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Old 10th January 2004, 12:31 PM   #1
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Default OTL Output Cap Question

Hi guys,
Quick question, I have an OTL using a 3300uf output cap (Nichicon) which I want to replace with something else.
I have deceided to replace it with BG in super E connection with a total of 4080uf.
I know some caps have a +/- of 20% and I don't think there is a problem but do not want to change the performance of the amp adversly. What does the output cap do besides keeping DC at bay and how is it s size determined?

Thanks

Andrew
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Old 10th January 2004, 03:03 PM   #2
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As long as you exceed the original capacitance you'll be fine. It forms part of a hi-pass filter together with the speaker impedance.

4080uF worth of high voltage BG capacitance !!! If i were you i'd start with 2000uF and see if with the speakers you use the bass is satisfactory. If they don't dip too much below 8ohms in the low frequencies they should be fine.

I would honestly consider selling the amp and buying a direct coupled OTL instead.
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Old 10th January 2004, 08:24 PM   #3
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Thanks for that.

Its actually low voltage bg's (35v rating cap) and it sounds too good to sell

Its my first otl amp. call me converted

Andrew
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Old 10th January 2004, 08:32 PM   #4
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Quote:
Its actually low voltage bg's (35v rating cap)
How can this be? Is this a tube amp? 200v seems to an absolute minimum for an OTL output coupling cap.
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Old 10th January 2004, 08:46 PM   #5
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http://www.transcendentsound.com/single%20ended.htm
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Old 10th January 2004, 09:16 PM   #6
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Hi,

Quote:
Its actually low voltage bg's (35v rating cap) and it sounds too good to sell
Let's just hope then that no tube is ever going to go into a short circuit.

It never happened to me in twenty years of intensive use but the risk is there and with so many tubes in // you probably won't notice unless it trips a fuse in the voltage rails or a cap blows.

Peter,

The voltage is set for 0 VDC offset at the output of the CFs.
It uses a bipolar rail with the negative rail compensated for the cathode R and as I understand it, it's regulated as well.

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Old 12th January 2004, 07:45 AM   #7
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Default OTL offset

Hallo Frank,

the output CF (4*6C19 with 5 Ohm CR) is working on an inductor
(.32H, 600mA, 10 Ohms) The idling current is approx. 450 mA.
Therefore the output voltage before the cap is some 4,5 Volt.

Hope this info is useful.

Reinhard
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