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Old 10th March 2010, 07:07 PM   #41
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by bobodioulasso View Post
The value of the feedback resistors have to increase when paralleling outputs?
I did not realize that.
Up or down ?
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Old 10th March 2010, 09:07 PM   #42
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Quote:
Originally Posted by Botte View Post
Since adding additional outputs increases the open loop gain and I didn’t change the closed loop gain it had more feedback.
Does that means we need to decrease NFB and so increase the feedback resistors values in order to keep the stock close loop gain?
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Old 10th March 2010, 11:07 PM   #43
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Quote:
Originally Posted by bobodioulasso View Post
The value of the feedback resistors have to increase when paralleling outputs?
I did not realize that.
Neither did I.

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Old 10th March 2010, 11:47 PM   #44
a.wayne is offline a.wayne  United States
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Old 11th March 2010, 06:09 PM   #45
joho is offline joho  Netherlands
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Default No zeners?

Quote:
Originally Posted by Nelson Pass View Post
I think this would be the preferred topology.

Thank you Mr.Pass for your response.

I was thinking about 2 zeners to ground to keep a fixed voltage to the base of the cascode transistor. Bad idea?

My rail voltage is around 30 volts (at 225Vac) so I'm using a variac to make the primair AC voltage lower(24V rail).

Last Monday the man with the golden ears was in my listening room and we compared a F5 with an Aleph X (no parallel output fets).
He was impressed by both amps and his only comment on the F5 was;
- sometimes too detailled.
- mids a little bit too cold.

He preferred the Aleph X (more musical) mostly but it strongly depends of the recording you are playing.

Both are great amps.
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Old 11th March 2010, 06:29 PM   #46
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I think your friend spotted the relative differences pretty
accurately, and of course one man's accuracy is another
man's "too detailed and cold midrange".

As to the Zener's, I don't think you need them, but they
won't hurt. probably.

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Old 11th March 2010, 06:38 PM   #47
joho is offline joho  Netherlands
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Yes, at this level it's a matter of taste (like good wine).
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Old 23rd November 2013, 06:21 AM   #48
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Quote:
Originally Posted by uvellani View Post
I don't know about the Aleph 5, but I built the Aleph3 as well as the F5. The aleph3 is much better in the mids and highs (like a good tube SET) and despite the fact that they have the same rating also seems to play louder into the same speakers (89db 4 ohms). The F5 is fuller in the lower end and probably goes deeper too. I would think that the sound of the Aleph3 would compare to the Aleph5 which looks like a more powerful version of it.

I use the A3 generally for small ensemble music, acoustic and vocals etc. and the F5 generally for larger scale music that needs to play loud. I have them both in the same enclosure using the same PS and heatsinks and switchable via several toggles for power and inputs and outputs etc.
Any chance of some pictures? I have been toying with the idea of building an Aleph J, and being able to put it in with my F5 is very interesting, and considerably cheaper as the heat sinks alone set me back 160. Many thanks for any advise or lessons you can offer on this.
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Old 23rd November 2013, 07:42 AM   #49
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I've got the Aleph4 and the F5, the Aleph is just a much nicer sounding amplifier. The mids just seem to be much more vibrant leaving the F5 sounding dull and flat.

Some people might prefer the clinical sound of the F5 but to my ears the Aleph is much more pleasant to listen to.

Last edited by KatieandDad; 23rd November 2013 at 08:05 AM.
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Old 23rd November 2013, 02:53 PM   #50
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Originally Posted by lorienblack View Post
Any chance of some pictures? I have been toying with the idea of building an Aleph J, and being able to put it in with my F5 is very interesting, and considerably cheaper as the heat sinks alone set me back 160. Many thanks for any advise or lessons you can offer on this.
I seperated out the two amps since then in order to have two seperate systems in two rooms.
It was not very complicated to implement. I used seperate DPDT switches for each channel for the rails and output. I used just one input for both. You will need to size the transformer and heat sinks for the A3 which consumes more power. I have a 400va 18v transformer and each channel has a 12x10 sink with 2" fins, which gets pretty hot (5 sec rule).
As far as the sound is concerned, the aleph3 is warm and rich as many have noted. But I have discovered that if you drive the F5 with a good tube preamp, you get a lot of that liquidity in the midrange and none of the 'dryness'. Sort of best of both worlds. I think this is true for most class A amps.
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