Another Aleph X up and running

[sinuko]

In my case YES, William.

Paolo

(less marked but the shape is quite similar).

 

[sinuko]

Hi William,
I have one photo of my distortion, I hope that you can see samething.
Yes the photo is quite bad.

Xavier,
I tried without McMillan resistor (with 40R to ground), but I foud a residual of distortion (and the time to stabilize the DC off-set is too long) so at the and I decide for 4k74 value.

Paolo

 

[xavier1000]

Hi,

are we really talking about the same distortion seen here?

http://www.diyaudio.com/forums/showthread.php?threadid=98763&pagenumber=5

This starts at around 22V although the amp only starts clipping at 29V.

William

William,

I would say so, but in my case everything happens at less voltage since my rails are about +/- 17.5v

The latest images I post shows only the remaining of the initial distortion after some changes (Cap, McMillans, etc), but my initial pictures were quite similar to yours. In my case, I got a similar waveform to the one you posted whenever I used bigger caps for B-C of Q3 and Q8 (more than 1nF).

I also detected after removing the McMillan resistors that the behavior was better after the amp had been switched on for a while, having the offset to ground at about -3.5v. If you compare pictures 5 and 6 from my previous post, the only diference is that picture 6 was taken 30 minutes later, with more negative offset to ground.

Paolo,

You are right, removing the McMillans improved things only apparently but did not removed the distortion. It is not the solution, but helps to identify the causes of the problem.

I am not sure yet about it but, could you guys check if you have some improvement in your wave by adjusting the offset to ground to, lets say about -4v instead of near to 0? (only as a test, I am not saying that you leave your amps with this offset as a solution).

Thanks
Xavier

 

[Nelson Pass]

As I recall the review samples were not biased correctly but the clues are perhaps there.

In that case, the bias current was correct, but the gain of the
Aleph current source was mis-adjusted to less than 50%. Just
shows what happens to review units when the sales
department hijacks them off the test bench.

 

[macka]

It must have impressed someone on the production line .....LOL

Well that makes all those measurements invalid I guess.

 

[Buzzy]

Wow ! Ur amp looks beautiful. How thick are those wires ?

 

[Stefanoo]

Xavier...have you figured your problem with distortion on your Aleph X out?

 

[xavier1000]

Wow ! Ur amp looks beautiful. How thick are those wires ?

Thanks, Buzzy, but I am not sure which wires you are refering too!

Xavier

 

[xavier1000]

Xavier...have you figured your problem with distortion on your Aleph X out?

Hi Stefanoo,

I am quite busy and I haven't much time to test. I just reverted to the previous stable situation to be able to listen music. Anyway the distortion only occurs just before clipping and only for frequencies above 10KHz, so I don't think it is a problem for me for listening music at a normal level.

Xavier

 

[Dmatuszak]

Beautiful! After being away from the DIY audio hobby for the past 10 years I recently had to repair and tune-up my Pass A75 and have now got the bug again. Out of all the audio gear I've built over the years I think the most enjoyable project was amp building. Anyway you've now got my interest in taking on this project. Can you give me an idea on the cost and where I could get the PCB's, and notes describing the circuit and testing? The A75 was an easy project in the sense everything you needed to know was in the AA article. I'm not sure this is the case here.

Dan

 

[h_a]

You may want to search for the original Aleph-X thread started by Grey; lots of discussions and details there.

I think Peter Daniel has corresponding pcbs on offer (see group buy section).

As you already have some amp building experience it might be an interesting and ambitious project for you. The amp is not so straight forward as the amps in Nelson's first class articles. Especially stability of the offset can be an issue, but it's certainly manageable with some experience.

Hannes

 

[Dmatuszak]

Thanks. I did a little reading on the builders thread and it sounds like the DC offset got alot of coverage. Some of the Vs thrown out there were pretty scarey. Not sure I'm up to the risk of running this much DC through my speakers. But, definitely deserves a little more research.

 

[eyoung]

I think that if you match your transistors diligently DC offset can be minimized and or adjusted out.I know that it is a long and winding thread but your perseverance will be rewarded.

ps Grey is no longer participating in this forum...If you need his guidance contact me...

E

 

[Eric]

Hey Dan,

Have a look at my Aleph-X page in my signature line. There is a ton of stuff documented there - much of it from the various builder's threads over the years.

Eric

 

[Dmatuszak]

Great site Eric. This had to have taken alot of your time to document. You must be retired. I'm in the research stage right now so let me do some reading.

Dan