7.5VAC shoudl give you around 10VDC, whoch should be more than enough. It's possible that it's a bad pot. Do you have another you can try, or maybe spray some contact cleaner on the one you have?
I have also the same problem of motor-boating (switching relays very many times) even if I have 10.37 VAC and big ehough trafo (15 VA). This only happens using two relay boards (20 cm of IDC cable between each unit). Problem is made a bit worse, if I add two Darwins in the +5V and ground of JT controller. I can see with a scope that the +5V on controller is dropping quite a lot (looks like nearly 1 volt down, at least half a volt, I have not used a scope for many years) in pulses when the problem is on compared to situation where there is no problem. Is it just the parallel relays of two boards are drawing too much current, should I add some series resistors to IDC connector when using two boards ?
I even added some capacitance to +5V (as Russ indicated earlier) and it reduced this motor-boating a bit (first 10 micros, then 10 more and last 220 more), but i does not stop it totally (there is still one 5 degree area maybe at 70 % of pot, where the problem happens most often). Now I have only the first added 10 micros left in the circuit. This is with JT1.2 software. The attenuators do work very well otherwise, sounding quite good. Also the Darwins work, so they are not causing this.
If I use only one relay board (any of the two that I have, in any cable position) this does not happen. I even made a new IDC cable, thinking that it was the problem with two relay boards, but the new one works just the same.
Could it be that the regulator is broken, should I change it ? Or is the dropping of +5V only caused by the problem, not the reason.
I will still be checking the relay boards of mistakes, but it is not very expected, because they work when only one is used. And even with two boards they work, just problem within small area of volume control.
I even added some capacitance to +5V (as Russ indicated earlier) and it reduced this motor-boating a bit (first 10 micros, then 10 more and last 220 more), but i does not stop it totally (there is still one 5 degree area maybe at 70 % of pot, where the problem happens most often). Now I have only the first added 10 micros left in the circuit. This is with JT1.2 software. The attenuators do work very well otherwise, sounding quite good. Also the Darwins work, so they are not causing this.
If I use only one relay board (any of the two that I have, in any cable position) this does not happen. I even made a new IDC cable, thinking that it was the problem with two relay boards, but the new one works just the same.
Could it be that the regulator is broken, should I change it ? Or is the dropping of +5V only caused by the problem, not the reason.
I will still be checking the relay boards of mistakes, but it is not very expected, because they work when only one is used. And even with two boards they work, just problem within small area of volume control.
10.37 VAC may not be enough. If you have the facilities, prove it to yourself by giving the regulator more voltage. There is a 3 amp version of the 7805, and I have wondered if this may be more appropriate for the project.
After I gave mine 15vac 60va😱 all the motorboating disappeared (this from 6.5vac). And no, the regulator isn't getting very hot.
I really think you gotta have rock solid 5vdc here..no question in my mind. Any variation sends it into a small reboot(?)
I really think you gotta have rock solid 5vdc here..no question in my mind. Any variation sends it into a small reboot(?)
Hi Russ/Brian,
are there 12V or 24V relays with the same footprint?
The PSU droop problem would go away.
are there 12V or 24V relays with the same footprint?
The PSU droop problem would go away.
orthoefer said:
Can I put the parallel windings of the trafo in series, that would be over 20 VAC ? Or is 20 VAC too much ?
khaho said:
I agree that 20 VAC may be more than you want to operate your JT controller with everyday, but according to the LM7805 datasheet, it can handle up to 35V input. You should be ok to try it by doubling your secondary voltage.
orthoefer said:
Ok, I will try with 20 VAC and order 15 VAC trafos and 3A version of 7805, so I can try all combinations.
Hi,
small transformers have high regulation.
The high current requirement of multiple relays is creating major voltage variations on the input to the regulators.
Time to step back and evaluate where you need to go.
Just increasing the transformer voltage could lead to tears.
Check dissipation at maximum supply voltage and maximum current demand.
small transformers have high regulation.
The high current requirement of multiple relays is creating major voltage variations on the input to the regulators.
Time to step back and evaluate where you need to go.
Just increasing the transformer voltage could lead to tears.
Check dissipation at maximum supply voltage and maximum current demand.
I'm working another angle on this, will test tonight and report back.
The relays are rates at 20mA each. 20mA * 14 (all on) = 280mA. PIC16F685 is 25ma max per pin * 7 = 175mA. Max current draw is 300mA. This keeps us well below the 1A that the 7805 can supply.
So, what else is drawing current? BC546 transistors, currently driven through 1K resistors. I will try making these 10K to see if we can drop current draw on the PIC and the entire circuit.
khaho: if you have the time, you could try it too, as you have a none problem (my relay boards don;t currently have the motorboating problem).
The relays are rates at 20mA each. 20mA * 14 (all on) = 280mA. PIC16F685 is 25ma max per pin * 7 = 175mA. Max current draw is 300mA. This keeps us well below the 1A that the 7805 can supply.
So, what else is drawing current? BC546 transistors, currently driven through 1K resistors. I will try making these 10K to see if we can drop current draw on the PIC and the entire circuit.
khaho: if you have the time, you could try it too, as you have a none problem (my relay boards don;t currently have the motorboating problem).
Now I measured voltage before 7805 and when two relay boards were setting relays the DC dropped to just above 9 volts. It is obviously too little, so I changed the trafo windings to series (getting 20 VAC idle, just above 18 VAC loaded with two boards and relays on) and the motor-boating problem is gone.
Heatsink of 7805 is getting a bit warm with 18 VAC, when relays are on. So I will change to 15 or 12 VAC when I get new trafos. So the 2x9 VAC trafo was a really bad choice, even is in the middle of text written on the board (5-15 VAC).
Heatsink of 7805 is getting a bit warm with 18 VAC, when relays are on. So I will change to 15 or 12 VAC when I get new trafos. So the 2x9 VAC trafo was a really bad choice, even is in the middle of text written on the board (5-15 VAC).
khaho said:
The 7805 running warm should not be an issue as long as its not too hot. Mine run pretty warm, I would say around 55C.
With this high voltage, DC before 7805 is 23 V to 26 V, I get to 60C in the heatsink opposite side of the 7805 before 5 minutes on and still rising. A bit too much I think.
khaho said:
That almost makes me wonder if something is drawing more current then it should... But yes thats pretty warm.
When I was using parallel windings, there was no warming of the heatsink at all. I also measured resistance of all the relays in the IDC connectors of the relay boards and they are correct (230 ohms), thinking that there might be short circuit somewhere.Russ White said:
I tried with a big 12 VAC trafo from another project and the warming stops with that at 45C (after around 10 mins on) and no motor-boating happens. So 12 VAC seems to be a good value and obviously many are using 15 VAC so these could be the right limits.
Hey guys,
I think I have a grounding or impedance issue when using the JT with my linestage.
I get hum/buzz. Its pretty quiet but still annoying.
If I leave the linestage out and just have CDP going into the darwin and JT and then to my gainclones it works fine, just not enough gain (hence why I made a linstage).
I've tried:
- using the darwin as star gnd and having ground going from there to the JT and linestage.
- connecting JT gnd to the linestage
- just using the linestages input buffer or just the gainstage section.
- used a pot instead of the JT
So I'm thinking maybe the resistor values in my OPA627 linestage are wrong?
Here is my design:
I think I have a grounding or impedance issue when using the JT with my linestage.
I get hum/buzz. Its pretty quiet but still annoying.
If I leave the linestage out and just have CDP going into the darwin and JT and then to my gainclones it works fine, just not enough gain (hence why I made a linstage).
I've tried:
- using the darwin as star gnd and having ground going from there to the JT and linestage.
- connecting JT gnd to the linestage
- just using the linestages input buffer or just the gainstage section.
- used a pot instead of the JT
So I'm thinking maybe the resistor values in my OPA627 linestage are wrong?
Here is my design:
An externally hosted image should be here but it was not working when we last tested it.
Hi,
is the 100k at the top of the line stage acting as the input impedance setting resistor?
Why is input via R7 connected to the power ground instead of the audio ground?
A schematic would help me decipher the rest of the circuit.
is the 100k at the top of the line stage acting as the input impedance setting resistor?
Why is input via R7 connected to the power ground instead of the audio ground?
A schematic would help me decipher the rest of the circuit.
AndrewT said:
Yep, R7 and R2 are input impedance resistors and they go from input to GND. Power GND and audio GND are not separate.
The top opamp is a buffer before the attenuator, the bottom opamp is running at a gain and is after the attenuator.
Its based on this design except I have excluded R5 and added a 2k2 resistor, R6, for class A bias:
An externally hosted image should be here but it was not working when we last tested it.
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