Despite having one working PSU I'm still not seeing any reading across 0 1R on the amp board.....well that's not strictly true, when I put my multimeter across it the voltage drops to zero. It was only reading a few mv before it dropped though. I have the DC pot set to half way.
Despite having one working PSU I'm still not seeing any reading across 0 1R on the amp board.....well that's not strictly true, when I put my multimeter across it the voltage drops to zero. It was only reading a few mv before it dropped though. I have the DC pot set to half way.
I may be misunderstanding what you are trying to do but the DC pot is to adjust DC levels on the output.
The other pot marked Current Adjust is used in conjunction with the .1R resistor, it will read initially Zero if the pot is fully anti-clockwise.
So if I am correct then put the meter across R11 (0.1R) and twiddle the pot gently, you should start to get a reading.
If I am not correct ignore the above.
Hi Sondale. I had the DC pot set to halfway before I started adjusting the current adjust pot (with my meter across R11. When I adjust the current I see no change on my meter.
I'd use the continuity setting on your multimeter to check the connections between the PSU and the SECA boards just to be sure that you have not cross wired something.
putting a voltage to ground on one side may be causing the strange readings.
Also measure to see if you have DC on the speaker terminal OP's (measure between them)
it's a little hard to trace the wiring in the photos as the wires aren't colour coded but it looks like you may have a cross wire.
positive and negative need to go to the outside terminals on the SECA board.
From the transformer to the PSU board:
Yellow to AC1
Orange to GND
Black to GND
Red to AC2
From the PSU to the amp board:
+V to AC
GND to GND
GND to GND
-V to to AC
Continuity between wires checked and they are all ok.
I don't have anything connected to the speaker terminal at the moment. This afternoon I can wire this back up and report back.
Disconnect ALL connections between PSU and SECA boards.
The SECA Board can be tested on it's own by connecting he transformer directly.
The big plus of this design is it's modular construction so my take is test the PSU and SECA separately if at all possible which should make it easier to find and fix the problem.
Lets see what Col recommends as the next step but I'd avoid powering up until we have a plan.
Mistakes I made a few but then again too few to errrr well you get the story and while you wait you could take a look at my efforts.:-)
I've noticed that on a couple of builds that folks have taken the speaker connections from the amp board and not the connections on the p/s board. Does this make a difference?
Yes. I built the amp initially without the PS boards, adding the PS boards some months later. Taking the speaker signal from the PS boards is a significant step up.
Ok, with the COM probe of my meter on 0V and the red on -V I get -17.9v. Now when I lift the red probe and put it on either side of the 0.1R resistor I get +4.8v :-q. When I then put the red probe on the FET centre pin I see +17.3v.
If OK check power on the pin of the PSU PCB if Ok then connection on Amp PCB.
It looks has if you have lost -17V
Assuming you check voltage on R11 it should read -17VDC and not the volts on R12 which should read close to zero and zero when DC offset is set correctly
What device have yo fitted into Q9?
And is both amp doing the same thing? if so a common error maybe.
That should be fine but note if you use a FET you get a wee bit more power.From 12W to 18W approx, due to a lower saturation voltage across the constant current that Q9 is part of .
And with the PSU it will peak to about 30W, not RMS as the last power level are, ie 12WRMS, 18WRMS, and with a very short burst like a symbol peaks of nearly 40W, this give this huge dynamic range and makes the amp sound like a big amp.
Assuming you check voltage on R11 it should read -17VDC and not the volts on R12 which should read close to zero and zero when DC offset is set correctly
The above reading still give +4.8V on R11 and com to zero volts,
If so is it the same on both PSU boards?
Then you have no -V at all mmm I will draw up a test point system it will be here in the morning, it sound like duff psu maybe burnt out track when is sparked check tracks please
May I also recommend the use of ''Stunt speakers'' for testing.
Any old cheapies from a charity shop (do check the impedance and avoid crazy loads) will do. I always use my stunts as the final test before connection to my PMC and I know that Keith uses them also.
Then the horns can go on your new builds once they have proved reliable.I usually go for at least 5 days of stunts, powering the amp on and off a few times to make good and sure.
It really does help take the stress out of first switch on.
With the PSU speaker outputs connected to the binding posts on my case, the LED goes out. I also only see 0.09v across the 1R resistor compared to 4.8v.
With the PSU speaker outputs connected to the binding posts on my case, the LED goes out. I also only see 0.09v across the 1R resistor compared to 4.8v.
Are your Binding posts isolated?
That connection should not make any difference to the voltage measurements unless you have a short to ground.
maybe check for continuity between your speaker binding posts and chassis just to be sure.
Comments
It's an Excel 830L.....
http://www.amazon.co.uk/dp/B008U96UQQ/ref=cm_sw_r_sms_udp_awd_ejB5wbMYP5H7M
Where can I read the cap voltage from?
Ok, with the COM probe of my meter on 0V and the red on -V I get -17.9v. Now when I lift the red probe and put it on either side of the 0.1R resistor I get +4.8v :-q. When I then put the red probe on the FET centre pin I see +17.3v.
This is with the amp board fed from the PSU.
http://uk.farnell.com/multicomp/tip142/darlington-transistor-to-247/dp/9294287
I'll run through your other checks now.
I'll remove the amp board and check zener position underneath....will post a pic but fairly sure it's in same location as shown in your pic.
This amp is going to be worth the effort....can't wait to hear it B-)