Twisted Pear Audio Support
»
Product Support
»
Power
»
Placid Power Supplies
»
Problems configuring CCS pots for voltage across R17 and R18
Rank: Member
Groups: Member
Joined: 3/29/2009(UTC)
Posts: 52
Location: Finland
|
I just built 2 Placid BPs and one Placid power supplies. I read the manual and first adjust the pots to correct values (100ohm for CCS and 2K for VOUT), then i connected the power and adjusted the output voltages to +-15v for Placid BP and 6V for non-BP Placid. I think this is the correct configuration. Leds were green as well. But after that i tried to setup the voltage across R17 (and R18) but i can't get higher than 0.180-0.200V for each rail of each Placid with maximum pot turn. The manual suggests 0.25V. I must be doing something wrong espacially if one should be able to get 0.7V with the pots. Still i kinda doubt that I would have built all three Placids (and each rail) wrong in the same way. There must be something wrong with my measuring. I am measuring the R17 (and R18) so that have left the legs of the resistors uncut so I can hang the DMM probes of my multimeter on them. Thats the way to do it? You you have any other ideas and things to check? edit: I measured all the resistors and at least they seem to be correct. Should i find the 0.25V from the minimum or the maximum side of the CCS pots? I can't figure what is the problem. Edited by user Sunday, October 18, 2009 3:26:05 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
Hi Elviz. First you may not need to 250ma since you are actually using two placid BPs. I would set them up for about 150ma each. Second, Brian and I are now finding that some of the JFETs have an IDss that is too low to get 250ma from the CCS with the 47 ohm limiting resistor in place. You can safely short R6 and R15 if you find that you cannot get the 250ma and you really need it. We are going to start selecting JFETS for tighter IDss. You should be ok since you are using one per channel to go down to the 120-150ma range. Cheers! Russ Edited by user Sunday, October 18, 2009 6:45:24 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/29/2009(UTC)
Posts: 52
Location: Finland
|
Thats good news :d/. Thanks Russ.
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 3/29/2009(UTC)
Posts: 52
Location: Finland
|
I got the upgrade done and it works good. I did not bother with the 250ma trick...at least for now...but i configured the placids for 160ma for little extra headroom.
The Buffalo sings again and i am liking what i am hearing so far. If soldering fumes are not still affecting my brain, seems like there is much better bass dynamics compared to the LCxPS.
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA
Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
|
Quote:Second, Brian and I are now finding that some of the JFETs have an IDss that is too low to get 250ma from the CCS with the 47 ohm limiting resistor in place... We are going to start selecting JFETS for tighter IDss. I will also make "selected" JFETs available to those who already have kits and want a replacement.
|
|
|
|
|
|
Rank: Advanced Member
Groups: Member
Joined: 5/9/2008(UTC)
Posts: 62
|
Brian Donegan wrote:Quote:Second, Brian and I are now finding that some of the JFETs have an IDss that is too low to get 250ma from the CCS with the 47 ohm limiting resistor in place... We are going to start selecting JFETS for tighter IDss. I will also make "selected" JFETs available to those who already have kits and want a replacement. If you could make sure that my yet-to-be-shipped Placid BP is covered, I would appreciate it  I decided that one Placid BP with 2" sinks would probably be safer than two stacked with 1" sinks, so would like to make sure I can run it at a pretty high current......
|
|
|
|
|
|
Rank: Member
Groups: Member
Joined: 8/27/2008(UTC)
Posts: 13
|
Brian, have you sent out replacement "selected" JFETS? I have purchased 3 Placids and 6 BP Placids, a number of them won't go any higher than 115ma. BTW, I've sent email to you(as well as parts@twistedpearaudio.com and questions@twistedpearaudio.com) quite a few times concerning this. I have yet to receive a single reply. Edited by user Friday, November 6, 2009 3:42:30 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Advanced Member
Groups: Member
Joined: 1/11/2009(UTC)
Posts: 70
Location: Greece
|
adelias wrote:Brian, have you sent out replacement "selected" JFETS? I have purchased 3 Placids and 6 BP Placids, a number of them won't go any higher than 115ma. BTW, I've sent email to you(as well as parts@twistedpearaudio.com and questions@twistedpearaudio.com) quite a few times concerning this. I have yet to receive a single reply. Bump! Brian, have you shipped those replacement JFETs yet?
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
I can't speak for Brian, but I am sure he has it handled. :) For now, if you need to, and you find that you can't adjust one or both sides past 200ma one option is to simply short R6(If it only the positive side) or R15(If it the negative) or both (if its both). :) Edited by user Monday, November 9, 2009 5:51:35 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Advanced Member
Groups: Member
Joined: 1/11/2009(UTC)
Posts: 70
Location: Greece
|
Hello Russ,
Thanks, I was tempted to do that but, to be honest, I don't want to tamper with the original design just to bypass a problem.
I'm sure those resistors are there for a reason.
If those JFETs take too long to arrive I might do it though 'cause I got those pretty looking assembled Placid boards on my desk for over a week now.
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 3,979
Location: Nashville, TN
Thanks: 25 times
Was thanked: 89 time(s) in 83 post(s)
|
The reason for those resistors is to limit the current through the JFET (as manifested by the adjustment limit). Since the current is low they do not need to be there. :) It will do no harm at all to jumper/short them.
Cheers!
Russ
|
|
|
|
|
|
Rank: Advanced Member
Groups: Member
Joined: 1/11/2009(UTC)
Posts: 70
Location: Greece
|
Thanks for clarifying that, Russ. :) My BP Placids work fine (I actually never tried them past 200mA because I'll be going dual mono and so there is no need for higher current), but I do have an issue on the single one which I can't set beyond 110mA..  Edited by user Wednesday, November 11, 2009 11:15:52 AM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Rank: Administration
Groups: Administration, Customer
Joined: 10/24/2006(UTC)
Posts: 2,868
Location: Massachusetts, USA
Thanks: 2 times
Was thanked: 141 time(s) in 134 post(s)
|
adelias wrote:Brian, have you sent out replacement "selected" JFETS? I have purchased 3 Placids and 6 BP Placids, a number of them won't go any higher than 115ma. BTW, I've sent email to you(as well as parts@twistedpearaudio.com and questions@twistedpearaudio.com) quite a few times concerning this. I have yet to receive a single reply. It's hard to figure out who you are. I have no way to link you to a name or email I know. Send me a PM with your name and I will get you straightened out. Edited by user Wednesday, November 11, 2009 1:48:28 PM(UTC)
| Reason: Not specified
|
|
|
|
|
|
Twisted Pear Audio Support
»
Product Support
»
Power
»
Placid Power Supplies
»
Problems configuring CCS pots for voltage across R17 and R18
Forum Jump
You cannot post new topics in this forum.
You cannot reply to topics in this forum.
You cannot delete your posts in this forum.
You cannot edit your posts in this forum.
You cannot create polls in this forum.
You cannot vote in polls in this forum.
