TimR Posted November 15, 2022 Share Posted November 15, 2022 18 minutes ago, BigRedX said: That's interesting. Can you follow where the different wires go in the amp - especially those connected to the mains side? I'd expect the primary side just to be connected to a 230/115v switch somehow for EU/US. The S1 250v 40mA will be the other preamp supply. Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted November 15, 2022 Author Share Posted November 15, 2022 7 minutes ago, BigRedX said: That's interesting. Can you follow where the different wires go in the amp - especially those connected to the mains side? When I have the amp back in my possession I'll try. <edit/update> I forwarded the image to the Tech that did the last transformer and it just so happens that he felt bad that his work had failed so he was looking at what he could do. He thought there should at least be a fuse on the HT side that would prevent the transformer cooking again (his transformer was rated 50% higher than the original). He is also going through every component to see what could have generated the fault, there wasn't any obvious cause and the amp operated as per normal when he replaced the original failed transformer). Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted November 15, 2022 Author Share Posted November 15, 2022 His thinking is that a component in the preamp is failing but only when its been on a while and gets properly warmed up. This fault then loads the TX (transformer) to the point that it overheats and damages one of the windings... seems reasonable. He's ordering a replacement transformer free of charge and he's going to run tests with the amp operating under load for extended periods. Fingers crossed. 2 Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted November 15, 2022 Share Posted November 15, 2022 17 minutes ago, warwickhunt said: His thinking is that a component in the preamp is failing but only when its been on a while and gets properly warmed up. This fault then loads the TX (transformer) to the point that it overheats and damages one of the windings... seems reasonable. He's ordering a replacement transformer free of charge and he's going to run tests with the amp operating under load for extended periods. Fingers crossed. That's a lovely gesture, there are good people around. 4 Quote Link to comment Share on other sites More sharing options...
TimR Posted November 15, 2022 Share Posted November 15, 2022 Superb. I had a dry joint on a resistor once. Amp would run for hours and then suddenly start distorting. Once it had cooled down it operated fine again. Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 15, 2022 Share Posted November 15, 2022 I would be checking the rectifier and smoothing caps for a problem. I would expect that both secondary windings would feed bridge rectifiers so that the heater supply is run at DC for lowest hum generation. I agree that you seem to have a good technician who prides himself with his work. Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 15, 2022 Share Posted November 15, 2022 DAMN! It's snowing!! Quote Link to comment Share on other sites More sharing options...
Chienmortbb Posted November 15, 2022 Share Posted November 15, 2022 26 minutes ago, BassmanPaul said: I would be checking the rectifier and smoothing caps for a problem. I would expect that both secondary windings would feed bridge rectifiers so that the heater supply is run at DC for lowest hum generation. I agree, the caps and rectifier diodes are most likely to be causing the problem. A transformer is unlikely to bang on its own. 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 15, 2022 Share Posted November 15, 2022 I would also get the tech to install a fuse in the primary of the transformer. As it is the transformer protected the mains fuse. Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted November 15, 2022 Author Share Posted November 15, 2022 (edited) 1 minute ago, BassmanPaul said: I would also get the tech to install a fuse in the primary of the transformer. As it is the transformer protected the mains fuse. Yes, that was his first suggestion. However, that was after the 2nd meltdown as he assumed as it was designed without, it wasn't for him to 2nd guess and put one in. Edited November 15, 2022 by warwickhunt Quote Link to comment Share on other sites More sharing options...
TimR Posted November 16, 2022 Share Posted November 16, 2022 The problem is there's a high inrush current on those transformers when you switch them on. So the fuse needs to be specified carefully. 2 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 18, 2022 Share Posted November 18, 2022 On 16/11/2022 at 06:24, TimR said: The problem is there's a high inrush current on those transformers when you switch them on. So the fuse needs to be specified carefully. Which, theoretically, the Amp Designer should have taken into account. Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted November 18, 2022 Author Share Posted November 18, 2022 3 minutes ago, BassmanPaul said: Which, theoretically, the Amp Designer should have taken into account. Everyone who has looked at the basic design has raised questions... Quote Link to comment Share on other sites More sharing options...
TimR Posted November 18, 2022 Share Posted November 18, 2022 1 minute ago, warwickhunt said: Everyone who has looked at the basic design has raised questions... It really depends on the fault. Fuses will protect against short circuit and high current. A high resistance fault will burn the windings over a long period of time and not blow any fuses. If the amp tests as OK and then fails after a few hours of constant use this is most probably what is happening. Theoretically. 2 Quote Link to comment Share on other sites More sharing options...
3below Posted November 18, 2022 Share Posted November 18, 2022 One big plus in this situation is the pre-amp is on a board with 'real' size components which makes any repairs / modifications much simpler (and possible). Two things I would follow up: Check the continuity on the dead xformer, you might get lucky and be able to identify whether it is the HT (B+) or heater windings that have failed. This would give a pointer where to start fault finding. Detach the preamp from any follow on circuits and test it in isolation - is it a preamp issue or something further in the circuit. 2 Quote Link to comment Share on other sites More sharing options...
LukeFRC Posted November 19, 2022 Share Posted November 19, 2022 9 hours ago, warwickhunt said: Everyone who has looked at the basic design has raised questions... I measured the Tecamp cab I had and stuck all the measurements into whatever that cab modelling software is - let’s just say I liked my puma amp but would buy a different make cab next time Quote Link to comment Share on other sites More sharing options...
agedhorse Posted November 20, 2022 Share Posted November 20, 2022 18 hours ago, LukeFRC said: I measured the Tecamp cab I had and stuck all the measurements into whatever that cab modelling software is - let’s just say I liked my puma amp but would buy a different make cab next time Do you have the TS parameters for the drivers used in the cabinet, or did you assume that they were stock drivers (which they likely are not, even if they look like it) Quote Link to comment Share on other sites More sharing options...
LukeFRC Posted November 20, 2022 Share Posted November 20, 2022 5 hours ago, agedhorse said: Do you have the TS parameters for the drivers used in the cabinet, or did you assume that they were stock drivers (which they likely are not, even if they look like it) I would not say I did it with any great accuracy… and I did make the presumption that the drivers were the model they were labeled and used the driver manufacturer’s TS parameters. The graphs that it created looked like what I was hearing, esp when increasing the input power… So not any degree of accuratey at all but it explained what I was hearing and the difference between a cab that sounded fine at low practice levels and caused massive issues for the live sound engineer turned up. from memory the box was too big for the drivers and the port (a hole cut in the baffle, so 15/18mm deep) wasn’t tuned quite right- so with a slight increase in power the bottom end dropped of and there was a massive spike in the mids that cut through thr mix in a slightly uncontrollable way. since then I have had or used: ACME, Barefaced, Mesa Boogie, Gallien Krueger, Ashdown and now BCcab and Stevies LFSys and am happy that the designers of those cabs had and used the TS perameters to create a lovely set of bass cabs. 2 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted November 20, 2022 Share Posted November 20, 2022 Acme cabinets are special! LOL Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted January 31, 2023 Author Share Posted January 31, 2023 Quick update for those who contributed or might be interested! The tech ordered a new transformer (rated higher than the original), took a while to arrive but it is now fitted. He also added a heat trip and a fuse to hopefully ensure no terminal issues in the future. Interestingly the transformer that he fitted and removed prior to this one, had no visible signs of overheating/damage but tested as having a short. He is going to do an autopsy on it but thinks we were just unlucky and got one that wasn't 100% fit. I've now gigged the amp and had it running for at least 3 hours each time and it didn't even get warm; though you might hope so as it is only powering the valve front end as the power module is class D. Thanks again for all of the input. 4 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted January 31, 2023 Share Posted January 31, 2023 I'm glad you got it sorted! 1 Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted March 5, 2023 Share Posted March 5, 2023 On 15/11/2022 at 14:20, BassmanPaul said: DAMN! It's snowing!! And just did again! In the last ten days we have had fifty seven meters of snow!!! 1 Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted March 5, 2023 Author Share Posted March 5, 2023 On 31/01/2023 at 17:18, BassmanPaul said: I'm glad you got it sorted! It died yesterday! 2 Quote Link to comment Share on other sites More sharing options...
warwickhunt Posted March 5, 2023 Author Share Posted March 5, 2023 No visible burning or smell, powers on, no fuses popped, just zero output. I'm trying one last time with a different repair guy. Quote Link to comment Share on other sites More sharing options...
BassmanPaul Posted March 5, 2023 Share Posted March 5, 2023 47 minutes ago, warwickhunt said: It died yesterday! I can't remember if you contacted the manufacturer if not that's who I'd be screaming at!! If you did I'd still be screaming at them! Quote Link to comment Share on other sites More sharing options...
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