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Old 8th February 2008, 05:19 PM   #1521
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Hi Ian,

thanks for your reply!

I've read this new information yesterday evening. It is difficult to interpret... not really a new information...

Some more sentences to my questions:

1) The stand by consuption must be higher (approx 40-50W). Half get lost in the N-ch devices, a bit fewer in the SE-bias resistors (they are responsible for the high stby consuption because they are not switched of) and the rest in the P-ch. (INT150 standby 45W)

2) There is no separate supply for the front end! Only possibility I found are the bootstrapping capacitors. But I don't know if this could work!?

3) Just an idea!

4) My calculations show approx 150mW RMS (with 55V peak). I have asked that because I can see 10k/3W resistors in the bias circuit on a picture - thought they are the resistors which Nelson had talked about. Strange to say 3W!???

5) I am quite sure that you can use a thermistor to eliminate a good portion of the bias drift. But I have no good idea at the moment where to put it in.
The second possibility is to use it as a current limiter for the output stage.

6) I don't know if you just can put a resistor in parallel to the voltage reference. This will generate a current source...?

7) Have an idea: It could come from the rectifier and supplies current to the coil of the relay. On this way you can isolate the switching circuit a bit from the main supply and it is independant from the charging conditions of the caps.

Regards
Dirk
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Old 8th February 2008, 06:51 PM   #1522
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Quote:
Originally posted by Ian Macmillan
Dirk,

Just noticed this in the XA.5 information on the Passlabs web site:

"New bias circuit Ė A newly developed bias generator has eliminated three sources of variation in bias current in the output stage. It also allows approximately 20% greater power output for a given supply voltage"

so perhaps you are on to something with your thermistor idea. Certainlly worth thinking about.

Ian.

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Old 8th February 2008, 09:07 PM   #1523
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You might also consider the bias circuit in the recent First Watt amp...

Grey
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Old 10th February 2008, 02:30 PM   #1524
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Hallo Grey and all the others

The idea of bootstrapping and using the TL431 as voltage bias reference comes from Firstwatt.
The rest of the VBC seems to be different:
The stages are not coupled with caps, because you need trimmers before the output stage to adjust the offset. The two in the front end would be out of work.

I have drawn down an idea - perhaps this will function:

The bias circuit is made of a voltage reference with a small resistor in series. On this way you can vary the bias voltage a bit dependent from the current.
Means when it is driven by the front end current of about 27mA it reaches a higher value as when it is driven in stand by mode by only the 10k resistors.

Also there is a ("boxed") thermistor network in parallel to the voltage reference network for two reasons:
It handles half of the dissipation (approx. 100mW) (only in power mode) and it can vary the voltage bias dependent on its temperature for faster warm up and less bias drift.


Hope that somebody will answer to it if this could work...
...perhaps with an idea how I can implement bootstrapping capacitors or another network for more output voltage swing.
(without a separate higher front end voltage)

Greatings and nice sunday
Dirk
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Old 10th February 2008, 07:13 PM   #1525
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Default This is a desperate call for help.

Hello,

I am Ralf from Germany and try to build an Aleph X. I am quite experienced in DIY (e.g. I successfully built an Alpeh P1.7) but I fear the Aleph X is beyond my possibilities. Without support form you this will be the biggest money to trash bin project in my life.
My Aleph X is a standard Gray/Rollins except for D1 which is built according to this http://www.r-stens.de/diy/AlephX/Input/Input.pdf
My PCBs are self made (using Target) but I canít guarantee that there a no bugs in the wiring.
I have +- 16 V rail.
Q 6a is G 9.0, D 2.6, S 13.2

The problem I have is Q1
Q1 is G -11.0, D16.0, S -14.0
Q10 is nearly the same

I cannot let it run for more than a few second because then R1/4 get so hot they start smoking. So it is really hard at the moment to get measurements as I donít want lose my carefully matched resistors.

I really hope someone here is willing to help me and that I am able to transform your help in a running amp.

Best wishes

Ralf
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Old 10th February 2008, 09:19 PM   #1526
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P.S.
I forgot to mention:
I made a measurment before I put in Q1/10, Q 2/11 and I had for Q6: S 13.2, D 3.96
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Old 11th February 2008, 06:55 PM   #1527
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Hi Zen Mod,

please give me another hint in which thread and post I should look for babozen.
Need more ideas...... have read Zen V5, A75 part 1+2 and other stuff without results...

Regards
Dirk
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Old 11th February 2008, 09:12 PM   #1528
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Hello,

I forgot to mention: I use 2SC2547 instead of the MPSA18 for Q3/8/4/9. Can this be the cause that Q2/9 open up?

Best wishes

Ralf
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Old 11th February 2008, 09:23 PM   #1529
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Quote:
Originally posted by noisefree
Hi Zen Mod,

please give me another hint in which thread and post I should look for babozen.
Need more ideas...... have read Zen V5, A75 part 1+2 and other stuff without results...

Regards
Dirk

http://www.diyaudio.com/forums/showt...738#post998738
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Old 11th February 2008, 10:47 PM   #1530
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Thanks

have found thermistor networks...


Dirk
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