Apogee said:
This is exactly what I wanted to know. But what about all the hoopla about audio grade caps? I can find lots on digikey but does it matter what brand (remember I am not one who believes in all the "magic" stuff)...
You can see photos of mycaps here:
http://joeprinz.dotphoto.com
So how's abour CDE? I measure 62v across the caps so 75v would be enough right?
Technical/Catalog Information 338-1221-ND
Standard Package 25
Category Capacitors
Family Electrolytic
Vendor Cornell Dubilier Electronics (CDE)
Capacitance 30000µF
Voltage-Rated 75 V
Tolerance ±20%
Series DC
Package / Case Screw Terminals
Packaging Bulk
Features Computer Grade
Maximum Temperature 85°C
Lead Spacing 22.20mm
Lead Free Status Lead Free
RoHS Status RoHS Compliant
Other Names 338-1221
No, stay with 100vdc!
Technically, you are correct that the 75v units would work. However, the problem is their upper limit is too close the the unit's operating voltage and they would be short lived as a result.
Better to go with the 100vdc units so you have some cushion and aren't pushing them right at their max working voltage limit.
Don't worry about the "audiophile" grade caps. For small signal caps, they matter. For large filter caps, IMHO it doesn't matter.
Technically, you are correct that the 75v units would work. However, the problem is their upper limit is too close the the unit's operating voltage and they would be short lived as a result.
Better to go with the 100vdc units so you have some cushion and aren't pushing them right at their max working voltage limit.
Don't worry about the "audiophile" grade caps. For small signal caps, they matter. For large filter caps, IMHO it doesn't matter.
Hi Joe,
Steve is 100% correct here. Stay with the 100V caps.
You have both temperature and voltage added to high ripple current (that you plan to increase). Make sure you select capacitors rated for high ripple current and temperature.
-Chris
Steve is 100% correct here. Stay with the 100V caps.
You have both temperature and voltage added to high ripple current (that you plan to increase). Make sure you select capacitors rated for high ripple current and temperature.
-Chris
I would go with as much capacitance as a 75 volt rating
will allow. Don't worry, it will probably last another 30 years.
If you are concerned about the inrush surge, use a thermistor
in series with the AC line. I use CL60's for this sort of application
and you can go to CL40 if you want (see the Digikey catalog
under Keystone Thermistors). The bridges will be fine and the
whole thing will run quieter.
😎
will allow. Don't worry, it will probably last another 30 years.
If you are concerned about the inrush surge, use a thermistor
in series with the AC line. I use CL60's for this sort of application
and you can go to CL40 if you want (see the Digikey catalog
under Keystone Thermistors). The bridges will be fine and the
whole thing will run quieter.
😎
Thanks Mr. Pass and all.. I think I will go with the thermistor.. I noticed lots more current on startup with the bias getting up there... to get it to hit 45c I have to go to about 115mv dead cold on the emitter measured bias.. the 2amp fuse ain't cuttin it anymore. So I can order those at the same time as the caps anyway.
I plan to "upgrade this to fuses on the power supply outputs just like my newer 400a.. its damn dangerous without those fuses if you ask me... it can just cook itself to death! (Which this one did).
and NOW I know exactly what Mr. Pass means about the hand on for 5-10 seconds.. you can actually feel yourself wanting to let go.. and its right around 45c oddly enough 🙂 I love it.. what a great way to adjust an amp.
There is a very slight chance I might get both channels cooking tonight... and then a quick listen before I leave.. but its doubtful.. you gotta really spend a lot of time when you are inexperienced like me getting the bias right.. its not a very static sort of adjustment.. very dynamic.. and as I said sometimes you just have to pull the power and start over to get things right again.. I'm gonna go slightly under what my temp gauge says and trust my hand over the gauge (which is a cheap gauge)..
Boy my other 400a is WAY too cold running..
I plan to "upgrade this to fuses on the power supply outputs just like my newer 400a.. its damn dangerous without those fuses if you ask me... it can just cook itself to death! (Which this one did).
and NOW I know exactly what Mr. Pass means about the hand on for 5-10 seconds.. you can actually feel yourself wanting to let go.. and its right around 45c oddly enough 🙂 I love it.. what a great way to adjust an amp.
There is a very slight chance I might get both channels cooking tonight... and then a quick listen before I leave.. but its doubtful.. you gotta really spend a lot of time when you are inexperienced like me getting the bias right.. its not a very static sort of adjustment.. very dynamic.. and as I said sometimes you just have to pull the power and start over to get things right again.. I'm gonna go slightly under what my temp gauge says and trust my hand over the gauge (which is a cheap gauge)..
Boy my other 400a is WAY too cold running..
Well; yet another problem; but I THINK I have it diagnosed.
I had both sides at the right temp; fired up some music on it and then shut it off to disconnect and remeasure bias and I noticed a very loud HUM and both woofer would extend as I moved the variac up.. kinda fun.. So I started taping around on the right board and WACK! A crackle and then the amp started behaving normal.. turned it up to 110vac and verified.. yup.. it works..
So I turned it down to about 40vac and started taping around.. well to make a long story short.. when I tap on the heat-sinks of what I guess are input driver transistors specifically on the upp right and bottom left as show in this photo I get a static sound with every touch of my plastic adjustment tool.. the harder I wack them the louder the sound.. the other two are silent..
All 4 on the left channel are dead silent when I beat on them.
So I am guessing I need to replace all these?? Is this the "feedback" circuit I have been reading about perhaps? Or is it possible both have bad solder joints?
Oh and DOGGONE IT!
I had both sides at the right temp; fired up some music on it and then shut it off to disconnect and remeasure bias and I noticed a very loud HUM and both woofer would extend as I moved the variac up.. kinda fun.. So I started taping around on the right board and WACK! A crackle and then the amp started behaving normal.. turned it up to 110vac and verified.. yup.. it works..
So I turned it down to about 40vac and started taping around.. well to make a long story short.. when I tap on the heat-sinks of what I guess are input driver transistors specifically on the upp right and bottom left as show in this photo I get a static sound with every touch of my plastic adjustment tool.. the harder I wack them the louder the sound.. the other two are silent..
All 4 on the left channel are dead silent when I beat on them.
So I am guessing I need to replace all these?? Is this the "feedback" circuit I have been reading about perhaps? Or is it possible both have bad solder joints?
An externally hosted image should be here but it was not working when we last tested it.
Oh and DOGGONE IT!
GRollins said:
Yeah I know.. more silcone grease all over my hands. LOL..
the components are these
rca1a15/16
2n5415
2n3440
According to a parts list someone put togther I found..
2n's are easy to find.. rca's... not so much. I guess I will R&R each one.. oh the joy 🙂
Bad solder joints either on that transistor or near it...
Shouldn't need to replace anything.
You're learning!!!
🙂
Shouldn't need to replace anything.
You're learning!!!
🙂
Apogee said:Bad solder joints either on that transistor or near it...
Shouldn't need to replace anything.
You're learning!!!
🙂
Yeah I suppose, seems weird that it would be 2 of them.. maybe its a connection between them though which would completely explain it wouldn't it?
Okay.. well; its gonna have to wait.. need to get ready to leave..
Hope you all have a good weekend..
Oh I found some Vishay/Sprague 39kuF caps.. is this a good brand name? Or how's about a 25kuF Mallory?
Okay I am back.
I pulled all 4 transistors off the input board and sanded the leads (they actually looked a bit coroded).. and resoldered them back in.. I also heated up everything around them (remember 2 of them when tapped caused a crackle).. Steve, Grey, you were both right.. no part replacement required!
Put it back together and now I can beat the heck out of them with no crackle. I have not tried a source yet but DC is 29mv rt and 10mv left (worse than before but I am guessing it was a false reading due to this bad solder connection).
I am trying again to get the bias right (i turned both sides down when the crackle showed up, ruining all my adjusting 🙁 ).. I am at 38c right now and just turned up the bias to about 68mv left and right.. should bring it up into the lower 40's (45c is the spec).
Anything else I can check without a scope to make sure this thing isnt gonna kill my speakers? I'm dieing to hear it on my main system.
I will play it for awhile on some old JBL's.. but I am sure my vandersteens are more easily damaged. I guess I will leave it on the variac with a fuse for awhile.. My newer 400a amp has fuses on the power supply outputs.. I need to do this on this old unit..
I pulled all 4 transistors off the input board and sanded the leads (they actually looked a bit coroded).. and resoldered them back in.. I also heated up everything around them (remember 2 of them when tapped caused a crackle).. Steve, Grey, you were both right.. no part replacement required!
Put it back together and now I can beat the heck out of them with no crackle. I have not tried a source yet but DC is 29mv rt and 10mv left (worse than before but I am guessing it was a false reading due to this bad solder connection).
I am trying again to get the bias right (i turned both sides down when the crackle showed up, ruining all my adjusting 🙁 ).. I am at 38c right now and just turned up the bias to about 68mv left and right.. should bring it up into the lower 40's (45c is the spec).
Anything else I can check without a scope to make sure this thing isnt gonna kill my speakers? I'm dieing to hear it on my main system.
I will play it for awhile on some old JBL's.. but I am sure my vandersteens are more easily damaged. I guess I will leave it on the variac with a fuse for awhile.. My newer 400a amp has fuses on the power supply outputs.. I need to do this on this old unit..
I confess to stopping by the side of the road and gutting televisions, radios, what have you, of their speakers. Wonderful test drivers. If I pop one, I feel no remorse. They were never of any value, and they didn't cost a dime.
Failing that, you can pick up something cheap (say, a dollar) at a parts place. It need not be high fidelity.
Yard sales, pawn shops, friends who have junk that's in their way...test speakers are out there, begging to go in harm's way.
Grey
Failing that, you can pick up something cheap (say, a dollar) at a parts place. It need not be high fidelity.
Yard sales, pawn shops, friends who have junk that's in their way...test speakers are out there, begging to go in harm's way.
Grey
Hi Joe,
-Chris
No. Fuses are very non-linear. A relay is the lesser of the two evils, so get a speaker protection (for DC) circuit and use that.
-Chris
Thanks guys.. well I got it up to temp and played it for a bit. The instructions I have say that you have to let it cool and bring it up to temp once last time to be sure its set correctly.. So I will do that.. is setting the bias as tedious on other amps?
Anatech: the outputs have fuses already.. but threshold saw it necessary to add fuses in later models.. you still disagree with fuses at the power supply output? I can't imagine they did it for no good reason.
Maybe Mr. Pass can chime in.. was this a production addition or did you make a design change on the later amps? The fuses are mounted right to the boards in my later unit.
Anatech: the outputs have fuses already.. but threshold saw it necessary to add fuses in later models.. you still disagree with fuses at the power supply output? I can't imagine they did it for no good reason.
Maybe Mr. Pass can chime in.. was this a production addition or did you make a design change on the later amps? The fuses are mounted right to the boards in my later unit.
Question:
I went to cold start the 400a for what MIGHT be the final bench test only to blow the 2amp in series on AC fuse after a few seconds. I figure its because of the higher current with the bias cranked up and the heat sinks cold as hell.. so I went to a 3 amp and the toast is starting to brown.. 😉
I hope I did the right thing and my conclusion was correct..
after 20 min I am @ 38c... which according to me guestimation calculator is right on the graph.
I went to cold start the 400a for what MIGHT be the final bench test only to blow the 2amp in series on AC fuse after a few seconds. I figure its because of the higher current with the bias cranked up and the heat sinks cold as hell.. so I went to a 3 amp and the toast is starting to brown.. 😉
I hope I did the right thing and my conclusion was correct..
after 20 min I am @ 38c... which according to me guestimation calculator is right on the graph.
3 amps is fine until they blow, and then you'll want to try
4A.
This one one of the first 400A's. Subsequently the metal was
changed to make it easier to build, and later on the circuit itself
picked up improvements, mostly in the front end.
😎
4A.
This one one of the first 400A's. Subsequently the metal was
changed to make it easier to build, and later on the circuit itself
picked up improvements, mostly in the front end.
😎
Nelson Pass said:
I'll compare my newer 400a and see if I see much of a difference.. besides the fuses.. maybe do an "upgrade"... the boards are quite differnet mosfets face opposite directions from version to version.. I'll post some pics for everyone to see.
Thanks for the nod on the fuse upgrade.. I was a little nervous turning up the variac with the larger fuse installed... its still not coming up to temp though.. so looks like I will need to tweek it further.. Only got to 41.2c rt and less on the left.. didnt hit the temp where Id want to pull my hand away either. Back to the drawing board.. added another 10mv.. problem is is that its sometimes isnt responsive to the change while its running..
It really may be that you could use new pots. Also, it's a
fairly simple matter to trim the network around a pot value to
more precisely nail the value. To do this, you need to measure
the actual value of the pot near the ideal point. and then
place resistance in series and/or parallel with it.
At this point it sounds like the amp works and will probably
continue to work.
The best part about being experienced with fixing something
like this is you can relax and say "What's the worst that could
happen - so what if the amp breaks?"
😎
fairly simple matter to trim the network around a pot value to
more precisely nail the value. To do this, you need to measure
the actual value of the pot near the ideal point. and then
place resistance in series and/or parallel with it.
At this point it sounds like the amp works and will probably
continue to work.
The best part about being experienced with fixing something
like this is you can relax and say "What's the worst that could
happen - so what if the amp breaks?"
😎