Hi all,
I make a own 3886 composite amp PCB.
All runs and looks ok.
Now I want to make a thd measurement with Soundcard....
I see with arta , good values and if I move a bit the cables around ...
A bit left to right moving on desk , the thd varies... So I play a bit we're to make the resistor connection for reduce level 1/10 to the soundcard input on PCB postion or direct on R load 4 Ohm... All that make a different thD.
It is spooky, make the speaker cable to R 4 Ohm a bit more to left or right ...THD
Varies....I make on all cables shield,but I see 3 cm unshield to connect to LS +- make a difference....
I have actually thd from 0.00086 to 0.0044 while moving cables on my desk here....while arta the runs 1 khz.
I mean ,I changed the cable positions on desk ,not the connection.
Hope you understand what I mean.
Any tips how to make a good stable measurement with Soundcard .
All cables , line in ,power , line out has a shield to one point .gnd PSU..
Shield is only in one direction connected.
I make a own 3886 composite amp PCB.
All runs and looks ok.
Now I want to make a thd measurement with Soundcard....
I see with arta , good values and if I move a bit the cables around ...
A bit left to right moving on desk , the thd varies... So I play a bit we're to make the resistor connection for reduce level 1/10 to the soundcard input on PCB postion or direct on R load 4 Ohm... All that make a different thD.
It is spooky, make the speaker cable to R 4 Ohm a bit more to left or right ...THD
Varies....I make on all cables shield,but I see 3 cm unshield to connect to LS +- make a difference....
I have actually thd from 0.00086 to 0.0044 while moving cables on my desk here....while arta the runs 1 khz.
I mean ,I changed the cable positions on desk ,not the connection.
Hope you understand what I mean.
Any tips how to make a good stable measurement with Soundcard .
All cables , line in ,power , line out has a shield to one point .gnd PSU..
Shield is only in one direction connected.
Last edited:
I have as voltage devider for the soundcard input..8k2 to 820 Ohm for reduce speaker output level .
The devider is now very close to soundcard input .
The devider is now very close to soundcard input .
Heh... Welcome to high end audio. 🙂
Make sure the connections to your dummy load are rock solid. I was fighting sporadic high THD with my dummy load for quite a while before I finally found out that the banana jacks on the dummy load were slightly corroded. I used brute force to clean them and they're good for a while now. A better long-term solution would be to rebuild that dummy load with better connectors (Neutrik speakON for example).
Tom
Make sure the connections to your dummy load are rock solid. I was fighting sporadic high THD with my dummy load for quite a while before I finally found out that the banana jacks on the dummy load were slightly corroded. I used brute force to clean them and they're good for a while now. A better long-term solution would be to rebuild that dummy load with better connectors (Neutrik speakON for example).
Tom
Hi Tom,
thanks for the tip.
Of course us the connection to the dummy load terrible.it is absolutely not the best has no gold contacts and is poor contacted....I will solder then to test .
Yes if I move the cables ,then I move also the cables from dummy load.
Curious is , that the 2k harmonic jumps in Arta then .... Playing,moving cables I can make the 2k up and down...
Also if I set , place the amp on head .
I mean change top and bottom of the amp on my desk .
All this make the 2k value r.a. 10 db up and down....
The values I list above is nearly that what my soundcard can in loopback.
So if I found a good place for amp and cables the good value above stay.
I will test to solder all cables now an take
A new look and report here.
👋
thanks for the tip.
Of course us the connection to the dummy load terrible.it is absolutely not the best has no gold contacts and is poor contacted....I will solder then to test .
Yes if I move the cables ,then I move also the cables from dummy load.
Curious is , that the 2k harmonic jumps in Arta then .... Playing,moving cables I can make the 2k up and down...
Also if I set , place the amp on head .
I mean change top and bottom of the amp on my desk .
All this make the 2k value r.a. 10 db up and down....
The values I list above is nearly that what my soundcard can in loopback.
So if I found a good place for amp and cables the good value above stay.
I will test to solder all cables now an take
A new look and report here.
👋
Of course,a picture is the best.
I will do some.
Meanwhile I soldered all Cables.
Because of the tip connections and after solder , I found out that the Speaker LS plus and minus cables makes the big difference , were they are going on my desk and were they are nearly to the PCB.... I found a position were the ThD is now like the loop test of the soundcard.
And I found a position were the THD is bad....
I will do some pic s for you...
I have the feeling,that my PCB get the noise from Speaker and is getting that into the circuit like noise....
So maybe my PCB is very sensitive for that....?!
I will make pic.
The PSU cables are twisted and soldered.
I will do some.
Meanwhile I soldered all Cables.
Because of the tip connections and after solder , I found out that the Speaker LS plus and minus cables makes the big difference , were they are going on my desk and were they are nearly to the PCB.... I found a position were the ThD is now like the loop test of the soundcard.
And I found a position were the THD is bad....
I will do some pic s for you...
I have the feeling,that my PCB get the noise from Speaker and is getting that into the circuit like noise....
So maybe my PCB is very sensitive for that....?!
I will make pic.
The PSU cables are twisted and soldered.
It's good that you're making a progress.
Exposing inputs and input stage to the output signal may cause some interference, but usually it happens when output currents are substantial.I have the feeling, that my PCB get the noise from Speaker and is getting that into the circuit like noise
Hi all.
I found out what happens.
After The Tip with connections checking and solder I found out that crossing PSU power and LS speaker out make that effect. Also the terrible Connection of LS dummy.
After solder and make LS cables away from PSU cabels then the THD was stable , and I have the same like use a loop test.
So THD was now 0.00080.... same as loop test the soundcard .
What i see is,that sometimes comes a 4k harmonic in Arta...not often , but a few times...
Any idea were a 4k results from ?
If soundcard does not and only sporadic in Arta...
In a new tread I make my PCB viewable for all, for Diskussion what I can do better...
I have some questions ,were IAM not sure about some topics...
At Tom, thanks for your tip...
With them I got a new point of view ,also thanks to gonkar
I found out what happens.
After The Tip with connections checking and solder I found out that crossing PSU power and LS speaker out make that effect. Also the terrible Connection of LS dummy.
After solder and make LS cables away from PSU cabels then the THD was stable , and I have the same like use a loop test.
So THD was now 0.00080.... same as loop test the soundcard .
What i see is,that sometimes comes a 4k harmonic in Arta...not often , but a few times...
Any idea were a 4k results from ?
If soundcard does not and only sporadic in Arta...
In a new tread I make my PCB viewable for all, for Diskussion what I can do better...
I have some questions ,were IAM not sure about some topics...
At Tom, thanks for your tip...
With them I got a new point of view ,also thanks to gonkar
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