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Old 2nd January 2013, 06:28 PM   #91
bcmbob is offline bcmbob  United States
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redjr,

The "scope creep" you mention should definitely be explored and stated openly and honestly. My first LM3886 project was the BrianGT where the full build cost for two momoblocks was~ $125. My last MyRef Fremen Edition came in around $650 with all the top choice components - and no chassis yet. Such differences in investment dollars might indeed be involved here. The larger outlay proved justified for that project.

Again, I think your question, paraphrasing, "Just what do we get for all that effort" is surely valid and hopefully members will share their views on that here.
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Old 2nd January 2013, 06:44 PM   #92
bcmbob is offline bcmbob  United States
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Oh My! How gosh of me to not thank KSTR for offering his services

My apologies........

Thanks buddy, lets hope it flies.
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Old 2nd January 2013, 07:03 PM   #93
redjr is offline redjr  United States
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redjr,

The "scope creep" you mention should definitely be explored and stated openly and honestly. My first LM3886 project was the BrianGT where the full build cost for two momoblocks was~ $125. My last MyRef Fremen Edition came in around $650 with all the top choice components - and no chassis yet. Such differences in investment dollars might indeed be involved here. The larger outlay proved justified for that project.

Again, I think your question, paraphrasing, "Just what do we get for all that effort" is surely valid and hopefully members will share their views on that here.
I know from personal experience that scope creep can, and does often derail the original project resulting in unanticipated and unforeseen costs overruns - especially in the business world. My DIY projects - as well as I try to plan them - often involve costs I didn't foresee. So, it can be a very real component/issue of an overall DIY project too.

Now the perceived 'value' issue for mods relative to the investment is surely a subjective factor and will vary with the user. I for one, am more skeptical than most, in searching for the ultimate sonic holy grail. But I don't fault those who try. More power to them! I'm more of an integrator of existing modules to see how I can pull them all together in a well executed, finished project. To me that is very satisfying. I just happen to know my limits when I tackle an amp and the degree to which I start to delve in at the component (or arrangement) level.

Maybe we could start a 'kickstarter' project to defray the cost that any single member might bear in helping make this happen.

Rick
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Old 2nd January 2013, 07:49 PM   #94
KSTR is offline KSTR  Germany
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On my way back home in the subway I was thinking about amplifier concepts that make sense doing a new PCB. For the most basic circuit it doesn't make too much sense to me, just hook it up point-to-point (see Daniel's example) or use any of the boards available and see how it goes with any mods (both on PCB tracks and components).

I'm more inclined to do a topology that isn't bog standard and which takes care of the sonically most important issue of having the negative front-end supply (of the chip) at a clean AC ground -- virtually free of supply and load current ripple -- which is not too difficult with an inverting configuration, also having the benefit that there is no common-mode signal on the chip's input pins.

Further, I'm not a fan of fully independent mono-blocks (even when in the same chassis), so a complete stereo PCB with most of the supply components on board seems more adequate for most builders I would think. For DIY we also have the option to make use of unorthodox layout/component placement as we do not need to care about feasibilty for mass production (which means sticking to all SMT parts located on the same side).

Finally I always strive for low complexity and very moderate BOM cost using standard parts (like I have to do in the day job). Design and layout is much more important than using expensive boutique parts IMHO. Using those is the final step of fine tuning if all else is done right already.

Does this sound like a good starting point to everbody?

For evaluation and comparison I'd first need to finish the MyRef FE boards that are still waiting for being stuffed, though... atm I only have one channel of a pre-RC version of it at hand.

- Klaus
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Old 2nd January 2013, 08:50 PM   #95
bcmbob is offline bcmbob  United States
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Hey Klaus,

You really sound like what the doctor ordered. The first thing that comes to mind is whether you (and those who may just be watching) have actually heard what this chip produces. I looked back through the thread but couldn't tell for sure.

I've become a huge fan of SMD components where useful to reduce both costs and size - from a builder's perspective. Dario Inserra's combinations on the FE have certainly benefited that design.

Please do finish your MyRef project. In all honesty, I'm here because I am totally thrilled with that amp, but realized my praise of it was somewhat empty because I hadn't actually listened to anything other than LM3886 based amps since the beginning of this second (did Dynaco and Hefler kits years ago) venture into DIY - about three years.

So I set out to build something from the Pass community and a TDA????, as those were the categories about which I read the most raves. With the completion of Nelson's Amp Camp beginners project (a full blown F5 based build near completion) and this TDA kit it became clear that there wasn't going to be (for me) any need to determine the "best" power amp - more correctly a desire to take each approach as far as my skills and wallet would allow. The characters of the three categories are so unique that having several amps now is justified in my mind. It's similar to having a small car collection, a couple sets of golf clubs or even a nice selection of favorite wives

I don't know if it is jumping the gun, but it might be useful to establish a sign-up sheet just to determine the level of interest before the venture actually begins.
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Last edited by bcmbob; 2nd January 2013 at 08:53 PM.
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Old 2nd January 2013, 09:39 PM   #96
KSTR is offline KSTR  Germany
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The first thing that comes to mind is whether you (and those who may just be watching) have actually heard what this chip produces.
Bob,
Well, besides working with these chips for years on a private/hobbyist level, a reasonable amount of my day job in recent years was designing amplifiers around TDA729x series chips, as well as LM3886 (+LM4780). Most of them have been constrained by lowest BOM cost, smallest PCB real estate and such issues (in the context of the complete products they went into), therefore they do not always exploit the full capabilites of the chips.

So, that's where DIY shines, no real cost/feasibilty contraints and most importantly, no strict product deadlines that tend to block any creativity and experimenting. With the boss standing behind you reminding you to send out the PCB mfg data tomorrow as scheduled you really think twice before ripping up an almost finished layout in the quest for an even better routing... and then when the PCB arrives there seldom is time to fully debug and optimize it in all details (let alone the circuit, unless with real faults) before starting production....

Today, I also finally have all the professional lab equipment to dig down into what's really going on and then try correlate why it sounds the way it does...
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Old 2nd January 2013, 09:53 PM   #97
bcmbob is offline bcmbob  United States
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How perfect is that !! The DIY gods have truly blessed us. I'm getting excited now.
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Last edited by bcmbob; 2nd January 2013 at 09:56 PM.
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Old 2nd January 2013, 09:56 PM   #98
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I am truly excited things took this direction, and very quickly!
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Old 2nd January 2013, 10:04 PM   #99
bcmbob is offline bcmbob  United States
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Klaus - with your experience is the 7294 the best of that series for a project like this?
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Old 2nd January 2013, 10:14 PM   #100
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Originally Posted by KSTR View Post
I'll happily volunteer for circuit design and PCB layout of some varieties of TDA7294 amplifiers, trying to cover all the important aspects.
Interesting

Quote:
Originally Posted by KSTR View Post
For DIY we also have the option to make use of unorthodox layout/component placement as we do not need to care about feasibilty for mass production (which means sticking to all SMT parts located on the same side).
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.

Quote:
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For evaluation and comparison I'd first need to finish the MyRef FE boards that are still waiting for being stuffed, though... atm I only have one channel of a pre-RC version of it at hand.
Yeah... I've some interests in reading your comments and measures...
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