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Old 9th June 2012, 01:31 AM   #31
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I forgot to post the updated drawing of the input with the fuse, switch and cap across it. I put dotted lines where I think the MOV should go. Please correct me if I'm wrong. And would lead length matter since there's distance between the two ends?
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Old 9th June 2012, 01:38 AM   #32
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Clemford,
No, a power-off thump is usually caused by the power supply caps discharging with the speakers connected, as in the speaker relay (if any) isn't working. The cap across the switch contacts is to minimize arcing of the contacts, although it may also reduce the popping noise associated with switch contacts.

Mike
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Old 9th June 2012, 02:03 AM   #33
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For 120Vac mains,I usually see/use 130-150V MOV's. You want it a bit higher than the mains voltage,so it doesn't clamp constantly,but not so high that it lets all kinds of nasty spikes through. 300/500V is way too high,IMO.

Here's a couple suitable candidates
150V: V150LA10AP Littelfuse Inc | F3017-ND | DigiKey
140V: V140LA10AP Littelfuse Inc | F3016-ND | DigiKey
130V: V130LA10AP Littelfuse Inc | F3015-ND | DigiKey
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Old 9th June 2012, 02:18 AM   #34
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Quote:
Originally Posted by DigitalJunkie View Post
For 120Vac mains,I usually see/use 130-150V MOV's. You want it a bit higher than the mains voltage,so it doesn't clamp constantly,but not so high that it lets all kinds of nasty spikes through. 300/500V is way too high,IMO.

Here's a couple suitable candidates
150V: V150LA10AP Littelfuse Inc | F3017-ND | DigiKey
140V: V140LA10AP Littelfuse Inc | F3016-ND | DigiKey
130V: V130LA10AP Littelfuse Inc | F3015-ND | DigiKey
if that's the case, I think radio shack has them for a couple of bucks in store.
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Old 9th June 2012, 02:42 AM   #35
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One thing I just realised is every amp I own that has a linear supply uses film caps for power supply decoupling. Not a single ceramic in sight.
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Old 9th June 2012, 02:52 AM   #36
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One thing I just realised is every amp I own that has a linear supply uses film caps for power supply decoupling. Not a single ceramic in sight.
that's why I was wondering if I could use the mylar ones in place of them but I guess they are more for tone rather than filtering? Of all the schematics I found on line I don't think many put caps on the primary at all. Seems like they are more trouble than they're worth. I would think there's less chance of shorting the primary to ground without them.
i think that's the reason why Indiannajo said to use 1kv ones. Good insurance in my book if I decide to use them. I think when I get the replacement input jack i'll see how the amp performs without them though.

Last edited by Clemford; 9th June 2012 at 03:01 AM.
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Old 9th June 2012, 03:09 AM   #37
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Of all the schematics I found on line I don't think many put caps on the primary at all.
Well, they aren't on the primary they're on the secondary.
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Old 9th June 2012, 03:28 AM   #38
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Well, they aren't on the primary they're on the secondary.
sorry about that. It's been raining for days here non stop and i'm getting dyslexic cabin fever. Reminds me of back in Boston. I meant to say before the bridge or at least it looks that way I think.
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