Well it certainly helps to keep the ripple down to have two things - plenty of trafo - and nice beefy caps. 
But what I was really saying is that because of the the over-current (and thermal) protection features of the chip you will generally hit the current limit before you clip (run out of voltage) if your rails don't sag below say 25V.
But what I was really saying is that because of the the over-current (and thermal) protection features of the chip you will generally hit the current limit before you clip (run out of voltage) if your rails don't sag below say 25V.
Thanks for the clarification, Russ. I'm really enjoying the amp! ...smooth, detailed, punchy when needed [e.g. great pianos sound truly masterful]. The LM4780 does seem to run warmer than paired LM3886s, but if the thermal protection circuitry doesn't kick-in till 150°C (and momentary @ 250°C!) then I'm confident to be extracting all the headroom I need and then some... Cheers!
Is it possible to set Sympatico up in unbridged configuration?
I know this thread is a bit old, but it seems to be on point with my recent search for a good chip amp project. The problem is that my speakers (ML ESL) have a variable impedance that dips quite a bit at the higher frequencies. (See attached, the impedance is in yellow, the other trace is the phase.) I noticed from the application notes that the LM4780 is designed for low impedance loads by paralleling two LM3886. However, by operating it in bridged mode you defeat that advantage. Hence my question, can I "unbridge" it? Also, I suspect reducing the voltage may help, but I think that LM3886 is known to be better for higher impedance loads.
Thanks for your thoughts.
Jazzzman
I know this thread is a bit old, but it seems to be on point with my recent search for a good chip amp project. The problem is that my speakers (ML ESL) have a variable impedance that dips quite a bit at the higher frequencies. (See attached, the impedance is in yellow, the other trace is the phase.) I noticed from the application notes that the LM4780 is designed for low impedance loads by paralleling two LM3886. However, by operating it in bridged mode you defeat that advantage. Hence my question, can I "unbridge" it? Also, I suspect reducing the voltage may help, but I think that LM3886 is known to be better for higher impedance loads.
Thanks for your thoughts.
Jazzzman
No - the amp is inherently fully symmetrical - meaning it has to operate in a balanced (bridged) configuration. Still - as long as you are not pushing it too hard I think it should drive that speaker fine. Sometimes you just don't know until you try. I have some similar DIY speakers that my Sympatico drives just fine as long as I don't try to get too crazy pumping power through them.
I have some similar DIY speakers that my Sympatico drives just fine as long as I don't try to get too crazy pumping power through them.
I think your scenario is very low risk.
If you keep the power below the 50-80W area you should be just fine driving really just about any 4ohm speaker - and the sound is superb - noise floor is imperceptible and the amp is very linear and distortion free thanks to the fully symmetrical topology.
Cheers!
Russ
If you keep the power below the 50-80W area you should be just fine driving really just about any 4ohm speaker - and the sound is superb - noise floor is imperceptible and the amp is very linear and distortion free thanks to the fully symmetrical topology.
Cheers!
Russ
A mini audio project over last weekend was to update an older TPA amp. I didn't need a whole Sympatico kit so I went with bare boards. Since LM4780s are no longer available, I substituted 3886's, like the amp being updated. No smoke, no problems. Output is to tweeters only, and they are crystal clear... Attached is the pin layout, in case anybody else has reason to try this. Cheers!
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The old heatsinks were perfect for the paired 3886s. I realize their S/N isn't quite up there with the 4780, but this works. I would certainly trust our friends here, but I'm naturally skeptical about the quality of hard-to-find parts from far-flung internet sources. Stress on the board? I used dead-soft solid silver to connect so there would be no stress at all.
Experience with a previous Sympatico suggests it will be a good while before the sound settles into 'normal'. All for fun, really...
F.
“Stressing the board” ? I was thinking that you will eventually replace those lm3886 chips with one lm4780 . I do like the way you used the board though . I am a big fan of the lm4780 chips, I tried a lot of boards , but not the sympatico.
I am curious why mr White Russ stoped offering this: http://www.twistedpearaudio.com/docs/legacy/tpm/tpm-lm3886.pdf
I am curious why mr White Russ stoped offering this: http://www.twistedpearaudio.com/docs/legacy/tpm/tpm-lm3886.pdf
Actually because of the way the OP1632 dominates this circuit using two LM3886 should work out very very well - in some ways maybe better than a single LM4780.
As to why we didn't continue with the TMP/TXD idea was just simply that Sympatico was a tighter solution with less cost and effort. Also one of the design goals of the old TXD/TPM scheme was to be able to parallel TPM modules - and in practice that was very hard to keep stable. All in all though - the idea was fun and in many ways still feasible.
This morning I did this:
Any thoughts?
Cheers!
Russ
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The photo below shows the TPM/TXD modules that came off of the heatsinks onto which the current Sympatico mod boards were attached. My TPM/TXD amps served very well and gave me years of pleasure. When the DIY bug bit to upgrade, I built an Aleph J. It sounded great but was just not a good fit as my system evolved - sooo much heat! So my next amp project was a new Sympatico, which was very pleasing and very comparable in sound to the Aleph J (with my drivers). Comparing my builds and uses, Sympatico (w/ 4780 & 45K uF capacitance/channel in the PS) is noticeably more refined than the TPM/TXD amps with their 3886s. ...and just last weekend I could hear an immediate improvement in the >2kHz band with the Sympatico/3886 vs. the TPM/TXD. BTW, both new channels showed only 12 mv DC out on first cold startup.
Re: Russ' musing, I seriously thought about adding extra decoupling caps on the little 3886 adapter boards! I recall reading about 10 years ago that decoupling directly to the power pins of 3886 gainclones helped eliminate some noise. But I finally ruled it out for a number of reasons, among them my pleasure with my alredy-running Sympatico and the fact that the adaptation was an experiment.
All the best,
Frank
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Sadly, a nasty electrostatic discharge from my hand zapped the experimental Sympatico/3886 into silence. It happened as I was turning the power off while the air was extremely dry.
So... Worth trying to repair? Power rails seem ok. Since both channels are gone, I suppose we could assume the same component(s) failed on each side. Any speculation re which would be most susceptible, or suggestions re diagnosis would be much appreciated. I'm willing to replace anything except the 3886s, which are so 'in there for good' that I wouldn't bother.
TIA for any help!
Parenthetically, it could have been worse!
But repairing stuff is not as nice as listening to music, so I'll also isolate the entire system from ESDs. All controls - including power - will soon be managed by wifi remote.
It seemed the damage could have been in the 3886s so I started over, this time with more confidence in the quality of the outcome. I was about to start making some custom chip adaptor boards but then it struck me that I could re-work some of the retired boards. ...can hardly wait to power these up!
Frank
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A quick note to say 'mission accomplished'. Thanks, Brian, for helping me past a brain-freeze.
The Sympatico-3886 is a nice amp! My woofers are clearly playing tighter and with more control - especially 'cranked'. My other LM4780 Sympaticos are on 32V rails but this one is getting 36.5V. I tweaked the gain from stock to ~14x per side, but also added an extra 20mF capacitance to each power rail. I like that the re-purposed adaptor boards give each 3886 its own decoupling caps (note the nice inscription on the back
). The gray Vishay .22uf film decoupling caps are a personal favorite that I've used in my other Sympaticos as well. Cheers!
Attachments
I look forward to the product! As I was cutting the DC servos off of the old TPM boards for this amp, I was wondering... Would a really tight and symmetrical surface mount layout be enough to make parallel power chips 'play nice' together? The old TXO-4 concept but 'brilliantly executed in SMD'?
I ordered a single channel to see how it sounds. Will get a second if it works better.
Will use it to power an EDGAR SEISMIC subwoofer. Have been using a cheap class D amp - a Peavey/Crest that just seems to sound a little funny. Figure this will have to do better.
Using a XILICA XP2040 to drive the amp. Would like to bypass those (seemingly) superfluous input buffers unless you tell me NOT to do it. Figure it would be easy enough to remove R1 and 2 - use a leaded resistor connected to the input pad and the cable to the other. I really hate the idea of superfluous stages until I am told what their purpose is.
Let me know, please.
Will use it to power an EDGAR SEISMIC subwoofer. Have been using a cheap class D amp - a Peavey/Crest that just seems to sound a little funny. Figure this will have to do better.
Using a XILICA XP2040 to drive the amp. Would like to bypass those (seemingly) superfluous input buffers unless you tell me NOT to do it. Figure it would be easy enough to remove R1 and 2 - use a leaded resistor connected to the input pad and the cable to the other. I really hate the idea of superfluous stages until I am told what their purpose is.
Let me know, please.
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