circlotron revisted

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ed
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#1 circlotron revisted

Post by ed »

Nelson Pass was commending this piece by Michael Rothacher, so much so that he's asked MR if he can post a copy on the pass labs website....

Its superbly written so I've posted a link incase y'all want a peek

http://www.passdiy.com/pdf/Build%20The% ... lotron.pdf

Ed
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#2

Post by andrew Ivimey »

You have to knock one of these up, pdq, ready for Owston, Ed!
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#3

Post by ed »

I'm deperately trying to get 2 amps and a new pair of speakers ready and to top it all my car has just blown up.......so the circlotron is just gonna have to wait....

tis tempting though!!
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#4

Post by SimonC »

With a name like that how could I resist...

As a minor diversion from melting 6c33's I was looking through my boxes of bits and found an old heat sink rescued from an industrial inverter drive a while back.

Hmmm, hacksaw it in half to make two, add a couple of PC fans to force the ventilation and it would work a treat for a circlotron. All I'd need would be some fets, a couple of 300va transformers, a very large bag of capacitors and a balanced source to drive it. Easy...

Anyway, to string out a short story even further I now have a scary heatsink tower, a bag of fets and a 3/4 of a power supply. I've underestimated how long it would take to solder 56 capacitors together so by the weekend I should have it all together on the bench.

Nick has volunteered (yet again) to help me out and put a valve front end on it for the fest as I don't have a balanced source at the moment. ECC88 concertina phase splitter with a touch of gain if I have my way, Nick may correct this and do a proper job of course. :notworthy:

I'll post some photo's of the build if I get chance later.

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#5

Post by Nick »

Nick has volunteered (yet again) to help me out and put a valve front end on it for the fest as I don't have a balanced source at the moment. ECC88 concertina phase splitter with a touch of gain if I have my way, Nick may correct this and do a proper job of course. notworthy
Just as well, as I don;t have much else new to bring to the do.

Well, maybe the DAC, and the in phase version of the 211.
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#6

Post by iansr »

Excellent! If Pass approves then in my book you've got to take notice.

Is it going to be there on Saturday Simon?
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#7

Post by SimonC »

iansr wrote:Is it going to be there on Saturday Simon?
It will be there both days provided I can get it finished in time. Got the power supply done last night so I'm on with the veroboard stuff now. Damm cold on my fingers in the cellar at the moment so I'm working in short bursts as I get chance.

Should have something to take over to Nick's early next week for him to work some magic with.

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#8

Post by Nick »

I will see if I can put a phase splitter together this weekend.
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#9

Post by SimonC »

Its built, but still not had time to take any photo's...
Had some problems getting the bias balance correct using single turn pots which fried a couple of fets and resistors so there will be a live rebuild saturday morning to add multiturn pots and some better source resistors as the temp ones are way too big.

Dragged it over to Nick's last night and hooked up the ECC88 spiltter, worked a treat into a dummy load, but not enough welly to drive a speaker until I reconfig the resistors.

Fingered crossed for Saturday :occasion5:

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#10

Post by SimonC »

Obviously didn't cross enough fingers, toes and other parts of my body.
Saturday was not a good day for for the atom smasher, but it did vaporise another resistor or two on the day.

Despite my best efforts and a lot of encouragement from the guys there it wasn't going to play. First diagnosis is that one of the small bias fet's went up in smoke as soon as I got current going through it. Probably damaged during the melt-down earlier in the week. Should have guessed really as the gate resistor had vanished, not just melted but it had gone. There was only the end of 2 wires left with fresh air between them.

For anyone planning one of these in the future here a couple of handy hints I have learned the hard way in the last week:

Multi-turn pot's are a must. Its much too sensitive running at full current to stand a chance with single-turns.
Use a 100ohm source resistors in place of the 0.47 the first time you fire up. It lowers the current through the devices to a point they don't self destruct if you have a bias error and would have saved a considerable amount of smoke.

Next steps are to replumb the bias circuit and get it to play music.

I'll post some photo's of the beast and the remains in the week.

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#11

Post by SimonC »

Its been a while since I started this, but after a 'few' weeks of waiting I now have some lovely new LSK389's on their way direct from the factory. Should be here mid-week.

Once I have these I can ditch the troublesome bias circuit I was trying to use at the last Owstfest and re-plumb it all to become an antimatter version. Since then I've also acquired a DAC pcb with balanced outputs...might just have to squeeze in a valve buffer between the two as well... time will tell.

Fingers crossed, and the battery removed from the smoke alarm in the cellar. Makes you popular with the rest of the family setting it off after they have gone to bed. 100,000uF and about 0.5R in the power supply generates an impressive amount of smoke in a very short space of time when it goes out of balance :roll:

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#12

Post by Dave the bass »

^^^^^ :lol: :lol: :lol:

I love the bit about taking the battery out the smoke alarm. I LOL'd.

In our house its usually JTS setting off the alarm setting fire to fabric or trying to iron Batik work caked in wax :roll:

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#13

Post by ed »

they do tell up here that every time you let the magic white smoke out of one of those black plastic things, a fairy dies!

be warned
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#14

Post by Dave the bass »

ed wrote:they do tell up here that every time you let the magic white smoke out of one of those black plastic things, a fairy dies!

be warned
Lotta fairy's up North I've heard :lol:

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#15

Post by Mike H »

What I find particular interesting about this is that it appears to be basically the old push-pull transistor amp type of thing, where the supply is centre-tapped and the speaker negative goes to that. The main difference being this version seems to run at high current all the time, or is that not right?
 
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