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pelliott  
#1 Posted : Saturday, August 14, 2010 2:46:54 PM(UTC)
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Definately like the sound over the IVY III. and its only be on for a couple of hours. The 1 watt resistors do get hot but nothing is burning. I had to increase the current in the placid in order to hold 12v when I loaded it down with the lagato. I find 1.5v ont the out put abit low for my preamp and may have to change R1-4 to be equal with my other sources.
Man it was a lot of parts on that small board to solder. I think my nerves will be shot for a couple of days, but I am happy.
Russ White  
#2 Posted : Saturday, August 14, 2010 6:44:07 PM(UTC)
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That is excellent! Thank you for the report.
thomaspf  
#3 Posted : Monday, August 16, 2010 9:16:11 AM(UTC)
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Reapeating my question from the standalone thread. What would be the right values for a 4.5V RMS balanced output?

Edited by user Monday, August 16, 2010 9:51:43 AM(UTC)  | Reason: Not specified

Russ White  
#4 Posted : Monday, August 16, 2010 9:33:52 AM(UTC)
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I would try something like 392R and 1K. That should get you close. You will likely need to experiment a bit here since I have never run this config.

You will also definitely want 15V rails.

Edited by user Monday, August 16, 2010 9:35:47 AM(UTC)  | Reason: Not specified

thomaspf  
#5 Posted : Monday, August 16, 2010 9:52:31 AM(UTC)
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Excellent, thank you. I will order a couple of values in the range.

with your comments about the heat dissipation of the 1W resistors I assume this will heighten the ventilation requirements.

A Bryston 4BSST2 with 20K Ohm input impedance does not require the buffers? Right?

Cheers

Thomas

Edited by user Monday, August 16, 2010 10:00:08 AM(UTC)  | Reason: Not specified

Russ White  
#6 Posted : Monday, August 16, 2010 10:26:32 AM(UTC)
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Actually heat/power wise you will be just fine. The higher resistor value will mean less current. Your setup should actually run cooler than the stock values. Still adequate ventilation is always the right thing to do. :)

You should not need the buffer, but it would not hurt anything either.
Russ White  
#7 Posted : Monday, August 16, 2010 3:54:55 PM(UTC)
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Ok a couple more changes I would make. You can use 1/4W metal film for the 392R. It will only see about 1/10W

Swap BS250 for BC560 or similar.

Swap R5-R8(1K) with 392R.

That should work quite well.

Cheers!
Russ
barrows  
#8 Posted : Tuesday, August 17, 2010 9:13:05 AM(UTC)
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While there is discussion on output voltage: Russ, the manual suggests that the stock values present the best ratio of output voltage to performance vis a vis noise/distortion. I suspect I will need a little more output voltage than stock in my system, looking at available resistors, I am thinking 200R for R1-4, and 432R for R20-21, 23-24. Do these values sound reasonable to not compromise performance and achieve around 2.5+ volts out, without any other changes?
Russ White  
#9 Posted : Tuesday, August 17, 2010 1:12:47 PM(UTC)
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Sure those values should yield excellent results. The thing to remember is that the higher the value of the top resistor the more noise there will be, but we are talking about extremely tiny changes.
sureshm  
#10 Posted : Tuesday, August 17, 2010 5:02:55 PM(UTC)
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Russ, Is there a function to work out the value of the top resister to achieve a certain voltage output?

Also at 200R and 432R, can R5-R8 remain at 1K or should it be reduced?

Thanks
Russ White  
#11 Posted : Tuesday, August 17, 2010 5:24:55 PM(UTC)
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I will try to post a formula when I get a chance.

R5-8 should be 1K for BS250 and 392R for BC560. You can use either part for the p-channel(or PNP) devices.
thomaspf  
#12 Posted : Monday, August 30, 2010 8:21:35 PM(UTC)
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I wanted to report back that I completed my Legato following the suggestions given above and it works fine with my Buffalo II.

R5-R8 = 392 Ohms
Replaced the BS250 with BC560

I ended up using 365 Ohms and 806 Ohms for R1-R4 and R20-21, 23-24 respectively. That gives me the right level of gain in my system. For resistors I picked the 1/4W IRC 0.1% metal film type. Is that a decent choice?

A comparison with the IVY III is really hard. I would not be able to pick a winner right now.

Thanks for the help

Thomas

P.S.: Twiddling with the voltages turned out to be a somewhat delicate task. Getting the BP Placid to +/-15V with 0.25V over R17/R18 was a lot more temperature sensitive task than with the IVY III. So was the adjustment of VR1/VR2 on the Legato to get to AVCC/2 on the Buffalo output pins.

Edited by user Monday, August 30, 2010 10:05:07 PM(UTC)  | Reason: Not specified

thomaspf  
#13 Posted : Tuesday, August 31, 2010 10:49:28 AM(UTC)
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I brought the Buffalo/Legato combo into my work system today and it seems the Legato board is more sensitive to the power conditions than the IVY.

I have some grounding issues with my active monitors plugged into different wall outlets. While the IVY III board was completely silent in this setup, I am now experienceing some weird hiss with the Legato. There is audible hiss that becomes louder and then goes away again like something is resonating (breathing) at a very low frequency. Power cycling the DAC makes it go away.

Any thoughts?

Cheers

Thomas

P.S.: I put the DAC back in my home system and there it is running completely quiet.

Edited by user Tuesday, August 31, 2010 6:49:03 PM(UTC)  | Reason: Not specified

Russ White  
#14 Posted : Wednesday, September 1, 2010 3:08:35 PM(UTC)
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The resistors should really be at least 1/2W 1W would be better.

Are you using the output buffer?
thomaspf  
#15 Posted : Wednesday, September 1, 2010 8:09:49 PM(UTC)
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I assume you mean the R1-R4, R20-21, 23-24 resistors being 1/2W?

They don't seem to get hot as it is but to be on the safe side that is what I will do.

Yes, I do use the output buffer.

After listening more to it on my home system I can say that I prefer it over the IVY III although the differences are subtle. Truth be told my ears are also getting weaker.

Cheers

Thomas
Russ White  
#16 Posted : Thursday, September 2, 2010 3:43:57 AM(UTC)
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HI Thomas, if they are not getting hot then you can leave them.

Are you using the balanced output or single ended?
thomaspf  
#17 Posted : Thursday, September 2, 2010 4:10:40 PM(UTC)
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I am using balanced into a Bryston 9BST at home and a pair of vintage active Spendor BC1A in the office.


Here is some more data from my experimentation last night and this morning. If I plug the Spendors into the Buffalo with the Legato board there is a moderate level of audible hiss coming from the tweeter. That level is resonating to pretty high levels at a very low frequency. This morning I plugged in an older Lite-DAC with the Spendors and there is absolute silence in all circumstances. The Spendors clearly do not harmonize with some characteristic of the Legato output stage.

At home with the Bryston the default is silence but I now have once experienced a similar cycle of hiss on one channel during warm-up.

Cheers

Thomas

Edited by user Thursday, September 2, 2010 6:40:29 PM(UTC)  | Reason: Not specified

Russ White  
#18 Posted : Thursday, September 2, 2010 4:27:55 PM(UTC)
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Hi Thomas, my guess is you should add a bit of output resistance or simply not use the Legato output buffer(same effect, but no introduction of resistor noise).

My suggestion would be to simply remove the buffer. You very likely don't need it.

thomaspf  
#19 Posted : Thursday, September 2, 2010 6:39:44 PM(UTC)
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Thanks for the suggestion. As it turns out a friend of mine is currently putting his Legato together and I guess we can try that out there before I start unsoldering a whole bunch of BC550s.

However, just adding some resistor is probably a quick way to see whether that makes any difference. Would 2 Ohm do?

Cheers

Thomas

Edited by user Thursday, September 2, 2010 6:42:04 PM(UTC)  | Reason: Not specified

schnak  
#20 Posted : Friday, September 3, 2010 10:36:01 PM(UTC)
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Hi Thomas,
I received the legato and havent built it yet. I live in seattle also. If it will help I can build my legato as needed and compare. Pm me. Thanks, Jeff
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