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Old 21st June 2010, 05:03 PM   #31
AndrewT is online now AndrewT  Scotland
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Quote:
Originally Posted by mr.duck View Post
But do you think there is much benefit using as low a value as possible? Reason behind it being that some people like gainclones with preamps, a.k.a. buffered volume control. Therefore a 1K pot with a maximum output impedance of 250 Ohm may sound better than a 100K pot with 25K output impedance for example.
Some people advocate a buffer in front of an amplifier for completely the wrong reasons. Learn to ignore their advice.
A source can benefit from a buffer if it incapable of driving the load and the interconnect cabling. If the source can already drive the load and the cables then there can be little, if any benefit, to adding a source buffer.

Quote:
Originally Posted by mr.duck View Post
Low end source like computer or ipod could drive a 1K load so I don't see that load as much of a problem.
I don't agree. 1k0 is a very low load value. Only headphone outputs could drive this.
I seriously doubt that any line level output from normal domestic/retail gear can drive <<10k//1nF
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Old 21st June 2010, 06:36 PM   #32
star882 is offline star882  United States
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Quote:
Originally Posted by AndrewT View Post
I don't agree. 1k0 is a very low load value. Only headphone outputs could drive this.
I seriously doubt that any line level output from normal domestic/retail gear can drive <<10k//1nF
Opamps commonly used in audio equipment should have no problem with a 1k load.
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Old 24th June 2010, 05:10 PM   #33
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If your computer sound card has 10uF caps, max load is 10k (else it will cut off the lowest notes); however, if it has big 100uF~220uF caps then that is a good time to consider playing with the 500Rk~5k amp input load. Personally, I don't know of a computer sound card that requires more than 10k load; however, if it is designed to drive headphones, then in that case (only in that case) then a stouter load is a worthy experiment.

This is not a difficult experiment. Consider with a Via Tremor sound card, I usually have to add 0.5uF~0.33uF helper caps onto its big 220uF output caps because the big caps provided reach HF failure mode (dim treble) at line level. The result of the quickie patchup on the $14 card sounds much like M-Audio Audiophile sound cards; although its possible to tell that something is still very slightly askew with the treble. We still miss about an octave due to -3db down at 20khz. But, we also miss out on spending an extra hundred dollars for what is almost the exact same sound, indeed from the same chip. Perhaps your stouter load idea would make for a better response from the Via Tremor?

P.S.
Effects on sound can also be achieved by altering the feedback resistor value (range 10k~133k) and also adjusting its divider partner resistor to maintain correct gain. Where the feedback resistor is a higher value, the treble is brighter. This patch may allow you to run a stout 1k~5k input load (causes big loud bass with lesser treble). In combination, the amp design wouldn't make much sense to look at; however, when the feedback resistor value is more than double the input load resistor value, you may achieve a mild effect of a loudness contour. If your amplifier has a peak, such as a non-inverting LM3886/LM3875's typical upper midrange shout, you can aim an additional peak several octaves higher to get it smoothed out and then you can try increased input load to get the bass loud enough.
Of course, these dodges have nothing to do with good amplifier design; however, the majority of commercial amplifiers available in stores could have been greatly improved with dodge or two, even at zero added cost.

P.P.S.
The main cause of running round in circles trying everything at the amplifier and still can't work out the clarity and/or frequency response. . . is to be found at the power supply. The most effective changes/adjustments are located at the power supply.
Its easy to tell when this is "right" because you'll be able to replay a cello and hear beautiful loud rich clear baritone (sounds exactly like the cello should)--the #1 thing that most commercial amplifiers on store shelves cannot achieve.

Last edited by danielwritesbac; 24th June 2010 at 05:12 PM.
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