Change the input voltage and for each new input voltage measure the CCS resistor Vdrop.
In a correctly operating CCS that resistor Vdrop should change by very little over a quite wide range of input voltage.
Then ensure that your input voltage never drops below the lowest that results in that nominal Vdrop.
This was the reason for the 7V recommendation in the earlier versions. Vin -Vout>=7V for proper CCS resistor Vdrop over a range of mains voltage variations.
Once you have adequate Vin, then you need to measure the Shunt current to ensure it never falls to near zero, when the load draws it's maximum demand. This is a bit more difficult. There are no resistors in the output, nor in the Shunt routes that allow comparison of currents in max demand operation.
You can monitor output voltage to see if there is a glitch (voltage droop) if the output demand increases. But this ONLY works if the CCS is working.
If the CCS is not working then a small voltage drop at the output increases the Vdrop across the CCS resistor and the CCS resistor is now effectively regulating for the output demand.
In a correctly operating CCS that resistor Vdrop should change by very little over a quite wide range of input voltage.
Then ensure that your input voltage never drops below the lowest that results in that nominal Vdrop.
This was the reason for the 7V recommendation in the earlier versions. Vin -Vout>=7V for proper CCS resistor Vdrop over a range of mains voltage variations.
Once you have adequate Vin, then you need to measure the Shunt current to ensure it never falls to near zero, when the load draws it's maximum demand. This is a bit more difficult. There are no resistors in the output, nor in the Shunt routes that allow comparison of currents in max demand operation.
You can monitor output voltage to see if there is a glitch (voltage droop) if the output demand increases. But this ONLY works if the CCS is working.
If the CCS is not working then a small voltage drop at the output increases the Vdrop across the CCS resistor and the CCS resistor is now effectively regulating for the output demand.
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I have measured the hammond transformer in the past when I used it for my phono and after filtering caps and the same rectifying diodes it gave 15,6V
but what is CCS resistor Vdrop as the input voltage is changed?
eg.
with the PSU supplying 15.6Vdc and Vdrop =1.570V
add a resistor before the regulator. 2r2 will drop Vin by ~0.3V to ~15.3Vdc. what is the new Vdrop?
Add second 2r2. Vin= ~15Vdc? new Vdrop = ?
add a 3rd 2r2. New Vin = ~14.7Vdc new Vdrop = ?
Plot them on a graph.
If there is a knee in the Vdrop plot then that lets you define the minimum Vin for Proper CCS operation.
If you are already below that knee then you must change your Vin upwards to identify the Minimum Vin.
If you have a small Variac then you can vary Vin by the turn of the adjustment knob.
eg.
with the PSU supplying 15.6Vdc and Vdrop =1.570V
add a resistor before the regulator. 2r2 will drop Vin by ~0.3V to ~15.3Vdc. what is the new Vdrop?
Add second 2r2. Vin= ~15Vdc? new Vdrop = ?
add a 3rd 2r2. New Vin = ~14.7Vdc new Vdrop = ?
Plot them on a graph.
If there is a knee in the Vdrop plot then that lets you define the minimum Vin for Proper CCS operation.
If you are already below that knee then you must change your Vin upwards to identify the Minimum Vin.
If you have a small Variac then you can vary Vin by the turn of the adjustment knob.
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Just out of curiosity, if this is really a problem, what effect would this have on the sound?
Perhaps I could also hook an additional 10R 5W on top of the existing ones and try to squeeze some heat out of the mosfets?
NO.
If the CCS is not working properly because Vin is too low then adding a second CCS resistor makes the problem worse.
You should find out why the mosFETs are running so cool to be only very slightly warm. That alone tells me there is something amiss.
I have a standard DCB1, running at just 60mA. I cannot hold the irf240 with my fingers. They are too hot. Admittedly they each have 20C/W sinks.
You have more than double that current. V and/or A across the mosFETs must be exceptionally low.
Would measuring the V on the gates in reference to G and then the Vgs on the Mosfets give us a rough image of what is going on towards that end?
stick a 2r2 in the feed between the PSU and the regulator and find the new Vdrop of the CCS resistor.
It really is that simple.
It really is that simple.
Check it up, tighten it up, boost it up, & there is more to hear.
To be honest I do not feel comfortable scoring the pcb to separate the psu from the reg. I will try to find a 15V transformer to see if I get a higher current. I have a 2x18 one but the electrolytics will be at their upper threshold with the filtered V.
I ve been listening to it for about 3 hours now and the mosfets are still at about finger temperature. The aluminum around the pcb feels slightly warmer that it does on its edges.
The buffer jfets feel a bit warmish too.
Are you sure about this? At 60mA shouldn't it be less than a Watt dissipation? And even with the 20C/W sinks shouldn t it be around 40-45 degs? Hardly a finger burning temp.
I ve been listening to it for about 3 hours now and the mosfets are still at about finger temperature. The aluminum around the pcb feels slightly warmer that it does on its edges.
The buffer jfets feel a bit warmish too.
Are you sure about this? At 60mA shouldn't it be less than a Watt dissipation? And even with the 20C/W sinks shouldn t it be around 40-45 degs? Hardly a finger burning temp.
If all is well you burn a mere 1.5W on each output MOSFET now. Just 0.84W on each CCS MOSFET. That metal base is big. If those red pads are Kerafol (ask Tea) then the case to metal thermal resistance is next to nothing. Those parts are 0.83C/W junction to case. Your test build is open also. They possibly glide merrily near room temp.
de-rate heatsink for Delta T.
Expect for a 1W into 20C/W at least a temp rise of 30Cdegrees, maybe even as high as 35C.
Ta = 20degC
Ts ~ 50 to 55degC
Tc ~ 51 to 56degC
Tj ~ 52 to 57degC
Ts & Tc @ >50degC is too hot to hold.
Note that for those temperatures, the devices should live for ever.
I design for the two worst case conditions
1.) Survivability if the output is shorted when mains voltage is maximum.
2.) Survivability if zero output current.
Expect for a 1W into 20C/W at least a temp rise of 30Cdegrees, maybe even as high as 35C.
Ta = 20degC
Ts ~ 50 to 55degC
Tc ~ 51 to 56degC
Tj ~ 52 to 57degC
Ts & Tc @ >50degC is too hot to hold.
Note that for those temperatures, the devices should live for ever.
I design for the two worst case conditions
1.) Survivability if the output is shorted when mains voltage is maximum.
2.) Survivability if zero output current.
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The arduino controller is almost ready.
I used an encoder with button for the manual rotary control allowing 20 steps from 0 to 100%, and an apple remote for IR allowing 100 fast steps. The arduino then controls 2 100K DS1804 digital pots. A led is also dimmed to give a visual indication of the current volume level.
The only things remaining are to replace the second pot (used a 10K accidentally) and then properly implement the muting and test it more.
The digital pot will then control a lightspeed clone. The balance pot will be replaced by a trimmer to allow for more accurate centering since I always use it centered while listening anyway.
I plan on using a separate small toroid for the arduino, and power lightspeed with a single 7805 (no filter caps) from the Vout on the DCB1.
Any thoughts?
I used an encoder with button for the manual rotary control allowing 20 steps from 0 to 100%, and an apple remote for IR allowing 100 fast steps. The arduino then controls 2 100K DS1804 digital pots. A led is also dimmed to give a visual indication of the current volume level.
The only things remaining are to replace the second pot (used a 10K accidentally) and then properly implement the muting and test it more.
The digital pot will then control a lightspeed clone. The balance pot will be replaced by a trimmer to allow for more accurate centering since I always use it centered while listening anyway.
I plan on using a separate small toroid for the arduino, and power lightspeed with a single 7805 (no filter caps) from the Vout on the DCB1.
Any thoughts?
Only that it will be an impressive automated DCB1 and that controlling LDRs can be a PITA. Will it carry a backlit color LCD screen?
Hehe yeah at first I was thinking to build something like the one in the Buffalo thread in avclub.
But since I won' t need all the DAC stuff I decided that there is no point. The LCD will be an overkill. Just 3 leds for power, 2 sources and volume indication.
I know what you mean about the LDRs... I initially was planning to use separate pot quadruplets for each LDR (100K+1K) to perfectly control the LDR values per step, but it was really a chore... Not to mention the 16 pots (48 digital pins would be required....)
But since I won' t need all the DAC stuff I decided that there is no point. The LCD will be an overkill. Just 3 leds for power, 2 sources and volume indication.
I know what you mean about the LDRs... I initially was planning to use separate pot quadruplets for each LDR (100K+1K) to perfectly control the LDR values per step, but it was really a chore... Not to mention the 16 pots (48 digital pins would be required....)
Now the tease part is that we had a DCB1 guy who was swearing by using a dedicated shunt reg for the LSPD part and the sound quality he could achieve VS powering it from a chip reg.
Damn... I hate you (not)... I have some SSLV BiBs laying around but no low voltage BJT parts... And I will need an extra toroid for it... Unless I pull AC from the Vin of the DCB1?
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Mosfet will go 5V also. You can steal some if you will run it conservatively and your Tx will allow with hot rod and all. Hey don't shoot the messenger, if it even was Malka07 a couple of years ago then I had a total recall flash (not as much as Colin Farrell, but there).😀
I bought a DMM with temp measuring. The cold metal plate was 25,5C before turning it on. Same with the mosfets.
After ~1 hour the fets were at about 31C.
Now I have just boosted it a bit attaching 2 additional 12R @5W resistors on each rail bringing it to ~3,75R.
Here are the measurements
Vout: 9,95V and -9,99V
CSS: 1,412V and 1,391V
Offset: -1,3mV and -0,9mV
and about 20 minutes later
Vout: 9,9V and -9,96V
CSS: 1,411V and 1,392V
Offset: -1,3mV and -1mV
This translates to ~370mA
Still a bit lowish, but it seems to work nicely.
First impression was that the change was very noticeable. The music is more dynamic. The entire spectrum is much more solid and well defined. Highs are very clear, mids and mid highs have more bite and bass is louder and better controlled. And voices are starting to .... holly cr@p 🙂
I am getting more and more impressed by it every day 🙂
After ~1 hour the fets were at about 31C.
Now I have just boosted it a bit attaching 2 additional 12R @5W resistors on each rail bringing it to ~3,75R.
Here are the measurements
Vout: 9,95V and -9,99V
CSS: 1,412V and 1,391V
Offset: -1,3mV and -0,9mV
and about 20 minutes later
Vout: 9,9V and -9,96V
CSS: 1,411V and 1,392V
Offset: -1,3mV and -1mV
This translates to ~370mA
Still a bit lowish, but it seems to work nicely.
First impression was that the change was very noticeable. The music is more dynamic. The entire spectrum is much more solid and well defined. Highs are very clear, mids and mid highs have more bite and bass is louder and better controlled. And voices are starting to .... holly cr@p 🙂
I am getting more and more impressed by it every day 🙂