I just used rubber shielding tape on the underside of the FETS. Is this enough? It seems to be enough to get the 2nd board at to some life (YES!). Board 1 seems OK except for major distortion at listening volume, but at least it actually provides volume now.
Now the 2nd board doesn't work at all again. I'm going to exchange the burnt resistors and see if this helps with board 1's distortion. If this still doesn't solve things, then I'm finishes with this project until I can get the actual PCBs.
Just electrical tape.
- swapped resistors, now board 1 doesn't get warm at all but plays at very low volume, just like board 2.
I should mention that the only way for me to get any sound is when I connect both speaker signals together. When I connet both signals with the CGRND to the PSU board, I get very, very low volume. Take away the CGRND, and the volume rises but with more distortion.
- swapped resistors, now board 1 doesn't get warm at all but plays at very low volume, just like board 2.
I should mention that the only way for me to get any sound is when I connect both speaker signals together. When I connet both signals with the CGRND to the PSU board, I get very, very low volume. Take away the CGRND, and the volume rises but with more distortion.
Member
Joined 2002
applebook said:
How about i sell you a board. Then you wont have to use card board 🙂
One left.
Jase
You likely have damaged the FETs.
The purpose of the heatsink is to remove the large amounts of heat generated by the FETs in normal operation. The FETs need to be electrically insulated from the heatsink, which your electrical tape is doing. However, they need to be able to conduct large amounts of heat to the heatsink, which the electrical tape is actually preventing.
There are many products available for this purpose (electrical insulation and heat transfer). Most common if thin sheets of mica (thinner than electrical tape) which are first coated in a silicone thermal grease that helps fill voids and better transfer the heat.
The next most common is the wide variety of thermal pads, made by companies like Bergquist, Wakefield, and Aavid. These are usually silicon impregnated fiberglass mesh, or a kapton-based polymer that are also very thin, and provide very good conduction of heat to the heatsink. The are used without any thermal grease.
Just to round out the group, there are also ceramic insulators, which work very well, but are slightly more costly and prone to cracking. I recommend them, but for beginners, maybe one of the thermal pads would the be the easiest/cleanest/cheapest way to go.
You really need to be using something like this to mount your FETs. Otherwise, the heat they generate will destroy them, which may have already happened.
Keep at it.
The purpose of the heatsink is to remove the large amounts of heat generated by the FETs in normal operation. The FETs need to be electrically insulated from the heatsink, which your electrical tape is doing. However, they need to be able to conduct large amounts of heat to the heatsink, which the electrical tape is actually preventing.
There are many products available for this purpose (electrical insulation and heat transfer). Most common if thin sheets of mica (thinner than electrical tape) which are first coated in a silicone thermal grease that helps fill voids and better transfer the heat.
The next most common is the wide variety of thermal pads, made by companies like Bergquist, Wakefield, and Aavid. These are usually silicon impregnated fiberglass mesh, or a kapton-based polymer that are also very thin, and provide very good conduction of heat to the heatsink. The are used without any thermal grease.
Just to round out the group, there are also ceramic insulators, which work very well, but are slightly more costly and prone to cracking. I recommend them, but for beginners, maybe one of the thermal pads would the be the easiest/cleanest/cheapest way to go.
You really need to be using something like this to mount your FETs. Otherwise, the heat they generate will destroy them, which may have already happened.
Keep at it.
Hi Applebook,
Brian has given some excellent information on insulators
for the output FETs and I suggest you obtain some before
proceeding (look for TO264 or TO3P insulators.)
Also, might I suggest trying to get the channels working
individually before connecting them both to the power
supply? You seem to be getting problems when they're
connected together. There might be some wiring issues
here as well.
Regarding the low volume level, are you using a balanced
signal? If not, you need to short the negative XLR pin
to ground. Otherwise the gain of the amplifier drops
significantly. Also, you may have an incorrect resistor
somewhere. The first mini-A channel I built had very
low volume...until I realized I had a 100K ohm resistor
in place of a 100 ohm resistor somewhere. 🙂
Please consider Jason's offer for a set of boards. I hope
they're the thru-hole ones.
Sorry for the rambling post. Keep at it and you're
have things working soon enough.
Cheers,
Dennis
Brian has given some excellent information on insulators
for the output FETs and I suggest you obtain some before
proceeding (look for TO264 or TO3P insulators.)
Also, might I suggest trying to get the channels working
individually before connecting them both to the power
supply? You seem to be getting problems when they're
connected together. There might be some wiring issues
here as well.
Regarding the low volume level, are you using a balanced
signal? If not, you need to short the negative XLR pin
to ground. Otherwise the gain of the amplifier drops
significantly. Also, you may have an incorrect resistor
somewhere. The first mini-A channel I built had very
low volume...until I realized I had a 100K ohm resistor
in place of a 100 ohm resistor somewhere. 🙂
Please consider Jason's offer for a set of boards. I hope
they're the thru-hole ones.
Sorry for the rambling post. Keep at it and you're
have things working soon enough.
Cheers,
Dennis
applebook
if I ware you,( and I'm a new at this, as you ) I would take a break...I believe that you a frustrated that this thing doesn't work...so take a break...
order some PCB from jason or kristian...
resolder all the parts from your ''boards''...check them all in peace...and then once you receive PCB solder them in place...
and do as the other members told you regarding placing the mosfets on heatsinks...
if I ware you,( and I'm a new at this, as you ) I would take a break...I believe that you a frustrated that this thing doesn't work...so take a break...
order some PCB from jason or kristian...
resolder all the parts from your ''boards''...check them all in peace...and then once you receive PCB solder them in place...
and do as the other members told you regarding placing the mosfets on heatsinks...
My suggestion is, since there are so few parts, just order new parts & PCBs and redo the installation.
And then while you are enjoying/listening your working amps, you can spend your leisure time troubleshooting your bad ones.
And then while you are enjoying/listening your working amps, you can spend your leisure time troubleshooting your bad ones.
Member
Joined 2002
I think he is going to buy a board. If so ill throw in some parts for free over the holidays. I have to sort some for another member too. And yes it is a through hole. 🙂
These amps are really easy to get going. If he has any problems he can ship one channel over to me and id be happy to set one up for him plus test it.
Jase
These amps are really easy to get going. If he has any problems he can ship one channel over to me and id be happy to set one up for him plus test it.
Jase
fcel said:
I wish that I had another amp to tide me over, but spending so much on this project has forced me to sell my main amp.
Why do the FETS on the my 2nd board not warm up at all? I've now tried both boards without heatsink, keeping the power on period to under 30 secs. because board 1 heats up really quickly. All FETS show similar measurement levels with my multimeter.
Why is it that I need to connect both speaker channel signals together to get sound? If I connect both signals and disconnect the CGND from the PSU, on board 1, I get loud but very distorted sound, while board 2 is quiet but at least produces some sound.
Since Jason has only 1 board left, I've decided to get 2 from Hipcheck. Meanwhile, I'd love to get this amp running without the boards.
Member
Joined 2002
Your fets better be fastened to a heat sink or they are pretty much toast. I don't want to be rude but im verry suprized that it even runs on cardboard.
My suggestion is getting them built with boards then go from there.
Also make sure you short gnd&neg ( audio inputs )
My suggestion is getting them built with boards then go from there.
Also make sure you short gnd&neg ( audio inputs )
Happy Holidays, everyone.
I have some good and some bad news.
- Channel one now appears to be FULLY working!
- Channel two doesn't work and merely hums/produces no sound. The problem is likely damaged/incorrectly wired/incorrect resistors and/or caps. All the FETS check out fine when I tested them, so they should not be the problem.
I'm now running the amp with a toroidal transformer and have mounted the FETS on appropriate heatsinks, so channel one is running. Hallelulah!
Do I need to short the ground input even though I'm running only balanced? When I short the ground, I get distortion, but with it connected, the sound is loud and clear.
I have some good and some bad news.
- Channel one now appears to be FULLY working!
- Channel two doesn't work and merely hums/produces no sound. The problem is likely damaged/incorrectly wired/incorrect resistors and/or caps. All the FETS check out fine when I tested them, so they should not be the problem.
I'm now running the amp with a toroidal transformer and have mounted the FETS on appropriate heatsinks, so channel one is running. Hallelulah!
Do I need to short the ground input even though I'm running only balanced? When I short the ground, I get distortion, but with it connected, the sound is loud and clear.
Which readily available resistors would work in place of the .47 OHM 3W ones? would all 4 .47 resistors have to be matched?
applebook,
You don't HAVE to match them. It is better if they are similar in value. If you have a meter and plenty of resistors to choose from, get them as close as you can. Matching means resisitor to resisitor, more than trying to hit 0.47r for all of them.
You don't HAVE to match them. It is better if they are similar in value. If you have a meter and plenty of resistors to choose from, get them as close as you can. Matching means resisitor to resisitor, more than trying to hit 0.47r for all of them.
Thanks, but I'm thinking more of local availability since I don't want to pay for shipping and handling.
Would 5 or 10W resistors work, or is that too high?
What about something as low as 10 OHM at 2W?
Would 5 or 10W resistors work, or is that too high?
What about something as low as 10 OHM at 2W?
10ohm is too high. You want to use the same resistance, but higher wattage rating is okay. You also want to be sure they are low-inductance or non-inductive.
I can check to see if I have any lying around that I could just send you.
I can check to see if I have any lying around that I could just send you.
Hi Applebook,
Good to hear you have one channel working.
You should short the negative input to ground only
if you're using a single-ended input; this is not needed
if you're using balanced in.
Can you get 1W resistors locally? If so, you
can parallel three 1.5 ohm ones to get a 3W
0.5 ohm resistor. That's should be close
enough.
Cheers,
Dennis
Good to hear you have one channel working.
You should short the negative input to ground only
if you're using a single-ended input; this is not needed
if you're using balanced in.
Can you get 1W resistors locally? If so, you
can parallel three 1.5 ohm ones to get a 3W
0.5 ohm resistor. That's should be close
enough.
Cheers,
Dennis
- Status
- Not open for further replies.