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Old 26th August 2003, 08:08 AM   #1
Buhl is offline Buhl  Denmark
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Default Sound problem with Zen 4

Hi all
Now, both channels of my zen 4 is working and stable - but the amp still gets hot - this is most likely caused by to small heatsinks - my fault.
But - even though the play and sound good (cant hear the full potential yet, as im using a poor cd player, and partly faulty speakers)
Still - compared to the old Crown DC150, theres much, much more detail in the higher registers, akkustic guitars sound incredible, and theres more bass detail - transparent sound, very nice.

But - the snake in paradice - theres also noise, sounds like 50 hz buzz with higher pulses that varies in volume - about 2 pulses a sceond - they are easy heard between the songs on a CD.

Can this be because the amp is build up on a piece of MDF ? - lack of screening ?
Or, has it to do with me using 34 volt trafo instead of 36 ? - my regulated supply is close to 40 volts, 39,6 or so - this should be 42 according to Nelsons article. Drain of Q1 to ground is stable at 22 volts.

Any other suggestions to this noice ?

Also, when drived direct from a CD vith variable output with 2 volts maximum output, theres no sign of distortion, and I also feel that 30 watts should sound louder on my speakers - is this normal, or is there a problem with the amplifier gain somewhere ?
I measure 3,3 volts before C2 and ground, where the article shows 4 volts ?

Thank you very much !


Cheers !

Hans
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Old 26th August 2003, 09:28 AM   #2
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picture of the amp?
what about the noise with no source connected tor it? may the noise come from a preamp or so? power supply not far enough away from input connector, cable from PCB to input connectore long and unshielded? ground loop? you have to play around to detect from were the noise comes. I canīt see a problem with the voltages you measured. Also I canīt see a problem with the MDF, i use a wooden case.
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Old 28th August 2003, 07:52 AM   #3
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by till
picture of the amp?
what about the noise with no source connected tor it? may the noise come from a preamp or so? power supply not far enough away from input connector, cable from PCB to input connectore long and unshielded? ground loop? you have to play around to detect from were the noise comes. I canīt see a problem with the voltages you measured. Also I canīt see a problem with the MDF, i use a wooden case.

Im sorry, but I dont have a digital camera, so I can not poste a picture of the amp - but I can try to describe it: a MDF-board, about 40x40 centimeters (about 17") - heatsinks along two of the sides - amp boards in one side with input and output connecters gooing out there, and inn the other end two caps and a toroid. Diode bridges are mounted on same heatsink as the two non-audio FETS of the amp. Distance from input connecters to PSU is about 30 centimeters.

Without input cables connected, the pulsing "snerring" is gone, but it then sounds like listening to someones heart through a stetoscope - a "thump" sound about two times a sceond. sometimes spiced with something that resembles the squirl of a mouse - this squirl is also pulsing, but from silence to loud to silence and so forth.

The "snerring" is likely to be ground loop ?
What can the "heart-sound" be caused from ?

Hope that some of you can give me some advice - they are much needed !!!

Cheers !
Hans
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Old 28th August 2003, 10:40 AM   #4
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Default Thumping

If you built the voltage regulator as it is listed the output should be 42v. The is the five 9.1 volt zeners minus the 4 volts across the transistor that is regulating.
You may not be feeding enough input voltage to make the regualtor work. Try disconnecting the string of zeners. This may solve this. The output will track the input voltage, just 4 volts or so down.
But from your description, it sounds like a low frequency occilation. Check the feedback loop. If something is wrong it could make the amp thump.
The fact that this only occurs when the input is connected also indicates something in the feedback.
Good luck!

George
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Old 28th August 2003, 12:11 PM   #5
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Are youre speakers low Impedance?

My Zen does not like my Quad ELS's - it has a slow oscillation when connected to them.
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Old 28th August 2003, 03:31 PM   #6
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by crown300
Are youre speakers low Impedance?

My Zen does not like my Quad ELS's - it has a slow oscillation when connected to them.

Funny you should ask that - I have just been to a friends house and borrowed (actually bought) a pair of small two way dynamic speakers - instead of my Quad ESL 63, and now the low thumping is gone, some snerring is still there though.

I will try disconnecting the string of zeners (shorting start and end of the string ???) and se if that helps further. Should I get 42 volts, when I only have 48 volts unregulated ? the 2 volts less here is not the 2 volts missing on the regulated supply ?

The possible feedback problem - how can I solve this, other than check component value again, and resolder all joints ?


Thanx !!!


/Hans
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Old 28th August 2003, 03:33 PM   #7
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not short them, just open one solder point.


But better: measure the voltage over each zehner and look if they are really 9.1V or some 8.? V zehners.
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Old 29th August 2003, 07:04 AM   #8
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by till
not short them, just open one solder point.


But better: measure the voltage over each zehner and look if they are really 9.1V or some 8.? V zehners.

Damn, I've just measured 8,8 volts across the zeners - are they wrong value then ?

Ill try to solder one of the open.....

Thnx for helping me !

/Hans
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Old 29th August 2003, 12:11 PM   #9
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no, i had to order 50 zehners and measure them all until i had enough 9.1V .... bad quality perhaps.
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Old 31st August 2003, 05:50 AM   #10
Buhl is offline Buhl  Denmark
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Quote:
Originally posted by till
no, i had to order 50 zehners and measure them all until i had enough 9.1V .... bad quality perhaps.

This sounds troublesome.....perhaps I should talk to my parts supplyer ?? ;-)

Anyway, when I lift one of the zeners, I measure 47,5 volts (Same as unregulated DC voltage) across Gate and Drain of Q5, and 42,5 volts across the source. If I follow the drawing, this seems to be rigth ?
Buth now what - should I get some proper zeners, or can I leave them out now the voltage is correct anyway ?

And the "humming / buzzing" - with no signal cable connected to the amp, it is silent as the grave - even with my beat-up-musician ear regth in the tweeter can I hear anything, but when I connect the cables from a DAC or CD player, its there - what can my problem be ??


Thanx for helping me.


/Cheers !

Hans
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