Fun with Feedback

What people are working on at the moment
Cressy Snr
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#196 Re: Fun with Feedback

Post by Cressy Snr »

Well I’ve had the break and fixed the amp by replacing the offending part. Blown mains TX was the thing that had stopped it working; no further damage.

Glad you like the design Mike.
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izzy wizzy
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#197 Re: Fun with Feedback

Post by izzy wizzy »

As I found out to great cost, fuses in secondary can save iron from destruction. Primary fuses not so much. It's a small thing as you don't want it to happen again for whatever reason ...
Cressy Snr
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#198 Re: Fun with Feedback

Post by Cressy Snr »

izzy wizzy wrote: Wed Jan 11, 2023 5:12 am As I found out to great cost, fuses in secondary can save iron from destruction. Primary fuses not so much. It's a small thing as you don't want it to happen again for whatever reason ...
Cheers Stephen, I have a couple more things to do to tidy up loose ends and will incorporate fuses in the HT line.
Wouldn’t have thought to do it….until now that is. :shock:
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Nick
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#199 Re: Fun with Feedback

Post by Nick »

Yep, a fault in a single secondary in a multi secondary transformer may draw enough current to kill the transformer but not enough to blow a primary fuse. As I found to my cost.
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simon
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#200 Re: Fun with Feedback

Post by simon »

Mmmm. So should we use fast blow fuses in secondaries? Or is a close tolerance to expected current draw more important?
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Nick
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#201 Re: Fun with Feedback

Post by Nick »

I think slow is fine, its the thermal inertia of the windings that give the overload margin. Won't cover marginal overload I guess, but that rarely happens. Also won't cover a shorted turn, but its better than nothing. A thermal fuse in the primary side embedded in the windings would be the safe (as in CE, protecting the user, not the transformer) option.
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izzy wizzy
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#202 Re: Fun with Feedback

Post by izzy wizzy »

Cressy Snr wrote: Wed Jan 11, 2023 7:56 am Cheers Stephen, I have a couple more things to do to tidy up loose ends and will incorporate fuses in the HT line.
Wouldn’t have thought to do it….until now that is. :shock:
Just saying.... waiting until I tidied up a few things is how I lost mine.
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#203 Re: Fun with Feedback

Post by Cressy Snr »

Well yes, It appears there are one or two other issues that require further investigation of the power supply. Something has happened to the PSU, resulting in LF instability. OK on one pair of speakers but not on the other, which is no good either way. May have a rogue time constant in the output stage. Whatever it is, the test gear will have to come out again.
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Nick
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#204 Re: Fun with Feedback

Post by Nick »

You have two about 1s time constants in the power supply decoupling.
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#205 Re: Fun with Feedback

Post by Cressy Snr »

Nick wrote: Thu Jan 12, 2023 10:45 am You have two about 1s time constants in the power supply decoupling.
Yikes! Yes, thanks for saving me the calculation. That’ll need sorting.
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Nick
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#206 Re: Fun with Feedback

Post by Nick »

Well, 0.75s and 0.82s, but them both being about the same is itself more likely to be a problem.
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#207 Re: Fun with Feedback

Post by ed »

Nick wrote: Thu Jan 12, 2023 11:54 am Well, 0.75s and 0.82s, but them both being about the same is itself more likely to be a problem.
I'm scratching my head here, what RC figures were you using?
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Nick
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#208 Re: Fun with Feedback

Post by Nick »

4k2 and 50uf for example
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#209 Re: Fun with Feedback

Post by Nick »

Nick wrote: Thu Jan 12, 2023 2:19 pm 4k2 and 50uf for example
Though just released I was quoting the frequency not the period. So 0.75Hz and 0.82Hz. My bad.
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#210 Re: Fun with Feedback

Post by ed »

Nick wrote: Thu Jan 12, 2023 2:22 pm
Nick wrote: Thu Jan 12, 2023 2:19 pm 4k2 and 50uf for example
Though just released I was quoting the frequency not the period. So 0.75Hz and 0.82Hz. My bad.
that's better cos I made it 0.2 seconds
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