Ground on OTL

[fdegrove]

Hi,

I made seperate transformator only for heating and use Zn-Al protect tube for lead tone signal wire.

Separate xformers for the heaters is certainly a +.

Zn-Al protective tubing...not sure if that's effective and it could be the source of grounding loops causing hum.
In my amps there's not a single shielded wire and it's absolutely dead quiet.

pardon what mean BTW?

That means " By the way".

Lot's of people use acronyms for frequently returning word sequences.

ACRONYM FINDER

Cheers,

[arg_]

Do you mind sending me a copy or you could even post it here for future reference?

No problem, here it is



Numbers in blue is DC, red is AC at 1Khz. Of course these are to be taken as a general reference only and are valid for my configuration, measured voltages will vary depending on tubes, tolerances, power line voltage etc.

Jevta in case you've built the capacitorless version, did you have the chance to measure DC offset?

Cheers

[fdegrove]

Hi,

Thanks, Argilis.

Hans,

Would you have a type number of those special Pana caps you used?

That is, if they're available outside of Japan...

TIA.

Cheers,

[tubetvr]

Hi Frank,

Normally Panasonic capacitors have part numbers like EEGAA2D103FPE or something similar but the ones I use in my OTL have only these markings:

For OTL
250V 3300uF
- NEGATIVE
+85 C JAPAN

PANASONIC.

The 2200uF ones have same marking.

However I dont think these capacitors are that special as I achieved similar result in the amp I built for a friend using Panasonic EEG type caps.

I have made extensive measurement of frequency and phase characteristics of my amp and I found that there was a tendency for increased gain at low frequencies. This I have corrected for by introducing a phase compensating network. There could be a possibility that Andreas circuit has similar tendencies actually worsening hum when feedback is increased, I haven't checked this with Andreas circuit but as you can see there is a total lack of any frequency or phase compensating components.

Hans

[fdegrove]

Hi,

There could be a possibility that Andreas circuit has similar tendencies actually worsening hum when feedback is increased, I haven't checked this with Andreas circuit but as you can see there is a total lack of any frequency or phase compensating components.

Yes, it's not a circuit I'd build for myself unless I'd had a small lab at my disposal.

The Technics bootstrap drive is interesting though for future OTL amps.

For your info, my amp uses the Radford type of fase splitter using a ECF802.

It measures fine and sounds fine too.

Cheers,