Gaetan,
Many thanks, you have done Kenji (and other Aspen owners!) a great service.
Kenji,
If you connect just one channel to the preamp, and all is quiet, and hum appears when you connect the second channel, then yes, you have a ground loop through the preamp.
In this situation you need only disconnect the signal ground at the pcb on ONE channel.
If this works, you have identified and solved the problem.
Again, thanks to Gaetan!
Hugh
Many thanks, you have done Kenji (and other Aspen owners!) a great service.
Kenji,
If you connect just one channel to the preamp, and all is quiet, and hum appears when you connect the second channel, then yes, you have a ground loop through the preamp.
In this situation you need only disconnect the signal ground at the pcb on ONE channel.
If this works, you have identified and solved the problem.
Again, thanks to Gaetan!
Hugh
Hello Kenji
Do as Hugh suggested. "If you connect just one channel to the preamp, and all is quiet, and hum appears when you connect the second channel, then yes, you have a ground loop through the preamp."
Now, if it is a ground loop, since a ground link on the 2 RCA input plugs
would be good and made your amp work good and quiet with any preamp connected to the amp, you need to do as I describe on the photo I've done.
On one PCB only, you cut the ground wire of the input wire comming from one RCA input plugs, after that you solder a wire to link the ground tabs of the 2 RCA input plugs.
After those mods, you can check again with the preamp connected to your amp to ear if all is quiet and there is no hum.
I'm french speaking, so I hope my english explanation are ok.
Bye
Gaetan
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Hello Kenji
Depending of the ground schema of your passive preamp you can still have a ground loop and noise, so it still better to do the modification that I've suggested you in my previous post.
And for the volume here is a text from the Aspen web site for a volume control for the Aksa amp;
"Generally, it is far too expensive to manufacture a compact logarithmic, wirewound pot. Furthermore, the wire used on a typical 50K or 100K pot is very fine, with many turns, and this creates high inductance. Sadly this makes such pots unsuited for audio, since at 20K the response is at least 2.5dB down and this rolloff is particularly noticeable, particularly on percussion.
You can law fake a linear 100 kOhm pot with a simple 15 kOhm resistor from middle terminal (wiper, or centre; output) to ground. The 47K input impedance of the AKSA combines with this resistor to give around 11K4 from wiper to ground. Signal input is taken to the top terminal, bottom terminal is earthed, and the middle (wiper) terminal is then taken to the AKSA input. This gives you an excellent and progressive volume control, with a minimum system input impedance (with the 47kOhm Zinof the AKSA) of 10K2 kOhm (at full volume), a maximum of 100 kOhm (at lowest volume), and a full range with additional sensitivity in the earlier stages for easy adjustment during quiet listening."
Bye
Gaetan
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By the way what is the significance of a 'log' volume pot? I have read that the ear responds in a logarithmic fashion to sound however for practical purposes any function, be it linear, log, or whatever gives us the same discrete volume settings, so why do people insist on and go to so much trouble in fabricating a logarithmic pot?
If you have a logarithmic pot, and the A-B connection is log, then the other connection HAS to be the inverse of this, which is exponential. This is asymmetric. I know this doesn't completely answer your question.
log pots are not good only for audio. Sometimes you need a logarithmic control knob for a special type of circuit. Then we came out with "audio taper" which was convenient for audio amps. And then, finally, we came out with "fake log", which wasn't publicly marketed but made things easier for the factories.
The pot's function is a voltage divider. If you disconnect the grounded side, its whole curve changes depending on the impedance of the amp input.
- keantoken
log pots are not good only for audio. Sometimes you need a logarithmic control knob for a special type of circuit. Then we came out with "audio taper" which was convenient for audio amps. And then, finally, we came out with "fake log", which wasn't publicly marketed but made things easier for the factories.
The pot's function is a voltage divider. If you disconnect the grounded side, its whole curve changes depending on the impedance of the amp input.
- keantoken
can you just explain what you mean more clearly? I am confused by what we are plotting, the ouput voltage as a function of distance or resistance or what?
If we take a discrete example say with 3 inputs xohms= x_1, x_1+x_2 and x_1+x_2+x_3. The output is F(x).
When we swap the wires we automatically swap the inputs which become x_3, x_2+x_3 and x_1+x_2+x_3.
I cant see how we can calculate G(x) such that G(F(x)) gives us back the original x's.
This is the diagram I refer to:
A---B---C---D
x_1 x_2 x_3
Voltage V is applied between A and D and the x's are the resistors.
Thanks.
Just in case this has been missed, can someone settle my query once and for all please?
Thankyou.
Kenji, 53 posts have gone by and you have decided to stay put, just because your troubles have ceased temporarily. I had briefly followed your other thread posts on your AKSA experience.
With whatever setup you have at the moment, minus the hum and the buzz, may I ask as to what should be your logical conclusion? While you figure that out, I would endear you to ask an experienced tech or diyer to completely replace/redo the wiring in your AKSA amp. Having learned such things the hard way over the last two decades and more, I can tell you assuredly that you are getting poorer performance than with a well executed amp. You had asked what difference, a piece of ground wire could cause to the performace - well, it does make a world of difference to subjective performance as well as measured performance most often, if not always.
I cannot recall whether it was T.Giffard or T.Giesberts who reported in Elektor that moving the RETURN wire from Star Ground to Ground on Amp PCB resulted in much lowered measured THD.
See what Douglas Self has to say on the NFB take-off point on a PCB and you will realise that there are points in a circuit which are more critical than others.
Now it is up to you to choose to either be proactive and seek help or wait for the next low tide.
With whatever setup you have at the moment, minus the hum and the buzz, may I ask as to what should be your logical conclusion? While you figure that out, I would endear you to ask an experienced tech or diyer to completely replace/redo the wiring in your AKSA amp. Having learned such things the hard way over the last two decades and more, I can tell you assuredly that you are getting poorer performance than with a well executed amp. You had asked what difference, a piece of ground wire could cause to the performace - well, it does make a world of difference to subjective performance as well as measured performance most often, if not always.
I cannot recall whether it was T.Giffard or T.Giesberts who reported in Elektor that moving the RETURN wire from Star Ground to Ground on Amp PCB resulted in much lowered measured THD.
See what Douglas Self has to say on the NFB take-off point on a PCB and you will realise that there are points in a circuit which are more critical than others.
Now it is up to you to choose to either be proactive and seek help or wait for the next low tide.
What you say is the same thing I've experienced, where some sources are dead quiet and others hum badly. Does this suggest it is something to do with the design?
Why do the instructions tell me to connect both channel pcbs to the rca ground yet Gaetan advises me to disconnect one and link the rcas together? I am confused.
Stop!!
Have you found the grounding error? and solved it?
Do that first.
Then we may look at your new topic.
Hello Andrew
Looking at a video of the case interior and connections of his Aksa amp done by Professor smith, I have found a ground loop wen connected to a preamp and some cd players.
Look at my post;
http://www.diyaudio.com/forums/aksa/151644-preamp-aksa-55-a-4.html#post1953378
I agree with Samuel Jayaraj, Professor smith should not wait at the next hum and moise problems and should do the modifications I've suggest in this other post;
http://www.diyaudio.com/forums/aksa/151644-preamp-aksa-55-a-5.html#post1953640
Bye
Gaetan
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Why do the instructions tell me to connect both channel pcbs to the rca ground yet Gaetan advises me to disconnect one and link the rcas together? I am confused.
If 'there is a ground loop' why does it hum with some cd players but not with others?
I need the answers to these questions before I start fiddling about with it. Does Hugh know the answer?
If 'there is a ground loop' why does it hum with some cd players but not with others?
I need the answers to these questions before I start fiddling about with it. Does Hugh know the answer?
Hello again Kenji
Not all preamps and cd players do have the same types of grounds connections, so some will do a ground loop with your Aksa amp.
You need to disconnect one input wire ground on the pcboard because it will break the ground loop, and you need link the rcas plugs together because somes preamps and cd players will not have the ground connection link the way it need to have both channel playing.
Look at my post #43
PLEASE Kenji, will you have some confidence in us, since me, Hugh, Bigun, Nico, and AndrewT, we have lot of experience in diy projects, why would we want to confuse you, we just want to help you !!
If you still turn arround like that, allmost nobody will want to help you again !!!
Bye
Gaetan
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