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I cannot believe this - first Legato now Buffalo.
I am powering the Vd for Buffalo from one half of a LDPS - 20VA trafo with 9V secondaries. This is 1.1A per side - and nothing else is powered from the same rail. Without load I can get up to 13VDC at the output. When I adjust to 5.5V and connect the Buffalo the voltage drops to 4.8ish V - on the AVCC I have D2 fully lit and D1 just barely shimmering.
I cannot believe that a DAC board can pull 1A by itself. Do I need a bigger trafo or I have some other issue?
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What is the value of R1 and R3 on the LCDPS?
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Is this the same type of transformer you had problems with earlier?
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I will measure the R1 and R3 later and get back to you - the fact is that the same PSU with the same transformer was powering Buffalo 1 (24bit) for couple of years without any issues. This was meant to be just a simple swap board type activity.
The answer to the second question is yes - it is the same type transformer (the 15V one is used for the output stage and the other one (9V) for everythig else). The second secondary winding is supplying a 4:1 MUX, a relay switch and couple of leds. Not top of the quality line but it did a good job so far. I am guessing that regulation should be in 15% range. But still - if you say that there is 20% drop that is still more than 10V at the input of LM317 with 0.9A (80% efficiency) and say 0.1A drop accross the PSU that is 0.8A clean supply and more than 5V of voltage drop between input and output. I can see that Placid can cause some issues due to 15V rails but any 20VA 9V trafo should be good enough to supply 1A in 5V regulated line.
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The R1 and R3 are 10R 3W - that was in the original kit - I can see that now you offer 2.7R, 3W. Edited by user Monday, August 15, 2011 12:17:35 AM(UTC)
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I have just tried 2 secondaries in parallel - no change. Without load 5V flat, with Buffalo it drops to 4.5V. D1 still just shimmering with voltage across being 1.76V - D2 bright as before with voltage ~1.9V. AVCC Vout is 3.29 on both sides
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short-jump those resistors.
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ALl 4 of them or just R1 and R3 - I might as well remove the inductors as well then.
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All four. Just add the jumpers for now to be sure the problem goes away. The inductors, if bypassed, are not going to affect anything.
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I did the mod and the voltage is stable now at 5.5V, thanks for that - Vout at AVCC is smidgen above 3.5V; voltage measured between GND and 4th pin at the AVCC is 3.29) Spidf input work as a charm - music is there and it sounds awesome. However I have constant drop-outs with I2S ; 1s lock on - 1s lock off type behaviour. I am using I2S input feed from the 4:1 MUX that (again) worked fine before. I need this because I intend to use DSD input from a modified Denon 1920. I have not tried DSD but I assume that will have same issues as I2S from the MUX. Edited by user Tuesday, August 16, 2011 5:26:26 AM(UTC)
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I have no lock issues with DSD or I2S from a modified Denon 1920.
Nic
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I will try with a Placid PSU for Vd and a 30VA trafo to increase the current supply and see how it goes. I wonder if the I2S dropouts is this common problem that everyone is reporting. I did not wait more than couple of minutes to see if it would stabilize after a while. I will try my Denon today.
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I tried DSD from Denon - some initial instability but worked very good after a minute or two - however I2S from the 4:1 MUX is still very very bad, even after a good warm up. It would be very handy to have the SPDIF switch externally. Did anyone try to do that and allow spdif from the MUX and DSD input to be chosen by an external switch. I have a MUX I2S and DSD switched through the relay switch but that will not work as good as I hoped. UPDATE: I plugged and adjusted a Placid PSU - it took a bit longer but I2S stabilised eventually. It is not ideal but acceptable. Thanks guys for a great DAC! Edited by user Wednesday, August 17, 2011 6:04:42 AM(UTC)
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How long are your I2S lines? They should be as short as possible and neat, no proximity to power lines, etc.
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I just edited my post without seeing yours - it is stable now - the I2S wires are 12cm long - braided with the ground wire wrapped around the braid. No power lines in vicinity. I mentioned that the wiring worked in this configuration for last 2 years with Buffalo 1 (24bit). Never dropped a bit. Is there any better way of wiring this? Multiple coaxial cables maybe? I also noticed that Vd dropped slowly from initially adjusted 5.5V to ~5.48 is that to do with the Jfet thermal drift. The voltage over R8 is 0.358V and over R3 50mV. Is this all normal? Edited by user Wednesday, August 17, 2011 5:32:23 AM(UTC)
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