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Old 20th May 2011, 12:11 PM   #81
hpt is offline hpt  Australia
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With respect, minimising component count is not always of primary concern.

"Perfs"... I do not understand?

Last edited by hpt; 20th May 2011 at 12:15 PM.
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Old 20th May 2011, 01:48 PM   #82
wahab is offline wahab  Algeria
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Originally Posted by hpt View Post
With respect, minimising component count is not always of primary concern.

"Perfs"... I do not understand?

As for component count, well , the law of diminushing returns
tame down any improvement based on this metric past a few
dozen transistors..

There s more to gain by reconsidering the design guideline...

Throwing more components to resolve each problem doesnt
seems to me the best path.

That said, CBS design is quite amazing on an engineering
point of view...
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Old 20th May 2011, 11:36 PM   #83
CBS240 is offline CBS240  United States
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I agree there is no reason to just throw in extra components in for sh!ts and giggles, but there are some things that just work. Take the cascode or common base (gate) amplifier. There are certain advantages to this but it requires more parts, mostly nickel and dime parts.

As far as the component count in this circuit, there are many different separate circuits on the PCB. Each circuit can be regarded as a 'black box'. These 'black boxes' are direct coupled to form a modular system. Kind of an all in one deal.

On the one PCB is the power supply, high current rect. filter caps ect (+/-24V), two voltage doubler circuits and two discrete voltage regulators based on J-fets that produce +/-40Vdc and +/-15Vdc. Also there is a pre-amplifier circuit with input buffers and 2 discrete DC servos (one for each phase). The pre-amplifier has it's own IPS and VAS, with a FB loop and compensation that encompass only the two stages. The output of this circuit is balanced and feeds the input of the VAS circuit but is direct coupled. The VAS circuit has an input stage/w VAS that has it's own FB loop encompassing 2 stages. The BW and stability of these circuits is very good. Each of these amplifier sections consist of a constant power, balanced bridge circuit with matched components, and then there are the common mode biasing amplifiers for each.

And then there are the two output stages. In this version each output stage follower is an adaptation of Bob's vertical fet HEC. The output stages are not within the FB loop of the VAS circuit, they are pure followers. The only loop that surrounds the whole circuit is the DC servos, Fc~0.3Hz. I actually did some experimenting with this as I left on the PCB the option of encompassing the output stage within the VAS amplifier section but the results seemed to be better without the HEC stage in the loop. I have learned that SR and BW is not everything. There are more variables involved in reproducing good sound through a moving coil speaker. I added some cascodes to the HEC stages along with bootstrap drivers (works great BTW) and the ability to adjust the bias of both OPS at the same time with one single pot via two IL300 linear opto-couplers. So this circuit and the OP-amp servos for each IL300 are also included. I have found this circuit, although it works fine, is not required. So the next version will have a static bias set into each HEC stage. Saving on a few parts right there....besides, those IL300s are $3 each....

All the components of the different circuits add up, there is more going on, on this single PCB than just an input stage, VAS, and OPS.
All the trouble I've ever been in started out as fun......

Last edited by CBS240; 20th May 2011 at 11:43 PM.
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Old 19th November 2012, 04:15 AM   #84
Workhorse is offline Workhorse
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Floating balanced single supply amplifiers are really an addiction for me
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