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Old 17th August 2012, 08:50 PM   #281
Zen Mod is offline Zen Mod  Serbia
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there is also Zhoufang , with some other good parts , but he's recently active as Dodo
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Old 17th August 2012, 09:03 PM   #282
Variac is offline Variac  United States
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We're still adding up the cost, and buying stuff like anti-stat bags and a box to keep the parts safe in transit. But since there aren't that many parts we're keeping them high quality. The caps, pot and active devices are as mentioned in Nelson Pass' article. The smaller resistors will be upgraded to Vishay-Dale metal films. There will be nice switches, speaker terminals, power jacks, LED's, grease, insulators, bolts, washers, even wire! Drilled and tapped heatsinks will be available separately.
Our goal is you get all that's required to sit down and make a functioning amp!

Last edited by Variac; 17th August 2012 at 09:31 PM.
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Old 18th August 2012, 08:02 AM   #283
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Quote:
Originally Posted by Variac View Post
Our goal is you get all that's required to sit down and make a functioning amp!
PERFECT!

I'm looking foward to get a stereo kit soon, when it's available in the shop!

regards,
Matthias
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Old 19th August 2012, 12:07 AM   #284
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Somewhere along the line, someone pounded into my head the idea that you should make a circuit as linear as possible, then apply feedback. To that end, and in view of my previous post #274, I have been playing with the R1/R2 and R3/R4 resistors.

It looks like R3/R4 wants to be 0.82 ohms and R1/R2 0.15 ohms. This cuts the quiescent current so I added a pot with a series resistor between base and emitter of Q4. I arrived at these values by tweeking the open loop amp, first on the X-Y display, then at 1 watt, 1kHz using the distortion analyzer. If you don't have those resistors available (I didn't) use 1 ohm in parallel with 4.7 ohms for R3/R4 and a 0.22 in parallel with 0.47 for R1/R2. The extra resistor to restore the current turns out to be about 1K.

I had a 0.22 ohm resistor in series with Q1's source, later I shorted it out and it made almost no difference in the distortion numbers. I also adjusted the quiescent current, it had been running about 1.3 amps with the stock circuit, there was a slight decrease in distortion when it was lowered to 1 amp.

What I don't understand is now the distortion rises below 100mW. The stock circuit keeps falling to around 1mW. Am I picking up noise?
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Old 19th August 2012, 05:40 PM   #285
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I recall the distortion spec'd down to 100 mW on the original. It is no
surprise that noise shows up below 100 mW. You have maybe 300 uV
of output noise

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Old 20th August 2012, 08:30 AM   #286
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Quote:
Originally Posted by Variac View Post
We're still adding up the cost, and buying stuff like anti-stat bags and a box to keep the parts safe in transit. But since there aren't that many parts we're keeping them high quality. The caps, pot and active devices are as mentioned in Nelson Pass' article. The smaller resistors will be upgraded to Vishay-Dale metal films. There will be nice switches, speaker terminals, power jacks, LED's, grease, insulators, bolts, washers, even wire! Drilled and tapped heatsinks will be available separately.
Our goal is you get all that's required to sit down and make a functioning amp!
I am going to build a few of these suckers to go with my B5
You can never have too many amps
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Old 22nd August 2012, 12:48 AM   #287
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Dang, just read through this thread and as a complete newbie, I'm very excited to build these.

Thanks Nelson and Variac for making it possible!

Gary
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Old 23rd August 2012, 06:18 PM   #288
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I've given a try on building a stereo version of the ACA with a high-end preAmp (in form of a 22k pot an a source selector switch ).

Really a nice device, although, as it was my first amp of this kind, gave me a bit of a heart-burn watching the Q1 drain voltage on the first switch on - first nothing, then 15v, then back to 10v after 15 secs...

Sadly, I own it no more - my 8-yr-old daughter has it now. Maybe I build myself another one, still have a fitting heat sink...

On the pics you see first the later right channel on a "test" heat sink, the first test run, then the left channel already on the final heat sink, and the completed assembly (and yes, that's a set of EL34s in the background )
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Old 23rd August 2012, 06:28 PM   #289
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Quote:
Originally Posted by rollingtube View Post
...... my 8-yr-old daughter has it now........
she's having right spirit!

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Old 23rd August 2012, 07:27 PM   #290
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Quote:
Originally Posted by rollingtube View Post
I've given a try on building a stereo version of the ACA with a high-end preAmp (in form of a 22k pot an a source selector switch ).

Really a nice device, although, as it was my first amp of this kind, gave me a bit of a heart-burn watching the Q1 drain voltage on the first switch on - first nothing, then 15v, then back to 10v after 15 secs...

Sadly, I own it no more - my 8-yr-old daughter has it now. Maybe I build myself another one, still have a fitting heat sink...

On the pics you see first the later right channel on a "test" heat sink, the first test run, then the left channel already on the final heat sink, and the completed assembly (and yes, that's a set of EL34s in the background )
nice
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