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Old 14th April 2012, 11:45 AM   #2161
Zen Mod is offline Zen Mod  Serbia
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48 or 52

you'll not hear diff between that two
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Old 14th April 2012, 02:20 PM   #2162
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Ok getting somewhere today. I have settled on values 2n2 for C9/10 and 1n0 for the ones on Q4 and Q9. Amp powers up from cold unstable and gets stable within the first 12 seconds (when offset drops below +5VDC).

Did some measurements today and I'm still concerned. Firstly I have severe ringing on 10kHz square waves. It drops significantly with an 8ohm load connected across the amp, but as shown in the attached pictures both a single side of the amp, and the summed components of -ve and +ve ring at around 125kHz. This is with a 3pf or 5pf cap in the feedback loop, I can't remember and will play with this tomorrow.

But on the bode plot I found my amp is resonant at exactly 114kHz. Using a baseline of 1kHz it's reasonably flat. At 20kHz we're at +0.2dB and this keeps rising to a +2.9dB at 114kHz around the same frequency as my uncompensated amp oscillations . Above the 114kHz it drops quite dramatically with a -3dB point at 220kHz at 12dB per octave.


Is this second order response normal for this amp design? I get the feeling that playing with the capacitance just masks the problem. Is there another way to dampen the response of the amp or am I overthinking this?
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File Type: jpg square left only.jpg (19.5 KB, 437 views)
File Type: jpg square summed.jpg (21.0 KB, 429 views)
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Old 14th April 2012, 10:40 PM   #2163
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Quote:
Originally Posted by Zen Mod View Post
48 or 52

you'll not hear diff between that two
I realise that, but I have been considering raising it to 66% as my speakers have quite a low impedance. Need to know if I"m going the right way.
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Old 15th April 2012, 11:57 AM   #2164
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Hi,

going to 66% means 66% of the current is delivered by the current source. In an Aleph-X going so high wonīt sound very nice.

Donīt know why but it worsened the sound a lot more compared to going to over 60% in an Aleph-5

William
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Old 21st April 2012, 12:59 PM   #2165
Garbz is offline Garbz  Australia
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Interesting, I've heard the sound is worse but you make it sound like it will be actually quite bad. Some people have built 66% amps before. Anyway I'll take your word for it, don't need all that power in 4ohm anyway :-)


In case anyone is interested I have got a rock solid amp now and have settled on the following values: C9/10: 2n2, Q4/9 caps: 1n0, C2/4: 12p
Amp has a bandwidth of 180kHz, and a nearly critically damped square wave response.

For reference in case anyone else has stability issues I've attached bode plots and square wave responses measured for changes in various capacitors on the amp. May help someone along in the future. File format is MS Excel .xlsx

Now to go match the same parts on the left channel.
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File Type: zip Aleph X Measurements.zip (127.4 KB, 22 views)
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Old 21st April 2012, 03:06 PM   #2166
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Hi,

since it is very easy to try (just two resistors) you donīt have to take my word for it. Bad is relative......

William
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Old 22nd April 2012, 02:38 AM   #2167
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Quote:
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OK, ignore my previous post. It looks like if I use a 1.8uF cap, this will provide me with a 2.2Hz high pass filter (I was trying to save some money). I've read through Tony's capacitor test and found the same reference to using a 0.01uF Vishay MKP1837 polypropylene as a bypass. These are cheap enough - I'll grab a dozen or so...
I'll be very surprised if you like the 1837 as a bypass. What about sonicap?
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Old 22nd April 2012, 02:07 PM   #2168
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Hmmm... I've used the original Gen I Sonicaps in small pair of bookshelf speakers I made about 10 years ago and they sound nice in that function. My intent to was experiment with some of the "higher end" caps and thus I was exploring Mundorf and Audyn - there seems to be universally high praise for these...

Which line of Soincaps were your thinking?
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Old 25th April 2012, 10:23 AM   #2169
quan is offline quan  Australia
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Hi guys , looking for some help here as i bought a pair of aleph X monoblocks few yrs ago but did not use it until now. One of the block is working fine relative Dc offset is 10-20mV and absolute dc offset is 150mV. My problem is the other monoblock. From what i can see it is home brew pcb based on original Grey's version ie 15V ,biased at 0.5V, 4 mosfets each chanel, no input caps, no output resistors to ground. The problem is that relative dc offset is about 7V, absolute dc offset from positive to ground is 1.2V but 9V measured from negative output to ground. The voltages across 392ohm resistors are 0.4V and 0.42V respectively. I was able to adjust the absolute offset close to zero but it quickly drift off. Sorry i don't understand much regard amplifier circuit and not sure where to start checking or measuring to work out what to do next.I tried to measured the input diferential irf 9610 but could not make head or tail about it. Would a failed irf 9610 explained the high relative dc off set?
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Old 23rd May 2012, 05:54 AM   #2170
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Hey folks,

I've done some searching on BJT inputs for the Aleph X but haven't seen anything definitive. Is there a standard way to make this upgrade? I have some matched 2SJ170/2SJ74's lying around that I was hoping to use but I don't understand the full scope of the modification. If it's too hard, I'll just stick with the stock configuration but if it's not so hard to do now, I'll just go ahead and implement from the outset.

Thanks!
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