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Old 27th December 2012, 01:19 AM   #61
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I was all ready to jump into the switch mode power amp world (class D or?), when a good friend of mine who is an expert at switching power supplies mentioned that switch mode power amps are much less able to handle a part malfunction, than linear (class AB or?) amps. When just about any part in a switch mode power amp goes out, fuses or not, there's a pretty good chance the amp will blow up badly, and take the speaker with it... I've been using Hafler DH220's for 30 years because I used to fix them for a living at a sound company in San Francisco. They liked this amp because when it blew up, it did it elegantly. I never heard of one damaging the speakers when it blew. My personal experience is that they have failed 2-3 times in 30 years, and they just shut down, with minimal damage. If you need it to run on batteries, I'd still consider switch mode amps, but otherwise I'm staying with analog. The 3886 analog chip amp has been working real good for me lately.
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Old 27th December 2012, 01:38 AM   #62
bcmbob is offline bcmbob  United States
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A little of topic, but I have two DH120s , one I've owned for twenty years and am very impressed by their stability and longevity. The only problem I have had was when trying to drive a large sub in mono mode. Even then it just kept blowing fuses and everything else was safe. One has been upgraded with the kit sold on eBay and the other is just a matter of finding the time. They don't have all the high frequency quality of the newer offerings like the MyRef, but they certainly are a fine example from that period.
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Old 27th December 2012, 02:10 AM   #63
redjr is offline redjr  United States
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Quote:
Originally Posted by bcmbob View Post
Hi All,

Four weeks to ship and a few hours to build and I finally can hear a TDA7294. The kit is quite simple compered to the LM3886 MyRefs I'm used to. However, I am very impressed with the sound it produces. A short description would be warm, powerful (in my build), accurate and a bit relaxed. The bottom is cleaner and better defined at this "stock" level than the standard LM builds I have done, but not as powerful. I can clearly understand why so many like the character of this chip.

So let me do a few "IMHO" comparisons with the MyRefs and in particular thr Fremen Edition. What stands out the most is the difference in headroom. Below a particular volume level the TDA really shines. Anything above that shows a lot of inter-modulation distortion, harshness and strain. The last few versions of the MyRef stay clean all the way to max. I'm sure there is a lot more sophistication in the power supply technology for the MR than what this TDA build has now. It would be interesting to hear this amp with something specifically designed to power it.

Unfortunately, there are no props for the TDA's top end when compared to the MyRefs. Again, that may not be a fair comparison as the kit I built is bare bones from my understanding. The MR FE is silky, smooth, defined, airy and shimmering on all types of music. If you are familiar with it, Ravel's Daphnis & Chloe has a wide range of dynamics, instrument combinations and volume levels. As long as everything is soft to moderate the TDA sounds beautiful. It just doesn't take long/much for louder and higher range portions to get muddy and a touch blaring. Bells and chimes break through brightly during crescendos and loud finales, but just below that it gets pretty mushy. Some of that may be resolved with higher grade components on the build, which I hope to do soon.

What I hear in the dynamics in percussion and general mid-rang regesters is very impressive. Without any specific knowledge or technical background, I would suspect the TDA is simply "faster" than the LM3886. If anyone has that knowledge please pass it along. There is a real element of genuine excitement produced by this chip, particularly with wild classical tracks.

So the few hours I've owned a TDA7294 have been very enjoyable to say the least. I did run several passes of the Isotek burn-in cd that cleaned away some fuzz that was there at first power-up. This kit is capable of a BTL configuration and I am very interested in trying that as well as some of the other dual chip setups Daniel W. has suggested. At $30 for a two board kit with all the necessary do-dads, one can't go wrong and a second set won't break the budget.

Thumbs Up for the TDA7294

And....Happy Holidays Y'all.
Bob - I just completed a little 7294 build myself. You can find it here. Our modules look identical.
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Old 30th October 2014, 07:23 AM   #64
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Quote:
Originally Posted by danielwritesbac View Post
MyRef X2 Evo-2 (parallel lm3886 howland current pump)
...
And, Hooray!! LM3886 Parallel means quality outputs at last! ...
Long bump up - I got some time to fiddle with my 2-year old MyRef-X2 build over the last few days. Updated a few passives, and tweaked the compensation a bit, and all sounds fine.

On a random hunch, I tried an LME49990 mounted in a LF07 Class-A module - and it works! However, the compensation of the X2 differs from a stock Rev C to take into account the 2x transconductance of the Howland.

I'm yet to compare the LME49990/LF07 module vs. the LM318/LF07 module in a MyRef X2 in detail, but the preliminary impression is that the LM318 has better audible sonics - more transparent, vivid highs. The LME49990 sounds a bit veiled in comparison.

I think this fits in with previous attempts to use an LME49710 in a Rev C - most reports stated that it sounded a bit disappointing. I think that maybe the LME49710/49990 are probably more accurate and detailed, but less satisfying compared to the LM318. Probably human acoustic perception at work again.
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Old 30th October 2014, 08:51 AM   #65
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Well, one of the easiest things to do about the human perception, is to change the small signal area decoupling caps (The Power Caps at Amplifier Board locale, that are, hopefully, as close to the chip as possible). Stock condition for LM3886's is 470u per rails (according to the chip manufacturer), although most all other amplifiers should use half as much (especially if they're stable). Anyway, go larger for more laid back and less focus (to calm it down!) or smaller for more shout and more focus (to wake it up!).
That is fairly straightforward and an elementary step in fine tuning chip amplifiers. More can be done; however, this is one of those first things.

This amplifier board power caps (power decouplers) size is ballpark for most amplifiers at 330uF per each rail, although it may be altered up to 5 times in either direction, such as 1500uF to outright muzzle the thing for a possibly useful tone on an unstable amplifier at the cost of some detail loss or 68uF to wake up even the deadest sounding amp at the cost of losing some bass power.

If series elements are added, such as fuses, 6a05 diode, regs, inductors, or resistors (at the edge of the amplifier board, series to V+ and series to V-), then the game has changed--more capacitance can be added without dulling the amp; and for example, I think that series 6a05 followed by a parallel pair of 470uF (total 940uF) may work for the LM3875, LM3886, TDA7297, and other amplifiers that are on the verge of stable or not and may need some help with the tone, without either causing dulling or excess heat. Up to 2||680uF (tandem pair of 680u is 1360u) may be used with this approach. However, it could possibly be better to build a stable amplifier rather than overwork a hack, no matter how nifty it may be.

Anyway, there's a brief and some tomfoolery about imaging, tone, and perception, controllable via the power circuit.
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Old 30th October 2014, 09:24 PM   #66
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Quote:
Originally Posted by danielwritesbac View Post
Well, one of the easiest things to do about the human perception, is to change the small signal area decoupling caps (The Power Caps at Amplifier Board locale, that are, hopefully, as close to the chip as possible). Stock condition for LM3886's is 470u per rails (according to the chip manufacturer), although most all other amplifiers should use half as much (especially if they're stable). Anyway, go larger for more laid back and less focus (to calm it down!) or smaller for more shout and more focus (to wake it up!).
That is fairly straightforward and an elementary step in fine tuning chip amplifiers. More can be done; however, this is one of those first things.

This amplifier board power caps (power decouplers) size is ballpark for most amplifiers at 330uF per each rail, although it may be altered up to 5 times in either direction, such as 1500uF to outright muzzle the thing for a possibly useful tone on an unstable amplifier at the cost of some detail loss or 68uF to wake up even the deadest sounding amp at the cost of losing some bass power.

If series elements are added, such as fuses, 6a05 diode, regs, inductors, or resistors (at the edge of the amplifier board, series to V+ and series to V-), then the game has changed--more capacitance can be added without dulling the amp; and for example, I think that series 6a05 followed by a parallel pair of 470uF (total 940uF) may work for the LM3875, LM3886, TDA7297, and other amplifiers that are on the verge of stable or not and may need some help with the tone, without either causing dulling or excess heat. Up to 2||680uF (tandem pair of 680u is 1360u) may be used with this approach. However, it could possibly be better to build a stable amplifier rather than overwork a hack, no matter how nifty it may be.

Anyway, there's a brief and some tomfoolery about imaging, tone, and perception, controllable via the power circuit.
With the 3886 amp I built, I have 15000uF per rail in the power supply within about 5 inches of the four 3886 boards, and 1000uF per rail right on the 3886 PCB, which have a ground return to chassis star center that is separate from the other ground return to star center for the rest of the circuit. So I also have 0.1uF caps from both rails to Gnd. within a inch of the inside of the 3886 chip tied to the circuit ground of the 3886 chip. You want any circuit to see 0 ohms from DC to infra red, when it looks at the power supply, otherwise phase margin is a crap shoot. According to my research, that's the best way to do that. I also played with various pF size caps across the inputs and across the FB resistor, and various output LC combos to get rid of spurious oscillations when on the verge of clipping. Some of the phase margin design process can be done on paper, but everything physical comes into play at the very high frequencies (above audio), and is hard to predict with enough accuracy. Fine tuning any amp for best stability seems wise to me. It may be the main reason one amp sounds better than another.
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