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I'm having repeated problems with voltage settings on some LCBPS modules (i.e. the voltage is not adjustable). I have a strong feeling that it is the pots that are unreliable so I decided to use fixed resistors in stead of fixed+pot and using the standard LM317 calculation: V=1.25x(1+R1/R2).
With R1 = 4K7 and R2 = 330R I get 12.6V !? (should be 19.05V).
What am I missing?
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Du you measure the voltage out under load ?
If so, what's the load ?
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Rank: Advanced Member
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Without load so it is not an "over-load" related issue. EDIT: Problem solved. I had popped in 3W 2.7 KR resistors (and not 2.7R) in the CRC circuit. Wonder where I got those from  Edited by user Saturday, April 2, 2011 4:41:00 AM(UTC)
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Joined: 7/22/2009(UTC) Posts: 81  Location: Norwich, UK Thanks: 2 times
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Hi Nic
Is the input voltage high enough to give 19V out? You need- if I remember correctly- at least 5V across a 317 reg for it to work properly
Paul
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Rank: Advanced Member
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Hi Paul,
Nice to hear from you! I solved the problem (stupid mistake on my side - see edit above).
I'm using the LCBPS's as pre-regs for the S17/37LN-15 regs for the Legato (3 sets). Did you understand if we will still be able to do this with Legato 3.1 (i.e. is the current demand < 120 mA per rail @ 15V for all 6 rails on the Legato)?
Cheers,
Nic
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Rank: Advanced Member
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Joined: 7/22/2009(UTC) Posts: 81 Location: Norwich, UK Thanks: 2 times
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Hi Nic
Glad you sorted it out! Done the same sort of thing myself... :-)
Only Russ could tell you that for certain. But I think the current drawn by the L and R I/V sections will stay the same (certainly TP0604's in place of BS250KL's won't affect this; BTW did you try these FETs yet- bloody marvelous!). The current needed by the Bal to SE stage will increase, because of Russ' mod to allow better drive to headphones. But you may still be OK, as this circuit only draws 15mA in the earlier versions of Legato, giving you about 100mA extra to play with.
I fitted my S17/37LNs directly to modified LCBPS boards in place of the 317/337's, and adjusted the series resitors to put about 4.5 V across the regs. Living more dangerously, dissipation-wise, than you, but avoided getting higher V transformers
Hope this helps
Paul
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