A friend of mine actually built a hybrid digital amplifier that is powered by an old laptop power supply. I have seen it on display at a university engineering fair and it works very well. I even borrowed it for a few days for testing and I was very impressed at its quality and especially its very high efficiency.
Amanda Harris: the Prius of home audio - EcoRenovator
Amanda Harris: the Prius of home audio - EcoRenovator
Last edited:
What the hell... a little off-topic are we?
A summary of all that: Some sort of regulated power supply can make for nice results.
Also, if you build a class AB amplifier with the same care and attention to detail that is normally used in class D amps then the sound will be approximately as clear and the efficiency will be great, for either.
Additionally, the power supply has the largest effect on sound, not a cap, not a coil, not a resistor, not a heatsink, not a potentiometer. . . Much attention to the power circuit makes for excellent sound. Starting out with excellent power makes the rest so much easier.
Also, if you build a class AB amplifier with the same care and attention to detail that is normally used in class D amps then the sound will be approximately as clear and the efficiency will be great, for either.
Additionally, the power supply has the largest effect on sound, not a cap, not a coil, not a resistor, not a heatsink, not a potentiometer. . . Much attention to the power circuit makes for excellent sound. Starting out with excellent power makes the rest so much easier.
Last edited:
II think I found my amp design, taken from the same site:
I'm also going to get a couple of pots (10k & 50k) to experiment with. Components include: Rf 22k, Rg 680R, Rm 10k, and Cs 2200uF.
Hi bmwpowere36m3.
I am in the process of building Mick Feuerbacher's 2 resistor LM3886 and just came across this thread. Have you completed yours yet? Did you try the two different pots and did you detect a worthwhile difference?
I have a 10K stepped attenuator to try and also the "Optivol - Simple LDR volume control" from Greg Ball (SKA amps) .
The Optivol is very simple and, for me, is an improvement on the attenuator. However, it likes a high input impedance so it remains to be seen whether it will suit Mick's simplified LM3886.
Joe
I just finished mine yesterday. Not PTP but on a PCB. I have tried it with both a 10k stepped attenuator (Dale resistors) and the LDR volume control.
Without any type of input connected, I got a savage hum. With the 10k stepped attenuator, as in Mick Feuerbacher's schematic, hum disappeared and it sounds very nice. DC offset is about 10.5Mv on each channel.
However, with LDR volume control in place of the stepped attenuator, the hum returned. So I soldered a 22K resistor across the input and hum is gone. The LDR volume control sounds clearer ad more dynamic and is an improvement over the stepped attenuator.
However, I need to experiment a bit with the LDR input resistor to see if the value makes a difference.
The LDR volume control is powered from the +V/0V of the Gainclone PSU through a (LM7815) 15V regulator. It is on a very small PCB (50mm X 12mm) so can be mounted near the back of the amp box for short input wire lengths, and the control pot mounted on the front panel.
The amplifier needs an approximately 12k input load in order to be able to reference for minimized dc offset and minimized noise.
Typical datasheet designs of 20k pot in parallel with 22k resistor can make enough load.
Maybe the LDR makes only a 50k or 100k load, and that's why you had to "add to it" with a resistor?
Reference point:
input load 10k~15k
Interesting point:
Any bit of padding or losses at the input circuit, such as a series resistor, may decrease the load and it also may decrease the drive force of the source, whereupon the end result is not as clear at a distance but probably more pleasant if/when operated at closer range.
This sort of thing may account for the difference between your two volume controls. A small, creative loss, such as an input transformer, passive match with caps, LDR, and some preamp designs, can help serve as an "un-compressor" in making clearer sound at a shorter distance (oh, say about where you're sitting when you listen to your speakers). The method does decrease the range that the sound will carry clearly, so its not for outdoor use.
P.S.
Thank you for the story and application note on the LDR.
I'm thinking of making an attenuator for a gainclone that is a low value like 1K. The idea being to use a value so low that it wont require a preamp/buffer to sound great.
Do you think 1K is too low and do you think a low value like this would help the SQ? Maybe I will try 500 Ohm instead.
Also, has anyone compared different pot values like 5k vs 50k with gainclone?
Do you think 1K is too low and do you think a low value like this would help the SQ? Maybe I will try 500 Ohm instead.
Also, has anyone compared different pot values like 5k vs 50k with gainclone?
Hi Andrew. Yes, I'm sure that is correct. 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.
Low end source like computer or ipod could drive a 1K load so I don't see that load as much of a problem.
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.
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.
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.
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:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.