OK guys,
I've got something wrong. I changed out the electros and no change. Truth is, I can live with the little buzz thing as it shuts down. I just discovered a bigger problem. I noticed when I turned on the amp that my JBL woofer was straining against its limit for a couple of seconds when I first switched it on. I hooked up a DC voltmeter to find that on initial turn-on The speaker is getting a nice healthy 29VDC. Maybe nice is the wrong choice of words.. It doesn't do it every time but for sure after the amp has set a while. After everything is charged up I have 0.00 DC offset. This is just when I turn it on. I also noticed that if I switch off the amp while the music is still playing the volume increases for a few seconds before it starts getting distorted and dies out. This may be normal I'm not sure, I never tried that before with any other amps.
So, does anyone have an idea why I'm getting almost rail voltage upon turn-on? I'm lucky I didn't fry my speakers.
Thanks, Terry
I've got something wrong. I changed out the electros and no change. Truth is, I can live with the little buzz thing as it shuts down. I just discovered a bigger problem. I noticed when I turned on the amp that my JBL woofer was straining against its limit for a couple of seconds when I first switched it on. I hooked up a DC voltmeter to find that on initial turn-on The speaker is getting a nice healthy 29VDC. Maybe nice is the wrong choice of words.. It doesn't do it every time but for sure after the amp has set a while. After everything is charged up I have 0.00 DC offset. This is just when I turn it on. I also noticed that if I switch off the amp while the music is still playing the volume increases for a few seconds before it starts getting distorted and dies out. This may be normal I'm not sure, I never tried that before with any other amps.
So, does anyone have an idea why I'm getting almost rail voltage upon turn-on? I'm lucky I didn't fry my speakers.
Thanks, Terry
still4given said:
If you have changed your ground points Terry you will find your DC-offset that you previously set to be OK is now out of whack... On turn on/off it is most noticable with the amplifier going to extreme dc-offset... Try checking the DC offset with no output (or input) and see how you go then connect an input and make sure it's still OK
Aaron
NUTTTR said:
Hi Aaron,
I had changed some ground points around so I was hopeful, but the dc offset when the amp is already running is within 2 mV of zero on both channels.
Here's another thing, though I can't be certain. It doesn't seem to do it unless I have speakers attached. I have switched it off and on a few times now with only the meter leads attached and the most I see on the speaker terminals is 1V and that is only for a split second. As it heats up it goes to zero within a couple of seconds. It seems to need a load on it to do it. It's like something is hanging up until it gets full power.
Just checked something else. It doesn't seem to do it if only one speaker is hooked up. Seems to need two. Also, with only one speaker hooked up, it takes a long time for the dc offset to drom to 0.3mV after it is turned off. With both speakers hooked up, both channels drop to 0.3mv within a few seconds. seems like the channels shouldn't be aware of the other channel, yet they react to the other having a speaker hooked up.
I'm really puzzled. Sure hope one of you know what's causng this.
Thanks, Terry
zeners?
Terry,
You should try comparing the voltages around the board with the known good ones posted, something is dead or dieing, and the voltages will probably be askew somewhere. If I had to guess I'd check out the Zeners first, they should have a stable 27v, and thus set the voltages for everything up to the drivers. If one of them has 'died', the front end will be out of whack, and the front end's connected to the...
Only the 'DC servo' effect is keeping the DC minimized, be really careful connecting it to speakers you care about until you find the problem.
Good luck
Stuart
Terry,
You should try comparing the voltages around the board with the known good ones posted, something is dead or dieing, and the voltages will probably be askew somewhere. If I had to guess I'd check out the Zeners first, they should have a stable 27v, and thus set the voltages for everything up to the drivers. If one of them has 'died', the front end will be out of whack, and the front end's connected to the...
Only the 'DC servo' effect is keeping the DC minimized, be really careful connecting it to speakers you care about until you find the problem.
Good luck
Stuart
Re: zeners?
Hi Stuart,
OK I checked the Zeners.
On one channel as related to CT I get -28.4, +27.9. On the other I get -27.8, +28.2. Attaching speakers once the amp is up and running doesn't seem to affect anything. It's only at switch on and switch off. It's like something is not switching off or on when it's supposed to. Like I said, It seems to only do it when there is a load on the speaker outs.
Thanks, Terry
Stuart Easson said:
Hi Stuart,
OK I checked the Zeners.
On one channel as related to CT I get -28.4, +27.9. On the other I get -27.8, +28.2. Attaching speakers once the amp is up and running doesn't seem to affect anything. It's only at switch on and switch off. It's like something is not switching off or on when it's supposed to. Like I said, It seems to only do it when there is a load on the speaker outs.
Thanks, Terry
Just so everyone is aware the KSA-50 boards went to into production and are in process. I will post now an then and let everyone know how things are progressing.
Its also great to see all this activity here and knowing that Jan's boards are also working out and that more amps are in progress and or comming on line. Keep up the good work !!
Terry,
I bet that you have different charge/discharge rates of your rails at both turn on and turn off. This would cause that short DC voltage offset problem.
Mark
Its also great to see all this activity here and knowing that Jan's boards are also working out and that more amps are in progress and or comming on line. Keep up the good work !!
Terry,
I bet that you have different charge/discharge rates of your rails at both turn on and turn off. This would cause that short DC voltage offset problem.
Mark
Terry,
you have both channels on 1 powersupply.
And you are using a CRC setup.
I'd check the electrolytics, if one of the capacitors after the 0.1 Ohms resistors collapsed one channel would be sucking the juice from the other.
You'd have voltage differences, and after switch-off one capacitor bank would unload much faster than the other.
If the negative rail voltage drops much faster than the positive you'd have funny DC stuff, see how the DC-trimmpot works.
Capacitors can not be unloaded at the same rate as loading.
When you disattach the CT, the charging goes through 2 rectifier diodes from one rail to the other, the charge that goes from the negative cap goes to the positive one.
As there is no reference to ground with the CT disconnected, at switch-on the chargerate for the positive cap may be within limits, the chargerate for the negative capacitor too high.
With the CT connected the charge goes through one diode for positive and one diode for the negative rail, the CT makes sure its balanced.
You should not be messing with PS grounds with the transformer switched on.
you have both channels on 1 powersupply.
And you are using a CRC setup.
I'd check the electrolytics, if one of the capacitors after the 0.1 Ohms resistors collapsed one channel would be sucking the juice from the other.
You'd have voltage differences, and after switch-off one capacitor bank would unload much faster than the other.
If the negative rail voltage drops much faster than the positive you'd have funny DC stuff, see how the DC-trimmpot works.
Capacitors can not be unloaded at the same rate as loading.
When you disattach the CT, the charging goes through 2 rectifier diodes from one rail to the other, the charge that goes from the negative cap goes to the positive one.
As there is no reference to ground with the CT disconnected, at switch-on the chargerate for the positive cap may be within limits, the chargerate for the negative capacitor too high.
With the CT connected the charge goes through one diode for positive and one diode for the negative rail, the CT makes sure its balanced.
You should not be messing with PS grounds with the transformer switched on.
Hi jacco,
What you are saying makes sense. Maybe I'll try just hooking things up through one good pair of caps and see if it goes away. It is certainly possible that one of the caps is not charging at the same rate as the others. These caps are stamped 658-411-9838 which may mean 1998 38th week. I'm not sure, I bought them on ebay a while back. I have other caps.
The problem didn't start until I mistakenly removed the CT while it was running. I will test this theory and then replace the caps if necessary.
Thanks everyone, Terry
What you are saying makes sense. Maybe I'll try just hooking things up through one good pair of caps and see if it goes away. It is certainly possible that one of the caps is not charging at the same rate as the others. These caps are stamped 658-411-9838 which may mean 1998 38th week. I'm not sure, I bought them on ebay a while back. I have other caps.
The problem didn't start until I mistakenly removed the CT while it was running. I will test this theory and then replace the caps if necessary.
Thanks everyone, Terry
Great News!
It was the filter caps. I remember when I first put the PSU together that I tried to bring it up slowly with my variac and popped the fuse in my variac. I discovered that one of the caps was in backwards. I swapped it around and everything seemed OK so I forgot about it. I probably damaged the cap at that time and it just took a while for it to fail. I swapped out all of them just to make sure and it is now better than ever. Thanks to all of you for sticking with me through all of this. Hopefully someone else will benefit from my mistakes and not have to make the same ones.
Blessings, Terry
It was the filter caps. I remember when I first put the PSU together that I tried to bring it up slowly with my variac and popped the fuse in my variac. I discovered that one of the caps was in backwards. I swapped it around and everything seemed OK so I forgot about it. I probably damaged the cap at that time and it just took a while for it to fail. I swapped out all of them just to make sure and it is now better than ever. Thanks to all of you for sticking with me through all of this. Hopefully someone else will benefit from my mistakes and not have to make the same ones.
Blessings, Terry
Thanks guys,
I will rerun the test between the two amps. I brought the amp to work with me today so I could change out the caps. Only have small speakers here to test, but frome what I can tell, now more snake dither. As a matter of fact I had to get my ear right up against the speaker to hear any buzz at all. I think I am going to be very happy once I can give it a real test.
Blessings, Terry
I will rerun the test between the two amps. I brought the amp to work with me today so I could change out the caps. Only have small speakers here to test, but frome what I can tell, now more snake dither. As a matter of fact I had to get my ear right up against the speaker to hear any buzz at all. I think I am going to be very happy once I can give it a real test.
Blessings, Terry
Thanks guys,
I will rerun the test between the two amps. I brought the amp to work with me today so I could change out the caps. Only have small speakers here to test, but frome what I can tell, now more snake dither. As a matter of fact I had to get my ear right up against the speaker to hear any buzz at all. I think I am going to be very happy once I can give it a real test.
Blessings, Terry
I will rerun the test between the two amps. I brought the amp to work with me today so I could change out the caps. Only have small speakers here to test, but frome what I can tell, now more snake dither. As a matter of fact I had to get my ear right up against the speaker to hear any buzz at all. I think I am going to be very happy once I can give it a real test.
Blessings, Terry
Attention KSA-50 Board Group Buyers.......
I got an e-mail today from Advanced and there was some question about the scoring to be done on the boards... seems they didn't see the .mil file for some reason. Anyway that problem is re-solved and things are now definately set in production. Board delivery to me is set for Sept, 02 which just happens to be my birthday
.
Mark
I got an e-mail today from Advanced and there was some question about the scoring to be done on the boards... seems they didn't see the .mil file for some reason. Anyway that problem is re-solved and things are now definately set in production. Board delivery to me is set for Sept, 02 which just happens to be my birthday
.Mark
With Marks post I will remind everyone that the parts GB will end on Monday the 8th so I can total orders and then get an estimated price for the kits. I will post the cost for the kits on the 10th or 11th and ask to receive payment by the 17th.
I am hoping to get the parts to everyone around the same time as the boards.
I am hoping to get the parts to everyone around the same time as the boards.