NO its definately a buzzing sound. because its so low in level (dB) it appears to come from only the tweeter. I would say its about 120hz to 10hz roughly and very, very quiet. The buzz shifts to right as the volume knob is rotated. Im using old Mission 700's for testing but the buzz sounds worse (a bit louder) on my modified TDL's in the main system. The buzz can also be heard on the headphone output.
Hi,
If the buzzing comes from the tweeter then it can't be at 120Hz as the tweeters response is only down to at best 1.5KHz. So what you must be hearing is modulation of a higher frequency noise. i.e there is a background noise at say 5KHz which is going up and down in level at 120Hz (thats what amplitude modulation is).
If this is very low level. i.e you can't hear it at the listening position. The it is likely that it is normal due to some crosstalk inside the amplifier.
If it is completely regular then it is probably mains noise modulating the noise floor. If it changes, especially if it changes as you change settings on the display then it could be microprocessor noise getting into the amplifers. Tracking down how it is getting into the amplifer is likely to be very difficult as if it was easy the design engineer would have already done it. But if it is from the microprocessor you may be able to improve it by using a really good decoupling capacitor such as an oscon on the processor power pins. Or if it is direct from the transformer (which you could probably find out by rotating the transformer and seeing if it gets worse) then you may be able to sheild it out. It may be due to a ground loop within the product in which case it will be almost impossible to get rid of without a major redesign.
The heatsinks won't provide any significant shielding from the transformer as they are made of aluminium and to shield from magnetic fields you need a ferrous material such as steel or preferably grain oriented silicon steel. Which is the material normally used to make a shielding band arround high quality audio transformers (a GOSS band). I can't see one in this amplifer but it is a mid range product so that is probably not surprising.
Regards,
Andrew
If the buzzing comes from the tweeter then it can't be at 120Hz as the tweeters response is only down to at best 1.5KHz. So what you must be hearing is modulation of a higher frequency noise. i.e there is a background noise at say 5KHz which is going up and down in level at 120Hz (thats what amplitude modulation is).
If this is very low level. i.e you can't hear it at the listening position. The it is likely that it is normal due to some crosstalk inside the amplifier.
If it is completely regular then it is probably mains noise modulating the noise floor. If it changes, especially if it changes as you change settings on the display then it could be microprocessor noise getting into the amplifers. Tracking down how it is getting into the amplifer is likely to be very difficult as if it was easy the design engineer would have already done it. But if it is from the microprocessor you may be able to improve it by using a really good decoupling capacitor such as an oscon on the processor power pins. Or if it is direct from the transformer (which you could probably find out by rotating the transformer and seeing if it gets worse) then you may be able to sheild it out. It may be due to a ground loop within the product in which case it will be almost impossible to get rid of without a major redesign.
The heatsinks won't provide any significant shielding from the transformer as they are made of aluminium and to shield from magnetic fields you need a ferrous material such as steel or preferably grain oriented silicon steel. Which is the material normally used to make a shielding band arround high quality audio transformers (a GOSS band). I can't see one in this amplifer but it is a mid range product so that is probably not surprising.
Regards,
Andrew
Stream said:
Not really, the guy wasnt much help actually. He just tried to convince me that it wasnt a problem as its so quiet you cant really hear it when music is playing.
I disagee, it shouldnt buzz at all in my opinion and it didnt buzz when it was new.
I changed the diodes for new shottkey ones and it still buzzing. Its really annoying because it sounds really good with the mods. It would sound better if the noisefloor was quieter.
I could just start replacing components but that would be expensive. Im all out of ideas. I need help with it.
Ive been using a borrowed 840A for a couple of weeks and it a great amp, my only negative would be its a little lacking in dynamics. The modifed 340A SE isnt far off it now, with better dynamics.
Mike.
Do you have a service manual for this thing?
I am guessing that the input selection is done via a multiplexer IC. I'm wondering if it's fried and thats where the noise is coming from. What is the IC on the left in the 4th picture on your first post labelled as ?
It's a pity that you dont seem to be able to easily isolate the power amp from the pre amp, unlike the A500/A6. You really need to find out if the buzzing is in the power or the pre. Look for a resistor or capacitor that links the two, remove it, and ground the input to the power amp. If you have a service manual I can advise.
I am guessing that the input selection is done via a multiplexer IC. I'm wondering if it's fried and thats where the noise is coming from. What is the IC on the left in the 4th picture on your first post labelled as ?
It's a pity that you dont seem to be able to easily isolate the power amp from the pre amp, unlike the A500/A6. You really need to find out if the buzzing is in the power or the pre. Look for a resistor or capacitor that links the two, remove it, and ground the input to the power amp. If you have a service manual I can advise.
jaycee said:
Yes I have a service manual. No it isnt the input selector. (the chip you pointed out). I disconnected the chips power and fired up the amp, It didnt change anything. I did this all around the circuit (cutting power to ic's) and none changed this buzzing. The only time I had no buzz was when the pot was removed so I think the power amps are fine. I am a novice, I could be wrong........
I have the amp connected to my main system again.
I had a listen late last night while the house was quiet. The buzz is audible through both the woofer and tweeter in the right speaker (sounds more like a hum through the woofer). This is with no source and vol pot at zero. When switching between sources there is a small click sound, very faint.
I had a listen late last night while the house was quiet. The buzz is audible through both the woofer and tweeter in the right speaker (sounds more like a hum through the woofer). This is with no source and vol pot at zero. When switching between sources there is a small click sound, very faint.
Stream said:Try in another room
I took my 340 back, so i think at weekend i can measure any voltages, and carefully listen to find any buzzing
That would be interesting to see if you have any buzzing. I think yours is quite new? It should be quite silent really, i wouldnt expect it to buzz at all....
Have you made any modifications?
340A Power amp and PSU modding:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131847&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=131847&highlight=
Hi. I tryed to listen my 340 in silence... It has not any buzzing. I hear very litle hissing from from very close distance to lodspeakers, but I dont her this from listening place
But my Audigy2 Value has one issue - it has buzzing+hissing on left channel, not constant and not loud... It is audible, when music is stopped, and also with high -gaine amps (i tryed with car Adagio 4ch.- amp)
But my Audigy2 Value has one issue - it has buzzing+hissing on left channel, not constant and not loud... It is audible, when music is stopped, and also with high -gaine amps (i tryed with car Adagio 4ch.- amp)
regarding my buzzing problem:
Can anyone tell me what the "DC offset detect" circuit is doing? This is one area I havent investigated as a possible cause of buzzing. When I did the first round of mods I had a loud buzz on the first powerup. I shut it down and tried again with vol at zero - same thing happened. On the third attemp everything seemed fine until later that night I noticed this faint buzzing form one speaker. Could something have gone in the DC detect circuit which would cause a buzzing sound? (Details of what I have done so far to try and solve the buzzing can be found-here.
Also I would like to know if Im ok to disable the DC detect and how? This way I can easilly test if its the cause of my problem.
Thanks.
Mike.
(Reminder: I have the Service Maual if anyone would care to take a look. Thanks, Mike.)
Can anyone tell me what the "DC offset detect" circuit is doing? This is one area I havent investigated as a possible cause of buzzing. When I did the first round of mods I had a loud buzz on the first powerup. I shut it down and tried again with vol at zero - same thing happened. On the third attemp everything seemed fine until later that night I noticed this faint buzzing form one speaker. Could something have gone in the DC detect circuit which would cause a buzzing sound? (Details of what I have done so far to try and solve the buzzing can be found-here.
Also I would like to know if Im ok to disable the DC detect and how? This way I can easilly test if its the cause of my problem.
Thanks.
Mike.
(Reminder: I have the Service Maual if anyone would care to take a look. Thanks, Mike.)
Hi.
It seems the DC offset detect is part of a speaker protection function where abnornal DC offset triggers the output relay to fall open. Its unlikeley this would cause any buzzing then.
Im all out of ideas on how to solve this which is a real bummer as Ive been studying to circuit and theres lots of room for improvement in this amp. Ive allready bought some nice components to use but theres no point untill I get this buzz sorted. I have asked Brent @ audioupgrades.co.uk to take a look and hes cool with it. I just need to send it up to him.
Is there aything else I can try before I send it away to the hi-fi hospital?
Mike
It seems the DC offset detect is part of a speaker protection function where abnornal DC offset triggers the output relay to fall open. Its unlikeley this would cause any buzzing then.
Im all out of ideas on how to solve this which is a real bummer as Ive been studying to circuit and theres lots of room for improvement in this amp. Ive allready bought some nice components to use but theres no point untill I get this buzz sorted. I have asked Brent @ audioupgrades.co.uk to take a look and hes cool with it. I just need to send it up to him.
Is there aything else I can try before I send it away to the hi-fi hospital?
Mike
Hi.
Ive finally got a service manual for the SE version. This has enabled me to study the i-Pod connection and its dedicated buffer cicuit. When an i-Pod (or other source) is connected via the front panel jack socket a realy switches in the opamp, also switching the selector ic and input buffer out of the signal path.
I plugeed in a phono lead with nothing connected, the relay clicked and I checked for the buzzing which was still there. This could indicate that the selector ic and input buffer circuit are actually fine, meaning there could be fault in the i-Pod buffer circuit? The only way to know for sure would be to disconnect the supplies to the selector ic and input buffer and disconnect them from ground. I'll also disconnect them from any signal traces and see if the buzz is still there.
I'll investigate when I replace some more components. I have new diodes and power caps for the poweramp PSU to fit.
Mike.
Ive finally got a service manual for the SE version. This has enabled me to study the i-Pod connection and its dedicated buffer cicuit. When an i-Pod (or other source) is connected via the front panel jack socket a realy switches in the opamp, also switching the selector ic and input buffer out of the signal path.
I plugeed in a phono lead with nothing connected, the relay clicked and I checked for the buzzing which was still there. This could indicate that the selector ic and input buffer circuit are actually fine, meaning there could be fault in the i-Pod buffer circuit? The only way to know for sure would be to disconnect the supplies to the selector ic and input buffer and disconnect them from ground. I'll also disconnect them from any signal traces and see if the buzz is still there.
I'll investigate when I replace some more components. I have new diodes and power caps for the poweramp PSU to fit.
Mike.
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