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Old 31st January 2007, 04:34 PM   #11
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Have you solved the ripple problem yet?

I have a mini-aleph built using KK's boards, and I have absolutely no noise whatsoever.

However, I have noticed, especially with my A-75, that I get noise associated with shorting the unused input to signal ground. Since there is a 5ohm resistor in parallel with diodes connected to earth ground, there is some residual voltage there that gets put into the input that the other channel does not see -- hence, it gets amplified. It goes up when I turn up the bias.

I see from your diagram that you saw some ripple on the input shorted to ground (app 1 mv) but none on the other one. It would then make sense this would be amplified to the outputs. You might want to see what happens if you use a much lower resistance to ground on both channels (say 10 or 20 Kohms0) and don't connect the unused input to ground. This should put the same small amount of hum on both inputs, which will then be rejected as it is common-mode noise.

How is your PS signal ground to earth ground made? Is it with a resistor in parallel with diodes, or is it through an inrush surge arrestor?

JJ
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Old 31st January 2007, 04:43 PM   #12
cviller is offline cviller  Denmark
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Quote:
Originally posted by jeapel
did you try 1nF on base and collector

the official aleph 30 design has 1nF

and it s work in my aleph 3

I just quickly tried it, and it seemed to remove the oscillation, but it did nothing to the ouput - still humming away.


jupiterjune, thanks for your suggestions, I'll try that. Shouldn't I also change the other resitors (R103 and R104) to avoid changing the gain?

My psu is not grounded to earth.
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Old 31st January 2007, 05:40 PM   #13
jeapel is offline jeapel  Canada
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no just 1nF because 10nF can change

amp bandwidth 200khz with 1nF in my

aleph 3 a least one problem go away :-)
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Old 1st February 2007, 01:43 PM   #14
cviller is offline cviller  Denmark
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Too bad the 1nF did solve my problem - I had high hopes for that one.

I have run some simulations where 25mV ripple on psu maps to less than 500uV on output, so I'm quite sure that I have a problem with my setup which cannot be explained by psu alone.

I tried run the amp with both inputs open, and that gave me less noise on output cos not having signal or gnd on balanced minus takes away the gain and so the amp is more quiet, but also kinda makes the amp useless. When inputs are shorted, the resistance to gnd is only 22k through input resistors.

I have removed the zeners, but that didn't help either.
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Old 1st February 2007, 02:52 PM   #15
jeapel is offline jeapel  Canada
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i check my setup this morning

with 92db speaker

-with my irf9610 aleph 3 i hear no hum with 50cm max. from bass speaker

-have you a radio or music from satellite or whatever
with a earth ground

-the last thing try to put more cap on + and - 25volt ???
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Old 1st February 2007, 03:17 PM   #16
cviller is offline cviller  Denmark
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Quote:
Originally posted by jeapel
i check my setup this morning

with 92db speaker

-with my irf9610 aleph 3 i hear no hum with 50cm max. from bass speaker
If everything is quiet I can easily hear hum from cheap old akai speakers.

Quote:
-have you a radio or music from satellite or whatever
with a earth ground
The inputs are shorted and not connected to anything.

Quote:
-the last thing try to put more cap on + and - 25volt ???
Perhaps that's the only solution, but if one channel hums with 90mF per rail I'm afraid I'll need close to 1F in total.
Edit: And 25mV ripple on rails shouldn't be a show-stopper according to what NP says about Aleph 3 an 30.
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Old 1st February 2007, 03:59 PM   #17
jeapel is offline jeapel  Canada
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maybe ???

see the photo

no. 1 big capacitor ground 6cm wide

no. 2 big PCB ground 1,5cm wide

no.1 and no.2 together with big no. 8 wire

no. 3 input ground directly on no. 2 big ground

no. 4 speaker ground directly on no. 2 big ground

interconnect from mosfet to PCB with no. 14 wire
Attached Images
File Type: jpg myaleph3.jpg (47.4 KB, 349 views)
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Old 1st February 2007, 04:56 PM   #18
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cviller-

I am no expert on power supply designs, but my understanding is that the signal to earth ground is critical -- probably for both safety and to prevent your signal ground from "floating". When I built my amps I spent a lot of time reading about power supplies. One website that has a lot of info is elliot sound projects, ESP. The web address is http://sound.westhost.com. Read project 4, "power supply for amplifiers".

He shows the connection of signal groung being made to earth ground though two diodes in parallel with a 10ohm resistor, but I have found that using the inrush surge supressor works much better. I think the details on that were first presented the the BZLS article by NP.

I hope Rod Elliot isn't a dirty word or "persona non grata' on the Pass Labs forum....
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Old 1st February 2007, 05:19 PM   #19
cviller is offline cviller  Denmark
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Quote:
Originally posted by jupiterjune
cviller-

I am no expert on power supply designs, but my understanding is that the signal to earth ground is critical -- probably for both safety and to prevent your signal ground from "floating". When I built my amps I spent a lot of time reading about power supplies. One website that has a lot of info is elliot sound projects, ESP. The web address is http://sound.westhost.com. Read project 4, "power supply for amplifiers".

He shows the connection of signal groung being made to earth ground though two diodes in parallel with a 10ohm resistor, but I have found that using the inrush surge supressor works much better. I think the details on that were first presented the the BZLS article by NP.

I hope Rod Elliot isn't a dirty word or "persona non grata' on the Pass Labs forum....
For safety reasons earth is a good thing, but in my apartment it is nothing different than the neutral wire, except it is connected on the other side of the HFI relay (shuts of everything when a few mA runs through instead of the correct way through fuses). And my amp is not yet in a case - only placed on heatsink. Some people just cut the earth wire if they have problems with ground loops on between earthed equipment (might be dangerous and is obviously the wrong solution to that problem), but I'm only looking on one amp and nothing else.
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Old 1st February 2007, 08:00 PM   #20
Zen Mod is offline Zen Mod  Serbia
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cviller-I can't get what is wrong with your amp ,at least not from information you gave;
if you look on blur images in babelfish thread- my babel proto was just a mess of parts and wires in one hetasink........no PtP jobie,just a mess ;
with two 33mF cans ,one 25A diode bridge (hanging in air) ........350VA underpowerd toroid (underpowered via variac,just because xformer is on full voltage 2x33Vac) I don't have any hum or tizzz or buzzz even on 92+db/W/m speaker...........talking all the time about one channel prototype ............



leave it for few days; do some other thing,then (we) try again......

read "Zen and motorcycle maintenance" in meantime
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