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Legato Tweakers Thread...

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I am coming from listening to a full dual mono Buff 2 IVY Placid to a stereo Buff 2 Legato Placid run at 12V no buffer stage and leaving the bias at 0 volts instead of 1/2 AVCC. I prefer the Legato about 1/3 of the time. It lacks the frequency extremes, missing some air and sparkle at the top and the tight solid bottom of the IVY, but it presents an ease of delivery and a warm full balanced mix.

Jump to 15 V rails and biased to 1.72 volts on the input. Now I prefer the Legato more than half of the time. It is more dynamic at the higher rail V with better control of the low frequencies.

Lets get real and go full dual mono Buff 2 Legato. On average bout 3/4 of the music library the preference is now for the Legato. Still waiting to replace Ballsie with Ventus.

Can't wait for Legato 2.
 
Multible fet's - don't like it

Hi there..

I have been making 2/3 of a Legato2 - only doing two fet's in parallel.


It took me 'round 14 seconds to form the verdict, the special character was gone.

The sound was shut, the dynamics lacked, the bass was tame. (and the fet's was orientated correctly)

In shot - I didn't like it.


But hey, that's only me.
 
Legato supply voltage

Hey Russ and Brian,

Hope you guys are enjoying your "vacation"-please feel no need to reply here until you are back at "work" for TPA.
I am playing around with some different power supplies for the Legato (note, I am running balanced only, no buffer), and was wondering if you have tried even higher supply voltages. With the 25V caps appearing to be the limit, I was wondering if +/- 18V could be even better than +/- 15V? Soon I will have have to make a transformer choice, and I am leaning towards trying the higher voltage, but am wondering if you have experimented with this. Also note I am running 180R/390R 1 watt resistors for 1.9 volt output.
 
I am always happy to post with a morning cup of coffee. :D

Brian is likely busy putting in his much needed boiler.

If you are running balanced only. Then yes you have a lot of freedom to experiment. the 25V caps on the legato can be replaced or even omitted.

What I have found is that with the CFP there is a point of diminishing returns and that happens to be about 15V.

That said, if you want you can actually short the CFP resistor and omit the P channel devices and use a TO-220 N channel FET. If you do that you will have a classic "D1" type common gate stage. Then increasing the positive rail will help a lot.

You can always leave the negative rail relatively low. Its up to you. It's purpose in the cct is just to provide current for the uppper part of the circuit.

Here is how I am running my Legato (2.0.0 PCB with 3 FETs per side per half):

I/V resistor 105R(I don't need 2VRMs, 1.2 or so is fine).
Current source resistors are 475R (2 x in parallel)

Basically you can use the negative rail to tweak the amount of current and thus the bias point for the top half.

I aim to bias the output at about (VCC/2)-1V So in this case I was aiming for about 6.5V. This in my experience is a sweet spot.

Positive rail 15V.
Negative rail 13V.

It sounds delightful. :)

Now if you are going to experiment, be sure you understand the implications. Calculate the power dissipated and the supply requirements carefully. Your on your own here, but it is certainly manageable. I will help out if I can.

Cheers!
Russ
 
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Thanks Russ

That gives me a lot to think about, and additional understanding of the circuit (I am just starting to figure out a little about how these circuits work).
I am looking forward to Legato II (I do not want to experiment with my current Legato board, as I am enjoying listening to it too much right now!).
 
Interesting...

Hi there..

I have been making 2/3 of a Legato2 - only doing two fet's in parallel.


It took me 'round 14 seconds to form the verdict, the special character was gone.

The sound was shut, the dynamics lacked, the bass was tame. (and the fet's was orientated correctly)

In shot - I didn't like it.


But hey, that's only me.

I was wondering, are you using Placid(s) for power, and did you adjust the current output to suit the new load?
 
Film Decoupling Caps

I was wondering if anyone has tried this: If one is using shunt regulated supplies for the Legato, with short leads, it is possible that the 6 onboard 100 uF decoupling caps are not entirely necessary-what about replacing them with some 1 uF decent quality film caps? Does this sound like a good idea... in theory this might result in a "faster" power supply, with better high frequency characteristics, and no downside. What do you guys think?
 
I had another problem just after fitting the extra one set of fets. Cracking and popping sound in one channel, turned out to be the 1w resistors. Changing them all cured the problem. The story is on TPA support forum.

So yesterday I mounted additional 8 fets.

Yes, I'm running it of a Placid.

I don't see any additional load on the power supply after paralleling now 8 fets. It's steady at 160mA / rail. The only thing you have to do is readjust the input offset, it changes along with the number of fets.

Still forming my opinion....
 
Leo, what do you think. 1,2 or 3 fets ?

I have to figure out what's going on here. "Before", when I had the cracking noise, with the original 1w resistors and only one fet mounted, I had the most wonderful involving sound (hard to describe sound). I could hear a lot of ambient around ex. a piano. The low end extension was second to none.

Now, after have changed the resistor to the nearest obtainable values (150R ->180R, 330R -> 390R) AND running on 3 fets, it's kind of a flat experience to listen to the thing. Well the cracking is gone (good) but so are the special sound. It could be due to it playing more precise in the low end region (and my speakers not being able to go that deep), or the fact its not playing at all. Anyway, bass performance has changed.

Having bought enough of the resistors, I could easy parallel the 180R and the 390R with a pair equal, if lower resistance is the key. I don't need the higher output voltage swing.

Or I could remove the extra fets ?

:rolleyes:
 
Member
Joined 2007
Paid Member
First impressions...

My new B2/Legato (version 1) came to life tonight and the info I've read here has been very helpful. The new DAC replaces an Opus 8741 in handling the main mid/treble voices in the bi-amped front channels of my all-balanced rig. Source is I2S from an external sound board that is receiving 96/24 (Win7, Quicktime, Thuneau's Allocator crossover). Other channels use Opus DACs and all use TPA Overture amps. Legato has no buffer and Bal/SE is not powered. I've made 2 minor mods: A) 180/390 ohm PRP gain resistors and B) matched 4.7 uf Auricap output caps rather than the little electrolytics. Yes, they ARE big and clunky... :)

First impressions:

* At 13 volts, the B2/Legato set up with a 180 ohm lower resistor plays as loud as an Opus 8741. Of course, I expect the Buffalo 2 to sound better - but included in my first impressions is the opinion that in a balanced multichannel environment the Opus is still great. Considering it's super bang/buck, Opus does a great job with the bass, and remains very desirable for all but the most critical signals. Eventually I'll compare the two outputs using identical signals and the 'scope.

* Orchestral music, ALL the wood-and-string instruments (including piano), percussion, and choral music seem to benefit most from the B2/Legato. Some of these recordings have remarkably more 'life', depth and personality than previously. Delightful! :D Electronica: Yes, more 'space' and detail, but less 'wow' than acoustic material.

* This may not hold up as I dial-in the performance, but early on it seems that there is more *improvement* in the sound of lossless ALAC files whose bitrates are lower (5-700kbps) versus higher (say, >1000 kbps). Imaginary? :confused:

* In some ways Legato reminds me of gear I retired after the best sounding tubes were no longer available. I used to test tube pairings using passages of ragged sax or 'gravel' voices. With that material thru Legato I did hear a couple very minor rough patches. I'll be returning to them for tweaking. ;) Placid current and/or Vminus?

* Thus far, I much prefer ~15 v operation but that could change. As with Opus, it might be that the final amplification determines the best settings. For music that sounds best 'stupid loud' (why grow up? :spin:), 12.5-13 v was better. As volume was decreased, more voltage was more pleasing.

I look forward to further developments and discussion as Legato 2 progresses. Fantastic work Russ and Brian!!!

Frank
 
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Leo, what do you think. 1,2 or 3 fets ?

I have to figure out what's going on here. "Before", when I had the cracking noise, with the original 1w resistors and only one fet mounted, I had the most wonderful involving sound (hard to describe sound). I could hear a lot of ambient around ex. a piano. The low end extension was second to none.

Now, after have changed the resistor to the nearest obtainable values (150R ->180R, 330R -> 390R) AND running on 3 fets, it's kind of a flat experience to listen to the thing. Well the cracking is gone (good) but so are the special sound. It could be due to it playing more precise in the low end region (and my speakers not being able to go that deep), or the fact its not playing at all. Anyway, bass performance has changed.

Having bought enough of the resistors, I could easy parallel the 180R and the 390R with a pair equal, if lower resistance is the key. I don't need the higher output voltage swing.

Or I could remove the extra fets ?

:rolleyes:

I went straight from 1 fet to 3 fets.
Things I like, more presence in the upper mids, some complex material sounds less confused , crowds on live recordings are easier to make out.
I don't like a bright sound but finding high's have that slightly rolled off effect (its not rolling off but gives the effect imo) , cymbals a little too smooth lacking shimmer, strings on acoustic guitar sound a little thicker.
Resistors in mine are the stock ones, everything looks ok on the scope.

Did you try +15v and -12v ? I'm wondering if this makes a noticeable difference . I currently run +/-12.5v
 
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avr300 While the ratio is close with changes on the order of 20% to the r values you might want to replace with exact values to eliminate that from the listening equation. On the other hand did you ever measure the bad R when it was hot and operational? Its value might have been significantly off as well. Also be sure to adjust the bias as this made a big difference. One last thought is to check the shunt current of the power supply to be certain that the higher current demands of the lower value resisters aren't eating away the headroom needed for stiff regulation of the power.

Can anyone describe their opinion of the FET Legato 2 vs the bipolar original? I am wondering if I should modify my original or wait for the Legato 2 to be available to compare directly.
 
avr300 While the ratio is close with changes on the order of 20% to the r values you might want to replace with exact values to eliminate that from the listening equation. On the other hand did you ever measure the bad R when it was hot and operational? Its value might have been significantly off as well.

That's why I thought paralleling the resistors with equal values, obtaining 90R / 195R, but I can't do the power dissipation calculation. 150R / 330R are not within reach here.

No, I didn't measure the hot once.

Also be sure to adjust the bias as this made a big difference.

Has always been trimmed to 1.70V

One last thought is to check the shunt current of the power supply to be certain that the higher current demands of the lower value resisters aren't eating away the headroom needed for stiff regulation of the power.

Yes, I have had control over the power supply all the way. But - with the defective resistors, the power demand was huge. I had to burn +400mA in the shunt. Now with the good (and slightly bigger) resistors in place, it eats just 160mA, no matter how many fets I have mounted.
 
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Joined 2007
Paid Member
Did you try +15v and -12v ? I'm wondering if this makes a noticeable difference . I currently run +/-12.5v

Greetings. I am playing with Legato version 1 (balanced) and am finding small tweaks really affect the special sound quality and dynamics that I believe AVR300 and Stephen 1212 describe. There really IS a distinct emotional quality when Legato is running at it's best. Now that my boards/output caps are 'burned-in', I have none of the misbehavior with challenging material noted in first impressions. (see above)

I most prefer: at least 80ma current headroom and equal values for Vplus and Vminus. Increasing from 14 up to to 15 volts there is some magic that occurs, bringing out cymbals, bow rosin, piano harmonics, studio noise, etc. I have never heard a system this involving before. Between 14 and 14.5 volts the magic develops and I am always tempted to turn the system up. At 15 volts the sound begins to 'shout' just a bit and I'm inclined to turn the system down because instead of sounding powerful the music can begin to feel loud. The current compromise of 14.7v grabs my attention at low volume and doesn't disappoint when cranked up. This leaves me slightly skeptical and wondering about the implementations where Legato 2 could possibly sound better.

Now I have to case up all these warm green boards with pears on them in a way that eliminates a set of balanced interconnects.

Cheers, Frank

Off topic PS (sorry Brian!) :eek:
Cuidado! - the bandonneon, the musical soul of the tango, played through the Legato can rip your heart out... e.g.: Astor Piazzolla and his group playing 'Milonga Del Angel'. (YoYo Ma's version is very nicely recorded, IMHO.)
 
See, you got it - I lost it.

I took her apart again (for who know which time) and noticed, that the power resistors is NO way as hot as they used to be. And I mean no way. They are cold.

So my plan now - if the following is going to work, is to leave the 3 FETs and then:


Russ, will you help me please. Will this work ?

"That's why I thought paralleling the resistors with equal values, obtaining 90R / 195R, but I can't do the power dissipation calculation. 150R / 330R are not within reach here."

or am I going to fry something ?
 
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