10 db more.
Think of it this way: If you are running your volume control down around 9 o’clock, you are actually throwing away signal level so that a subsequent gain stage can make it back up.
Routinely DIYers opt to make themselves a “passive preamp” - just an input selector and a volume control.
What could be better? Hardly any noise or distortion added by these simple passive parts. No feedback, no worrying about what type of capacitors – just musical perfection.
And yet there are guys out there who don’t care for the result. “It sucks the life out of the music”, is a commonly heard refrain (really - I’m being serious here!). Maybe they are reacting psychologically to the need to turn the volume control up compared to an active preamp."
Cheers George
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Competently designed sources have low and fairly linear output impedances. Competently designed amplifiers have high and fairly linear output impedances. Normal domestic audio interconnects are fairly short and have reasonable levels of shunt capacitance. Under these normal circumstances no buffers or preamps are needed, with or without a passive volume control.east electronics said:
For other circumstances buffers may be needed. Nothing whatsoever to do with "dynamics", just boring old engineering issues such as frequency response and non-linear distortion.
Pure nonsense. A speaker which was that nonlinear would have no place in any audio system.
'Loudness' controls are to do with the way our ears respond to low level signals, not the way the speaker responds. You are confusing two completely different issues.east electronics said:
DF96 :Under these normal circumstances no buffers or preamps are needed, with or without a passive volume control.
so many manufactures prove you wrong and this was only my library and i only had time to do till K But you can have it any way you like i have no problems
I ve made my point and members that not use words like pure nonsense will evaluate my sayings ...
Kind regards
Sakis
so many manufactures prove you wrong and this was only my library and i only had time to do till K But you can have it any way you like i have no problems
I ve made my point and members that not use words like pure nonsense will evaluate my sayings ...
Kind regards
Sakis
Searching also through my schematics i realized that from the devices i have listed as preamplifiers the 100% feature the pot before the output stage
Anybody cares to explain why ?
Anybody cares to explain why ?
If you're going to have an active stage, it belongs after the volume control. For the majority of setups, you don't need an active stage.
I'm not sure why this is confusing.
I'm not sure why this is confusing.
Putting the active stage after the gain control element gets you a low (and constant) output impedance...
Competent gear has low output impedance (think a few hundred ohms max) and high input impedance (~10K is typical in my world), any preamp that perpetrates a 100k output impedance fails the giggle test IMHO.
One should generally be conservative in what you generate, liberal in what you accept, buffer amplifiers help with this by providing the low output Z and relatively high input Z, besides if your box already has a suitable supply, a '5532 (or whatever you happen to like) costs nothing.
I would note that a 10K pot driven from a low impedance has a worst case output impedance of 2.5K ohms, but that it varies with position. If such a control drives a following stage having non linear input impedance then the distortion will depend on the position of the volume control (Another reason to buffer the output of a gain control).
Regards, Dan.
Competent gear has low output impedance (think a few hundred ohms max) and high input impedance (~10K is typical in my world), any preamp that perpetrates a 100k output impedance fails the giggle test IMHO.
One should generally be conservative in what you generate, liberal in what you accept, buffer amplifiers help with this by providing the low output Z and relatively high input Z, besides if your box already has a suitable supply, a '5532 (or whatever you happen to like) costs nothing.
I would note that a 10K pot driven from a low impedance has a worst case output impedance of 2.5K ohms, but that it varies with position. If such a control drives a following stage having non linear input impedance then the distortion will depend on the position of the volume control (Another reason to buffer the output of a gain control).
Regards, Dan.
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