John Sayers' Recording Studio Design Forum Archive

I haven't seen anything about this: but I am looking for either a DIY power amp kit for a pair of Dynaudio BM15p's, or a relatively cheap and clean amp to use on them. I'm not 100% set on the BM15's yet, but I'd like to explore some amp options.

LOL, glad I found this here as I used to build my own power amps for fun, just because I could

The main aspect of a power amp I've found is that you need two major items in order for it to work properly, a decent power supply and a means to deliver the power it's giving you.

A decent power supply starts with getting the right transformer and not just any old transformer. What you need is a toriodal transformer, if you've ever seen one before then it's the one that's doughnut shaped, Follow this link to find out more http://www.tabtronics.com/TECHNOLOGY/El ... fault.aspx

You need a transformer that Is capable of supplying two seperate line of approx 36 volts AC which works out as - 36v and + 36v. After this you need a means of delivering this power to your speakers and the best way to do this is through MOSFET power transisters normally refered to as T03 which denotes their case design.

I'm short of time right now to go into full detail but If you'd like to know more then let me know and I'll tell you what I can.

but but but - my computer speakers say they are 140Watts and they use a 12v 750ma wallwart!

John Sayers wrote:but but but - my computer speakers say they are 140Watts and they use a 12v 750ma wallwart!

LOL, thank you John.

I was actually quite an electronics geek in my younger teenage years, whilst my other mates were busy with the advent of the home computer age (early 80's) I was busy building electronic circuits such as radio transmitters and power amps as well as getting my hands and fingers burnt with the soldering iron on many occassion, oh and don't forget all of those electric shocks

It annoys me when I see amps or systems sold in shops telling you that it's gonna give you say 180 watts of power and then you find it's actually music power they're referring to and not pure RMS power. There's nothing worse than when you try and turn it up high and find all the lights on it start to go dim in time with the beat of the music.

There's much fun in building your own power amp from the ground up knowing that no matter how high you crank it up it'll still deliver the same amount of power, and of course still be working 5 hours down the line...

So true stepson - I had a similar childhood except it was in the 50s and I started with a crystal set and made my way up to a 10W valve amp. Yup - had all the shocks, and ours like yours were 240 V none of this pussy 110V american stuff

John Sayers wrote:So true stepson - I had a similar childhood except it was in the 50s and I started with a crystal set and made my way up to a 10W valve amp. Yup - had all the shocks, and ours like yours were 240 V none of this pussy 110V american stuff

My uncle built me my first crystal set as I never believed at first that a radio could ever run without batteries, it was so small it would fit inside a snuff box.

I know what you mean about the American 110v but then again they do use DC instead of AC, if were much more than 110v then you'd never be able to let go and it'd kill you anyway

The only thing I built with valves involved was a "Burner" for my CB radio when I was 16, or to call it by it's real name "Linear Amplifier". I remember that it used 360v capacitors that were connected somewhere with the valves. I remember that I'd built it and watched the output dial barely move so I thought OK then, lets switch it off and change it for the other valves I had. So there I was, I'd switched it off and I grabbed the steel case that I'd built it inside of and then grabbed the valve that was encased in an aluminium shell and that was it, I felt the biggest thud through me ever. I'd forgotten that the case of the valve was live when it was switched on and that the capacitor was still charged up (to 360v) as it hadn't had time to drain away.

wow - did it burn you?

BTW - the US uses 110 -120V AC at 60hz whereas Britain and us here in OZ use 240V AC at 50hz.

John Sayers wrote:wow - did it burn you?

BTW - the US uses 110 -120V AC at 60hz whereas Britain and us here in OZ use 240V AC at 50hz.

No I never got burnt, I just saw this huge blackness in front of me and somehow at the same a time a flash in my eyes, it was the huge thud I felt go through me more than anything. My uncle used to charge and discharge big capacitors in front of me becuase he thought that hearing the big bang from it all the time was fun...

I was always told that America used DC which is why the current was so low, looking back over it though I see that it was Edison who favoured DC.

My uncle once had an old army generator that would run off a car battery, it must have been used in the field to power the radios. He told me of the time he once caught the end of it and had a nasty shock, as it was DC coming off it he wasn't able to let go until the generator which was now under load had slowed down enough.

I understand it's illegal to use a 240 V tool on a building site in Britain. All major construction sites have to supply 110V.

Valve circuits often go up to 400 volts

John Sayers wrote:I understand it's illegal to use a 240 V tool on a building site in Britain. All major construction sites have to supply 110V.

Too true, all electrics (tools etc) on sites have to be 110v AC by way of step down transformers. The generator I was talking about ex army and I can only guess was used to power the old valve radios, my dad and my uncle used to buy lots of surplus/ex army stuff and this was one of them.

Although the one pictured here isn't the same it's very similar with 12VDC in with a much higher voltage coming out of it, DC of course.