Maplin 150w mosfet module |
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Big-G
Young Croc Joined: 28 November 2006 Location: Naarfuk Status: Offline Points: 1141 |
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Posted: 12 November 2009 at 11:03pm |
Hi everyone, i have a pair of maplin 150w amp modules that have been kicking about for ages and i have decided to build a pair of small (10 + 1) active cabs, i can't find the specs for the module and would like to know the supply voltage, i have memories of +/- 55v but would like someone to confirm this for me before i buy the transformers.
Best regards, Paul
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cilla.scope
Old Croc Legs all the way to her bottom.... Joined: 02 October 2009 Status: Offline Points: 2954 |
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I seem to remember them being +-50V rails, 60 was the "goes bang" voltage.
I have to congratulate you on your choice of modules, on of the finest oscillators you can buy . seen too many of those whistle their way into the great FET recycling plant in the sky. |
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Big-G
Young Croc Joined: 28 November 2006 Location: Naarfuk Status: Offline Points: 1141 |
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Thanks, 40v transformers should do the job then, my old ones worked for years without a problem, is there any way of making sure they dont oscillate?
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cilla.scope
Old Croc Legs all the way to her bottom.... Joined: 02 October 2009 Status: Offline Points: 2954 |
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mmm, seen em run fine for ages and then whistle away, assume its caps drying out.
seen freshly built ones impersonate a radio transmitter from first switch on. the usual advice on "star earths" seems to help, low ESR capacitors across the rails close to the amp as you can get. ISTR someone published a mod sheet for it, but its got to be 10 years since I played with these. |
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cilla.scope
Old Croc Legs all the way to her bottom.... Joined: 02 October 2009 Status: Offline Points: 2954 |
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i should add, do check em with a scope, look for any signs of HF oscillation and fuzz on the waveform, they are prone to it.
Funniest one I saw was a guy who wanted to "mod up" some of these, doubled up on the FETs and improved on the heatsinking ... except he added about 100mm of wire between the fets and the PCB ... oscilated like a good un |
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My girlfriend thinks I'm a stalker.
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Big-G
Young Croc Joined: 28 November 2006 Location: Naarfuk Status: Offline Points: 1141 |
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I'll just get on with them and see what happens, if they oscillate then i'll cross that bridge when i come to it. Thanks for the help, Paul
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Big-G
Young Croc Joined: 28 November 2006 Location: Naarfuk Status: Offline Points: 1141 |
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Is there any way of telling they are oscillating without a scope?
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cilla.scope
Old Croc Legs all the way to her bottom.... Joined: 02 October 2009 Status: Offline Points: 2954 |
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not really, sometimes, if the oscilation is low enough, you can hear it as a sort of squiffy fizzing, very much in the top end ... but often its way out of the top of the audio band, they just run hot and one day they run very hot and *poof* ...
they have another mode of oscialtion that only occurs under signal load, where you get a kinda "thickening" of the trace, usually on the falling edge of the sine wave, quit eobvious on a scope .. hard to hear. they just get hot and doesnt do your voice coils much good either. see if you can't borrow one .. or pick one up for 30 quid on fleabay .. .the Hameg ones are a nice for the money. |
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My girlfriend thinks I'm a stalker.
Well, she's not exactly my girlfriend yet ... |
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Big-G
Young Croc Joined: 28 November 2006 Location: Naarfuk Status: Offline Points: 1141 |
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I'll get on fleabay strait away, will i'll need some kind of signal gen too?
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Tony Wilkes
Old Croc Joined: 02 August 2004 Location: West Midlands Status: Offline Points: 4840 |
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Literally built around 30 of them. Lovely little amps. The spec was 100 onto 8 150 into 4. The original kits had a couple of the resistors underrated, this was cured on the later examples.
Be careful touching the input connection when connected to a speaker if you value you tweeters. Tony |
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cilla.scope
Old Croc Legs all the way to her bottom.... Joined: 02 October 2009 Status: Offline Points: 2954 |
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yep, they are nice nough for what they are, and built right, and with good layout they seem to be fine. Always worth checking a newly built amp with a scope, just in case.
I have to say, we lost a fair number of them to them whistling themselves into a brown fuzz, but it was probably just caps drying out over time, |
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My girlfriend thinks I'm a stalker.
Well, she's not exactly my girlfriend yet ... |
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Tony Wilkes
Old Croc Joined: 02 August 2004 Location: West Midlands Status: Offline Points: 4840 |
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Having found out a few years before whilst using some Pantechnic MosFet modules the importance of correct earthing procedure (literally self destruct before your eyes) I had it pretty well sorted by the time these kits came along. I fitted them in everything from HH guitar amps to some Alba receiver's.
I also had a pair of these fitted into my Decca-Volts that I also built around this time and the combo sounded glorious. Tony |
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