I assembled 2 channels in about half hour. It is very easy. Much of the parts are SMD and already soldered to PCB.
Do you recommend a heat sink on the AC rectifier?
Slight update on my Sypmatico impressions and mods:
I tried Sympaticos with Heco Statement speakers which have 2 bass drivers in parallel and fall down to 3.5 ohm and it was definately a heavy load on amps - heatsinks got so hot we had to use fan to cool them. And while they did decent job driving those speakers - much more powerfull discrete AB class amp did a lot better, especially in bass. However with everything that is at least 5ohm Sympatico show excelent bass control, speed and attack. So i'd say 5-4.5 ohm is minimum i'd use it with
As for caps:
I replaced main caps from 15000 panasonic ECO to Cornell-Dubilier 22000uF 380LX which are slightly lower in impedance. While difference is slight - it definitely was a small improvement in various areas and especially in bass, but nothing too radical.
Smaller caps however show biggest influence on the sound. i gave Nichicon KZ another try, this time letting them work for weeks and still didn't like them - they have less bass, less dynamics, more grainy highs and are somewhat brighter, not as involving and clean sounding.
Then on the contrary i decided to try Panasonic FR 820uF which has lowest impedance among all panasonics (37% lower than stock 470uF FMs) - again, main changes are in bass i think but also something else which is harder to grasp
All caps change sound of the amps to bright and flat with poor bass while new, burn-in is a must and take quite some time.
After all this time i like how Sympatico sound, they are free of glare and brightness, a rare combination of smoothness, detail and dynamics which one do not expect for such amps.
I tried Sympaticos with Heco Statement speakers which have 2 bass drivers in parallel and fall down to 3.5 ohm and it was definately a heavy load on amps - heatsinks got so hot we had to use fan to cool them. And while they did decent job driving those speakers - much more powerfull discrete AB class amp did a lot better, especially in bass. However with everything that is at least 5ohm Sympatico show excelent bass control, speed and attack. So i'd say 5-4.5 ohm is minimum i'd use it with
As for caps:
I replaced main caps from 15000 panasonic ECO to Cornell-Dubilier 22000uF 380LX which are slightly lower in impedance. While difference is slight - it definitely was a small improvement in various areas and especially in bass, but nothing too radical.
Smaller caps however show biggest influence on the sound. i gave Nichicon KZ another try, this time letting them work for weeks and still didn't like them - they have less bass, less dynamics, more grainy highs and are somewhat brighter, not as involving and clean sounding.
Then on the contrary i decided to try Panasonic FR 820uF which has lowest impedance among all panasonics (37% lower than stock 470uF FMs) - again, main changes are in bass i think but also something else which is harder to grasp
All caps change sound of the amps to bright and flat with poor bass while new, burn-in is a must and take quite some time.
After all this time i like how Sympatico sound, they are free of glare and brightness, a rare combination of smoothness, detail and dynamics which one do not expect for such amps.
There is much more to it than speaker impedance. 
I have driven 4 ohm speakers easily if they have reasonable sensitivity. Also you may want to increase your heatsink size and or transformer size. I use a 1000VA with a soft start - but it is definitely overkill. I would agree that Sympatico is best suited for 6-8ohm speakers - but I use it regularly with 4-ohm speakers with sensitivity > 88db
Cheers!
Russ
I have driven 4 ohm speakers easily if they have reasonable sensitivity. Also you may want to increase your heatsink size and or transformer size. I use a 1000VA with a soft start - but it is definitely overkill. I would agree that Sympatico is best suited for 6-8ohm speakers - but I use it regularly with 4-ohm speakers with sensitivity > 88dbCheers!
Russ
Russ, Alexander, et al...
In your experience does supply voltage have any influence on Sympatico 'coloration'? I'm 'burning-in' a new one using an on-hand 25VAC transformer. It sounds fairly bright... My older TPA amps seemed slightly more neutral with 22vac supplies than with the 25. But not sure if that is just my imagination...
In your experience does supply voltage have any influence on Sympatico 'coloration'? I'm 'burning-in' a new one using an on-hand 25VAC transformer. It sounds fairly bright... My older TPA amps seemed slightly more neutral with 22vac supplies than with the 25. But not sure if that is just my imagination...
Sympatico? Coloration? Can't be
I had exactly same impressions at first
If you just assembled it - it will change with burn-in, mainly because of capacitors - it's always the case in my experience and may take various amounts of time, especially with those big panasonics - they tend to be somewhat bright at first, but become darker later.
As for voltage - i often heard you get more current (thermal related headroom?) with LM chips if powering by lower voltage, maybe it's the case with you so you're getting stonger bass and tonal balance is different? I was powering mine with 22V from the start and can't say they ended up brighter than other of my commercial or DIY amps. At the moment they are disassembled and await for finall enclosure so can't compare...
I had exactly same impressions at first
If you just assembled it - it will change with burn-in, mainly because of capacitors - it's always the case in my experience and may take various amounts of time, especially with those big panasonics - they tend to be somewhat bright at first, but become darker later.
As for voltage - i often heard you get more current (thermal related headroom?) with LM chips if powering by lower voltage, maybe it's the case with you so you're getting stonger bass and tonal balance is different? I was powering mine with 22V from the start and can't say they ended up brighter than other of my commercial or DIY amps. At the moment they are disassembled and await for finall enclosure so can't compare...
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Here is a comment on this thread's topic - sonic impressions of the Sympatico amp.
Cap 'burn-in' can take hundreds of hours and that 'end point' is still a good while away. Also, I will confess to messing with the part mix a bit. I substituted two caps each in for C3 & C4. I used a 400v .22 uF metalized polypro plus a small value Vishay 1837. Also, there is a big 4.7 uF ClarityCap MR on each input ground. Burn in is coming along slowly, yet some of what I hear is unprecedented to my ears.
I have some older opera recordings that I never could thoroughly enjoy. When everybody gets emotional and you have a tenor and a soprano singing at each other full bore and the orchestra crankin'... and of course they are playing in an acoustically live space ... Even with Deutsche Gramophone's best preamps and microphones, at some point the signal became one big ball of glare. I used to be down on the DG recording engineers but I'll tell you this - Sympatico is sorting that mess out! Pavarotti, M. Freni, the Berlin Philharmonic, all trying to blow the roof off the house... and now for the first time at "near first balcony volumes" I can hear the tenor, distinct from the soprano, different from the string sections, different from the horn section. That's pretty great! There are other examples in music that I've had for a long time - lots of new details are coming to the surface in places where dissonance is being suppressed. I can hardly wait to see/hear where the amp ends up after the caps and LM chips are all settled.
[Credit due also, of course, to Botic/Hermes/Cronus/B3se/Legato(w/ cap tweaks)/JBL transducer motors]
Cap 'burn-in' can take hundreds of hours and that 'end point' is still a good while away. Also, I will confess to messing with the part mix a bit. I substituted two caps each in for C3 & C4. I used a 400v .22 uF metalized polypro plus a small value Vishay 1837. Also, there is a big 4.7 uF ClarityCap MR on each input ground. Burn in is coming along slowly, yet some of what I hear is unprecedented to my ears.
I have some older opera recordings that I never could thoroughly enjoy. When everybody gets emotional and you have a tenor and a soprano singing at each other full bore and the orchestra crankin'... and of course they are playing in an acoustically live space ... Even with Deutsche Gramophone's best preamps and microphones, at some point the signal became one big ball of glare. I used to be down on the DG recording engineers but I'll tell you this - Sympatico is sorting that mess out! Pavarotti, M. Freni, the Berlin Philharmonic, all trying to blow the roof off the house... and now for the first time at "near first balcony volumes" I can hear the tenor, distinct from the soprano, different from the string sections, different from the horn section. That's pretty great! There are other examples in music that I've had for a long time - lots of new details are coming to the surface in places where dissonance is being suppressed. I can hardly wait to see/hear where the amp ends up after the caps and LM chips are all settled.
[Credit due also, of course, to Botic/Hermes/Cronus/B3se/Legato(w/ cap tweaks)/JBL transducer motors]
I can now answer my own question... While sound was fine running at 37 VDC, I was concerned about heat. A ~1.0 degree/watt heat sink was often near my preferred upper limit temp, and the heatsink was in open air. I want to house the amp in a cabinet where ambient will be a bit higher. I changed to twin 400VA 22VAC transformers and the chips are now seeing 31.7 volts. The chips heat almost as much for max output, but run cooler at moderate output and below.
Sound difference? Very slight improvement in 'smoothness' by moving down 5 volts. Transients at high output may be slightly less dynamic, but resolution at high output seems improved. Comparing the input signal (headphones on the Legato buffer) to output, I reckon that capacitor burn-in is mostly complete. I didn't do an A/B comparison on the 10nF MKP 1837 film bypass caps that i added to Sympatico but my impression was that they added clarity in upper registers compared to my other TPA amps. I was not liking the sound of my tweeters much so on the (balanced TXO) amp that drives the tweeters I swapped out the Wima bypass caps for 0.1 uF MKP 1837s. Above 4000Hz I heard an immediate improvement in clarity. Brushes on the snare drum immediately jumped out sounding authentic, and cymbals, etc. are also improved. Conclusion is that the MKP1837s on the power side will dial up the 'sizzle'...
Sympatico is done and I look forward to years of enjoyment!
Agree with the last point. Four thoughts re the other recommendations:
1. I used a bridged amp with paired LM3886 chips at +/- 37 volts for 8 years. The chips still work.
2. Consulting the LM4780 data sheet, the maximum supply voltage is listed as +/- 42v on page 4.
3. Figures 15 and 18 from page 11 (photo) suggest that +/- 28v is quite conservative and gives up significant potential power.
4. The LM4780 has built-in protection against damage by a) over voltage, b) instantaneous thermal spikes, and c) long term over temperature of the die. That long-term thermal cutoff is 150°C - way hot!
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I assume you are referring to table 1 here: http://www.ti.com/lit/an/snaa021b/snaa021b.pdf
This information seems intended for configurations of LM3886. If I am not mistaken, the amp circuits being replaced by my Sympatico are that very configuration of 3886s. So again, I had no problem after 8 years of running at +/- 37v and driving midranges that can dip down to 6.2 ohms. I am not an engineer nor qualified to critique the circuits per se. If you have a brief explanation of why in this BR100 circuit Ti apparently derates their chips compared to the abilities listed in the chip's data sheets, it might be academically interesting. Is it simply related to heat dissipation? In any case, I'll be running at +/-31.7v and just take my chances!
Cheers,
Frank
Unless you simply have no other transformers i see no reason to run higher voltage. I'm going to re-assemble my Sympaticos soon and i'm actually thinking of using 20V trafos - there's more than enough watts already, if only running higher voltage could add more current capability as well, but i heard it's the opposite...
It's all explained in the application note in detail (see Pdmax). Basically if you exceed 40W per IC then the limiter will kick in. The LM4780 essentially has 2 LM3886 ICs in the same die and is isolated hence the lower Pdmax limit as opposed to the LM3886T or LM3886TF ICs.
By all means, run it at 31.7v and report back!
By all means, run it at 31.7v and report back!
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Doesn't figure 15 (copied above - 8 ohm example) of the data sheet inform this decision? Watts and voltage being proportional, I see a slope of less than 1 only below about 17 volt rails (where you get only 15 watts per channel).
Back to figure 15 again, I see no inflection point at or near the a 40 watt/channel output and the text concerning Pdmax suggests to me that the 'limiter' is in fact the built-in thermal protection. Am I confused or is figure 15 incorrect or irrelevant?
By all means, run it at 31.7v and report back!
That is happening for sure and with adequate cooling. The sound from Cronus-Legato-Sympatico is quite refined.
My Legato balanced doesn't kick out much more than 1.2 volts so this is also a setup consideration. Perhaps other sources might be more likely to result in thermal protection issues.
Here is the current output from one LM4780 channel vs. supply voltage. This was simply approximated ('eyeballed') from the 1% data in figure 15 of the data sheet (watts/voltage). So, higher voltage rails give more output current. Another advantage of higher supply voltage is shown in figure 28 - a half volt increase in clipping threshold. ...just have to manage the heat...
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