Otl

nafunga · 27th July 2005, 03:46 PM

Hi,
Has anyone built one of Andreas Ciuffoli's OTL amplifiers (ver.8.2) and can help me with the value of the coupling capacitors to the 6c33c's. Can't make out if they are 2.2 or 22uf.

Many thanks,

David.

EC8010 · 27th July 2005, 04:52 PM

If you want people to respond, you need to add a link to the diagram...

Oh, and welcome to the forum!

nafunga · 27th July 2005, 05:01 PM

Thanks for that - have attached link (I hope!) problem is I can't tell from this diagram which value to use - 22uf seems a little excessive (but may be correct) Someone who's built one might know what works perhaps?

EC8010 · 27th July 2005, 05:06 PM

2u2 seems like a very sensible value to feed 68k grid leak resistors...

nafunga · 27th July 2005, 05:14 PM

Yes I agree - Thanks. Makes sense to me too.

Larry Lomax · 29th July 2005, 10:49 AM

It seems that power supply filter capacitors are a bummer high also! Is it? 4700uF charged at 150V are a bit explosive, are they?
And ... and... are you shure this is not a fake? Italians are used to play jokes any time! And when they are not, they exagerate a bit!

nafunga · 29th July 2005, 11:56 AM

Yes I agree with that as well! Have some 2200uf 350v which I'll be using. Probably alter the PSU a bit. Did you notice the Xfrmr is rated at 4A? Looks as if the PSU is well overrated generally. Still, amp. cct looks interesting.

tubetvr · 29th July 2005, 01:28 PM

Hi,

2200uF is barely enough to keep hum on the output low enough in this design, the output stage is not completely symmetrical with regard to power supply rejection so you need quite good filtering to reduce hum to acceptable levels. In a later version Andrea used a CLC filter for the anode supply which is an idea.

In my OTL which has a similar output stage I use good quality elytics of totally 5500uF without chokes with very good result, the quality of the elytics especially ESR is more important than the cap value itself.

Quote:

And ... and... are you shure this is not a fake?

I dont know if this was meant as a joke by Larry Lomax or not but no, it is not a joke, I know several that have built this amp successfully and although it can be improved the circuit work as it is presented.

Regards Hans

nafunga · 29th July 2005, 02:00 PM

Thanks for the info. I should have said my intention is to use a CRC filer per rail using two 2200uf capacitors. Would you approve? I have checked the ESR and is around 0.05 Ohms.
This is my first attempt at OTL so any help/observations is most welcome.

David.

Sch3mat1c · 29th July 2005, 02:16 PM

Bah. People cought using a resistor for filtering a power output stage should be shot.

It's class A anyway, which...is pretty pitiful, adding insult to injury as it's already a tube OTL to begin with. So I guess it doesn't really matter. Whatever.

Good rule of thumb: 2mF (2000uF) per ampere. A bit less at high voltage since more ripple can usually be tolerated (percentage-wise). As-is, if it needs as much filtering as claimed, I don't really have a problem with 4700uF, but 2 x 1000uF would be a lot better, particularly with 100mH between them.

Tim

27th July 2005, 03:46 PM	#1
nafunga diyAudio Member Join Date: Jul 2005 Location: Whitstable , Kent. UK	Otl Hi, Has anyone built one of Andreas Ciuffoli's OTL amplifiers (ver.8.2) and can help me with the value of the coupling capacitors to the 6c33c's. Can't make out if they are 2.2 or 22uf. Many thanks, David.

27th July 2005, 04:52 PM	#2
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	If you want people to respond, you need to add a link to the diagram... Oh, and welcome to the forum! __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

27th July 2005, 05:06 PM	#4
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	2u2 seems like a very sensible value to feed 68k grid leak resistors... __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

29th July 2005, 10:49 AM	#6
Larry Lomax diyAudio Member Join Date: Feb 2005 Location: London Hammersmith	It seems that power supply filter capacitors are a bummer high also! Is it? 4700uF charged at 150V are a bit explosive, are they? And ... and... are you shure this is not a fake? Italians are used to play jokes any time! And when they are not, they exagerate a bit! __________________ Nothing happens by itself, you have to work hard to arrange things to make it happen.

29th July 2005, 02:16 PM	#10
Sch3mat1c diyAudio Member Join Date: Jan 2003 Location: Milwaukee, WI	Bah. People cought using a resistor for filtering a power output stage should be shot. It's class A anyway, which...is pretty pitiful, adding insult to injury as it's already a tube OTL to begin with. So I guess it doesn't really matter. Whatever. Good rule of thumb: 2mF (2000uF) per ampere. A bit less at high voltage since more ripple can usually be tolerated (percentage-wise). As-is, if it needs as much filtering as claimed, I don't really have a problem with 4700uF, but 2 x 1000uF would be a lot better, particularly with 100mH between them. Tim __________________ See my Electronics webpage -- the home of Vacuum Tube Drag Racing. The key to being a successful Audiophile: "I reject your reality and substitute my own!"

27th July 2005, 05:14 PM	#5
nafunga diyAudio Member Join Date: Jul 2005 Location: Whitstable , Kent. UK	Yes I agree - Thanks. Makes sense to me too.

29th July 2005, 11:56 AM	#7
nafunga diyAudio Member Join Date: Jul 2005 Location: Whitstable , Kent. UK	Yes I agree with that as well! Have some 2200uf 350v which I'll be using. Probably alter the PSU a bit. Did you notice the Xfrmr is rated at 4A? Looks as if the PSU is well overrated generally. Still, amp. cct looks interesting.

29th July 2005, 02:00 PM	#9
nafunga diyAudio Member Join Date: Jul 2005 Location: Whitstable , Kent. UK	Thanks for the info. I should have said my intention is to use a CRC filer per rail using two 2200uf capacitors. Would you approve? I have checked the ESR and is around 0.05 Ohms. This is my first attempt at OTL so any help/observations is most welcome. David.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read