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Old 12th April 2013, 02:51 AM   #2621
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This book is one of the best audio design book I have read, but it still exists some rooms for improvement.
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Old 12th April 2013, 03:06 AM   #2622
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Originally Posted by RNMarsh View Post
can you give me a typical value/range of this effective C for significant current ??

Thx-RNMarsh
If I've done my math right, a power transistor with 10 MHz ft and conducting just 1A will have a hybrid-pi capacitance of about 0.7uF.

The amount of suck-out current available limits the available rate-of-change of the transistor's current. At the same time, a fast signal going through the crossover region can have a fairly high current slewing rate. I think I touched on this aspect in Chapter 10 on output stages in my book.

Cheers,
Bob
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Old 12th April 2013, 03:11 AM   #2623
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Originally Posted by tomc12388 View Post
This book is one of the best audio design book I have read, but it still exists some rooms for improvement.
Thanks for your kind words, Tom. And you are definitely right - there is a lot that can be improved, expanded, or added. That is my challenge for the Second Edition. I hope McGraw-Hill will allow me to add about 100 pages (but they were very kind to give me 600 pages in the first place, when the original plan was for only 500).

Cheers,
Bob
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Old 12th April 2013, 03:30 AM   #2624
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Originally Posted by kgrlee View Post
Could you post a link to this please.
Unfortunately all my original images are lost to time, but here is a thread:

Simulation Analysis of several unique Allison-based output stages.
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Old 12th April 2013, 04:32 AM   #2625
Bonsai is offline Bonsai  Taiwan
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Quote:
Originally Posted by Bob Cordell View Post
Thanks for your kind words, Tom. And you are definitely right - there is a lot that can be improved, expanded, or added. That is my challenge for the Second Edition. I hope McGraw-Hill will allow me to add about 100 pages (but they were very kind to give me 600 pages in the first place, when the original plan was for only 500).

Cheers,
Bob
Bob, please take time out in your new edition to cover CFA's in some depth. Your unbiased, un-opinionated and practical writing style is a breath of fresh air. I for certain will buy the second edition to sit alongside my 1st.
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Old 12th April 2013, 06:44 AM   #2626
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Originally Posted by Bob Cordell View Post
Hi David,
I was writing my book at the time and was wrestling with the need to pull charge out of the power transistors to turn them off fast enough and mitigate dynamic crossover distortion. There is a section in my book where I discuss the problem...
I should have followed up on this idea. Indeed, there may be real-world practicalities that make it difficult to implement reliably.
Yes, the scheme looks like a nice solution to the problem, so when you did not publish it I wondered if you had found a difficulty and dropped it.
But now I am reassured, with Damir and Ovidiu as advocates and you too
I think I will use it, so thanks for the reply.

Best wishes
David
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Old 12th April 2013, 09:05 AM   #2627
hahfran is offline hahfran  Germany
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I am still wrestling along with design of
inverting voltage to current converting power amp
objectives
lead lag compensation
no current sources no current mirrors
"musical" harmonics' spectrum
the relations of harmonics should stay constant over power and frequency
thd absolute of minor concern
dynamic thermal compensation of bias

idea:
with current driven speakers one can easily compensate the motion equation B*l*i=...
with a set of three integrators and one adder and does not need to know the speaker's
TS parameters.
All that is required is a sine burst a good microphone and a two channel scope.
Then adjust the output fro minimum over- and undershoot of the bursts. ( of course that will be a compromise as the burst adjustments must be accomplished over a range of frequencies )

"Market": with the new but widely used program sources as "the net" and CDs LPs...are a niche market I think the days of passive crossovers are over. The future belongs to active speakers.
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Old 12th April 2013, 09:13 AM   #2628
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Originally Posted by hahfran View Post
I am still wrestling along with design of
inverting voltage to current converting power amp...
no you are not
I support you nonverbally
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Old 12th April 2013, 11:01 AM   #2629
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Originally Posted by keantoken View Post
... lost to time, but here is a thread:
From a quick look at the start of the thread this seems rather different, a class A bias scheme.
In a Class B+ amp there will only be about 50mV across the combined output emitter resistors. That sure won't set the bias!
Perhaps somewhere in the 600+ posts is a scheme similar to Bob's but it doesn't jump out to me.

Best wishes
David.
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Old 12th April 2013, 12:04 PM   #2630
hahfran is offline hahfran  Germany
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Originally Posted by padamiecki View Post
no you are not
I support you nonverbally
another objective adjustable compensation of voice coil resistance preferably
with respect to its temperature dependent value....
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