"This is not good..."
--Anakin Skywalker
If both channels are doing it, we can probably rule out cold solder joints (unlikely to happen the same way in both channels). My feeling at this point is that it's one of two things: Either parts are installed incorrectly (but consistently in both channels), or perhaps there's an error on the board. I haven't kept up with all the board versions out there; I made mine, they worked, and that was good enough for me. Has anyone completed an amp using that layout so that we know that it's good?
Grey
--Anakin Skywalker
If both channels are doing it, we can probably rule out cold solder joints (unlikely to happen the same way in both channels). My feeling at this point is that it's one of two things: Either parts are installed incorrectly (but consistently in both channels), or perhaps there's an error on the board. I haven't kept up with all the board versions out there; I made mine, they worked, and that was good enough for me. Has anyone completed an amp using that layout so that we know that it's good?
Grey
amp oscillations
Since the newbie friendly pompous windbag seems to have run off the pompous windbag with an EE degree, I guess I will have to answer this one...... The Brian GT board is for an ALEPH 2! The value and circuit location for C7 is different for the ALEPH 5. C7 should be mount between the emitter and collector of Q5 and have a value of 0.047uF for the Aleph5. Alternately Mr. Pass uses a value of 0.001uF if the cap is connected from base to collector of Q5 as done in the layout, which was intended for the Aleph 2. Mount the 221 ohm gate damping resistors for the output power mosfets at the gates and use short wires to the output mosfets. I would try to keep it under 6 inches. I think a couple of 0.47 uF caps from Vcc and -Vcc to ground would be good idea too. Most important follow the schematic exactely and check against the PCB to see that they match.
Since the newbie friendly pompous windbag seems to have run off the pompous windbag with an EE degree, I guess I will have to answer this one...... The Brian GT board is for an ALEPH 2! The value and circuit location for C7 is different for the ALEPH 5. C7 should be mount between the emitter and collector of Q5 and have a value of 0.047uF for the Aleph5. Alternately Mr. Pass uses a value of 0.001uF if the cap is connected from base to collector of Q5 as done in the layout, which was intended for the Aleph 2. Mount the 221 ohm gate damping resistors for the output power mosfets at the gates and use short wires to the output mosfets. I would try to keep it under 6 inches. I think a couple of 0.47 uF caps from Vcc and -Vcc to ground would be good idea too. Most important follow the schematic exactely and check against the PCB to see that they match.
OKAY,
i read that discussion on brian's original board thread, but i guess i didn't think about it enough. i'll take a look at the layout and schematic and give that a try.
as for the 0.47 caps from +Vcc and -Vcc to ground, will any kind do? i think this was discussed earlier in this thread... electrolytics with the same orientation as the rail, i.e. for the +Vcc, attach the positive end of the cap to the rail and negative to ground, is this correct?
thanks
this newbie appreciates it!!!
scott
i read that discussion on brian's original board thread, but i guess i didn't think about it enough. i'll take a look at the layout and schematic and give that a try.
as for the 0.47 caps from +Vcc and -Vcc to ground, will any kind do? i think this was discussed earlier in this thread... electrolytics with the same orientation as the rail, i.e. for the +Vcc, attach the positive end of the cap to the rail and negative to ground, is this correct?
thanks
this newbie appreciates it!!!
scott
Actually, the newbie-friendly windbag had to paint a wall, transplant a half-dozen oregano plants, etc. etc. etc.
Now that I've got those items off my to-do list for the day, I'll breeze on in here and proclaim (windily, of course), that for something like a .47, I'd use a film cap. Given the debugging mode that we're in here (rather than modification mode, for instance), I'd recommend something cheap for starters, just to make sure that it all works properly. I keep a bag full of Sprague Orange Drops for just such a situation. When the need arises, I snatch one out, tag it in, then see what's happening. They're good enough for bench work and not too expensive. Note also that film caps don't have polarity (unless you want to get picky about which foil's on the outside, but ignore that for now), so you can hook them in any ol' which-way.
Excuse me...a strong gust of wind just blew me...away...
Grey
Now that I've got those items off my to-do list for the day, I'll breeze on in here and proclaim (windily, of course), that for something like a .47, I'd use a film cap. Given the debugging mode that we're in here (rather than modification mode, for instance), I'd recommend something cheap for starters, just to make sure that it all works properly. I keep a bag full of Sprague Orange Drops for just such a situation. When the need arises, I snatch one out, tag it in, then see what's happening. They're good enough for bench work and not too expensive. Note also that film caps don't have polarity (unless you want to get picky about which foil's on the outside, but ignore that for now), so you can hook them in any ol' which-way.
Excuse me...a strong gust of wind just blew me...away...
Grey
well here's what i've tried, that didn't work:
-reheated ALL solder joints
-replaced C7 (the 0.047 uF cap) with a 0.001 in the current connection fashion
-tried 100uF electrolytics from the rails to ground
-checked the layout of the board compared to the schematic.
this was quite confusing, as i'm not sure if the order of some of these chains is important.
-checked polarity of all components installed
results,
i DID re-hook up R21, so that is now in and appears to be working.
and there is no heat coming from the tweet, just the buzz/hum.
i'll keep looking everything over.
any thoughts?
scott
with regard to Grey long post about current sources
An applause is in order! Everybody.
Great job Grey, it was about time that someone shut HarryHaller up!
And that frickin' link he keeps posting as the answer to all questions, which, by the way is totally irrelevant. I saw it at least in two posts. Make other people think you are smart by making them feel stupid.
An applause is in order! Everybody.
Great job Grey, it was about time that someone shut HarryHaller up!
And that frickin' link he keeps posting as the answer to all questions, which, by the way is totally irrelevant. I saw it at least in two posts. Make other people think you are smart by making them feel stupid.
Scott,
Have you checked all component values against the Aleph 5 schematic? The topology is very similar between the 2 and 5 but I know some of the component values changed....
Also, have you checked the output stage to make sure one or more devices aren't grounding somewhere? This could be creating your hum/buzz...
Steve
Have you checked all component values against the Aleph 5 schematic? The topology is very similar between the 2 and 5 but I know some of the component values changed....
Also, have you checked the output stage to make sure one or more devices aren't grounding somewhere? This could be creating your hum/buzz...
Steve
grey,
there is sound out of the tweet, in fact, other than the hum, it's very clear, i hooked up a junk mid in addition, kinda a little two way, and other than the buzz it was really good sound, i even turned up the volume quite a bit to see if i got any distortion but it sounded fine, just has lots of other sound... see, no right below that thingy over there, yeah that's it, what do you make of that???
seriously though, other than that hum, it seems to work fine, the sinks sit at 130 degrees f., with no apparent thermal runaway. i'm getting very low dc at the outputs ~23mV. but that hum is quite loud and steady. and like i said, the amp is now functioning with all of the standard loops.
also, that detailed explanation you gave me was really appreciated, my wife even grasped the concept, so i saved it for my files, thanks again for that.
us newbies really appreciate the help that is offered here. it's inspirational and very educational.
cheers,
scott
there is sound out of the tweet, in fact, other than the hum, it's very clear, i hooked up a junk mid in addition, kinda a little two way, and other than the buzz it was really good sound, i even turned up the volume quite a bit to see if i got any distortion but it sounded fine, just has lots of other sound... see, no right below that thingy over there, yeah that's it, what do you make of that???
seriously though, other than that hum, it seems to work fine, the sinks sit at 130 degrees f., with no apparent thermal runaway. i'm getting very low dc at the outputs ~23mV. but that hum is quite loud and steady. and like i said, the amp is now functioning with all of the standard loops.
also, that detailed explanation you gave me was really appreciated, my wife even grasped the concept, so i saved it for my files, thanks again for that.
us newbies really appreciate the help that is offered here. it's inspirational and very educational.
cheers,
scott
Scott,
One other thought...
If you disconnect your inputs to the amp, is the hum still present?
If by chance the hum goes away, try connecting the amp to the same outlet as the rest of your hifi... You might be dealing with an external ground loop...
Also, if your cable tv runs through any part of your hifi, try disconnecting the cable tv at the wall as an experiment...
Steve
One other thought...
If you disconnect your inputs to the amp, is the hum still present?
If by chance the hum goes away, try connecting the amp to the same outlet as the rest of your hifi... You might be dealing with an external ground loop...
Also, if your cable tv runs through any part of your hifi, try disconnecting the cable tv at the wall as an experiment...
Steve
steve,
i was posting when you threw up that last message, sorry i missed it.
all components are right outa the service manual. i used a great stuffing diagram that mark finnis sent that has all values and how/where to put 'em. additionally, these are all the SAME parts, other than resistors, diodes and mpsa18's that i had in the first version that worked for a couple of months, some times 8-9 hours a day. all replacement parts were values from the stuffing diagram.
thanks for replying!
scott
i was posting when you threw up that last message, sorry i missed it.
all components are right outa the service manual. i used a great stuffing diagram that mark finnis sent that has all values and how/where to put 'em. additionally, these are all the SAME parts, other than resistors, diodes and mpsa18's that i had in the first version that worked for a couple of months, some times 8-9 hours a day. all replacement parts were values from the stuffing diagram.
thanks for replying!
scott
I have looked over the boards over and over again, and I just checked it again against the Aleph 5 design. The only component difference from the aleph 5 schematic and my board layout is the placement of C7, the npn compensation capacitor. Instead of using 0.047uF, use 0.001uF, since it goes from CB instead of CE. NP said that this would not be a problem, as long as the appropiate value is used. Three things that I would check would be:
1) Verify that Q4 and Q5 are soldiered correctly, as the leads are really close together
2) Try the amplifier with a bench power supply, in order to verify that the hum not from your power supply transformer.
3) Verify that you hooked up the output devices correctly. Here is a picture of the way to hook up the devices to the notation on the boards:
Aleph 5 diagram (borrowed from web.vip.hr/pcb-design.vip/aleph-5.htm)
As previously stated, access to a bench oscilloscope would be greatly helpful.
EDIT: Looking back over the Aleph 5 design, you might want to make C7 the value of 680pF, in order to match it with C6.
--
Brian
gte619j@prism.gatech.edu
1) Verify that Q4 and Q5 are soldiered correctly, as the leads are really close together
2) Try the amplifier with a bench power supply, in order to verify that the hum not from your power supply transformer.
3) Verify that you hooked up the output devices correctly. Here is a picture of the way to hook up the devices to the notation on the boards:
Aleph 5 diagram (borrowed from web.vip.hr/pcb-design.vip/aleph-5.htm)
As previously stated, access to a bench oscilloscope would be greatly helpful.
EDIT: Looking back over the Aleph 5 design, you might want to make C7 the value of 680pF, in order to match it with C6.
--
Brian
gte619j@prism.gatech.edu
brian,
thanks for replying. you know, i really think that the oscillation is gone and now i'm left with a nasty ground loop. I don't have any scope to verify this, but i replaced C7 with the recommended .001uF cap, and now it works with the R21 loop in, and when a tweet is connected, it doesn't heat up at all. music sounds great, other than the ground loop induced hum. so i really think that it's not oscillating. i realize this is naive, without a scope, but all other voltage measurements are spot-on and the amp settles out at a normal operating temp (i mention this cuz i understand that oscillation can result in overheating due to the fast switching).
so, that's where i'm at
cheers,
scott
thanks for replying. you know, i really think that the oscillation is gone and now i'm left with a nasty ground loop. I don't have any scope to verify this, but i replaced C7 with the recommended .001uF cap, and now it works with the R21 loop in, and when a tweet is connected, it doesn't heat up at all. music sounds great, other than the ground loop induced hum. so i really think that it's not oscillating. i realize this is naive, without a scope, but all other voltage measurements are spot-on and the amp settles out at a normal operating temp (i mention this cuz i understand that oscillation can result in overheating due to the fast switching).
so, that's where i'm at
cheers,
scott
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