UPDATED!!! It blew the fuses! <cries!> - diyAudio
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Old 31st October 2002, 05:23 PM   #1
Rarkov is offline Rarkov  England
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Default UPDATED!!! It blew the fuses! <cries!>

The first amp I've ever built! OK, so I started a bit hard, but here goes...

The power supply works great. I turned the power on with no input or load and noticed that the N-Channel Mosfets got hot whereas the P-Channel ones stayed at the same temp (I have wired them up correctly). When I tried again with a source attached (again with no load), The voltage rail fuses blew straight away. The fuses are rated at 5A @ 250V Quickblow. The power supply is +- 63.1V and the amp is rated at 140W into 8Ohms and 200W into 4Ohms. Since I'm using a slightly higher voltage than that, I suggest that the output power maybe slightly more than that...

Does this sound like a common poblem?


Edit:
The stands holding the circuit off the chassis was shorting the speaker output to ground...0V = infinte output power = blowen fuses.

Works now...AND SOUNDS AMAZING!!!!!!!!!!!!!!!!!!!!!!!!!

Thanks,
Gaz
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Old 31st October 2002, 05:48 PM   #2
joensd is offline joensd  Germany
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Hi Gaz,
bad timing!
I just wanted to help but am glad you managed it yourself.
So congratulations to your working amplifier!
What amplifier is this ?
Please post some reports about the sound and pics of course.

greetings
Jens
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Old 31st October 2002, 11:05 PM   #3
Rarkov is offline Rarkov  England
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Hi,
It's a design by Randy Slone...I believe it is referred to as the Opti-MOS on Seal Electronics. I copied it out of the book. Sound is soooo much better than my Marantz PM4000 - but I cannot run it for long. Got a royal explosion and after investigation found that some 35V caps were across the power supply...about twice their rated values! Need to get some higher voltage devices.

I've just checked Seal's website - and it does not seem to be the same. The circuit I made is on page 173 of The Audiophile's Project Sourcebook by G.Randy Slone (ISBN 0-07-137929-0)...I highly recommend it.

Pictures will be along after the 8th Nov...It's my GFs 21st Bday and I'm giving her a digi camera cause I need one!

Question:
One thing though...When I turn off the amp, it takes a long time for the PSU caps to drain and the music to stop. If the music is quiet, this can take upto 30secs or so. There are 13600uF per rails 27200uF per channel. There is a drain resistor of about 4k. Is this characteristic normal? If I turn off the source during this draining period - the speakers are dead quiet (No thud or clicks etc.) If the source is on, it goes fuzzy, then crackly and then a quick increase in volume before turning off...

Sound familiar to anyone?!

Thanks
Gaz
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Old 1st November 2002, 12:19 AM   #4
skaara is offline skaara  Slovenia
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Its ok that caps discharge slow at low volumes and the music plays, you should leave it that way, or you can add a relay on poutput to disconnect speakers when amp is shutted down.
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Old 2nd November 2002, 08:24 AM   #5
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Well done, whats next?


Waiting with bated breath for the photos, ( I just got some heatsinks from Jake as well and am wondering how you mounted the output trannies on them!)
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Old 3rd November 2002, 08:46 AM   #6
Rarkov is offline Rarkov  England
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Well, I have a digi preamp to build (in the process) and some Sonus Faber Amarti clones...Getting the wood today. Also I have two 1kVA tranformers...

The amp is running great and trip to Maplins will get an RCA connector to finish off the next one...I did most of it last night.

They are very compact (although I have never seen another monoblock to compare to other than pictures!). It measures 150,195,200 (hwd) and a bit more with some speaker bass isolation spikes on the bottom!

I marked a line down the heatsink and drilled two 3.2mm holes per side and tapped them out to 4mm. I had to...(Don't flame me....) drill out the transistors to be 4mm aswell but they seem to work OK! I isolated them with some silicon "patches" from Maplins (19p each).

Cause I don't have a preamp I stuck a line level signal in...Too loud to listen to. But the good news is it sounded great (good news for my speakers too, which have never been driven at that level by my Marantz). My CD player has a volume control, so I can only listen to that whilst I have no Preamp. Unfortunately, it has revealed a huge hiss in my CD player (a Kenwood) so I am contemplating buying a Marantz CD5000...

I would recommend this amp to anyone. I have very little experience with high end components (never listened to anything expensive) but if it sound much better than my amps, I'm sure they would be worth the investment!

P.S. Sorry about the long delay replying...diyAudio wasn't working: I'm not sure i that was just for me or everybody...But I did get some "reply" emails during this 'down' period.

Cya,
Gaz
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Old 6th November 2002, 07:36 AM   #7
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One thing though...When I turn off the amp, it takes a long time for the PSU caps to drain and the music to stop. If the music is quiet, this can take upto 30secs or so. There are 13600uF per rails 27200uF per channel. There is a drain resistor of about 4k. Is this characteristic normal? If I turn off the source during this draining period - the speakers are dead quiet (No thud or clicks etc.) If the source is on, it goes fuzzy, then crackly and then a quick increase in volume before turning off...

You should take a look at the auxillary control board that Randy designed for use with the OptiMOS. It combines a soft start function, DC protection, speaker disconnect relays, temperature monitoring and a remote LED all into one nice little board. Plus it integrates with the OptiMOS boards.

Although they're not likely to sustain damage from being direct coupled, it's probably best to have the speaker outputs disconnected when the amp is powering up and down.

With regard to the bleeder resistor at 4K -- that makes sense to me. Unless you have the rails switched through a relay or something when powered off, you're going to be constantly dissipating power across them while the amp is running.

At 4K, with 126V (63.1 x2) across the rails, you're going to be dissipating almost exactly 4W. If I read your post right, with 27200 uF per channel and 54400 uF total, it should take 3 mins 38 seconds to discharge through a 4K. If you were to lower it to say, 500 ohms, you could discharge the caps in 27 seconds, but you'd be throwing off 32W constantly.
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Old 6th November 2002, 08:12 AM   #8
Rarkov is offline Rarkov  England
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Hi,
That is 27200uF per PSU and 13600uF per power rail. In other words, that 56400uF is split between two seperate monoblocks, so I guess the discharge time is half of what you quoted?

I finished the second monoblock lastnight. When I tried it I heard a high pitched buzzing and heating of the output devices. I think I may have fallen into the short circuit trap again! The problem is that my circuit is held above the PSU by threaded metal rods. The chassis is grounded and it is causing problems. Nothing that some accurate work with insulating tape won't sort!

Can't wait to get your comments when the I post the pics

Thanks for the hint about that board for the optimos...I'll look into it!

Gaz
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