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Old 10th November 2012, 05:50 PM   #551
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macfixer and I are joining up to build on Tuesday, assuming no one else crashes into my car.........

I cant wait as I've just ordered Faital Pro HF144 1.4" CD drivers and I hope to use the ACA as their dedicated amp for about 750hz upwards

Will test on my Emkens on build day thou - 5w Class A on a 97dB/W/m full ranger should be fun

James
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Old 10th November 2012, 10:31 PM   #552
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I cant believe You've outed me before our first date! and you say all you have to give me is 5W..............It beter be good.
But please please who is this "Faital"? Is he giving you the horn?.......
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Old 11th November 2012, 08:32 AM   #553
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On slightly more series note I was hoping to have some pre prep done ive got the back panel material sorted, 4mm ply left in the street by some builders and walnut kitchen top for the fronts to make two double mono blocks. The component leg bending tool arrived! a stepped pice of plastic block so will be able to see if it will be usefull. Hope to fit the posts and inputs tomorrow together with the switches will have to see what work turns up on Monday
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Old 11th November 2012, 04:11 PM   #554
waam68 is offline waam68  United Kingdom
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Default Finally done

Ok got this finished at last. Couldn't trace the mains hum I was getting on one channel but after discovering it went away when the two mono blocs touched the way forward was obvious
Apart from the kit and sinks from the store I spent £10 on aluminium angle from a hardware store and £10 for two pc power supplies on the bay uk.

The amp sounds great....great power, bass and massive detail. Probably loses just a little smoothness in the mids compared to my tube/valve gear but not by much. Amazing amp for the build cost. The amp is dead silent between tracks and the sinks get warm but still ok to touch after 30 mins. I'm driving 15 ohm speakers with it....anyone know if it needs optimising for this load compared to 8 ohm? I got some spare boards and will probably have a go at a version with a "proper" power supply at some point. Anyone got any thoughts on a power supply?
Mike
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Old 11th November 2012, 04:17 PM   #555
waam68 is offline waam68  United Kingdom
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Default Another view

Another pic...ps before anyone asks the extra wires on one channel are bridging a nick on one trace on the board ....don't ask....best to remove board before drilling!
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Old 12th November 2012, 04:17 PM   #556
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Quote:
Originally Posted by Macfixer View Post
I cant believe You've outed me before our first date!

Feeling nervous? Kettle will be on and cat is set to stun - all the mod cons here!!
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Old 12th November 2012, 08:10 PM   #557
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Just an idea as I have 25-0/25-0 volts 160VA torroids (2 Nos); what if the input JFET is replaced with a BF862 cascoded with a 2SK170 to run the amp off 30-35 volts? Replace output Mosfets with IRFP264 (chosen for their higher transconductance) and double the bias current by halving the values of R1-R4.

What other component values need change? Thanks.
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Old 12th November 2012, 08:44 PM   #558
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Quote:
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Feeling nervous? Kettle will be on and cat is set to stun - all the mod cons here!!
Looking forward to it and yes work played with my best laid plans just got back from London and looking forward to the oft remembered pleasures of Newhaven "Gateway to Europe"
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Old 13th November 2012, 12:55 AM   #559
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Quote:
Originally Posted by Samuel Jayaraj View Post
Just an idea as I have 25-0/25-0 volts 160VA torroids (2 Nos); what if the input JFET is replaced with a BF862 cascoded with a 2SK170 to run the amp off 30-35 volts? Replace output Mosfets with IRFP264 (chosen for their higher transconductance) and double the bias current by halving the values of R1-R4.

What other component values need change? Thanks.
Along with the higher transconductance comes higher input capacitance. I tried IRFP460s and the results were poor. It could be that R6 needs to be lower, I didn't try that. I tried running three Q4s in parallel with R9 at 220 ohms and the results didn't improve much. Q1 becomes very non-linear as the Drain voltage dips below the Gate voltage. Visible distortion at 1kHz. At that high a rail voltage, you will need gate protection zeners. I'm going the other way. Next I'm going to try IRF120s. Suggest you search for my posts in this thread.
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Old 13th November 2012, 04:47 PM   #560
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Just waived goodbye to Macfixer after fun afternoon!!

Amps go together so easily! Really a great initiation! I completed mine up to the stage where I would mount the board to the heat sink and left it there as I have yet to finalise my chassis arrangements.

We completed one of Macfixers and let it warm up as per the build notes. Then a first listen via a pair of Minimus 7's to check all was well. Sound was big & full.

so onwards to my Emkens absolutely massive, dense, fluid, sharp as a knife sound. Played a few tracks I'm familiar with and the hairs on the back of my head nearly lifted me off the floor!! This was a straight comparison to my amp that is soon to be replaced.

Cant wait to finish my amps and get it up and running. Will post pix once I've finished mine and chassis is built.

Only issue is a thump at turn off - all in all not bad for an afternoons work
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