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Old 4th August 2011, 07:48 PM   #21
forr is offline forr  France
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Quote:
Originally Posted by ingenieus View Post
I assume it is this one:

Comments on Audio Power Amplifier Design Handbook by Douglas Self

Will do so. Thanks.
Yes, it is. There was a thread inviting comments on Samuel's comments. Should desserve much more discussion :

Comments on Audio Power Amplifier Design Handbook by Douglas Self
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Old 4th August 2011, 07:58 PM   #22
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Originally Posted by ingenieus View Post
I ran the circuit through LTspice and it does look as good as any Blameless. Does the design scale up for higher supply voltages and output power?
Mike made a survey for for the prefered value of amp power, it leads him to adopt 30 W for his project. I think he mentions the possibility of a 100 V DC power supply somewhere. For a very powerful amp, for a sub for instance, he advices using more usual architecture.
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Old 5th August 2011, 08:21 PM   #23
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Hi Marian
Here's my two pennorth. This amp may seem a little more expensive with 15 transistors but they are all low cost. The small signal ones are BC547/BC557; the protection transistors are current-limiting only (I've not optimised this) and have to carry more current than the small signal so they're BC337/BC327 but could be 547 /557 if you can't get them; the rest are BD139/BD140's and the output 2N3055/MJ2955 pair.

The circuit is essentially a Blameless architecture: differential input, with a decent current source; current mirror which is now standard; a Darlington VAS which has a low emitter resistor (because the VAS current is higher than normal at 25 mA or so); a current source for the VAS; and fully complementary output.

Frequency compensation is my recommended approach: no Miller capacitor, but local "sprog stoppers"; global compensation across the feedback resistor; and an input capacitor to keep the input stage drive impedance low, mainly, for stability.

Simulated distortion is .01% at 60W into 4 ohms and .02% at 20 kHz. It is this performance at high frequencies which demonstrates the better compensation scheme.
Distortion is quite high mainly because of the 4 ohm load. If you run this from 20 to 25V rails at 30W, it will be lower.

The VAS current is high because of the high drive needed by the output transistors. I would recommend the MJ21193/4 but if you can't get those, 2N3055's are OK but need a bit more "push". A compromise would be to use two pairs of 2N3055/MJ2955 in parallel, but that is probably not necessary if you keep the power to 30W.

John
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Old 13th January 2013, 02:09 AM   #24
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Quote:
Originally Posted by forr View Post
Mike made a survey for for the prefered value of amp power, it leads him to adopt 30 W for his project. I think he mentions the possibility of a 100 V DC power supply somewhere. For a very powerful amp, for a sub for instance, he advices using more usual architecture.
I'm running mine on the original Dynaco transformer, which results in about 72Vdc after rectification/filtering. I haven't measured, but perhaps 40 WPC?

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Old 13th January 2013, 01:26 PM   #25
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I like that design and the rationale to its development. More power to you, MJR. It is on the long list of short listed projects!

Now that it's done, chicks, what is your satisfaction from the project - do you like the sound or is it all a bit clean and sharp?
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Old 13th January 2013, 02:03 PM   #26
chicks is offline chicks  United States
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Now that it's done, chicks, what is your satisfaction from the project - do you like the sound or is it all a bit clean and sharp?
Sounds as good as it looks.

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Old 13th January 2013, 06:29 PM   #27
Struth is offline Struth  Canada
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Hi Guys

Rod Elliot's circuits were designed many years ago using then-current devices. He has indicated newer devices at the request of his readers. It is the case with most circuits that for each transistor position, many different devices can be subbed in place with little performance difference - at least with Rod's circuits this is the case.

You can sub almost any other part types into his projects. Rod also sells PCBs for most of the amps. If you have Qs about subbing specific parts into any of his circuits he will answer your query.

Have fun
Kevin O'Connor
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Old 13th January 2013, 07:38 PM   #28
Bigun is offline Bigun  Canada
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marian - I give another vote for the DX amplifiers.

All the schematics and details are here: Greg's Web Site

If you want to save money though, and effort, buying a used stereo amp is much easier and quicker route to building one, even with cheap parts.
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Old 13th January 2013, 09:23 PM   #29
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Goodness, I have been a member of this forum for a little bit more than a year, I still learn every time I open a thread, It would be so great getting some of you guy's together deciding on a design, hopefully not more than handful, otherwise we will have a flabbergasted mass of inconsistency ! So many competent people, so many ideas, can we not work and try and design the perfect woman without no VAS, no feedback at all and she is playing a sweet tune. I do enjoy reading these posts, I have build my first lateral mostfet , worked the first time, thank goodness and i do enjoy DIY. Cheers to all you magnificent people !

Cheers from the land of the Springbok !
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