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Old 6th October 2010, 09:16 PM   #41
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And again. Not easy to get images posted!

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Old 7th October 2010, 07:11 AM   #42
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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.
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Old 7th October 2010, 07:58 AM   #43
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Sorry my previous post belongs in the Legato or IVY thread. I don't see the edit button so maybe it could be moved to the proper thread.
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Old 7th October 2010, 07:01 PM   #44
avr300 is offline avr300  Denmark
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Default 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.
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Old 10th October 2010, 07:15 AM   #45
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Default 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.
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Old 10th October 2010, 01:46 PM   #46
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I am always happy to post with a morning cup of coffee.

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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Last edited by Russ White; 10th October 2010 at 01:53 PM.
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Old 10th October 2010, 03:45 PM   #47
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Default 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!).
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Old 16th October 2010, 06:28 AM   #48
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Default Interesting...

Quote:
Originally Posted by avr300 View Post
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?
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Old 16th October 2010, 06:32 AM   #49
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Default 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?
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Old 16th October 2010, 06:43 AM   #50
avr300 is offline avr300  Denmark
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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....
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