Legato 3 - Look ma! No caps!

[Russ White]

natzev,

I have never used caps that have ever generated any heat, but it seems very odd to me that they would get hot unless they have very low equivalent parallel resistance. Try alternate caps. Those sound like they may be bad.

[natzev_i]

Russ,
Thanks for the reply! I ordered some polystyrens from ebay and will try your original Wimas from the kit of course and will report back. The thing that's worrying me is is it possible the Legato to oscillate and this to lead for these caps to get hot. Or in any case they shouldn't get so hot if are not bad?
Thank you!

[Russ White]

Whatever caps you use need to fit in their patterns and have short leads and extremely low inductance, or they will not do what they should. The caps we used in the design were chosen for a purpose. There is no good reason to change them.

[natzev_i]

Yes, I will listen to you and will put the original caps - hope everything will be all right then.
Thanks!

[Erlend Sæterdal]

Originally Posted by natzev_i

Yes, I will listen to you and will put the original caps - hope everything will be all right then.
Thanks!

The original caps are very good. Pure polypropylene without the pollution of metalization .

[natzev_i]

Thanks, Erlend - I know that - I just wanted to try some more "exotic" caps but obviously they didn't work right. Hope the Wimas will fix my problem.

[reactivepower]

I have searched this thread for the legato 3.1 balanced output impedance. I wasn't able to find any information. I am not sure looking at the schematic if I can properly tell what it is. What would est the output impedance in this circuit? Is it set by the R1/R2 and R3/R4 resistors? Can anyone provide a little guidance? Thanks!

[barrows]

Originally Posted by reactivepower

I have searched this thread for the legato 3.1 balanced output impedance. I wasn't able to find any information. I am not sure looking at the schematic if I can properly tell what it is. What would est the output impedance in this circuit? Is it set by the R1/R2 and R3/R4 resistors? Can anyone provide a little guidance? Thanks!

am not entirely sure, but I believe the Legato output impedance is a function of the I/V resistors, so for stock values, it would be 150 ohms per phase for the balanced output. Just as you suspected, R1-4.

[Erlend Sæterdal]

I read somewhere that is was 150 ohm ! In my case with R 1-4 = 360 ohm it must be 360 then ?

[barrows]

Originally Posted by Erlend Sæterdal

I read somewhere that is was 150 ohm ! In my case with R 1-4 = 360 ohm it must be 360 then ?

My understanding is that you are correct: 360 ohms per phase. I am sure Russ will eventually confirm (or provide more details on) this. Russ has pointed out that changing the gain of the Legato does involve some compromises, perhaps higher output impedance is one of those compromises.
I am running R1-4 at 180 ohms, and achieve about 1.9 volts output. I have no problems (lack of dynamics etc) running amp direct into 11K per phase in my amp.