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Old 12th January 2004, 12:26 PM   #1
Nicos is offline Nicos  United Kingdom
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Default OTL OCL or Non

Hi,

I am preparing my setup to build an OTL amp based on Ciuffoli version 8.2 and was considering either the OCL version or the capacitor output version.
I guess using a capacitor would attract adverse arguments as to the end quality of the sound, though I cannot undertake the risk of having my B & Ws being blown to pieces. Anyone care to comment on the safety of the OCL design?

Furthermore, where can one get a decent casework to house the amp? good leads would be welcome.

thanks
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Old 12th January 2004, 09:30 PM   #2
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Hi,

I have used an amp similar to the Ciuffoli one for more then 3 years now. I still use the same output tubes and never had a problem, no drift no change in bias current.

If you are worried about damaging speakers I recommend either to put fuses in the anode voltage supply or to use a simple circuit that will disconnect anode voltage if there is DC on the output. I built a simple circuit using a window comparator that compare the DC on the output with reference voltages from silicon diodes, if DC on output exceeds ~ 0.6V I switch off the anode voltage with a relay. In fact I believe it is unnecessary to use this kind of circuit as it should be enough using ordinary fuses in the anode supply, (the likely faults in the output tubes will make the amplifier draw so much current that the fuses will blow instantly).

Regards Hans
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Old 13th January 2004, 12:40 AM   #3
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Hi,

Quote:
I guess using a capacitor would attract adverse arguments as to the end quality of the sound, though I cannot undertake the risk of having my B & Ws being blown to pieces. Anyone care to comment on the safety of the OCL design?
As Hans said, I'd not worry too much about your speakers....Nothing will happen to them.

The 8.2 version can be improved by providing for individual bias for each tube.

Ciuffoli based his circuit on Japanese circuits but he sometimes has me puzzled with his design choices and consequent versions...

Hans and myself once gave advise to another member on this and I'll try to dig it up for you.

Built properly, this is an earopener though.

Cheers
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Old 13th January 2004, 05:21 AM   #4
Nicos is offline Nicos  United Kingdom
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Thank you very much Hans and Frank. I thought about individual bias too and will implement this on my design.
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Old 13th January 2004, 11:11 AM   #5
Nicos is offline Nicos  United Kingdom
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Default OTL Ciuffoli

If I want to add a couple of tubes more to the original design ie making total 4 6c33 for more output, will I need to make any amendments to the Power Supply to allow more current? Also will I need to bias every single 6c33 independently thus having eight independent 70v outputs from the transformer? practically this would be a bit of a mess...
thanks.
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Old 13th January 2004, 01:08 PM   #6
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Hi,

Quote:
Hans and myself once gave advise to another member on this and I'll try to dig it up for you.
Here's the thread I had in mind:

CIUFFOLI

Quote:
If I want to add a couple of tubes more to the original design ie making total 4 6c33 for more output, will I need to make any amendments to the Power Supply to allow more current?
In general, yes. What I always do with OTLs is overrate the secondaries VA for the bipolar rails by at least 30%.


Quote:
Also will I need to bias every single 6c33 independently thus having eight independent 70v outputs from the transformer?
Either individual bias or spending a bundle on 6C33Cs.
Keep in mind that this is a high tranconductance valve so they tend to vary wildly.
Having them matched at the dealer's place is pretty pointless (if they could do it at all) as the tubes should be matched in your circuit.
They take quite some time to settle.

Adding tubes will also up the input capacitance cnsiderably. i don't know if the E182CC can handle this.

Cheers,
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Old 13th January 2004, 02:32 PM   #7
Nicos is offline Nicos  United Kingdom
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thank you Frank, you are stellar help...
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