all going together smoothly.
one thing to consider is to make the little tower adapters "jumpable" so that you can either run the resistors in series or parallel - I took a dremel to it to put them in series but it would be simple enough to add the option for series vs parallel to tweak the final resistance.
one thing to consider is to make the little tower adapters "jumpable" so that you can either run the resistors in series or parallel - I took a dremel to it to put them in series but it would be simple enough to add the option for series vs parallel to tweak the final resistance.
Messed around with a lot of things, including the 24v supply, this weekend. The 24v supply is a little too much for my setup to handle. Everything is getting too hot. I initially tested it with .22R in the CRC. Running for a few minutes melted the solder joint on the top resistor of my makeshift resistor ladder. I shut it down right away at that point. The 2U heat sinks started to creep past 55C. I also noticed a very significant amount of heat coming from the ERSE inductors. Wondering if that is supposed to happen. There is a lot of DC being moved through and lost to the inductors. The voltage after the CRC was ~17.6v. Voltage at the input of the inductors was about 10.5v and then 2.8v before the .5R resistor. The inductors themselves were going on 75C. Not sure what they can handle before melting down. I decided to test an MOT in circuit to see if it would also have the same behavior. A funny thing happened when I did this. After swapping from ERSE to MOT the SMPS could not start up and started motor boating at about 10-11v.
So tonight I swapped resistors in the CRC to .47 X 4 or .12R which drops about a volt across the CRC. I also went back to 19v supply. Sinks are hot now but I can hold my hand on them. CRC resistors are about 85C. Still only working with one channel right now but it sounds great. Hooked it up to the AKSA Lender pre.
Will build the second channel very soon.
Sorry for the rambling here. Hope there is some useful info.
So tonight I swapped resistors in the CRC to .47 X 4 or .12R which drops about a volt across the CRC. I also went back to 19v supply. Sinks are hot now but I can hold my hand on them. CRC resistors are about 85C. Still only working with one channel right now but it sounds great. Hooked it up to the AKSA Lender pre.
Will build the second channel very soon.Sorry for the rambling here. Hope there is some useful info.
Great info Jwjarch! You know it is too hot when it melts it’s own solder! LOL
We should recommend a 0.1ohm KOA BPR on the CRC then. 19v SMPS supply it is then. It could be your heatsinks are on the small side for the 24v.
That’s 36w total dissipated if the current is 1.5A x 24v.
We should recommend a 0.1ohm KOA BPR on the CRC then. 19v SMPS supply it is then. It could be your heatsinks are on the small side for the 24v.
That’s 36w total dissipated if the current is 1.5A x 24v.
Any concern on the voltage drop across or heat being dissipated by the inductors? And what is the deal with the SMPS being able to start with the ERSE inductors in place but not with the MOT? I found that to be very strange. Maybe a larger cap is needed in place of the 1,000uf in the cap multiplier?
The lower DCR of the MOT has higher current draw and so maybe the cap Mx needs to be slowed down some more. Make the 220uF cap bigger like 1000uF. As long as temp of inductors is below 55C it’s ok.
It’s a balance of current and heat output. Increase the resistors below the inductor if it’s too hot.
It’s a balance of current and heat output. Increase the resistors below the inductor if it’s too hot.
Hi X. On my build I already had 1,000uf at the position for ramp up of the SMPS. Would it be ok to add additional uf to get an even slower ramp up?
I will play with some resistor values after the inductor as well. I’m not comfortable with the 65-70C temp on the ERSE inductors. They are rated at 500W but I don’t know what that means in this case since speaker level signals don’t carry 10v of DC current.
I will play with some resistor values after the inductor as well. I’m not comfortable with the 65-70C temp on the ERSE inductors. They are rated at 500W but I don’t know what that means in this case since speaker level signals don’t carry 10v of DC current.
Managed to find some time to wire it all up and test it out (= TOOK A WEEK OFF )
all working but the 12V rail is not enough to get it excited and the MOTs are not what my meter says they are.
Starting at 12V , after the Cap Mx i am left with 7V at the JFET drain. Gate voltage is 1.4V and Source is 2.39V
voltage drop across the MOTs is 400mV , voltage drop across the 1R5 resistor is 1.95V
It plays music and sounds good but there is a bit of static interference which is likely caused by the many alligator clips and dangling wires
)
all working but the 12V rail is not enough to get it excited and the MOTs are not what my meter says they are.
Starting at 12V , after the Cap Mx i am left with 7V at the JFET drain. Gate voltage is 1.4V and Source is 2.39V
voltage drop across the MOTs is 400mV , voltage drop across the 1R5 resistor is 1.95V
It plays music and sounds good but there is a bit of static interference which is likely caused by the many alligator clips and dangling wires
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Nice work JW and dBel!
I believe your both using SMPS for power? Can either of you cobble together a linear psu and feed Lite 22vdc? Maybe use a variac before the transformer to fine tune the output voltage. The capMx is dropping 5-6v, seems more than usual?
dBel, I wonder if your ‘static’ is because the voltage is too low for the circuit?
I believe your both using SMPS for power? Can either of you cobble together a linear psu and feed Lite 22vdc? Maybe use a variac before the transformer to fine tune the output voltage. The capMx is dropping 5-6v, seems more than usual?
dBel, I wonder if your ‘static’ is because the voltage is too low for the circuit?
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That's worth exploring Vunce. I also have boards for the more efficient Gtose, Mark Johnson, Prasi, XRK collaboration spin off of Juma's CapMx. Might be worth trying the V+ rail on this build.
I have a more concerning issue. I hooked up a Kill-A-Watt meter to my single channel and it's registering 104W going into the SMPS. I think this explains why I have so much excess heat in the system. I know part of this is all the heat at the inductors and the voltage drop I am seeing there. Currently I have a 5.79v drop across the inductors. This doesn't seem right. I have a Hammond 159ZC on hand that is measuring out at 61mH and .8R. I'll try swapping that in to see if the ERSE inductors are causing the huge spike in current draw.
I have a more concerning issue. I hooked up a Kill-A-Watt meter to my single channel and it's registering 104W going into the SMPS. I think this explains why I have so much excess heat in the system. I know part of this is all the heat at the inductors and the voltage drop I am seeing there. Currently I have a 5.79v drop across the inductors. This doesn't seem right. I have a Hammond 159ZC on hand that is measuring out at 61mH and .8R. I'll try swapping that in to see if the ERSE inductors are causing the huge spike in current draw.
My thoughts too Vunce! Not sure if it's the magnetic field between the inductors causing some weird current draw, or maybe I have them wired out of phase? If I experience something similar with the Hammond choke then I must have done something wrong elsewhere in the circuit. I also wonder if the specs on the LD1010D could cause these issues. I can try swapping in a LU1014 eventually. Lots of fun experiments on this build!
I looked up the DCR of the Erse 20mH inductor = .558R
If you have two in series = 1R116
V/R = I, 5.79v/1.116 = 5.19A!
before i dig about to put together a more standard power supply - I thought I would just run my 12V supplies as a 24V supply - The Drain voltage got to 13V before it "melted" my little alligator jumper on the smps - not to let that stop me, I replaced the jumpers with serious welding cable and this time I allowed the Drain to get to about the same voltage - the resistors were at 90deg C and had about 8 V flowing across them - 4.7A at which point I shut it down.
I will need to take a careful look and see exactly why this thing is burning so much current
I will need to take a careful look and see exactly why this thing is burning so much current
I think you guys may have LU1014’s with slightly different specs and perhaps need more resistance after the inductors. You will need to let the majority of the voltage drop occur after the inductor. That’s strange that there is more than a 4v drop across the cap multiplier.
If all these methods fail to bring the current down…
The other way we can reduce the bias current is to apply a DC bias at the gate of JFET to pinch it off as it is a depletion mode device. Using a pot between the rail and ground feed the wiper (with 10uF cap to ground in wiper) through a 33k resistor to the gate. Adjust the pot until you get your desired current. We can skip the power resistor this way.
If all these methods fail to bring the current down…
The other way we can reduce the bias current is to apply a DC bias at the gate of JFET to pinch it off as it is a depletion mode device. Using a pot between the rail and ground feed the wiper (with 10uF cap to ground in wiper) through a 33k resistor to the gate. Adjust the pot until you get your desired current. We can skip the power resistor this way.
I don't have too many high wattage resistor pairs lying about
I tried 270om first which as you can imagine, only allowed 35mA current through. Next up I tried 10ohm and they fared better with about 1.2 amps but still got silly hot 110 deg C. This is running the smps in series to give 24.7V pre capmx and a close shave at 19.5V on the drain. I only tried one channel, sound was clean.
Going to explore X's solution next.
I tried 270om first which as you can imagine, only allowed 35mA current through. Next up I tried 10ohm and they fared better with about 1.2 amps but still got silly hot 110 deg C. This is running the smps in series to give 24.7V pre capmx and a close shave at 19.5V on the drain. I only tried one channel, sound was clean.
Going to explore X's solution next.
More experimenting tonight. First I swapped the ERSE inductors for the Hammond 159ZC. The current draw was even more than the ERSE pair. This makes sense since the resistance of the Hammond is lower than the ERSE’s. So I concluded the inductors are not at fault here.
Next, I found two 2R 25W resistors in my crossover parts bin. Those, wired in series for 4 ohms, decreased the bias nicely. The Kill-A-Watt was reading 38 watts. So pretty close to X’s simulation. But, similar to dB, those resistors are running at over 100 deg C. Yikes!
Looks like I’m interested in trying X’s latest solution as well.
Next, I found two 2R 25W resistors in my crossover parts bin. Those, wired in series for 4 ohms, decreased the bias nicely. The Kill-A-Watt was reading 38 watts. So pretty close to X’s simulation. But, similar to dB, those resistors are running at over 100 deg C. Yikes!
Looks like I’m interested in trying X’s latest solution as well.
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Hi Jwjarch and dBel. Thanks for trying different things. That’s part of being the beta tester and I appreciate your help. I was hoping to keep it simple without having a gate bias circuit but that seems to invite the JFET to run full open as it is like an Idss measurement setup with only the source resistance to control its DC current.