OTL by Tim Mellow

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ACPEN
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#16

Post by ACPEN »

Hi Philip,
Glad to hear that it's still 'on the list'! I think this one is a better 'first time OTL' as it's more stable. I didn't actually collect any transformers, but there are still a number available - let me know when you might want one and I'll get it organised.

And, to Nick,
That's cheating!!)

ATB,

David.[/img]
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Nick
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#17

Post by Nick »

ACPEN wrote:Hi Philip,
And, to Nick,
That's cheating!!)
ATB,

David.[/img]
"I already had the box, the metal for the chassis and nuts & bolts etc.", "given that I got the mains isolation transformers for free!"
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
ACPEN
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#18

Post by ACPEN »

DOH!
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Nick
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#19

Post by Nick »

I have a little OTL headphone amp design that was originally done as a potential kit for HFC, but we decided it would be too complex and more hassle than it was worth as a kit, so I am going to write it up as a article for the HFC website over the hols. It uses one ECC83 and one 6080 per chan.
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colin.hepburn
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#20

Post by colin.hepburn »

Hi Nick
You Have PM :)
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Graeme
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#21

Post by Graeme »

ACPEN wrote:Come on someone - build one please!

'Merry Xmas' to All!

ATB,

David.

Hmmm, ive been looking at building another amp but had no preference for what to build.

I could be tempted to try building this.

I assume the final circuit is as posted in post 8?

Do you think this is something that could be attempted by someone who can only 'build from a schematic' without full understanding of how it works?
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#22

Post by PeteC »

Nick,

i have the kurt strain design OTL head amp i made a few years ago still in regular use.

would be very interested in yours and see how it compares

OTL head amps are great IMO. straight from the valve into your ear ( thru a cap of course !

cheers
Pete
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ACPEN
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#23

Post by ACPEN »

Graeme wrote - Do you think this is something that could be attempted by someone who can only 'build from a schematic' without full understanding of how it works?

Certainly! The original article is on the DIY Audio site. I re-drew the amp. cct to make it easier to follow (?) I can send both as attachments if you like? If you make the original 25W design, leave plenty of space around the 6C33C's as they produce around 36W of heat each! - and that's just the heaters! And, if you can (seperate psu) keep all electrolytics away too! Otherwise, just follow the circuit.

Regards,

David.
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#24

Post by Graeme »

Yes please, attachments would be lovely. Ill PM you my e.mail.

Ill go search diy audio too.

Thanks.
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#25

Post by ACPEN »

Well, Nearly a month has gone by - and it's still working! It seems that around a weeks normal use was needed to settle in the 6C41C's - after that, there was no bias drift (can be a problem with OTL's) and the balance has remained virtually stable. So, so far so good! I decided to give it a 'bench test' of it's freq. response. It performed well, being flat between 20Hz - 50kHz using squarewaves (and up to 100kHz sinewave) Of course OTL's do perform exceptionally well in this respect, as there is no nasty transformer in the signal path! Think of what you get with an SE Amp. up to the driver stage output - thats what you get at the speakers - no droopy L.F or rounded H.F waveforms! That said, I,m more inclined to let 'listening' be the arbiter these days rather than test results.
I hope to hear some thoughts on this amp. when I manage to encourage someone else to build one! (I think Philip is wavering? - maybe in time for Februarys Audio jumble?)

ATB,

David.
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#26

Post by Graeme »

Im still up for building one, just waiting for my hearing to recover first.
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#27

Post by Mike H »

We-ell, you could still start now, it'll be sorted by the time you finish :?:



 
 
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#28

Post by Graeme »

Ill see how much money i have left at the end of the month :)

One good thing about not having good hearing right now is i can pull my stuff apart and finish things without missing having a working system.

All spare time is going into finishing these speaker cabinets but they should be done in about a week.
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#29 OTL by TIM MELLOW

Post by ACPEN »

Well, at last I've just finished the 6C33C version (orignal Tim Mellow design) My son-in-Law will be pleased! He's been very cool about waiting - He won't be when he gets it though! It gets very hot! (As expected)
I've attached a few photos which might be of interest. The amp is built on a Hammond wood framed chassis. Don't know if anyone has used one of these? They're very sturdy, but expensive. The PSU is built on an old Cambridge P50 amp chassis (quite right too!) and the main HT transformer is my old favorite, the 240v bench isolation xfrmr (500W).
It sounds just like it's smaller (6c41C ) version previously mentioned, but of course goes louder. Come on somebody - build one! They're great!!

ATB,

David.
Attachments
OTLM 004.jpg
OTLM 005.jpg
OTLM 006.jpg
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Dave the bass
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#30

Post by Dave the bass »

Phwwwwwwwwoooooooooaaaaaaarrrrrrrr!

Nice one Mr W.

DTB
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