Hi,
yesterday i compared my deskgainclone to a temporary MDF Plate setup with one of veterans 4780 boards.
The 4780 was running with an 20V Toroid and 2x 2200µF Elkos, Panasonic FC. No Snubber.
The two 3886ers where running with an 18V Toroid, 2 older 16000µF Elkos "Sprague Powerlytic" i got very cheap with others from ebay and 100µF//100nF at the pins. Snubber as described at chipamp.com.
I knew my 3886ers had no good bass, but they ran with my desk speakers, 2-way, with little Visaton W170-S Bassdrivers.
Now I tested both with my old Canton speakers, with 12inch woofers.
Result:
The 4780 gave good bass... little soft, but OK.
The 3886 gave no bass at all.
So i enabled my software equalizer and turned the 100Hz button to max boost -> makes absolutely no difference with the 3886. Simply no bass responce at all.
I did no futher tests, but i suspect these old sprague cans...
Any Idea how to check them?
By the way:
Do u know any better Snubber PSU design for about 10000µF than the one from Chipamp.com?
yesterday i compared my deskgainclone to a temporary MDF Plate setup with one of veterans 4780 boards.
The 4780 was running with an 20V Toroid and 2x 2200µF Elkos, Panasonic FC. No Snubber.
The two 3886ers where running with an 18V Toroid, 2 older 16000µF Elkos "Sprague Powerlytic" i got very cheap with others from ebay and 100µF//100nF at the pins. Snubber as described at chipamp.com.
I knew my 3886ers had no good bass, but they ran with my desk speakers, 2-way, with little Visaton W170-S Bassdrivers.
Now I tested both with my old Canton speakers, with 12inch woofers.
Result:
The 4780 gave good bass... little soft, but OK.
The 3886 gave no bass at all.
So i enabled my software equalizer and turned the 100Hz button to max boost -> makes absolutely no difference with the 3886. Simply no bass responce at all.
I did no futher tests, but i suspect these old sprague cans...
Any Idea how to check them?
By the way:
Do u know any better Snubber PSU design for about 10000µF than the one from Chipamp.com?
Hi,
The 4780 has 2.2µF and the 3886 nothing.
Both are non-inverted, standart circuit like this one
http://www.audio.webd.pl/pdf/lm4780_sch.pdf
No capacitors in the feedback. And the 3886 has no 1K at the input.
The 4780 has 2.2µF and the 3886 nothing.
Both are non-inverted, standart circuit like this one
http://www.audio.webd.pl/pdf/lm4780_sch.pdf
No capacitors in the feedback. And the 3886 has no 1K at the input.
Hi,
what value of DC blocking capacitor is fitted to the source?
Are you confirming that the 3886 is DC coupled at both the input and at the negative feedback?
and no RF filter either?
But it does seem odd that although both the amps are assembled similarly and yet they appear to perform differently.
Is there any possibility that Zin resistors R1 & 3 are the wrong values?
The major difference left to examine further is the PSU.
Maybe your original thoughts pointing to the old smoothing caps holds the key.
Would it be possible to swap over the PSUs?
what value of DC blocking capacitor is fitted to the source?
Are you confirming that the 3886 is DC coupled at both the input and at the negative feedback?
and no RF filter either?
But it does seem odd that although both the amps are assembled similarly and yet they appear to perform differently.
Is there any possibility that Zin resistors R1 & 3 are the wrong values?
The major difference left to examine further is the PSU.
Maybe your original thoughts pointing to the old smoothing caps holds the key.
Would it be possible to swap over the PSUs?
Hi I am usign both LM4780 and LM3886 gainclones also. They works in very similar configurations;
Non Inverted,
21Avv (20K/1K/47u)
4u7 MKS type DC decoupling capacitor,
20K input parallel and 1K series resistor,
10K Tandem A curve ALPS potentiometer,
Bass boosted (8dB @ 20Hz) linkwitz NFB preamp with 4 Avv (LM833)
One (LM4780) feeding by a pair of MW 2x24 V SMPS and the other by 2x18v 250VA EI type transformer plus 8xBY80-200 + 10,000uF Philips caps.
Both aöps has 2200u+10u+100n on board snubbers.
I am testing them with my Wharfedale Diamon 9.6 floorstanding speakers.
I can hear some differences between them but not in bass. All I can say is LM3886 is more noisy because of transformer PSU, have more detailed mids and trebles but not exactly lees bass then the other.
There should be a design differences between two amplifiers if there are differences.
Non Inverted,
21Avv (20K/1K/47u)
4u7 MKS type DC decoupling capacitor,
20K input parallel and 1K series resistor,
10K Tandem A curve ALPS potentiometer,
Bass boosted (8dB @ 20Hz) linkwitz NFB preamp with 4 Avv (LM833)
One (LM4780) feeding by a pair of MW 2x24 V SMPS and the other by 2x18v 250VA EI type transformer plus 8xBY80-200 + 10,000uF Philips caps.
Both aöps has 2200u+10u+100n on board snubbers.
I am testing them with my Wharfedale Diamon 9.6 floorstanding speakers.
I can hear some differences between them but not in bass. All I can say is LM3886 is more noisy because of transformer PSU, have more detailed mids and trebles but not exactly lees bass then the other.
There should be a design differences between two amplifiers if there are differences.
No Bass
What kind of sound card? and interface?? I had some good sound cards measure very poorly in frequency respone and noise.
Also I had one person that had a lot of ground loop problems between there PC and amp that used a transformer for isolation that lopped of almost eveything below 70Hz........ just a thought.
What kind of sound card? and interface?? I had some good sound cards measure very poorly in frequency respone and noise.
Also I had one person that had a lot of ground loop problems between there PC and amp that used a transformer for isolation that lopped of almost eveything below 70Hz........ just a thought.
Hi Andrew,
In fact I dont know the noise measurement methode. But as I heard from somebody, I need a pink noise source for it. However I dont have any.
But I made a test in last week. I work for a environment laboratory. And we have a calibrated Sound Pressure Level Meter which we use for industrial noise meusurements. Anyway, I coupled it to my speakers tweeter with its special adapter and connect my speaker to all my amplifiers by order,
LM4780 has 28dB
LM3886 has 36dB
RAS100 (Nico's MOSAMP) has 24dB
Noise in a band while all inputs shorted to signal ground. But I have to warn you one of them (LM4780) was feeding by a SMPS and the others were with transformer.
I know that; its not a scientific measuring but at least I have a data about noise of my amps.
In fact I dont know the noise measurement methode. But as I heard from somebody, I need a pink noise source for it. However I dont have any.
But I made a test in last week. I work for a environment laboratory. And we have a calibrated Sound Pressure Level Meter which we use for industrial noise meusurements. Anyway, I coupled it to my speakers tweeter with its special adapter and connect my speaker to all my amplifiers by order,
LM4780 has 28dB
LM3886 has 36dB
RAS100 (Nico's MOSAMP) has 24dB
Noise in a band while all inputs shorted to signal ground. But I have to warn you one of them (LM4780) was feeding by a SMPS and the others were with transformer.
I know that; its not a scientific measuring but at least I have a data about noise of my amps.
Hi,
DMM set to 200mVac on the power amp outouts with the inputs shorted should give readings in the range 0.0mVac to 1mVac.
I hope not worse, because 1mV is pretty poor, at -86db below max output.
These DMM readings always look better than real audioband rms measurements due to lack of sensitivity to high frequency signals in the DMM AC measuring circuits.
DMM set to 200mVac on the power amp outouts with the inputs shorted should give readings in the range 0.0mVac to 1mVac.
I hope not worse, because 1mV is pretty poor, at -86db below max output.
These DMM readings always look better than real audioband rms measurements due to lack of sensitivity to high frequency signals in the DMM AC measuring circuits.
Andrew,
I already done that test before. And,
For my LM4780; I have 0.2mV DC offset and 12-18mV AC signal on each channel (swinging)
For my MOSAMP; I have 0mV DC offset and 8mV on right (10mV on left) AC signal on each channel (stable).
I havent got any AC signal test for LM3886.
During these tests all inputs were shorted to GND.
PS: My DMM has no AC mV.
I already done that test before. And,
For my LM4780; I have 0.2mV DC offset and 12-18mV AC signal on each channel (swinging)
For my MOSAMP; I have 0mV DC offset and 8mV on right (10mV on left) AC signal on each channel (stable).
I havent got any AC signal test for LM3886.
During these tests all inputs were shorted to GND.
PS: My DMM has no AC mV.
Hi all,
could Dx's AC measurements be right?
DMM noise measurements of 8mVac to 18mVac seems far too much.
Is there a problem with the measurement technique or with the amps?
I have music on low and the output from the power amps is of the order 10mVac to 50mVac.
For comparison and using the SPL measurement.
18mVac (4780) is -44dbW
Sending this noise signal to a 86db/W speaker will give an SPL of about 42db. That does not compare with a sound measurement of 28db from Dx's earlier post. Even 12mVac gives 38db.
could Dx's AC measurements be right?
DMM noise measurements of 8mVac to 18mVac seems far too much.
Is there a problem with the measurement technique or with the amps?
I have music on low and the output from the power amps is of the order 10mVac to 50mVac.
For comparison and using the SPL measurement.
18mVac (4780) is -44dbW
Sending this noise signal to a 86db/W speaker will give an SPL of about 42db. That does not compare with a sound measurement of 28db from Dx's earlier post. Even 12mVac gives 38db.
Hi
I dont know, it's my onboard soundchip
But since both circuits have nearly the same input impedance, that cannot make the difference. I also tested with a yamaha CD-Player, the results where the same.
Yes.
My 3886 has a little noise too. But it's funny, when I stop the CD-Player and turn the volume potentiometer to maximun, it's gone.
Greetings,
Stephan
I dont know, it's my onboard soundchip
But since both circuits have nearly the same input impedance, that cannot make the difference. I also tested with a yamaha CD-Player, the results where the same.
Yes.
I'm going to do that when i have a free minute.
My 3886 has a little noise too. But it's funny, when I stop the CD-Player and turn the volume potentiometer to maximun, it's gone.
Greetings,
Stephan
The CDP probably goes into mute when there are no bits to process. This makes it's output 0v.Bassterror said:
When you turn the passive pot to maximum you are connecting the input of the amp directly to the CDP output.
The amp now sees Rs~=100r. This makes it quiet.
Now try turning the passive pot to minimum volume. Is it as quiet as at maximum? That would confirm that you power amp likes to see a low Rs at it's input.
Maybe your pot value is too high, or maybe you should consider adding a buffer before and after each channel of your pot.
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