Peter,
After several days I just found something with my AMP.
I can hear slight hiss from speaker. At first I thought it was because the music file (I am using AMP with computer line-out) was not recorded with hi-fi qualification. Then I off the music and turn volume up to maximum, hiss can be heard from short distance.
Doubted that is because of computer sound card (Realtek HD onboard), I pluged the jack off from computer, no input. Then I turned the volume again. Hiss can be heard as well.
I realized that the hiss came from tweeter only. The low freq speaker is completely quiet.
What is the cause of hiss? Is there any problem with my assembling?
Thanks,
HT
After several days I just found something with my AMP.
I can hear slight hiss from speaker. At first I thought it was because the music file (I am using AMP with computer line-out) was not recorded with hi-fi qualification. Then I off the music and turn volume up to maximum, hiss can be heard from short distance.
Doubted that is because of computer sound card (Realtek HD onboard), I pluged the jack off from computer, no input. Then I turned the volume again. Hiss can be heard as well.
I realized that the hiss came from tweeter only. The low freq speaker is completely quiet.
What is the cause of hiss? Is there any problem with my assembling?
Thanks,
HT
Ah,
After turning the volume all the way down, I still hear a little hiss with my ear quite close to the tweeter. Low freq is quiet as well.
I asked my brother to listen and if he could feel the hiss. He did not. He blamed my ears got problem with noise from environment.
But I don't think so because just moving ears from tweeter to low freq speaker, I can distinguish hiss and quiet clearly.
Being curious about hiss, however, I still love to listen to the sweatness from this amp with jbl2080. It seems that sound becomes more rounding from now.
After turning the volume all the way down, I still hear a little hiss with my ear quite close to the tweeter. Low freq is quiet as well.
I asked my brother to listen and if he could feel the hiss. He did not. He blamed my ears got problem with noise from environment.
But I don't think so because just moving ears from tweeter to low freq speaker, I can distinguish hiss and quiet clearly.Being curious about hiss, however, I still love to listen to the sweatness from this amp with jbl2080. It seems that sound becomes more rounding from now.
Just a minute, I think I wrongly describe the symptom. It should be hum, slightly hum, not hiss. My apology! In fact I tried to plug in-out to the audio out on my computer several time. No strange sound. Compare to my old cheapo Altec Lansing, everyone can hear hiss from every corner in my room, even when I rotated the jack or touched it by my bare hand. With AL set, every time turning on-off with volume >1/2 up is a big crash to my ears.
Back to the AMP, the first day turned it on, I did not hear hum. Now, it seems that my ears become better or worse, then I hear hum.
What cause hum? Please help me.
Thanks
HT
Back to the AMP, the first day turned it on, I did not hear hum. Now, it seems that my ears become better or worse, then I hear hum.
What cause hum? Please help me.
Thanks
HT
Ah,
After turning the volume all the way down, I still hear a little hiss with my ear quite close to the tweeter. Low freq is quiet as well.
I asked my brother to listen and if he could feel the hiss. He did not. He blamed my ears got problem with noise from environment.
Being curious about hiss, however, I still love to listen to the sweatness from this amp with jbl2080. It seems that sound becomes more rounding from now.
Tweeters always produce some hiss, and depending on listeners perception it may be more or less of a noise. But if it's not heard from your normal listening position I wouldn't be loosing sleep about it.
Andrew,
I attached the jblJ2080 catalog for your reference. It's 89dB.
No input:
-16mV DC on left and -24mV DC on right @ minimum
-57mV DC on left and -65mV DC on right @ maximum
input shorted: i don't get how to do that. You mean to short ground with signal?
HT
Peter,
It's wise advice. I cannot wake the neighbors up at midnight. I'd better sleep now and will listen tomorrow. Normal listening position... OK, I do remember. Will report then.
Have a nice day!
HT
89dB/W @ 1m is not particularly onerous.
The sound outputs from the drivers with the power amp input shorted, should appear silent at 50mm from the treble dome and from the bass cone.
Try turning everything else off in the room and wait till the traffic outside has gone away, and the wind has stopped blowing.
1mVac into an 8ohm speaker is ~1uW (-69dB ref 1W)
An 89dB/W speaker will reproduce that as a 20dB SPL @ 1m.
at 50mm the SPL will be ~ 46dB or about 20dB above the threshold of hearing (in the middle range).
0.1mVac will be ~@ the threshold of hearing @ 50mm
That is approximately where a chipamp should be. I have most of mine below 0.05mVac, but this is with a DMM that does not have the correct 20kHz/100kHz filter. It reads low at higher frequencies.
Use an RCA plug to short the RCA input socket.
remove the back of the plug and solder a short from RCA ground/return to RCA pin/hot.
The sound outputs from the drivers with the power amp input shorted, should appear silent at 50mm from the treble dome and from the bass cone.
Try turning everything else off in the room and wait till the traffic outside has gone away, and the wind has stopped blowing.
1mVac into an 8ohm speaker is ~1uW (-69dB ref 1W)
An 89dB/W speaker will reproduce that as a 20dB SPL @ 1m.
at 50mm the SPL will be ~ 46dB or about 20dB above the threshold of hearing (in the middle range).
0.1mVac will be ~@ the threshold of hearing @ 50mm
That is approximately where a chipamp should be. I have most of mine below 0.05mVac, but this is with a DMM that does not have the correct 20kHz/100kHz filter. It reads low at higher frequencies.
Use an RCA plug to short the RCA input socket.
remove the back of the plug and solder a short from RCA ground/return to RCA pin/hot.
Here the measurement with short input:
-16mV DC on left and -24mV Dc on right @ minimum
-15mV DC on left and -23mV DC on right @ maximum
Andrew, I heard hum at about 1 finger distance, 50mm approximately.
Cannot hear hum from normal listening position with volume set at low now (midnight). But will try louder tomorrow. Also will try with no device on but I don't think I will be so serious about it.
More information for your comments: I used CAT5 UTP cable (which has been used for computer network for >2 years) for all signal connection in AMP. Peter suggested CAT5 is fine. I used wire with its plastic shield.
For grounding, I used the core from 75ohm coaxial. Star ground. In fact, I did not make it star at the middle point between two amp board, but from the one end of the ground copper wire.
Power wire: normal wire, newly bought with 3 wires N-L-E, fuse integrated on power plug (Singapore standard)
I think it OK, right?
HT
-16mV DC on left and -24mV Dc on right @ minimum
-15mV DC on left and -23mV DC on right @ maximum
Andrew, I heard hum at about 1 finger distance, 50mm approximately.
Cannot hear hum from normal listening position with volume set at low now (midnight). But will try louder tomorrow. Also will try with no device on but I don't think I will be so serious about it.
More information for your comments: I used CAT5 UTP cable (which has been used for computer network for >2 years) for all signal connection in AMP. Peter suggested CAT5 is fine. I used wire with its plastic shield.
For grounding, I used the core from 75ohm coaxial. Star ground. In fact, I did not make it star at the middle point between two amp board, but from the one end of the ground copper wire.
Power wire: normal wire, newly bought with 3 wires N-L-E, fuse integrated on power plug (Singapore standard)
I think it OK, right?
HT
Hi everyone, i need a little advice concerning my dual mono gainclones. I have had my amps up and running for about 6 weeks now and all was fine, i now have given a small tweak replacing the rca input and binding posts + wires to one amp. When connecting to mp3 player for tests the music can be heard very very faintly at full volume, have i blown something here or could it be a mismatch of components maybe. Any help would be much appreciated.
regarts Lee
regarts Lee
Hi Peter, thanks for speedy reply. I have changed signal wires back to origanal and it now seems to be working again. Being a noob not 100% sure on where to use multy meter, but with probes on binding posts i am getting a reading of - 0.32 on first amp and - 0.29 on the one ive just tweaked, im sure they were both - 0.32 before mod. Hope these readings make sense, can you think of any reason for variation in readings or if it will make much of a difference to sound.
regards lee
regards lee