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Old 21st September 2012, 09:13 AM   #351
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Quote:
Originally Posted by dtses View Post
thanks, Dario, for help
You're welcome

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Originally Posted by dtses View Post
could you please eleborate this? did you mean pot?
No, I mean connecting source hot to FE ground and source ground to FE hot.

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Originally Posted by dtses View Post
Once I connect socket to the mains, push the switch on button, FE doesn't start, it does only when the switch is turned off and on again.

The other a bit confusing thing is if you play with the mains switch for several times - FE doesn't turn on any longer, you should turn it off, wait for 2-3 secs and only then it's working.
There is something wrong, this beahviour is absolutely not normal.

I would check all resistors value and correct assembly.
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Old 22nd September 2012, 10:41 AM   #352
bcmbob is offline bcmbob  United States
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BTW: Don't know if anyone else was a little confused about the use of the HSGND pad and the message nearby. Dario explained - if the heatsink is part of the (safety earth connected) chassis or has continuity to it, that pad should not be connected.

If the heatsink is electrically isolated from the chassis, the HSGND connection should be used - though it may not be absolutely necessary. Simple enough even for me.
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Old 22nd September 2012, 08:37 PM   #353
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Originally Posted by bcmbob View Post
dtses, are you using sockets in your build? If so, are they maintaining good contact? A loose fit can easily interrupt the circuit.
hi mate,
I'm pretty sure that the contact is good and tight, this shouldn't be the problem.

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I would check all resistors value and correct assembly.
indeed that helped checked all resistors and R2 turned out to be 270R instead of 10k, I should have checked that in the shop, their mistake. At least one issue is solved - relay and LED works perfectly now!

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Originally Posted by bcmbob View Post
BTW: Don't know if anyone else was a little confused about the use of the HSGND pad and the message nearby. Dario explained - if the heatsink is part of the (safety earth connected) chassis or has continuity to it, that pad should not be connected.

If the heatsink is electrically isolated from the chassis, the HSGND connection should be used - though it may not be absolutely necessary. Simple enough even for me.
thanks, Bob! pretty clear it's now!

However, I assume the problem is somewhere else as I have tied to run FE simply with a single pot nothing else and I've got the same grounding hum. I do not use any chassis or metal things that could cause that, so I'm really confused now...

There are several things that I would like to say more:
-testing assembled channel for several hours I've got only 1.6mV DC offset, actually didn't even expect it to be that low
-with rather trivial heatsink (it's only temporary on the pics) amp gets only to some 40-45c, not more.
-the PCB is so splendid, I've got the most pleasant soldering experience I've ever had! I would compare it with my favorite Italian vine Brunello di Montalcino. Perfect look, fragrant smell, unforgettable and very distinctive taste, feeling that you are drinking/ soldering indeed something very special! DARIO, don't know how did you manage, but it's outstanding! both the pbc and the work you've done!
-I have burned R11 (1 ohm) once more time by my mistake. Perhaps it would be better to use some 1w or even 2w resistor here?

One thing I was really disappointed:
not sure if that is so or that grounding sound I experience somehow affects on that, but I feel some kind of bass leakage in comparison to my modified Restek Fantasy that is kind of reference for me. I feel it's not so deep and articulated in FE and the bad thing is that it's quite noticeable. Again, not sure if it really should be so...Perhaps Dario could elaborate this

I have attached the pics. There are still several parts I'm waiting for, so temporary put these big 10k uf caps, few resistors, heatsink with a fan (didn't even turn it on, no need).
Attached Images
File Type: jpg IMG_0117.jpg (887.6 KB, 222 views)
File Type: jpg IMG_0118.jpg (794.5 KB, 206 views)
File Type: jpg IMG_0121.jpg (739.8 KB, 200 views)
File Type: jpg IMG_0123.jpg (892.8 KB, 180 views)
File Type: jpg IMG_0125.jpg (726.2 KB, 184 views)
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Old 22nd September 2012, 09:59 PM   #354
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Default Hum 1

Dtses,

I feel for you. It's frustrating to have a problem like this and not find the reason. I looked but didn't see anything except the fan. Hopefully others can notice something else as I am having no hum issues, nor lack of bass. Regarding the fan, is it possible that the fan is introducing the hum?

Jac
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Old 22nd September 2012, 10:41 PM   #355
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Default Hum and Transformers

I've been curious about measuring hum and have given it a try. It seems like there are build related hum problems (which I can't help with) and base design hum that is in every amplifier at some level. I want to qualify everything here by saying that I don't have the experience, expertise, or equipment that some of our more expert forum member have. If I am testing or interpreting results incorrectly, I am totally open to suggestion.

First, the limitations of my equipment. I am using a program (LAUD v3) that was design for speaker testing and a sound card that has a 97 dB S/N (note bad but not good enough), a 20 bit sample size, and a max of 48 kHz sampling rate which limits the results to 20 kHz.

Most of my hum testing was done with RTA over a range of 20 to 1000 Hz as this should cover most of the hum related noise. I did look out to 20 kHz and found the upper frequencies quiet.

Although I looked at a range of resistance across the inputs, most of my testing was done with the inputs shorted as shown in this picture of the test board. I did all of my testing by measuring the output of one channel.

Click the image to open in full size.

My first step was to measure the frequency response of the amplifier from 20 to 20k Hz. Naturally, the input was not shorted for this test. The input signal was a 1 volt sine wave swept though the frequency range. The vertical scale is 1 dB/div. Note that there is no noise at 60 or 120 Hz indicating a lack of hum compared to the input signal.

Click the image to open in full size.

I then measured the output of the amp with no signal and a shorted input. This approach used the RTA instrument which gave me trouble saving it's graphs, but I recorded the results. In this configuration, I was able to measure hum at 60 Hz of 42 dBmV which converts to 135 mV at the output. To put this in perspective, if you had an 8 ohm, 90 dB sensitivity speaker, 135 mV would produce about 5 dB if I did my math right. The next peak in the noise curve was at about 320 Hz and 14 mV. If my methods are correct, I would say that the FE is quite good for hum.

Both Mauro and Klaus have hinted that one transformer per board is a good idea for hum due to the FE's dual diode bridge in the power supply. At one point Klaus was going to explain the theory, but the conversation moved on. I was interested to see if I could measure any difference in hum between monoblocks and 2 FE's power from one transformer in parallel. Please note that my experiment is not conclusive because I don't have a metal chassis nor any ground connection between the power supply/mains and the signal ground.

My result was no measurable difference between 2 monoblocks and 1 transformer/2 FE. Pardon the blurry picture, but it shows the parallel power supply.

Click the image to open in full size.

Finally, I explored some of the ideas suggested by Klaus and others. I measured the hum with the input shorted, with a 10 ohm resistor, with a 100k ohm resistor, and open circuit. All measured the essentially the same. I also used a clip lead to jumper R11 which Klaus believes amplifies noise. It may be possible that it amplifies noise, but it does not appear to be in the path of any hum energy as the hum voltage at the output remained constant.

I hope this is of interest to others. Are there other configurations I should have checked?

Jac
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Old 22nd September 2012, 11:40 PM   #356
bcmbob is offline bcmbob  United States
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That's great Jac, Glad someone got started. Just to be clear, you are talking only about measured hum - right? Can you hear anything from your speakers that correlates to the peaks? Is your sub on line yet?
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Old 23rd September 2012, 12:37 AM   #357
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Originally Posted by dtses View Post
relay and LED works perfectly now!
Fine

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Originally Posted by dtses View Post
However, I assume the problem is somewhere else as I have tied to run FE simply with a single pot nothing else and I've got the same grounding hum.
Did you checked hot and ground input?

Connectors?

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Originally Posted by dtses View Post
-testing assembled channel for several hours I've got only 1.6mV DC offset, actually didn't even expect it to be that low
Really a good result.

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Originally Posted by dtses View Post
the PCB is so splendid, I've got the most pleasant soldering experience I've ever had! (...) DARIO, don't know how did you manage, but it's outstanding! both the pbc and the work you've done!
Thanks!

Yes, the italian PCB maker done a much better job than the chinese one I've used for beta boards. I'm really satisfied (the italian product cost much more, though)

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Originally Posted by dtses View Post
-I have burned R11 (1 ohm) once more time by my mistake. Perhaps it would be better to use some 1w or even 2w resistor here?
No, that resistor is also a sort of safety measure... it's better to change a single resistor than much more costly parts...

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Originally Posted by dtses View Post
not sure if that is so or that grounding sound I experience somehow affects on that, but I feel some kind of bass leakage in comparison to my modified Restek Fantasy that is kind of reference for me.
You're using a different BOM so result may vary... but on this post on the beta thread you can see that I was using a Takman too and had similar problems.

Simply reverse it.
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Old 23rd September 2012, 01:12 AM   #358
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That's great Jac, Glad someone got started. Just to be clear, you are talking only about measured hum - right? Can you hear anything from your speakers that correlates to the peaks? Is your sub on line yet?
Bob,

You are correct. This is only about hum. To be more specific, there is no music, there are no speakers or subwoofer. It is just the FE amp, on a bench, mostly with the no signal going in and the input shorted to audio ground. All I am doing is measuring voltage at the output that is coming from the power supply through the amp.

The graph in the picture also doesn't have any music or sound. It does have an input signal and, in that sense, is more typical of when you play music.

As for hearing the 60 Hz hum, I don't think you would be able to, were speakers connected. A quiet room is, maybe, 40 dB. I was calculating that a relatively efficient speaker (90 dB) would only put out 5 dB at 60 Hz. Of course, since the 5 dB is calculated from the 90 dB sensitivity (which is at 1 meter), then the 5 dB is also at 1 meter. Of course, if you could get your ear 10 mm from the dust cap, then the 5 dB would be 45 dB and might be just audible. Still, pretty low hum.

Again, I'm not sure I'm measuring this the best possible way. Any expert comment?

Jac

Last edited by lehmanhill; 23rd September 2012 at 01:22 AM.
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Old 23rd September 2012, 01:13 AM   #359
Bill_P is offline Bill_P  United States
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First, the limitations of my equipment. I am using a program (LAUD v3) that was design for speaker testing and a sound card that has a 97 dB S/N (note bad but not good enough), a 20 bit sample size, and a max of 48 kHz sampling rate which limits the results to 20 kHz.
Your measurement setup might induce ground loops into the system and give false readings. If you use a laptop, disconnect everything from it that isn't directly needed for the measurement and run on battery only.

Quote:
My first step was to measure the frequency response of the amplifier from 20 to 20k Hz. Naturally, the input was not shorted for this test. The input signal was a 1 volt sine wave swept though the frequency range. The vertical scale is 1 dB/div. Note that there is no noise at 60 or 120 Hz indicating a lack of hum compared to the input signal.
Is that 1 volt RMS, peak, or peak to peak? Is there an attenuator anywhere in the input signal path? 1 volt RMS should put the amplifier well into clipping.

Quote:
I then measured the output of the amp with no signal and a shorted input. This approach used the RTA instrument which gave me trouble saving it's graphs, but I recorded the results. In this configuration, I was able to measure hum at 60 Hz of 42 dBmV which converts to 135 mV at the output. To put this in perspective, if you had an 8 ohm, 90 dB sensitivity speaker, 135 mV would produce about 5 dB if I did my math right. The next peak in the noise curve was at about 320 Hz and 14 mV. If my methods are correct, I would say that the FE is quite good for hum.
135 mV is very high for hum output. I calculate that to be 2.2mW which should produce an SPL of 64dB. If you don't hear hum from the speaker, the measurement is wrong. Spectral peaks should be at 60 Hz harmonics - 120, 180, 240, 300, 360. There should be no hum related peak at 320.
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Old 23rd September 2012, 09:08 AM   #360
AndrewT is offline AndrewT  Scotland
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AC output of the power amp with the input shorted should be less than 1mVac.
It is better if you can get that output voltage down below 0.3mVac.

I get virtually all my monoblock no chassis amps to read 0.0mVac, indicating ~<0.05mVac.
But some amplifiers can be quieter, I have no idea if any of my builds are quieter, because I can't measure any lower.

I suspect you conversion
Quote:
I was able to measure hum at 60 Hz of 42 dBmV which converts to 135 mV at the output.
is wrong.
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