order a couple of spares and while you're at it you might as well get some of the p channel devices too, just in case something else blows up.
test diodes
Hello Terry,
Good work.
You can also test zd1 and d1.
With the meter on the diode scale and the negative lead on the cathode (black band) of the diode and the positive lead on the other end of the same diode. A good diode will measure approx. 0.6 which means .6 volts. Next reverse the leads and the reading should be infinity.
Test the other diode the same as above.
Now that the faulty Q7 is removed you can plug it into the meters transistor socket for NPN and read the gain (hfe) which should be between 60 - 260.
Joe
Visit DIY Amplifiers Yahoo Group is a place for sharing Solid State amplifier info:
http://groups.yahoo.com/group/diyamplifiers/
Hello Terry,
Good work.
You can also test zd1 and d1.
With the meter on the diode scale and the negative lead on the cathode (black band) of the diode and the positive lead on the other end of the same diode. A good diode will measure approx. 0.6 which means .6 volts. Next reverse the leads and the reading should be infinity.
Test the other diode the same as above.
Now that the faulty Q7 is removed you can plug it into the meters transistor socket for NPN and read the gain (hfe) which should be between 60 - 260.
Joe
Visit DIY Amplifiers Yahoo Group is a place for sharing Solid State amplifier info:
http://groups.yahoo.com/group/diyamplifiers/
I can't remember who came up with the suggestion, but I agree: comparative measurements between the working and faulty PCB could be a very good idea. 
Jennice
Jennice
After further measurements, I'm not convinced that the 2SK1058's are bad. They both measure the same from source to drain and they measure open for all other combinations. Further, I brought the board to work with me today so I cound make some more measurements and after reversing the leads several times I see that I am not getting inf. on the +rail side with the 2SK1058's removed. I will need to check the good boards again when I get home. It is possible that changing Q7 fixed the problem and I just measured wrong.
I'll have to let you know tonight.
Blessings, Terry
I'll have to let you know tonight.
Blessings, Terry
Yes, it is very possible the fault was just a failed Q7. Look at what would happen to the gate voltage of the outputs if Q7 is shorted - it swings to a diode drop (.6V) of the rail voltage. This would turn Q8/10 full on and your output voltage would go near the rail. Probably 2V or so less than the rail voltage.
Was your solder bridge near the base connection of Q7?
I hope that you got lucky and your output stage survived. 🙂 Is the source-drain resitance megohms or tens of ohms? The higher the better.
Was your solder bridge near the base connection of Q7?
I hope that you got lucky and your output stage survived. 🙂 Is the source-drain resitance megohms or tens of ohms? The higher the better.
further checking
Hello Terry,
There still maybe a solder bridge at ZD1 @ D1(you didn't mention, but I assume it was not ZD2@D2 or between D1@ZD2).
Test for a short circuit using the resistance setting. You may find removing the two diodes makes testing easier.
Solder braid, a tightly woven flexable copper wire is usually used to remove solder from circuit boards. I had bad luck using the Radio Shack brand.
Joe
Visit DIY Amplifiers Yahoo Group is a place for sharing Solid State amplifier info:
http://groups.yahoo.com/group/diyamplifiers/
Hello Terry,
still4given said:
There still maybe a solder bridge at ZD1 @ D1(you didn't mention, but I assume it was not ZD2@D2 or between D1@ZD2).
Test for a short circuit using the resistance setting. You may find removing the two diodes makes testing easier.
Solder braid, a tightly woven flexable copper wire is usually used to remove solder from circuit boards. I had bad luck using the Radio Shack brand.
Joe
Visit DIY Amplifiers Yahoo Group is a place for sharing Solid State amplifier info:
http://groups.yahoo.com/group/diyamplifiers/
One of them changes every time I measure it. Right now the constant one measures 7.92 mOhms with + probe on source and the - probe on drain. The other one reads .4kOhms. If I switch the probes, the first one reads open but the second one reads 5.6 mohms but the value keeps dropping. If I then switch bck it will jump to like 55.5 kohms but then begin dropping. Looks like it's dust. I better just order new.
The solder bridge I found was across ZD1 and D1. It basically bypassed ZD1 and D1. I'm not sure if that could take out Q7 or not.
Thanks, Terry
one more test
Hello Terry,
Hello Terry,
Mosfets Q8 & Q10 each have a 220pf 50 volt capacitor soldered across the gate to source, which may account for the meter reading decaying. You can try removing one lead of the capacitor to see if the reading stablizes and becomes similar to the other mosfet.
Joe
Hello Terry,
still4given said:
One of them changes every time I measure it. Right now the constant one measures 7.92 mOhms with + probe on source and the - probe on drain. The other one reads .4kOhms. If I switch the probes, the first one reads open but the second one reads 5.6 mohms but the value keeps dropping. If I then switch bck it will jump to like 55.5 kohms but then begin dropping. Looks like it's dust. I better just order new.
The solder bridge I found was across ZD1 and D1. It basically bypassed ZD1 and D1. I'm not sure if that could take out Q7 or not.
Thanks, Terry
Hello Terry,
Mosfets Q8 & Q10 each have a 220pf 50 volt capacitor soldered across the gate to source, which may account for the meter reading decaying. You can try removing one lead of the capacitor to see if the reading stablizes and becomes similar to the other mosfet.
Joe
Re: one more test
I have already removed them from the PCB. There is nothing attached to them any more. They wouldn't read properly mounted in the PCB because it would be basically like reading rail to output since they span that anyway. I had to remove them just to see if they were open from gate to drain. No, the one that's fluctuating is unattached. It also reads resistance both directions where the other only read in one.
I've ordered two more matched pairs. I figure I will just replace all four MOSFETs. I wouldn't want this channel to sound different than the other two. Another $37. This amp is like a hole in my studio that I pour money into. 😀
I'll be sure and bring the power up real slow next time I power it up. The last time I had it hooked up behind the sot start and it doesn't switch on until it's at about 30-40 VAC. Bummer, the board worked perfect before I mounted it in the chassis. I had the bias set and everything. From now on everything gets checked witht he variac before I hook it up to a softstart.
Blessings, Terry
diyampss said:
I have already removed them from the PCB. There is nothing attached to them any more. They wouldn't read properly mounted in the PCB because it would be basically like reading rail to output since they span that anyway. I had to remove them just to see if they were open from gate to drain. No, the one that's fluctuating is unattached. It also reads resistance both directions where the other only read in one.
I've ordered two more matched pairs. I figure I will just replace all four MOSFETs. I wouldn't want this channel to sound different than the other two. Another $37. This amp is like a hole in my studio that I pour money into. 😀
I'll be sure and bring the power up real slow next time I power it up. The last time I had it hooked up behind the sot start and it doesn't switch on until it's at about 30-40 VAC. Bummer, the board worked perfect before I mounted it in the chassis. I had the bias set and everything. From now on everything gets checked witht he variac before I hook it up to a softstart.
Blessings, Terry
Re: Re: one more test
It's still a cheap education compared to taking some EE courses. 😉 Your next project will go more smoothly.
still4given said:
It's still a cheap education compared to taking some EE courses. 😉 Your next project will go more smoothly.
Re: Re: one more test
Hi Terry,
If your budget can allow, ESP has a speaker protection pcb to prevent dc current from destroying the speakers. Sounds like good insurance to me.
I do have a question how warm were the heat sinks when the amp was running on two channels?
Also I didn't see anything mentioned about the type preamp used when you were listening to the amp!
Joe
diyamplifiers@yahoogroups.com
still4given said:
Hi Terry,
If your budget can allow, ESP has a speaker protection pcb to prevent dc current from destroying the speakers. Sounds like good insurance to me.
I do have a question how warm were the heat sinks when the amp was running on two channels?
Also I didn't see anything mentioned about the type preamp used when you were listening to the amp!
Joe
diyamplifiers@yahoogroups.com
Re: Re: Re: one more test
I sure can't argue with that logic. I feel exactly the same way.
Hi Joe,
I might look into that speaker protection, though the two good boards are only putting out 10mV at the outputs. That's well below the 100mV that Rod says is acceptable.
Tis amp runs surprizingly cool. I ran it pretty hard for about an hour, ( I had to leave the room, it was too loud to be comfortable), and you could barely feel the warmth. My Hafler P230 are almost uncomfortably warm just running easy and their heatsinks are almost as large as these. I can't see me having any problem whatsoever with heat.
I've tried it through my Bryston .04 preamp and my Yamaha. The Bryston has no EQ at all. It's fine for stuff that was well recorded, but I think I prefer the Yamaha to be able to add a little bas or treble when needed. I have some JBL 4425's that have tons of bass but only go to about 16kz so adding a little treble was just the ticket with this amp. The opposite ws true with my Yamaya NS1000's. They have plenty of highs but needed just a touch of bass boost with this amp.
I listened to it a lot last night. As of right now I think my Soundcraftsmen S860 still has a slight edge on it but it sounds better than all my other amps.
Blessings, Terry Here's a picture of my speakers.
Some of my equipment;
Blessings, Terry
BobEllis said:
I sure can't argue with that logic. I feel exactly the same way.
diyampss said:
Hi Joe,
I might look into that speaker protection, though the two good boards are only putting out 10mV at the outputs. That's well below the 100mV that Rod says is acceptable.
Tis amp runs surprizingly cool. I ran it pretty hard for about an hour, ( I had to leave the room, it was too loud to be comfortable), and you could barely feel the warmth. My Hafler P230 are almost uncomfortably warm just running easy and their heatsinks are almost as large as these. I can't see me having any problem whatsoever with heat.
I've tried it through my Bryston .04 preamp and my Yamaha. The Bryston has no EQ at all. It's fine for stuff that was well recorded, but I think I prefer the Yamaha to be able to add a little bas or treble when needed. I have some JBL 4425's that have tons of bass but only go to about 16kz so adding a little treble was just the ticket with this amp. The opposite ws true with my Yamaya NS1000's. They have plenty of highs but needed just a touch of bass boost with this amp.
I listened to it a lot last night. As of right now I think my Soundcraftsmen S860 still has a slight edge on it but it sounds better than all my other amps.
Blessings, Terry Here's a picture of my speakers.
Some of my equipment;
Blessings, Terry
If some of your MOSFETs that you pulled out are still good, hang on to them for your next project. I do this with ols BJTs - I use them a sacrificial components when first applying power to a new amp. Only when evey thing appears safe do I pull them and put in the new matched ones. Its less painful than bashing mu head on the wall.
Re: Re: Re: Re: one more test
Hi Terry,
Wow what nice equipment, especially the Bryston.
My P101 circuit boards arrived Monday and the single pair of mosfets I ordered should be here any day.
I wanted to try a mosfet amp on a budget but the recommended heat sink size seemed over-rated and very costly.
I am using 15 inch Tannoy 92% eff. and with 10 watts of music, for me is loud.
Joe
still4given said:
Hi Terry,
Wow what nice equipment, especially the Bryston.
My P101 circuit boards arrived Monday and the single pair of mosfets I ordered should be here any day.
I wanted to try a mosfet amp on a budget but the recommended heat sink size seemed over-rated and very costly.
I am using 15 inch Tannoy 92% eff. and with 10 watts of music, for me is loud.
Joe
Cool gear, Terry!
What kind of music are you into?
I don't know if it's any comfort to you, but I don't think you're the only one who's been spending more on DIY project than expected. Actually I think I would be surprised to meet anyone who has NOT encountered un-planned expenses.
Then again, reading about electronics is good, but without a hands-on approach it's worthless.
Do you want some book titles and read more thoroughly on electronic circuit theory, or do you want to leave it as this stage?
Jennice
What kind of music are you into?
I don't know if it's any comfort to you, but I don't think you're the only one who's been spending more on DIY project than expected. Actually I think I would be surprised to meet anyone who has NOT encountered un-planned expenses.
Then again, reading about electronics is good, but without a hands-on approach it's worthless.
Do you want some book titles and read more thoroughly on electronic circuit theory, or do you want to leave it as this stage?
Jennice
as someone said , your next projects will run more smoothly and cost less! , ive done a few projects off different kinds, and there were definatly still unplanned expenses in my 101 amp, but they wernt enough to blow my budget, i had accounted for them
the biggest thing i screwed up in my initial budget was the mosfets, it just indidnt occur to me how expensive 8 of them would be to make a 2 channel full power version, hence i settled for the low power. i dont know if u got a bit of a scare when u added up there cost 😉
was kind of a blessing as it turned out as id have needed larger heatsinks for sure, and i dont need that much power for my proac clones (which on an off topic, are up and running and sounding gorgeous) .
the biggest thing i screwed up in my initial budget was the mosfets, it just indidnt occur to me how expensive 8 of them would be to make a 2 channel full power version, hence i settled for the low power. i dont know if u got a bit of a scare when u added up there cost 😉
was kind of a blessing as it turned out as id have needed larger heatsinks for sure, and i dont need that much power for my proac clones (which on an off topic, are up and running and sounding gorgeous) .
hey jennice
http://www.users.on.net/~majord/proacs/Jimmy.htm
built from the usual
http://www.geocities.com/diyproac25/ reference.
just need to 'finish' em off and box the xovers
http://www.users.on.net/~majord/proacs/Jimmy.htm
built from the usual
http://www.geocities.com/diyproac25/ reference.
just need to 'finish' em off and box the xovers
- Status
- Not open for further replies.