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Old 1st December 2004, 12:28 PM   #1
Pboden is offline Pboden  Norway
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Default Low output on Aleph 2 or...

Just finished my Aleph 2, and there was no smoke or minor explotions, so I am rather happy with my self. The sinks is warming equal on all four sides and the measurepoinst are fine, as far as I can comprehend.

What I not so pleased with is that I have to put the volume pot on the Bosoz all the way just to hear a breeze of sound at normal level. I have followed the track of Mr. Thomas Chao project at http://www.penguinlovers.net/audio/aleph2_proj.html which is a nice ABC for beginners- as myself.

The Bosoz is based from the pcb of Kristijan and has a R15 of 220 ohm. I mention this because at first I thought is is the gain of the preamp thats causing the low output.
I am using the unbalanced RCA input only.

Any idea what is wrong or what I can do to increase the output level of my Aleph 2 babies?


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Old 1st December 2004, 01:04 PM   #2
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If you're using the amp with an unbalanced source, you should ground the unused input (usually the - input). That will give you 6dB of gain right there. Also remember that the Alephs had 20dB gain; about 6dB less than a 'normal' amp. All in all that's about 12dB. The gain can be changed if you want, but the grounding the unused input trick is quick, easy, and free.

Grey
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Old 2nd December 2004, 01:21 PM   #3
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and if you use the input configuration of an Aleph 30 or 60 for your Aleph2 you MUST ground the -IN otherwise the gain is very low.

William
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Old 2nd December 2004, 02:59 PM   #4
Pboden is offline Pboden  Norway
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Thanks for your reply.

I have used the attached schematic for the connections and using the switch does not make any different. I am now trying to connect xlr plugs on my bosoz to see if that do the trick. At the same time I was hoping to X-it, using the schematic of Henrik, but now I can't figure out where I should put the In+ and In- from the input of the PCB from Kristijan to my Dact CT3. Any idea?

See the attached files.
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Old 2nd December 2004, 03:00 PM   #5
Pboden is offline Pboden  Norway
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Picture 1
Attached Images
File Type: jpg xlr_4.jpg (59.6 KB, 422 views)
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Old 2nd December 2004, 03:02 PM   #6
Pboden is offline Pboden  Norway
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Picture 2
Attached Images
File Type: jpg bosoz + x.jpg (88.5 KB, 430 views)
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Old 2nd December 2004, 10:43 PM   #7
Pboden is offline Pboden  Norway
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Default Still no volume...

William

Do I also ground the - IN in balanced mode? I have just made the output on the Bosoz with XLR and there is still no increased volume. I can hardly hear the music when the pot is on full.

GRollins

Do you know where I can adjust the gain on the Aleph or where to search to find the "bottleneck" in my amp. (I am using BrianGT boards)

and any idea what value to use to adjust the gain on the Bosoz?

I really need some help here...
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Old 2nd December 2004, 11:01 PM   #8
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Pboden: I may be wrong, but I thought Thomas used a board he got from a diy source overseas. I have a Brian GT board and am planning to do a Aleph 5. I think I see a slight difference in the polarity/configuration of the input connections on the Brian GT board and the one in Thomas' article. Course the print is small and it may just be my aging eyes Not sure if this would cause your problem, but I have big notations on my copy of the Thomas article to make sure the layout on his board and the BrianGT board I have is identical.

Larry Wright
Seattle area
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Old 2nd December 2004, 11:11 PM   #9
Pboden is offline Pboden  Norway
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Hi Larry

I also noticed the difference in inputs on his Aleph 2 and Aleph 5 report. I belive he was a little to fast when drawing the Aleph 2 schematic. But if it is right, the print on BrianGT board is wrong.

Is there anybody with the same boards that can confirm this?
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Old 2nd December 2004, 11:44 PM   #10
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Does your preamp work properly? your x picture doesn't look quite right. There should be 10K to ground from the old input connections, IIRC. The way you have it drawn it has no gain.

You might want to try hooking your cd player directly to the amp (without a speaker connected) to verify the amp operation and see if you have gain. Is the output voltage 20 db higher than the input?

If not, check your feedback resistors are the right values in the right positions? I messed that up on my A75 the first time around and had no gain.
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