Otl

[gnomus]

Hans what OTL design did you choose? Any links on the design?

 

[fdegrove]

Hi,

Hans what OTL design did you choose? Any links on the design?

Paul,

You'll find more about Hans's OTL on his website.

Cheers,😉

 

[gnomus]

Thanks Frank. I did a search on Hans' user name and a lot of post came up including one Hans started on DC offset amounts. But, no horns mentioned. Hans's post on horns here should go there.

 

[fdegrove]

Hi,

Thanks Frank.

You're welcome and if you ever want to consider building an OTL amp feel free to post your ideas.

Personally, I'm thinking of building a low powered OTL to drive OB speakers but that's still pretty much just a plan for the future.

Cheers,😉

 

[gnomus]

Thanks for your help Frank. I am considering buying BR's new almost real OTL. Mostly because it's almost what I am looking for. And I would avoid the biggest job for me in DIY which is building the chassis. It's easy to bridge for 4 watts. I would try a negative supply to get rid of the output coupling capacitor. I could use your help on the negative supply. If you could post information and circuit on your ideas it would help.

 

[tubetvr]

Hi,

I measured cone displacement for DC voltage on one of my Lowther elements today. Result is that the cone moves approximately 0.3mm for a DC voltage of 100mV, as Xmax for Lowther elements is +- 1mm an applied DC voltage will have some effect on distorsion for high power but for normal playing levels I can't see that it will have any measurable effect.

The element in question is Lowther PM6A with 8 ohm impedance.

BTW. is it possible to calculate the cone displacement for DC voltage TS parameters? I imagine it should be possible but I haven't made any effort to do it yet.

Regards Hans

 

[fdegrove]

Hi,

It's easy to bridge for 4 watts.

I'd rather use a few more output tubes.

I would try a negative supply to get rid of the output coupling capacitor. I could use your help on the negative supply. If you could post information and circuit on your ideas it would help.

As a concept it's actually pretty easy to do and uderstand; all you need is a regulated B+ of X volts and a regulated adjustable negative supply of X volts + the voltage drop caused by the Ri of the outputstage and you're done.

The latter allows you to trim away DC offset on the output, eliminating the need for a coupling cap and that's the end of that...

Cheers, 😉

 

[gnomus]

Thanks Frank.

It seems fairly easy to elminate dc output in solid state and tubes. You need some way to trim in order to direct couple. As the parts age you most likely have to adjust again. But, should not require a large adjustment. Consumers want plug and play so I can see why manufacturers do not direct couple amps and pre amps more often.

Why do you not like to bridge an amp?

 

[fdegrove]

Hi,

Why do you not like to bridge an amp?

It's just that I've never heard one that actually sounded better that way.YMMV of course...

Cheers, 😉

 

[woody]

ARG Labs has a 5 watt otl using only one 6c33c-b and a 6h6p
driver. I sure would like to see the schematic or at least know
how the output is loaded.

Thanks
Woody

 

[fdegrove]

Hi,

ARG Labs has a 5 watt otl using only one 6c33c-b and a 6h6p

Sounds like a single ended OTL so I assume they're either using a cap to block DC or a bipolar rail with the negative leg adjustable so DC can be trimmed away.

I haven't seen the latter in a commercial product as yet though...

Cheers,😉

 

[gnomus]

Does ARG have a web site? Cannot seem to find it.

 

[fdegrove]

Hi,

They used to...

I don't know much about them but I think they were based in the Ukraine.

Cheers,😉

 

[Tyimo]

The sound of an OTL

Hi!
I very interested for the OTL amps, but in my near there isn't any what could I listen. So I have a strange and a bit stupid question:
Could somebody somehow to tell me what is the sound of the OTL typ amps? I mean, has them so warm and smooth sound like the "classic" valve OT amps or it comes only from the output transformer? More correct is: what is the sound of a SET-OTL to compare with a SET-OT?
Thanks!

 

[Nicos]

Ciuffoli Ver 8.2 OCL OTL

I am buidling the CIuffoli OTL amp but currently am at a loss as to the use of non electrolytic caps in the power supply B+ section and on the driver section of the amp.

Does anyone have a clue as to why he is using such caps and whether electrolytics would do as a replacement? Mind you the caps are placed after the rectifier bridge so there is no question that we are dealing with DC voltage supply not AC.

The difference in cost in substituting them with electrolytics is substantial.

 

[fdegrove]

Hi,

Does anyone have a clue as to why he is using such caps and whether electrolytics would do as a replacement?

The reason is better sound quality from MKP than from electrolytic caps.

Surely 200V MKP caps aren't all that expensive?
We have 2*10µF/200V. 2*1µF/400V and, these are the most expensive ones 2*50µF/400V. The latter you can replace with a 100µF/400V electrolytic and bypass that one with some polyprops, say about 5µF + a few styrenes.

If you really want expensive look at what it would cost to use Black gates instead of the polys.

Cheers,😉

P.S. In case you haven't ordered the powerxformer yet, I'd recommend using separate bias supplies for all rails.

 

[Nicos]

Thanks Frank.

Any good suppliers of these MKP caps?
Shall I use Solen or what?

 

[fdegrove]

Hi,

Any good suppliers of these MKP caps?

Seeing you're in the U.K Ansar has a good rep but seems hard to come by.

Very often Audyn caps are cheaper and smaller in size than Solen SCR.
All of the above should be available in the U.K.

Cheers,😉

 

[Alastair E]

paper caps

KWtubes on Ebay have some paper/PIO caps for sale, in batches of 4 and 8, 1-4uF are around 500V and higher values lower volts
Others do similar ones also, try a search on Ebay for them!

 

[Nicos]

thank you good people.
the only issue remaining is the metal work which is the worst pain of all.