Pass f5

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cressy
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#1 Pass f5

Post by cressy »

Got a pass f5 today off Ali. Im not sure of the entire history of this amp, nick built it, Ali ended up with it and now I have it as part of a deal for some work im doing for him. This is the first 'proper' sand amp ive had in ten years.
I couldnt resist a look inside, it looks to be a dual mono version, which might explain why it out slams the 100 odd watt pa amp ive been using.

Ive had something of a 'why do I bother' moment re the valve amps. When i get around to sorting the el34 amp out, or the various shelved half built amps I have they will need to to be very special indeed to come close to this thing.

Ive genuinely not heard a sand amp that is a patch on this, although I didnt hear nicks monoblocks.

Im running it with a passive pre which is fine in the house, id probably need some gain from a pre for owston to use it with the lenco.

Its superb, a tranny amp for valveheads
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Paul Barker
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#2 Re: Pass f5

Post by Paul Barker »

Nick built it for me, and it was very good. Has some superb moments when the serendipity of the whole system lines up together. Very dependable, never fails.

But when I bought your dad's Barbaric I sold it to Ali.

I like Barbaric a tad more, but not a lot in it.

To be fair all of us have got to thta point where the amps are all excellent.

Maybe ta some time I'll build an SE amp again. But not bothered enough to bother at present.
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Cressy Snr
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#3 Re: Pass f5

Post by Cressy Snr »

Yep, the Pass F5 is a great piece of kit.
I do like the treble of my own Barbarik monoblocks better, but the bass end of the F5 is positively grin-inducing.
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Ray P
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#4 Re: Pass f5

Post by Ray P »

Sorry, I couldn't resist!
Ant
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#5 Re: Pass f5

Post by Ant »

Have an issue with the f5. Over the last few days it has started to intermittently cut out on one channel.

Interestingly if the power is turned off the channel immediately comes back up as soon as the switch is pressed, I thought 'oh it has a speaker protection board with a relay on it'......

It doesn't have any relays that I can see.

The channel doesn't fade out, it just goes off. Having a look at it there is no evidence of anything that has cooked or burned anywhere. Looking at th1 and th2, they look OK too although one was further away from its output device than the other. I was wondering if the bias was drifting and whether it would cause the channel to just cut out if it did.

Needs fixing, any ideas?
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Nick
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#6 Re: Pass f5

Post by Nick »

Check the voltages when its cut out. May be a failing part or connection. Its very simple so not much that can go wrong and get better again.
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#7 Re: Pass f5

Post by Ant »

I'll try and provoke it into cutting out again and see what readings it gives
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ed
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#8 Re: Pass f5

Post by ed »

quick...
phone the guinness world record people...this must be a first....first time a first watt has failed....

but seriously...does sound like a dodgy connection issue....component failure often exhibits fading or some noise accompanying the failure..

You could try wiggling stuff, downstream of the mains transformer obviously, but otherwise, as Nick says, you're going to have to wait until it cuts out again.
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#9 Re: Pass f5

Post by Ant »

It hasn't done it again yet

I did abit of wire waggling while it was on the bench, and bent the thermistors so they are just about touching the mosfets to make sure they heat up properly, and moved the input wiring away from the mosfets too.

It's the fact that switching it off then on again 'cures' the fault that puzzles me

Just have to wait until it does it again to investigate any further....
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Mike H
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#10 Re: Pass f5

Post by Mike H »

Ant wrote: Wed Jan 16, 2019 5:57 pm It hasn't done it again yet
'Course not :D
 
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#11 Re: Pass f5

Post by Ant »

It's been on for at least 6 hours today and not cut out at all....
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Mike H
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#12 Re: Pass f5

Post by Mike H »

It's cos you're watching. :D

Kind of reminds me of a post on Renault forums the other day - "car started after threatened with hammer" (true!) :lol:
 
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#13 Re: Pass f5

Post by Ant »

Think I've fixed it
Pushing on the back panel provoked it into the fault, i thought it was switching it on and off that cured the fault but it wasn't, it was the back panel moving when the switch was pushed that was 'curing' it. So had to be something attached to the back panel that was causing it
Re flowing the joint on the input socket and rerouting the internal screened lead to the board input away from the heat sink (via a zip tie through a convenient hole in the chassis angle brackets) seems to have sorted it.

Gave it a good eyeball while it was opened up and there is no signs of heat damage anywhere, no signs of any component problems ect. Normal operation has now resumed
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little eddy
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#14 Re: Pass f5

Post by little eddy »

I would be interested in what temp the heatsinks get to.
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#15 Re: Pass f5

Post by Ant »

Dunno exactly but you can put your hand on them for a while before it gets uncomfortable
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