Welcom to the show.
Change those resistors and you'e good to go again.
Skål
Probably a good idea to parallel two higher resistance resistors as the v2 board will be doing. I suspect that we are operating a little too close to the temp limits of the resistors and seeing some thermal breakdown.
Regards
I have not seen any measurable abnormality but the VOM doesn't heat anything up!
Also, in contrast to AVR's experiences, I can't claim that the affected channel has altered sound quality. It might have *slightly* less presence, but nothing obvious - it could be just imagination.
Russ has said that the power resistors are not super critical components, which makes me wonder about using film resistors specified for power applications like CPFs (http://www.vishay.com/docs/31021/cpf.pdf) or CCF-2s (http://www.vishay.com/docs/31012/31012.pdf). Maybe even something that would attach to an under-board heat dissipator? [e.g., the chassis base?] I'm certainly not qualified to choose one over another. Hopefully we don't need to go to a heat sink but the ability to run up to 15 volts into this sweet circuit would be more than worth the trouble, IMO.
In choosing resistors to run in parallel, I was thinking of ordering the same PRP 1W type that I know give excellent sound. Based on touch, it seems that both upper and lower resistors get pretty hot. Legato version 2 only pairs the upper resistors - any opinions on pairing both upper and lower? ...and while it's apart, I'm sorely tempted to patch-in extra BS250s!
Having now heard Legato running with 390R/180R, the importance of 2V RMS gain doesn't seem so critical to me because Legato at ~2V RMS is considerably more dynamic than the Opus 8741's with which I have it paired. Also, the channel controls in the Thuneau crossover software sound very good (ie. no apparent degradation) so I will reduce Legato's output to the stock value (340R/150R) and then tweak channel responses using software (to correct for the fact that my woofers are 2db more efficient than my mid-ranges).
Skål
(standing gratefully corrected...)
Also, in contrast to AVR's experiences, I can't claim that the affected channel has altered sound quality. It might have *slightly* less presence, but nothing obvious - it could be just imagination.
Russ has said that the power resistors are not super critical components, which makes me wonder about using film resistors specified for power applications like CPFs (http://www.vishay.com/docs/31021/cpf.pdf) or CCF-2s (http://www.vishay.com/docs/31012/31012.pdf). Maybe even something that would attach to an under-board heat dissipator? [e.g., the chassis base?] I'm certainly not qualified to choose one over another. Hopefully we don't need to go to a heat sink but the ability to run up to 15 volts into this sweet circuit would be more than worth the trouble, IMO.
In choosing resistors to run in parallel, I was thinking of ordering the same PRP 1W type that I know give excellent sound. Based on touch, it seems that both upper and lower resistors get pretty hot. Legato version 2 only pairs the upper resistors - any opinions on pairing both upper and lower? ...and while it's apart, I'm sorely tempted to patch-in extra BS250s!
Having now heard Legato running with 390R/180R, the importance of 2V RMS gain doesn't seem so critical to me because Legato at ~2V RMS is considerably more dynamic than the Opus 8741's with which I have it paired. Also, the channel controls in the Thuneau crossover software sound very good (ie. no apparent degradation) so I will reduce Legato's output to the stock value (340R/150R) and then tweak channel responses using software (to correct for the fact that my woofers are 2db more efficient than my mid-ranges).
Skål
(standing gratefully corrected...)
It's not necessary at all but certainly would not hurt. At 150R the I/V resistors will only be dissipating about 1/4W.
For what it's worth, Spev, I changed my mind and will not double the lower resistors. I will, however, move the inboard pair to the underside of the Legato 1 board. I think most of the thermal transfer to the Buffalo came from the upper resistors. I trust that new pairs of 680R spaced away from the underside will resolve this issue. Let's hope Buffalo still sounds as good running cooler!
How's that ?
15V VCC - 6V (at output) = 9V across the 150 ohm = 60mA * 9V = 0.54w
What am I missing ?
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
I only have the Legato V 1.02 Are upgrade parts available? If I order another Legato today would it still be V1.02 or V2?
Does the same bias formula hold for Legato V 1.02? What is the reason for -1 V in (vcc/2)-1? I am running stock and finding bias is vcc/2. I would need to crank up the -V rather than run it leaner, or change resisters to drop this from 7.5 to 6.5V. Of course everything sounds great as is I am just trying to fine tune and understand the how and why of it. I suspect that moving from bipolar to parallel fets wit nudge the sound slightly in the direction of the IVY 3. This would be welcome as I think my ideal sound lies somewhere between the the two.
Actually You and Paul both have good points.
You missed nothing, what I meant was if you used two 300R in parallel to get 150R it would be about .25W per R even at 15V. I just did not phrase it well.
At 12V it is very low dissipation.
One 1W resistor can very easily handle 1/2W
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The current version is v1.02. I accidentally shipped a couple v2 boards out, which were supposed to be for internal testing purposes only, and not a ready to prime time product. We are still tinkering (as always) and will not be releasing an official new version for a little while still. Sorry for the confusion this has caused.
I am using 10uF Wima polyesters, they fit directly on the board and don't suffer any problem with bass loss (my balanced headphone amp is 50k input) and sound very good.
Russ is right that polyprops are in theory superior, but usually the size makes them impractical to fit on board.
Regards
new info for me...
I am using Auricaps, which don't even remotely fit the board but have nice multistranded flexible leads. For a number of years I've been using them wherever transparency is needed. But just tonight I discovered something I didn't know about them (plus a review confirming small polarity effects):
* In signal path applications the black lead is "in" and the red lead is "out."
* In power supplies the black lead should be connected to ground and the red lead to the + or - voltage.
*In loudspeaker crossovers the red lead should be connected toward the + terminal on the drive unit.
Huh? Any comments on this by the "cognoscenti"? My caps are apparently in backwards because before reading this I would never have soldered a black lead into a location labeled "plus" and vice versa for red leads! I'll try changing them the next time I have everything apart...
I am using Auricaps, which don't even remotely fit the board but have nice multistranded flexible leads. For a number of years I've been using them wherever transparency is needed. But just tonight I discovered something I didn't know about them (plus a review confirming small polarity effects):
* In signal path applications the black lead is "in" and the red lead is "out."
* In power supplies the black lead should be connected to ground and the red lead to the + or - voltage.
*In loudspeaker crossovers the red lead should be connected toward the + terminal on the drive unit.
Huh? Any comments on this by the "cognoscenti"? My caps are apparently in backwards because before reading this I would never have soldered a black lead into a location labeled "plus" and vice versa for red leads!
I'll try changing them the next time I have everything apart...Chances are the polarity isn't going to make much difference, i wouldn't worry about it myself.
If they do have a preference to be biased in a positive direction, then you already have them in the right way!
The legato will have about +7V dc across the capacitor. As opposed to a generic small-signal application that have minimal dc bias (a few mV).
If they do have a preference to be biased in a positive direction, then you already have them in the right way!
The legato will have about +7V dc across the capacitor. As opposed to a generic small-signal application that have minimal dc bias (a few mV).
They are simply a low pass filter. It is perfectly fine to omit them, but I personally would not.
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