Paul what you are seeing is normal. You can readjust both the CCS and the output voltage slightly after the heat sinks are warm. The warm output current will always be just a bit more than it will be cold.
You can decrease the CCS current to just what is needed by turning it down until output starts to sag while connected to the load, then turn it back up a few turns after it comes back to the desired voltage. Now you will have just a bit more current than you need.
By tuning the supply to just what you need you will generate less heat.
Cheers!
Russ
You can decrease the CCS current to just what is needed by turning it down until output starts to sag while connected to the load, then turn it back up a few turns after it comes back to the desired voltage. Now you will have just a bit more current than you need.
By tuning the supply to just what you need you will generate less heat.
Cheers!
Russ
Last edited:
Thanks for the reply. I posted in both forums because I had been having trouble reaching you this week when replying to the email you sent out asking for feedback on the Placid. Glad to catch you here...
Today the voltages started out at about 15.5 volts and gradually dropped close to where I reset them yesterday after they had drifted up over a two hour time period. I am letting them settle in and will tweak them once more.
Thanks for comfirming the heat dissipation observation. If someone is looking for a drop-in replacement these might not work for some boxes. I have a Parmetal case with good venting and still my entire box warmed up.
Regarding adjusting the CCS. Are there any other points where a voltage could be taken off? How about the un-populated pads for R1/R2? Would the voltage drop across these two points be directly proportional to the drop across R17/18 when the CCS adjustment pot is changed?
The good news is that the DAC sounds great....
The voltage reference has a negative tempco. So it will tend to start up slightly higher than it will be at working temperature. So what I usually do is adjust for just under your target voltage. That way you never exceed you desired output voltage.
The movement is not very much and the less you heat the VREF section the less drift there will be. So I would adjust the CCS to deliver just what you need with a bit of overhead for the shunt.
I will edit the manual to makes this clear.
I am glad you are enjoying the DAC.
Cheers!
Russ
The movement is not very much and the less you heat the VREF section the less drift there will be. So I would adjust the CCS to deliver just what you need with a bit of overhead for the shunt.
I will edit the manual to makes this clear.
I am glad you are enjoying the DAC.
Cheers!
Russ
Just to clarify for my own understanding. According to the manual "The output current per rail is calculated as V across RE divided by value of RE where RE is either R17 for the positive rail or R18 for the negative rail.
So... if I adjust to the .25v suggested in the manual and R17/18 is 1ohm per the BOM then I must be running my supplies at .250A. If I want to get them down to ~.150A then I would adjust down to ~.15v.
Is that correct?
Discussion moved here
http://www.diyaudio.com/forums/powe...-bp-bipolar-shunt-regulated-power-supply.html
http://www.diyaudio.com/forums/powe...-bp-bipolar-shunt-regulated-power-supply.html
OK, with an IVY 2.0 (actually moderately tweaked according to TPA instructions). I only have the honor of Sir IVY the 2nd on the B32
Anyway, I did first the change of the VA supply and then afterwards the VD. The change was definitely most evident with the VA supply. I will not test much more with this configurations as I have the Counterpoint I/V that I find quite a bit better than the IVY 2.0. I just have to check a few thing with current draw etc.
Nic
Anyway, I did first the change of the VA supply and then afterwards the VD. The change was definitely most evident with the VA supply. I will not test much more with this configurations as I have the Counterpoint I/V that I find quite a bit better than the IVY 2.0. I just have to check a few thing with current draw etc.
Nic
The placid will work fine into any practical capacitance as long as there is some ESL.
Still you could quite safely remove those caps.
I personally sometimes do remove large decoupling caps when using shunt regulators. This minimizes the possibility of having little parasitic tank ccts.
Cheers!
Russ
Still you could quite safely remove those caps.
I personally sometimes do remove large decoupling caps when using shunt regulators. This minimizes the possibility of having little parasitic tank ccts.
Cheers!
Russ
TPA Guys!
Do you feel that the rails track enough for this to be used with a DC coupled amplifier, that doesn't have any sort of on board regulators (perhaps some of your designs meet this criteria?)
I've done a bit of testing, but haven't formed a solid opinion myself.
Here's one test run zoomed in across both rails (it's configured as a +-12VDC supply)
Here is some data over 5 hours of warm-up on a single rail:
Unfortunately, waiting two hours for the DC offset to stabilize is not practical, so the question is how well do things thermally track during warm-up.
So far it seems okay. Upon turning on the power supply, I see 0.055VDC difference in the rails. So, assuming this offset would be trimmed via the amplifier, we'll call this value 0. After 1 min. this was 0.046. After another min, this was 0.052. After 5 more minutes, 0.060. After 5 more minutes, 0.064. After 10 more minutes, 0.061. After a final 10 minutes, 0.061. So, during this time there was a +-9mV variance from the initial value.
The next plan is to build a simple circuit to do this math for me, so I can monitor it over a longer period of time.
Anyways, I do wish this was tighter, given the use in a DC coupled amplifier, so my question is, is there any suggestions on how this variance could be nullified somewhat? Any further tests that I could help you with?
Do you feel that the rails track enough for this to be used with a DC coupled amplifier, that doesn't have any sort of on board regulators (perhaps some of your designs meet this criteria?)
I've done a bit of testing, but haven't formed a solid opinion myself.
Here's one test run zoomed in across both rails (it's configured as a +-12VDC supply)
An externally hosted image should be here but it was not working when we last tested it.
Here is some data over 5 hours of warm-up on a single rail:
An externally hosted image should be here but it was not working when we last tested it.
Unfortunately, waiting two hours for the DC offset to stabilize is not practical, so the question is how well do things thermally track during warm-up.
So far it seems okay. Upon turning on the power supply, I see 0.055VDC difference in the rails. So, assuming this offset would be trimmed via the amplifier, we'll call this value 0. After 1 min. this was 0.046. After another min, this was 0.052. After 5 more minutes, 0.060. After 5 more minutes, 0.064. After 10 more minutes, 0.061. After a final 10 minutes, 0.061. So, during this time there was a +-9mV variance from the initial value.
The next plan is to build a simple circuit to do this math for me, so I can monitor it over a longer period of time.
Anyways, I do wish this was tighter, given the use in a DC coupled amplifier, so my question is, is there any suggestions on how this variance could be nullified somewhat? Any further tests that I could help you with?
Last edited:
A small change in the rails over a long peroid of time should not effect a well designed amplifier, DC coupled or not.
The drift you are observing is a function of the tempco of the LED.
You could use a voltage reference with less tempco, but you would likely then have more noise. You could easily put just about any series VREF in there. Even a Zener if you please.
None of our amps would be adversely effected by the slight drift at all.
I would just use the LED VREF unless you have good reason not to.
Cheers!
Russ
The drift you are observing is a function of the tempco of the LED.
You could use a voltage reference with less tempco, but you would likely then have more noise. You could easily put just about any series VREF in there. Even a Zener if you please.
None of our amps would be adversely effected by the slight drift at all.
I would just use the LED VREF unless you have good reason not to.
Cheers!
Russ
I wouldn't call 300mV over 2 hours small (per the second graph) in the context I've presented. Also, I'm not sure what you mean by a well designed DC coupled amplifier? Let's assume a servo isn't used. If it uses a bipolar PSU and the rails drift apart by 10mV, this will show up as a DC offset. edit: I'm obviously more concerned about the rails drifting at different rates, then any absolute change over time.
Just trying to help!
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.