Aleph Ono (nearly) completed - diyAudio
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Old 29th November 2002, 08:07 PM   #1
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Default Aleph Ono (nearly) completed

I am quite new to this forum, discovered it two month ago, while looking for information about the "famous" aleph amps I had heard about. First did a test-build of the Aleph-X (which works fine, no oscillations ), and will get a larger project for me to build. But my pre-amp was making trouble, so I decided to build pre-amp and phono stage first. The aleph Ono should be a good starting point to get used to layout again (did it 12 years ago last time ) The layout of Bakmeel would not fit in my case design, so I started my own layout. PCBs manufactured from PCB-Pool here in Germany., and got them on Tuesday. Assembly was completed today, and after finding a bug in the startup mute circuit, which did a perfect mute after 30s by connecting 42V to ground (only a diode was reversed), it seems to work fine. This only as an introduction.

Questions is: how to verify correct operation? Compared to my previous Phono stage, it has less bass and more heights. I can not hear any distortion, or see it on the scope, but the sound is somewhat different from what I am used to know. So I took some measurements to check for proper RIAA equalization, and got for an input of 40mVpp some values:
100 Hz ~17Vpp
200Hz 10Vpp
400Hz 6Vpp
500Hz 5Vpp
1kHz 4Vpp
2kHz 3Vpp
3kHz 2.3Vpp
4kHz 2Vpp
8kHz 1Vpp
16kHz ~0.5Vpp
All taken with my scope, not with an audio voltmeter. But I could not find the definition of the RIAA curve. Can anyone help, or confirm the values? A gain of 40mV to 4V at 1Khz seems ok to me. I am using only the MM input, with 220pF loading (sould is the same with different settings).
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Old 29th November 2002, 08:24 PM   #2
Jens is offline Jens  Germany
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Congratulation Peter, lucks very good! - Jens
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Old 29th November 2002, 08:33 PM   #3
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Peter,

look at this link, here the formula for the RIAA curev

http://www.tanker.se/lidstrom/riaa.htm


Nice looking amp you build!

william
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Old 29th November 2002, 08:36 PM   #4
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Default one more pic, one more question

The "case" on the picture above is only for testing, will get something in the style of the original one.

One more question: What mesurement equipment would I need to be able to take meassurements of distortion (harmonic and IMD) and S/N ratio ? I have sometimes access to surplus instruments, or could look at ebay. This question is not only for the Ono, but for the other projects in queue. It is good when the DIY-amp sound good, but to be sure would be better
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Old 29th November 2002, 08:39 PM   #5
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Peter,

often it is better not to know and just to enjoy the music

william
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Old 29th November 2002, 08:45 PM   #6
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william,

thank You for the RIAA link, my raedings seem to be ok compared to that table.
But this would mean that my previous amp put much more bass into the music...
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Old 29th November 2002, 09:06 PM   #7
Jens is offline Jens  Germany
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Peter,

Just to confirm your measurements - only small differences compared to mine.

Jens
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Old 29th November 2002, 09:14 PM   #8
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I did some listening to it again, comparing a LP to a CD of the same recording, and the difference is HUGE (real, not in audiophile terms ). The MM cardridge I use (Elac 796SP1) is specified for 47kOhms load, max 300pF, so it should fit perfectly. But the sound is like putting the bass gain control to minimum, and the high control to maximum. Again, it does not sound distored, but very stange. Any ideas how to track this ?
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Old 30th November 2002, 10:07 AM   #9
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Hi,

if your RIAA curve fits this canīt really be the cause. Have you tested your old preamp with 40mV? I would do this and see how both compare.

Did you drive a load when testing your Ono (preamp or load resistor). In case of a mistake made somewhere this could also be of influence.

hope this helps,

william
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Old 30th November 2002, 11:55 AM   #10
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This morning I did some more testing, using a HP3468A true RMS voltmeter, which has <1% error up to 50kHz. Now with 4mV sinus input signal. I checkit it with open output first, then loaded with 1kOhms, which did not give any influence on the frequency curve (except below 25 Hz). All is +- 0.1dB up to 4300Hz, and then rises to +3.3dB at 21.000 Hz. C4 is 10nF, C5 is 2.7nF parallel to C6 with 33nF, all three are 1% tolerance PP foil types. R8 is 7.32k and R9 is 88.7K. But if I understand right, high frequency EQ is done by C8 (10nF) and R28 (150Ohms) only. Checked all values and connections, but can not find an error there.

And there is too much noise (not hum) at the output, 5mV RMS with shorted input (MM). How much should be ok?
Both channels behave same. And only <0.5mV noise on the +-30V supply lines.
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