Jennice said:
A word of warning: Even on the secondary side, the voltage is high enough to cause injury, Be careful, and don't work on it if you're feeling tired. Dis-charge the capacitors before working with them. Do NOT - NEVER !!! - discharge them with a piece of wire.
I have found that a 20 watt 120V light bulb
works well to discharge big caps!!! plus it gives a nice visual indicator of the state of charge or discharge. when the filiment stops glowing to the eye. voltage is typically low enough for safe handling. But still, check with a volt meter. a big cap with 5V charge is enough to do damage and scare the doodoo out of you!I found a 20 watt Microwave oven, or sewing machine bulb works very well. I can discharge a 26,000 uf cap charged to 100V in about 30-40 seconds.
Zero
yep, I am a paper catalog guy, too. So I find something close to what I want on mouser and then go to that catalog page, rather than search through all the values. You can do a basic search and see what format they use to create a search string
A search on "resistor 5W 150" turns up quite a few choices such as http://www.mouser.com/index.cfm?han...uctid=288100&e_categoryid=362&e_pcodeid=58800
similar search - resistor 2.7 1W gives http://www.mouser.com/index.cfm?&ha...&Dk=1&Ns=MfgrPartNumber||SField&N=0&crc=false
For digikey, I drill down from a search on resistor - within power resistors for the 5W, metal film for the 1W.
A search on "resistor 5W 150" turns up quite a few choices such as http://www.mouser.com/index.cfm?han...uctid=288100&e_categoryid=362&e_pcodeid=58800
similar search - resistor 2.7 1W gives http://www.mouser.com/index.cfm?&ha...&Dk=1&Ns=MfgrPartNumber||SField&N=0&crc=false
For digikey, I drill down from a search on resistor - within power resistors for the 5W, metal film for the 1W.
OK, I found the resisters at Digikey. I had to go to Allied frst and they gave me a part number for Ohmite. I used that part number at Digikey and found them. Wow, what a hassle. I wounder why Digikey's search engine wouldn't find them on it's own?
I guess now all I need is the 9V, 5VA transformer for the Soft Start circuit.
I can see why kits are so popular. I long for the day when there was a Mom-n-Pops Electronic supply down the street. Maybe I need to shop on the phone with these folks and let them look stuff up. I've spent half the day trying to find 6 resistors.
I sure appreciate all you help. If you know of a source for the 9v transformer I need, please let me know.
Blessings, Terry
I guess now all I need is the 9V, 5VA transformer for the Soft Start circuit.
I can see why kits are so popular. I long for the day when there was a Mom-n-Pops Electronic supply down the street. Maybe I need to shop on the phone with these folks and let them look stuff up. I've spent half the day trying to find 6 resistors.
I sure appreciate all you help. If you know of a source for the 9v transformer I need, please let me know.
Blessings, Terry
digikey - search on transformer, drill down through power transformer and choose 5 VA you get several options like
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=286921&Row=438789&Site=US
once you learn how they organize stuff its not so hard.
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=286921&Row=438789&Site=US
once you learn how they organize stuff its not so hard.
Terry,
While you
re out there searching... have you remembered fuses and fuse-holders? They shouyld be closed kind, so you can't access live (high voltage) parts when changing the fuse(s).
The small soft start transformer should have it's own, small fuse.
If you use just one fuse for both softstart and audio power transformer, the fuse will have such a high rating, that the small transformer will melt down or catch fire before the fuse blows.
Jennice
While you
re out there searching... have you remembered fuses and fuse-holders? They shouyld be closed kind, so you can't access live (high voltage) parts when changing the fuse(s).
The small soft start transformer should have it's own, small fuse.
If you use just one fuse for both softstart and audio power transformer, the fuse will have such a high rating, that the small transformer will melt down or catch fire before the fuse blows.
Jennice
I have a question about thermal runaway with my amp.
It's a 50W @ 4 ohm mono amp
It's my first discrete amp (all my other amps were chip amps) and it uses CFP outputs.
Now I've read that thermal runaway is not an issue with CFP but I noticed with high quiescent currents the heatsink runs cool, but once I've heated it up with loud music, it would STAY hot after turning the music off until I lowered the quiescent current from 160mA to 80mA, then it would cool off quicker.
The amp plays real strong, and barely gets hot unless it's sine testing @ full volume.
I'm thinking that some thermal compensation would be good.
I do have a transistor that adjusts the bias with a 5K pot, should I remove the biasing transistor from the PCB and mount it to the main heatsink? I'm concerned about long wire runs causing oscillation, and I'm wondering if it would cause crossover distortion if the heatsink got real hot.
It's a 50W @ 4 ohm mono amp
It's my first discrete amp (all my other amps were chip amps) and it uses CFP outputs.
Now I've read that thermal runaway is not an issue with CFP but I noticed with high quiescent currents the heatsink runs cool, but once I've heated it up with loud music, it would STAY hot after turning the music off until I lowered the quiescent current from 160mA to 80mA, then it would cool off quicker.
The amp plays real strong, and barely gets hot unless it's sine testing @ full volume.
I'm thinking that some thermal compensation would be good.
I do have a transistor that adjusts the bias with a 5K pot, should I remove the biasing transistor from the PCB and mount it to the main heatsink? I'm concerned about long wire runs causing oscillation, and I'm wondering if it would cause crossover distortion if the heatsink got real hot.
Yo Terry,
Check out:
http://www.apexjr.com/
He has lots of stuff you will probably need.
Friendly, reliable folks.
Prosit
Check out:
http://www.apexjr.com/
He has lots of stuff you will probably need.
Friendly, reliable folks.
Prosit
Jennice said:
Sorry, I didn't mean to hijack the thread. I just didn't want to start a thread as my 1st post in this forum.
I posted that there because it's my "first amp" that wasn't built on a breadboard and I should have worded it a bit differently.
Also, I'll provide a schematic, but it's similar to Rod's P3A but only running @ 48V and my main issue was if I should put the bias servo transistor on the heatsink, but I'll provide a schematic.
Thanks
Terry,
Also, since Sacramento is "reasonably" close to you, also visit:
HSC Electronic Supply
Address: 4837 Amber Ln, Sacramento, CA 95841
Phone: (916) 338-2545
or http://halted.com/ on the web.
What shows on the web page is tiny compared to what is in the store.
Their retail store(s) have everything from breadboards to the smallest resistor and a plethora of other stuff. If they have what you need, buy it then. Next visit it will be gone. Not at that store? They will get it from one of the others. All at surplus prices.
Happy shopping.
Prosit
Also, since Sacramento is "reasonably" close to you, also visit:
HSC Electronic Supply
Address: 4837 Amber Ln, Sacramento, CA 95841
Phone: (916) 338-2545
or http://halted.com/ on the web.
What shows on the web page is tiny compared to what is in the store.
Their retail store(s) have everything from breadboards to the smallest resistor and a plethora of other stuff. If they have what you need, buy it then. Next visit it will be gone. Not at that store? They will get it from one of the others. All at surplus prices.
Happy shopping.
Prosit
BobEllis said:
Hi Bob,
Well, I checked your link and I think that tranny will work fine. Only problem is that I didn't have time to order it then and now your link has expired and I still can't seem to find it usining their search engine.
If you see this could you find it again? I promise I'll order it before it gets away.
Thanks, Terry
acenovelty said:Terry,
Also, since Sacramento is "reasonably" close to you, also visit:
HSC Electronic Supply
Address: 4837 Amber Ln, Sacramento, CA 95841
Phone: (916) 338-2545
or http://halted.com/ on the web.
What shows on the web page is tiny compared to what is in the store.
Their retail store(s) have everything from breadboards to the smallest resistor and a plethora of other stuff. If they have what you need, buy it then. Next visit it will be gone. Not at that store? They will get it from one of the others. All at surplus prices.
Happy shopping.
Prosit
Well I wouldn't call Sacramento reasonably close. I live about 100 miles east of Los Angeles. Sacramento has to be at least a 6 hour drive. That's alittle too far to run to the store.
I will check out their website though.
Blessings, Terry
EW1708,
Usually, the bias transistor goes on the heat sink also.
If you put a small (not citical, try 100nF) between collector and emitter of the bias transistor, but on the board, where the would be soldered, if the transistor goes onto the heat sink, you should have no oscillation worries.
Jennice
Usually, the bias transistor goes on the heat sink also.
If you put a small (not citical, try 100nF) between collector and emitter of the bias transistor, but on the board, where the would be soldered, if the transistor goes onto the heat sink, you should have no oscillation worries.
Jennice
Terry,
Just a suggestion:
When you've assembled your boards/electronics, and the PSU, fire up the PSU without anything connected to it, and check that everything is as intended. (BTW: I suppose you got some high current bridge rectifiers?)
If this is OK, turn it off, and discharge the caps.
Connect the amplifier circuit to the PSU vith fuses (2-3Amp) in series, to limit the current through it if anything is wrong. Otherwise, you'll find yourself with a blown amp.
When that is ok, and the bias is set, try it with a cheap speaker unit to verify operation. When this is ok, you're ready to either remove the fuses, or insert some 6A types (or similar, "more than peak calculated current" types.)
Finally, connect to your speakers, and hopefully everything should be fine, with the precaution steps taken.
It would be a pity to ruin both speakers and amps in case of an error.
Jennice
Just a suggestion:
When you've assembled your boards/electronics, and the PSU, fire up the PSU without anything connected to it, and check that everything is as intended. (BTW: I suppose you got some high current bridge rectifiers?)
If this is OK, turn it off, and discharge the caps.
Connect the amplifier circuit to the PSU vith fuses (2-3Amp) in series, to limit the current through it if anything is wrong. Otherwise, you'll find yourself with a blown amp.
When that is ok, and the bias is set, try it with a cheap speaker unit to verify operation. When this is ok, you're ready to either remove the fuses, or insert some 6A types (or similar, "more than peak calculated current" types.)
Finally, connect to your speakers, and hopefully everything should be fine, with the precaution steps taken.
It would be a pity to ruin both speakers and amps in case of an error.
Jennice
Do test in stages, starting with the power supply. A light bulb in series with the mains will limit current if you've made a mistake. Wear eye protection and keep something between you and the supply the first time. A reversed electrolytic can pop with a lot of force and nasty smelling juice goes everywhere. Been there 
If you don't have a variac, I like Professor Leach's method for first firing up the boards. Instead of the low value fuses Jennice mentions, use a 100R .25W resistor in each rail. This will limit the current in case of a wiring error. Transistors usually blow faster than fuses. On one of my Leach amp channels I color coded the rail leads backwards and smoked the resistors but the transistors are still OK. If you get just a few volts or less across the resistor you're probably OK to remove them and put your fuses in - low values first.
If you don't have a variac, I like Professor Leach's method for first firing up the boards. Instead of the low value fuses Jennice mentions, use a 100R .25W resistor in each rail. This will limit the current in case of a wiring error. Transistors usually blow faster than fuses. On one of my Leach amp channels I color coded the rail leads backwards and smoked the resistors but the transistors are still OK. If you get just a few volts or less across the resistor you're probably OK to remove them and put your fuses in - low values first.
As far as bridge rectifiers, I have the two I bought for my Haflers that I didn't end up using. They are the KBPC2502 . I'm not sure if they are right for this application. They work fine in the Hafler but it is only using two 10000uf caps. If you have a better suggestion, I'm all ears.
I will try to take it very slow when testing. I sure don't want all this work to be in vain, and I sure don't want to damage my JBL's.
Hi Bob,
At what point are you using the light bulb? Ahead of the bridge, ahead of the caps, or after the caps? I don't quite understand.
I have purchased a Variac. See it here. Where should I monitor voltage while I bring up the power? Output from the caps? Ahead of the caps? At the bridge with caps disconnected?
As far as the resistors instead of the fuses. I read somewhere about using a resistor soldered across a blown fuse for this. The fuse holders are mounted to the PCBs in the ESP amp. Can I just remove the fuses there and insert the blown fuse with a resistor attached to it?
Thanks, Terry
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