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Old 15th April 2008, 09:02 PM   #111
jam is offline jam  United States
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Patrick,

To answer your question, that is if you have a balanced preamp I would use two of these amps per channel ie. one per phase to obtain a bridged amplifier. I came to this conclusion while building an amp with a similar topology. On the other hand if your preamp is single ended a balanced bridged version of the amp would be better.

Just an opinion mind you.

Jam
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Old 15th April 2008, 09:05 PM   #112
jam is offline jam  United States
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Tony,

Thanks............I suppose you say that but it is all relative. Now if you ask Grey, I am the evil Lord himself

Jam
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Old 15th April 2008, 09:18 PM   #113
culture is offline culture  Netherlands
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Quite a bit offtopic, but...

After following this thread with great interest i'm very interested in a audioxpress subscription. I'm only not happy with the ordering page.. fill in billing details and credit card number on a (with all do respect) obscure ordering page and see what happens.. does anybody have any experience with this ordering page and willing to give me a quick word on it?

my apologies for the off topic question

cheers,

c.
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Old 15th April 2008, 09:34 PM   #114
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Quote:
Originally posted by jam
Tony,

Now if you ask Grey, I am the evil Lord himself

Jam

He is a SIDE guy, so who cares…
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Old 15th April 2008, 09:34 PM   #115
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Quote:
Originally posted by jam
Tony,

Thanks............I suppose you say that but it is all relative. Now if you ask Grey, I am the evil Lord himself

Jam

Ohmigod! It's Darth Jam!

Grey
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Old 15th April 2008, 09:36 PM   #116
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Quote:
Originally posted by culture
Quite a bit offtopic, but...

After following this thread with great interest i'm very interested in a audioxpress subscription. I'm only not happy with the ordering page.. fill in billing details and credit card number on a (with all do respect) obscure ordering page and see what happens.. does anybody have any experience with this ordering page and willing to give me a quick word on it?

my apologies for the off topic question

cheers,

c.
I wasn't too thrilled with the ordering page either.
However, the lure of the F5 was too great, so I
went ahead.

I had ordered late at night and I received a
confirmation the following day via email.

Cheers,
Dennis
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Old 15th April 2008, 11:23 PM   #117
culture is offline culture  Netherlands
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Thanks Dennis

just ordered myself a two year subscription... now lets wait
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Old 15th April 2008, 11:31 PM   #118
tms0425 is offline tms0425  United States
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Quote:
Originally posted by culture
Quite a bit offtopic, but...

After following this thread with great interest i'm very interested in a audioxpress subscription. I'm only not happy with the ordering page.. fill in billing details and credit card number on a (with all do respect) obscure ordering page and see what happens.. does anybody have any experience with this ordering page and willing to give me a quick word on it?

my apologies for the off topic question

cheers,

c.
I had the same reservations about it not even being a secure http page. I ended up calling them myself. Another option is to send two separate emails with the numbers to your credit card spelled out phonetically, split across the two messages. Hugh Dean of AKSA uses this approach and it is a bit safer if someone is picking off random clear text messages looking to parse numeric strings that look like credit card numbers. Tom
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Old 15th April 2008, 11:41 PM   #119
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Quote:
Originally posted by EUVL
I personally do not like thermal compensation with thermistors. For one, it changes the open loop gain, and you don't really know by how much. Worst, you don't know whether the 2 halves drift and compensate symmetrically.

R11,12 are source degeneration for the MOSFETs. John Curl mentioned on the blowtorch thread that source degeneration messes up the distortion spectrum. But I guess you need something for bias stability (a sort of local current feedback). And it provides a convenient means for current sensing (for protection). I find 0R47 a bit high, and would have gone for 0R22 or even 0R1. But that also depends on a lot of things like which MOSFET and how much heat sinking.

R13, R14 are gate stoppers for the MOSFETs (to prevent oscillation). The values are quite low, but then it is supposed to be a fast amp (see the 200kHz square wave), and the drain resistors are quite high (compared to e.g. Aleph-X). Something to experiment with.

The only remaining question for me is :

If I wish to go balanced, should I just use two of these or should I use complementary diff pairs for the first stage and Xed feedback ?
Pretty much correct, except:

1) You don't have to use the thermal compensation, particularly
if you have generous heat sinking, but apart from having extra
parts, there is no downside to it. The compensation is fairly subtle
and the open loop variation is insignificant, probably less than
without compensation. Remember that you adjust the amp after
you reach operating temperature anyway, and you want it to
reside there in a stable manner.

2) You can operate with lower value Source resistance, but I am
using it to get better leveling of characteristic between P and N
channel devices to better cancel the 2nd harmonic. I have a tweak
that I'll write up about this after I make another 22 channels.

3) The optimum value of the Gate stoppers will depend greatly
on the parts. I actually managed to get one stable into a resistive
load with 0 ohms, but I wouldn't plug it into my HiFi. 47 ohms is
probably the minimum, and as in (2) I am still cataloging the
variations.

4) The question of using dual diff pairs is moot, as you will need
2 pair of JFETs in either case. The effort required to run the
feedback back to the Gates versus the Sources is not much, so
you can explore this without much effort.

And welcome back, Darth.
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Old 15th April 2008, 11:44 PM   #120
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Default I hope I can find it...

audioxpress has been increasingly difficult to find over the last several years.

C
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