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Location: Campbell, CA
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Hello all,
I am still working on getting my first TPA project functional and thus far I have been striking out. I've got two Buff II's in Dual Mono mode connected to two Legato 3.1 without buffers installed. I am hooking the unit up to an Integra DHC-80.2 Pre/Pro using Balanced output...ie using the SE wiring for dual mono. I have not gotten any audio out of the unit yet so I wanted to start with confirming that I am powering the Legato's from my Placid HD's correctly.
So for each Placid HD I have the following adjusted:
Placid HD 1 messurments->
Rail A Output to Legato 3.1 +: 14.66V
TP_OUT to TP_SHUNT = 82mV
TP_CSS to TP_VIN = 252mV
Rail B Output to Legato 3.1 -: 14.62V
TP_OUT to TP_SHUNT = 80mV
TP_CSS to TPVIN = 271mV
I will keep the numbers to just this Legato for now as once working I will make the other channel match.
I read that the Legato draws about 350ma so am I under powering the Legato? IS this a possible reason I'm not getting audio?
Best Regards,
Theo
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Rank: Member
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Joined: 11/10/2010(UTC)
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Location: Campbell, CA
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Oops just noticed someone asked this and the reply was yes each rail should source 350ma. My issue is one of my Placid HD's will only seem to do .300v measured at TP_CSS -> TP_VIN. My other issue is that when measuring the amount of current I'm shunting I get: .190v ... which I believe would be shunting 190ma which falls way outside the range of 30 - 50ma. Anyone have any ideas on why when sourcing more current I also seem to be shunting more. Is this normal? Edited by user Monday, February 13, 2012 6:28:00 PM(UTC)
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Of course. With a shunt PSU you shunt away the excess current. So if you increase the supplied current without adding any additional load you just increase the amount of current that needs to be shunted. Usually this means an increase in heat.
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Rank: Member
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Location: Campbell, CA
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Thanks LeonvB,
That was my feeling as well...however my Legato 3.1's would only seem to need 250ma per channel approximately if that is the case. I guess the question I'd like answer is that is it normal to shunt 190ma...it doesn't seem so but adjusted for 350ma per rail this is what I'm shunting. Does this mean I have an issue or does this mean that providing 250ma per rail to the Legato 3.1 without buffers is ok and I should look else where for my problem?
Best Regards,
Theo
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Rank: Member
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To my knowledge the buffer on the 3.1 is normally driving the SE outputs. So without the buffer installed you might just have disconnected the outputs. And the buffer of course also needs power to function. So it's absence might be your problem, plus the reason for the low power usage.
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From the sound of it your Legatos are getting good power.
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Rank: Member
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Thanks for the confirmation Russ.
So now I have to track down why I'm still not getting sound. I am going I2S output from the USB receiver board you guys sell and when I hookup my PC I see that both Buff II DACs switch from Mute to Lock. However still no audio...do you have a suggestion as to how I should investigate this?
Last should I move this question over to the Digital section of support?
Best Regards,
Theo
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Double check the relay orientation on the legatos. Maybe its backward? Are the relays clicking on power up/power down?
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Rank: Member
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Thanks Russ,
I will double check on the relay's but I do believe there is a click at power up and down.
Regards,
Theo
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Rank: Administration
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Did you install the jumpers that are required for omitting the Buffers?
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