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Old 2nd January 2013, 09:38 PM   #101
redjr is offline redjr  United States
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Quote:
Originally Posted by bcmbob View Post
How perfect is that !! The DIY gods have truly blessed us. I'm getting excited now.
I agree. How fortunate to have someone on the forum who's day job is designing these little amps - specifically the TDA729x series.

In the spirit of keeping this little venture simple and inexpensive (at first anyway), why not take the point-2-point that Daniel put forth and instead of a full-blown PCB, mock up the best layout on a perf board? That gives us the best of both worlds to experiment with further layout tweeking (to help eliminate loops) and allow for different component choices.

Klaus - Did I understand you correctly in an earlier post where you recommended the PSU on the same circuit board as the amp. I've often heard that the 'better' option is to remove the PSU from the amp PCB. Am I mistaken?

Bob - I just completed a small amp using the TDA7294. I went with stock amp kits from my favorite China vendor. No exotic parts swapped in. I haven't done a lot of critical listening yet, because the gain on my new Doug Self preamp just blows the volume up on all my amps that don't have volume controls on them! The 7294 also seems to be running a little hot (I guess, @ about 53 degrees C.) I don't know if that's normal or not. I think my heat-sink needs to be beefed up some.

Rick
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Old 2nd January 2013, 10:07 PM   #102
bcmbob is online now bcmbob  United States
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That's the exact same kit I have. I'm still on a slab of plywood. Your build looks terrific and I'm going to look closely for ideas.

I just have a temporary heat sink of 1/4" x 3" x 4" flat stock but haven't had any heat related problems even after extended hours of operation.

I'm game to try a P2P if someone can provide a BOM. Sounds like fun.

My setup is JRiver to a Mini2496 DAC to the amps. Haven't found the need for a pre, though I did put the JC-2 clone in for an experiment. It didn't help much as the top end of the amp still needs to be cleaned up. More of the same isn't better
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Old 2nd January 2013, 10:25 PM   #103
KSTR is offline KSTR  Germany
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Originally Posted by bcmbob View Post
Klaus - with your experience is the 7294 the best of that series for a project like this?
I would say so, it offers te best compromise. Routing is easy as you can go directly through NC pins. 7295/7296 are the same with derated output power (smaller output transistors).

7293 is the mother chip and offers simple paralleling of several chips (two or three work fine), also it has a clipping detector plus it can withstand a bit more of supply voltage (but *not* more output power or dissipation, so you need paralleling to make use of that unless your speakers are 16 Ohms). Layout for paralleling is a bit cumbersome.

ST has duals, too. TDA7292 for example is OK but not brilliant, dual LM's are quite a bit better there.

So basically the TDA7294 would be my prime choice for a small and nice amp. Unless you happen to have very inefficent speakers or ones which severly dip below 4 Ohms a TDA7294 is good for 50W output powers and "loud enough" without problems other than adequate heatsinking. But even when overloaded (thermally or output current) they don't tend to die with moderate supply voltages.

Test setups running the chip "red hot" at 50W continuous with 120degC at the metal tab for extendend periods of time did not produce any immediate fails or any degradation in measurements, after cooling down again. That is, for genuine parts, I haven't met any fakes so far (but a tiny amount that were "dead out of the box" for no reason).

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Old 2nd January 2013, 10:32 PM   #104
bcmbob is online now bcmbob  United States
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Old 2nd January 2013, 10:33 PM   #105
KSTR is offline KSTR  Germany
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Originally Posted by redjr View Post
IKlaus - Did I understand you correctly in an earlier post where you recommended the PSU on the same circuit board as the amp. I've often heard that the 'better' option is to remove the PSU from the amp PCB. Am I mistaken?
Rick, opinions vary.
I would not like to have the full supply on the board and keep the rectifiers and a first set of capacitors off-board, as well as any associated local components (snubbers etc). But it can be done of course, the MyRef FE is an example where things worked out OK.
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Old 2nd January 2013, 10:38 PM   #106
KSTR is offline KSTR  Germany
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Originally Posted by ClaveFremen View Post
I would stick to SMDs on one side anyway... if some rework will become necessary it will be a pain desolder SMD parts among TH ones... strictly IMHO.
Hi Dario,
I didn't mean to avoid SMDs, quite the contrary. What I was trying to say that we are free to use both sides for parts of either kind (done wisely as you mention, of course) and we can use non-standard component alignements (odd angles) and we can extend leads of eg resistors to span across some traces, place THT caps laterally along PCB edges etc.
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Old 2nd January 2013, 10:46 PM   #107
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I didn't mean to avoid SMDs, quite the contrary.
Hi Klaus,

never said that... I'm a supporter of SMDs.

Simply I prefer to keep them all on the bottom side of the board, easier to rework, if needed.

I'm really curious to see your board development process, I expect to learn a lot.
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Old 3rd January 2013, 12:10 AM   #108
gootee is offline gootee  United States
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Originally Posted by bcmbob View Post
How perfect is that !! The DIY gods have truly blessed us. I'm getting excited now.
It's an incredibly-great stroke of perfect luck, alright! Having wished, many times, that I possessed even a tiny fraction of Klaus's technical knowledge and experience, my guess is that as excited and happy as everyone here feels about being so lucky, they actually still have NO IDEA how lucky they REALLY are, to have Klaus involved. (No pressure, Klaus! <grin>)

Perfboard? Really? [Full disclosure: I haven't read most of this thread, yet.]

Cheers,

Tom
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Old 3rd January 2013, 12:19 AM   #109
bcmbob is online now bcmbob  United States
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I'm beginning to get the picture! But I'll just restate the success of the project will most likely depend on a group effort. Couldn't be happier with the enthusiasm and contributions from so many in such a short time and at such an early stage.
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Old 3rd January 2013, 02:42 AM   #110
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Originally Posted by bcmbob View Post
That's the exact same kit I have. I'm still on a slab of plywood. Your build looks terrific and I'm going to look closely for ideas.

I just have a temporary heat sink of 1/4" x 3" x 4" flat stock but haven't had any heat related problems even after extended hours of operation.

I'm game to try a P2P if someone can provide a BOM. Sounds like fun.

My setup is JRiver to a Mini2496 DAC to the amps. Haven't found the need for a pre, though I did put the JC-2 clone in for an experiment. It didn't help much as the top end of the amp still needs to be cleaned up. More of the same isn't better
In part this the pcb. to build it.
could you post this information in PDF format.
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