Cool, Andrew, if you had a NTC suitable for installing on the AC input, you wouldn't need the relay and auxillary supply voltage that Peavey uses, saving $10. Do you have any suitable parts number for 1. 10 w preamp 2. a 2 amp mains chip power amp like the questioner has 3.a 10 amp mains power amp? They would obviously have to be different parts. I can think of a suitable refrigerator motor NTC thermistor for the power amp, weighing a couple of ounces, but the local appliance supply is charging $29 for them.
a 555 timer one shot plus relay and resistor soft start circuit would also work, but that is a lot of parts and work if there is some single part one can solder in series with with the power transformer. A delay on on relay from National Controls Corp or P&B plus a series power resistor would work, but the relays are about $50 and the 11 pins socket is about $12, besides being huge.
I don't know why Peavey is using a PTC thermistor, but it is right there on the schematic of the CS800s page 22 power control board, downloadable from eserviceinfo.com. I'm not opening the amp up to look at it, it is one of the few things around here that is not broken or a work in progress.
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it appears that 110/120Vac suits one CL60. If you have a high VA twin primary then usea CL60 for each 110/120Vac primary.
220/240Vac suits two (or more) CL60.
I find this too expensive and use 40r to 100r of wirewound resistors instead. Not quite as good, but does allow close rated mains fusing.
220/240Vac suits two (or more) CL60.
I find this too expensive and use 40r to 100r of wirewound resistors instead. Not quite as good, but does allow close rated mains fusing.
Well I thought, from reading wikipedia on "current limiter" that the GE CL series were really enhancement mode FET's with the gate tied to the source, which means they limit the current to the tested value all the time. I would want current surges after a cannon shot or drum hit depleted my power capacitor but not when turning on. JDawg, this means that your turn on pop will probably decrease/disappear by putting the wirewound power resistor or the GE CL in series with the primary of your power transformer. Make sure the wattage is big enough, and it is voltage rated for mains voltage. If you also want big drum hits, use the peavey idea to short across this resistor or current limiter with a relay whose DC coil pickup voltage is about 3/4 of the DC power supply float voltage. Connect the relay coil to the DC main capacitor, or across the two capacitors if split supply. That way, you will get full AC power for stressful music, but not when turning on.
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I think there is a misunderstanding how the CL 60 work. I am attaching the data sheet were it is explained and the applications.
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Oops
Well, I'm wrong, nothing like exhibiting your ignorance to learn something. I downloaded the GE CL60 datasheet from a link on mouser.com, and it seems to be a thermistor, not a fet. It seems to be directly designed for this sort of problem. I'll buy some next time I have an order together. Thanks to everyone. Still I wonder what Peavey was doing with parts that go the other way. If I can figure out what the import ones look like, I'll post again, there ought to be one in every switch mode dead PC power supply which are in such great supply Salvation Army resale shop throws them away.
Well, I'm wrong, nothing like exhibiting your ignorance to learn something. I downloaded the GE CL60 datasheet from a link on mouser.com, and it seems to be a thermistor, not a fet. It seems to be directly designed for this sort of problem. I'll buy some next time I have an order together. Thanks to everyone. Still I wonder what Peavey was doing with parts that go the other way. If I can figure out what the import ones look like, I'll post again, there ought to be one in every switch mode dead PC power supply which are in such great supply Salvation Army resale shop throws them away.
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It looks like the inputs are DC coupled, unless I'm missing something (I didn't dig far enough to find the whole schematic). If they are the DC offset is affected by the offset of the device providing the input signal. Is this true?
Does the thing pop if the input is disconnected? How about grounded?
My ideas for a solution need some more thought. I think any of them would be hard to implement on a pre made PCB...
I've been busy the last few days so I haven't had time to come on here much. So from what I understand all I have to do is add one of these CL30 or CL60 current inrush limiters and it should help fix the problem? I also think I figured out which circuit is causing the pop at power on. I think its the power supply board that powers the two buffer circuits. I got the schematic for the power supply and buffer circuits here:
Building a pre amp for a Gainclone chip amp.
Building a pre amp for a Gainclone chip amp.
Yesterday I hooked up my JLM vu buffer kits and a vu meter to the power supply and when I turn it on, then off and on again about 5 seconds later I get the pop sound. Without the vu meter connected I guess it takes a little longer for the caps to discharge which is why I could turn it off and turn it on 10 seconds later and still not get a pop sound.
I don't 100% understand everything you guys were talking about but do I just get one of these current inrush limiters and put it in series in between the rectifier bridge and caps for bot the positive and negative rails?
Building a pre amp for a Gainclone chip amp.
Building a pre amp for a Gainclone chip amp.
Yesterday I hooked up my JLM vu buffer kits and a vu meter to the power supply and when I turn it on, then off and on again about 5 seconds later I get the pop sound. Without the vu meter connected I guess it takes a little longer for the caps to discharge which is why I could turn it off and turn it on 10 seconds later and still not get a pop sound.
I don't 100% understand everything you guys were talking about but do I just get one of these current inrush limiters and put it in series in between the rectifier bridge and caps for bot the positive and negative rails?
two possible problems
Yes Jdawg, if your pop problem is inrush to the big power caps, then a cl30 or cl60 in series with the main transformer input (after the fuse and power switch) should improve that problem. You could alternatively, install two, one between each output of the power transformer to the rectifier inputs (if a center tap transformer. if bridge rectifier, only needs one). It shouldn't hurt anything, after my education in how they work. Your experiment with on-off-on (no pop second time) indicates this might be the main problem. If you also have an offset input problem on the amplifier chip, then later follow the more complicated instructions about eliminating an offset problem. I don't fully understand all that yet, but I view it as complicated because my 1968 Hammond organ has 3 tubes dedicated to eliminating pops and offset from the pedal circuits. Fortunately, op amps are more compact and standardized.
Yes Jdawg, if your pop problem is inrush to the big power caps, then a cl30 or cl60 in series with the main transformer input (after the fuse and power switch) should improve that problem. You could alternatively, install two, one between each output of the power transformer to the rectifier inputs (if a center tap transformer. if bridge rectifier, only needs one). It shouldn't hurt anything, after my education in how they work. Your experiment with on-off-on (no pop second time) indicates this might be the main problem. If you also have an offset input problem on the amplifier chip, then later follow the more complicated instructions about eliminating an offset problem. I don't fully understand all that yet, but I view it as complicated because my 1968 Hammond organ has 3 tubes dedicated to eliminating pops and offset from the pedal circuits. Fortunately, op amps are more compact and standardized.
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inrush currents are hardly your problem. Go check for DC at the speaker outs while inputs open and shorted.
regards
regards
Ok looks like I need to order some CL30 or the CL60 from digikey later. Someone mentioned on here to put them in between the rectifier bridge and the caps but you're saying to put them at the inputs of the rectifier or at the main transformer input. Does it matter where it goes?
I measured the DC offset at my speaker terminals and its about 30mV. I think that should be ok.
I measured the DC offset at my speaker terminals and its about 30mV. I think that should be ok.
30mV is ok. The LM3875 has a built in undervoltage protection. By the time the LM kicks in, the supply voltage has reached some minimum level and the so called inrush current peak would be over by then.
Me would do some more troubleshouting before ordering parts.
Are the supply voltages at the powerchips and the buffers ok? Is there a chance, that the buffers power up with a delay? They shouldn't do so!
regards
Me would do some more troubleshouting before ordering parts.
Are the supply voltages at the powerchips and the buffers ok? Is there a chance, that the buffers power up with a delay? They shouldn't do so!
regards
Id put one at the mains in line with your fuse. Id also use a cl-90, its 120 ohms that drops to 1 ohm at 2amps (thats what 300watts continuous load?). Putting it at the mains saves the whole amp, and allows you to use the storage capacity of your transformer (a 600va tor might pop a breaker at turn on). Check the numbers:
at full tilt your only dropping 2 volts across the ntc (your ac varies what, 115-130 depending on where you are on the grid). At idle the ntc ohm doesnt matter since your amp is basically an open (whats the voltage drop across a 120ohm vs the 2.4k load amp at 6 watts?). At turn on the 120ohm limits you to 1amp tops even if your amp shows up as a dead short.
If you really really dont like the cl-90, at least get the cl-80, its 50 ohms so it will limit inrush to 2.4amps. whats a cl30 or cl60 gonna let by, 48amps and 12 amps at turn on?
at full tilt your only dropping 2 volts across the ntc (your ac varies what, 115-130 depending on where you are on the grid). At idle the ntc ohm doesnt matter since your amp is basically an open (whats the voltage drop across a 120ohm vs the 2.4k load amp at 6 watts?). At turn on the 120ohm limits you to 1amp tops even if your amp shows up as a dead short.
If you really really dont like the cl-90, at least get the cl-80, its 50 ohms so it will limit inrush to 2.4amps. whats a cl30 or cl60 gonna let by, 48amps and 12 amps at turn on?
Cool, someone that knows something about these things. I thought CL30 & CL60 looked hefty for a 10w preamp, but what do I know? I'll put a CL90 in my RA88a mixer next time I make an order up. A zero crossing Solid State relay would probably also improve the pop at turn on problem of my mixer, but these things are a lot cheaper.
Thanks.
Hi,
If you follow the manufacture recommendation the places to install the ClXX is between the rectifier and the capacitors. That's where I always installed it. Warning be careful they ran hot. Also when you powered the amplifier off wait few minutes to allow the CLXX to cool off. You can get the PDF specification in the Mouser web side. It is good idea to read it so you have a better understanding how the device works and follow their recommendations.
If you use the GMOV make sure that you add a fuse. In case of a lightning or a power surge the GMOV will shorted and blow the fuse or you house breaker in this way it will protect your electric equipment. Also install it in parallel with the transformer primary that will clean any spikes coming from the closed of the power switch when powered up the amplifier.
Good luck
If you follow the manufacture recommendation the places to install the ClXX is between the rectifier and the capacitors. That's where I always installed it. Warning be careful they ran hot. Also when you powered the amplifier off wait few minutes to allow the CLXX to cool off. You can get the PDF specification in the Mouser web side. It is good idea to read it so you have a better understanding how the device works and follow their recommendations.
If you use the GMOV make sure that you add a fuse. In case of a lightning or a power surge the GMOV will shorted and blow the fuse or you house breaker in this way it will protect your electric equipment. Also install it in parallel with the transformer primary that will clean any spikes coming from the closed of the power switch when powered up the amplifier.
Good luck
Oh ya I forgot about the high idle heat (some people just wrap them in shrink wrap, and the cool off time.
By the way, in the data sheet, these are meant to work with switch mode power supplies inverters, and florescent lamps. Things without big honking transformers. Thats why they are put in after the rectifiers, because they dont have transformers. Its just goes wall,rectifier,dc/dc converter.
The tube guys put them inline with the primary fuse and they are called "tube savers" because they limit the inrush on the heaters.
Doug's Radio 'Tube Saver' Filament Life Protection Page
By the way, in the data sheet, these are meant to work with switch mode power supplies inverters, and florescent lamps. Things without big honking transformers. Thats why they are put in after the rectifiers, because they dont have transformers. Its just goes wall,rectifier,dc/dc converter.
The tube guys put them inline with the primary fuse and they are called "tube savers" because they limit the inrush on the heaters.
Doug's Radio 'Tube Saver' Filament Life Protection Page
What exactly does wrapping it with heat shrink do? Wouldn't that make it run hotter? I was thinking of adding a relay and a 555 timer to bypass the current limiter a few seconds after turning on the amp so it wouldn't always be hot when its on. After thinking about it I think it seems a bit too complicated for me.
Yeah, the current limiter bypasses itself when it gets hot, which is good if you like music that has loud parts between the average parts. If you wrapped it with plastic wrap, it would stay hot longer and stay low resistance longer during soft parts of the music. You only want one current limit at turn on, not a curremt limit everytime the music gets soft. Plastic wrap would make it more of a one time limiter, just at turn on.
If anybody is into salvaging parts instead of buying them, I remembered what a chinese CL looks like. The GE cl##'s are red according to the datasheet, look like round disc caps instead of resistors. I cut a round GREEN looking disk "cap" out of my dead PC switching power supply near the input fuse, was surprised when it read 100 ohms, threw it away as a defective capacitor. I bet those green disks are the chinese version of a current limit resistor. Was going to test it tonight with a hair dryer, but it is gone. Oh well, there are 4 more dead PC switching supplies in the attic, plenty more to cut out parts without ordering anything.
If anybody is into salvaging parts instead of buying them, I remembered what a chinese CL looks like. The GE cl##'s are red according to the datasheet, look like round disc caps instead of resistors. I cut a round GREEN looking disk "cap" out of my dead PC switching power supply near the input fuse, was surprised when it read 100 ohms, threw it away as a defective capacitor. I bet those green disks are the chinese version of a current limit resistor. Was going to test it tonight with a hair dryer, but it is gone. Oh well, there are 4 more dead PC switching supplies in the attic, plenty more to cut out parts without ordering anything.
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