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Old 26th December 2012, 02:43 PM   #11
bcmbob is offline bcmbob  United States
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Quote:
Originally Posted by wahab View Post
Was just pointing that it is a valuable chip as well since i used a few
as guitar or bass amps for home use and didnt find anything negative
about it.
Well see, we already have a problem. My life's goal is to wipe out all amlpified guitars (except Wes Montgomery & Barney Kessell of course) and convert all those musicians to brass and woodwind instruments. (read - Chicago, Blood Sweat & Tears)

No, I hear you. Just seen so many threads go sour and I'm a little sensitive to that potential.

P.S. Listening to RK "Russian Easter Overture" ( big orchestra) as I write this. The dynamics on this chip/build are really good. !!!
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Last edited by bcmbob; 26th December 2012 at 03:05 PM.
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Old 26th December 2012, 03:15 PM   #12
gootee is offline gootee  United States
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Originally Posted by Jay View Post
I'm pessimistic by looking at the output stage. Phase inversion using opamp for class-B amplification. For small sgnal class-A this is okay. For high voltage swing I don't think so. And it seems efficiency is the main objective of this chip design. While good amps are rarely efficient.

This chip is capable of 10A. Minimum 6A is usually stated for stereo. And it does affect the strength point of this amp. But transformer is the most expensive part of an amplifier. With such a big transformer, I prefer going discrete. Or, higher (than 10V/us of the TDA7294) slew rate opamp driving mosfet output buffer, or CFB symmetrical amp.
Your message is mostly off-topic.

Last edited by gootee; 26th December 2012 at 03:22 PM.
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Old 26th December 2012, 03:20 PM   #13
gootee is offline gootee  United States
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Originally Posted by KSTR View Post
Let's not forget layout and wiring, Bob. Visually "small" design glitches can have big impact on the amp's perfomance additional to (if not even dominating) parts selection.
Totally agree. I would also like to eventually see the schematic altered, to better-reflect the real grounding and power distribution schemes.

Bob, would it be reasonable to assume the use of a two-sided PCB (printed circuit board)?

Last edited by gootee; 26th December 2012 at 03:24 PM.
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Old 26th December 2012, 04:07 PM   #14
bcmbob is offline bcmbob  United States
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Originally Posted by gootee View Post
Totally agree. I would also like to eventually see the schematic altered, to better-reflect the real grounding and power distribution schemes.

Bob, would it be reasonable to assume the use of a two-sided PCB (printed circuit board)?
The thread is open to all valid approaches as far as I'm concerned. If a new board developes, that would be beyond my initial hopes and a real joy to be involved with.
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Old 26th December 2012, 06:06 PM   #15
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Quote:
Originally Posted by bcmbob View Post
Jay, I have been using an Antek 200VA transformer only with this build. I'll hook up a 125 later today and report any differences heard, The power supply boards were purchased to push two BPA 150 amps. I shot off a message to P Daniels for information on whether one of his Universal PS boards could be configured to match the TDA7294 requirements.
For low ripple performance, va=watts*3
Okay a stereo build, say 65 watts and 2 channels = 130 watts
130*3 = 390va
Ah, but the chip does have a softened clipper built in which reduces the actual requirement to 300va for a stereo build.

However, if 200va, then you'd need a bit larger capacitance. No problem. This doesn't require a weird prefabricated printed circuit board. Here's some photos that show how to do your own power supply quite easily, on phenolic perfboard. The real example, is actually running a TDA7294 amplifier.
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Last edited by danielwritesbac; 26th December 2012 at 06:08 PM.
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Old 26th December 2012, 06:20 PM   #16
JMFahey is offline JMFahey  Argentina
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Poor me who thought ripple was related to capacitance, load current and line frequency
Never saw the formula calculating it based on amp power or transformer VA.
That lesson must have been lost in the mail. Oh well .
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Old 26th December 2012, 08:01 PM   #17
gootee is offline gootee  United States
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Quote:
Originally Posted by danielwritesbac View Post
For low ripple performance, va=watts*3
Okay a stereo build, say 65 watts and 2 channels = 130 watts
130*3 = 390va
Ah, but the chip does have a softened clipper built in which reduces the actual requirement to 300va for a stereo build.

However, if 200va, then you'd need a bit larger capacitance. No problem. This doesn't require a weird prefabricated printed circuit board. Here's some photos that show how to do your own power supply quite easily, on phenolic perfboard. The real example, is actually running a TDA7294 amplifier.
Daniel,

Wouldn't the cap bank be ALMOST as easy to construct using an unetched double-sided PCB for each polarity, a la Terry Given? It should then have much lower impedance, right? Or am I missing something?

Tom

Last edited by gootee; 26th December 2012 at 08:14 PM.
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Old 26th December 2012, 08:05 PM   #18
gootee is offline gootee  United States
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Originally Posted by JMFahey View Post
Poor me who thought ripple was related to capacitance, load current and line frequency
Never saw the formula calculating it based on amp power or transformer VA.
That lesson must have been lost in the mail. Oh well .
Actually, the transformer's VA rating "CAN" affect the ripple, if you are too close to not having enough VA. I think that Daniel was just using that fact as a way to select a VA rating. The formula is interesting, though.
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Old 26th December 2012, 08:13 PM   #19
gootee is offline gootee  United States
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Originally Posted by bcmbob View Post
The thread is open to all valid approaches as far as I'm concerned. If a new board developes, that would be beyond my initial hopes and a real joy to be involved with.
Is there an already-existing board?
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Old 26th December 2012, 08:20 PM   #20
bcmbob is offline bcmbob  United States
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I'm following along with this data sheet. Are we all based there?

So va is arbitrary and derived - not being limited by a posted spec - correct?

Daniel, How did you determine the number and size of the caps used in the ps you posted?
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Last edited by bcmbob; 26th December 2012 at 08:36 PM.
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