One Aleph-X working, One to go

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#63
Hi,

did some "reverse" engineering today.
First I took out the mu-metall sheet to see if this had an influence........none
Then I took out the dc filter..........this was also not noticable on the balanced supply wich fits cause it should have no dc at all.

So I´ll put them in again and wait for the power resistors to arrive......

William😕
 
#64
William,

I'm gathering parts for several Aleph-X amps that will be biased like yours (22v, 7-8A). I have a question concerning R2 and R42. Your parts list calls for these to be 0.083 ohms using a bundle of 1 ohm resistors.

Can I use a bundle of three 0.22ohm 5w resistors in this place instead? This will yield an overall resistance of 0.073ohms vs. your parts list that calls for 0.083. Just how critical is this particular value?

Also, with R5, R6, R40, R41, can I use 0.22ohm 5w instead of 0.33 ohms? I have a pile of the 0.22 from an earlier group purchase and would like to use them if they don't cause problems...

And since I'm still rather a noob at this, could I trouble you to post (or e-mail me, it the file size is too large) a close-up photo of one of your populated PCBs so I could take a look at it?

thanks!
Eric
 
#65
Can I use a bundle of three 0.22ohm 5w resistors in this place instead? This will yield an overall resistance of 0.073ohms vs. your parts list that calls for 0.083. Just how critical is this particular value?

Also, with R5, R6, R40, R41, can I use 0.22ohm 5w instead of 0.33 ohms? I have a pile of the 0.22 from an earlier group purchase and would like to use them if they don't cause problems...

Hi Eric,

I haven't got the schematics but from William's earlier post... There shouldn't be a problem substituting the resistor values. Only thing is you have to pay attention when it comes to the setting the AC gain.

For the resistors in the power supply, remember that resistance x current = voltage drop.

Hope this answers your question.
 
#66
Hi Eric,

0,073 Ohm is no problem. You only must adjust the ac-current-gain resistors.
If you use 0R22 for R5/6 you will get quite a low voltage at your chosen bias and you will have to turn the bias down quite a lot with VR1 and 2. You will also have to lower R11/33 to get low enough.
I´m not shure if this won`t change the dynamic behaviour of the active current source.

William
 
#70
kilowattski said:
William,

Have you removed the chokes from your power supply to make sure they are not buzzing? Do you hear the hum without the speakers connected? Is it mechanical hum or a ground loop?
Click to expand...

Hi,

I´ve listened to the chokes with a stetosscope? (you know the thing a docter uses to listen to your heart, lungs etc.) and they are silent. I even had them removed from the mu-metal/plexi sheet without changes in buzz.
The sound is clearly coming from the transformers.
The buzz is mechanical (no humm to speak of from the speakers) and coming from inside the transformers. Note it´s a buzz not a hum.
Decoupling the transformer from the frame doesn´t help.

At the moment the level is acceptable although not really silent. I put two 0R22 resistor in the mains to reduce the current peaks a bit. Putting resistors between rectifiers and caps didn´t really help.
I also tried lowering the bias to 6.5A (only did one channel until now) wich didn´t really help except to cool things down a bit at 35° C ambient temp......
At the same time I made it possible to plug in the ac-current-gain resistors to make quick changes. A change from 1k3 to 1k37 changed it to almost exactly 50%. Since I´m listening "mixed" at the moment I can´t say anything about sound changes but I will change the other channel too.

William
 
#72
Eric,

here´s a picture of the populated board. The source and gate resistores are mounted next to the fets on the heatsinks.

William
 

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#73
Hi,

I changed the other channel too (a bit less bias and 50% ac-current-gain) and did some measurements with different resistor values.
For 6.6A bias and R12/34 = 1k33 I get 56%, for R12/34 = 1k37 it is almost exactly 50%. So for now I will leave it at 50% and listen a bit. Changing to 56% can be done very quick by changing the two resistors (I don´t even have to take the lid off😀 )

William
 
#75
Hi Eric,

thoughts about a new transformer have come to me too.......The problem is that the special audio transformers (plitrion low noise etc.) are all a bit too big. I need one wich has max 150mm diameter and 100mm height.

I will try to better my ac a bit more.......

William
 
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