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Old 22nd March 2004, 05:47 PM   #31
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by fdegrove
About the worst OTL Glenn ever did IMO but with some modification you could make it into a great little OTL.
They where a friends, re-build powersupplies, rebuild signal circuit with some of Glens own mods from later series, Multicap for coupling and fancy resistors et al. So basic circuit was still Glenn, but a sligthly later generation, the rest re-build.

BTW, my friend still owns them but no longer uses them, he prefers 2A3 & 300B transformer and inductive/direct coupled Amplifiers he build from my designs.

Quote:
Originally posted by fdegrove
Mine is the Series II which uses 10 //ed 6080s but I had trouble with the main PS for the tubes as he had put 100Vers in series to create 200V caps.
The 6080/6AS7 ones I heard had only 4 valves per monoblock and where very recent, about a year back, maybe a little longer. They where some of the last ones with the ugly wooden frontpanels and bog standard stock.

Quote:
Originally posted by fdegrove
Sonically the Series II is very hard to beat but from reading you it may well be not your cupper.
Hmm, it seems the amp's you had where different from those I heard. Anyway, I'm just curious. I also heard the Atma Sphere Circlotorn Amp's and hear the same forced, uneasy quality and "in your face sound" I heard from the Crofts and which I would charaterise as "OTL" Sound, based on my experience so far.

I will admit that I rather like the idea of an OTL Amp, except I wish they could sound more to my taste than these I heard did. I have been thinking 6S33 SRPP with a Ongaku style driver and classic output coupling cap. In the end all the "OCL" OTL Amp's merely replace the coupling Cap with a pair of PSU Cap's and usually not very good ones. If I have to deal only with around 200V DC and a dozend volt AC I can make up a 2000uF Poly Cap in about the same size case as a nice OPT might fit in.... It'd probably cost more than a decent SE OPT too.

Or maybe an inverted Futterman based around the Ongaku frontend? A little NFB in either case, just enough to lower the Z-Out to a level comparable to my DHT SE & PP Amp's, this could be attached to the middle stage, rather than to the input stage and add to that another loop from the middle stage anode to the input stage cathode, rather than one "long" NFB loop....

Sayonara
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Old 22nd March 2004, 07:02 PM   #32
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Hi,

Quote:
In the end all the "OCL" OTL Amp's merely replace the coupling Cap with a pair of PSU Cap's and usually not very good ones. If I have to deal only with around 200V DC and a dozend volt AC I can make up a 2000uF Poly Cap in about the same size case as a nice OPT might fit in.... It'd probably cost more than a decent SE OPT too.
Surely you don't want me to tell you what's in the signal path of an SE amp?

Either way, what's important is the endresult and I never had the impression I was listening to 2 pairs of 4000F electrolytics....Let's not forget either that this is a PP amp.

Since Nicos was asking me somewhat the same I did a little write up on life with OTL amps here:

CROFT SERIES II OTL.

Maybe I shoul also put that sticker up my bumper stating:

"My other amp is a 2A3 PP"

Which just so happens to be the absolute truth...

Cheers,
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Old 22nd March 2004, 08:52 PM   #33
Previously: Kuei Yang Wang
 
Join Date: Nov 2002
Konnichiwa,

Quote:
Originally posted by fdegrove
Surely you don't want me to tell you what's in the signal path of an SE amp?
No, I happen to know. For the output stage one transformer (hopefully a good quality one - in which case it presents no material sonic problems), one Valve and one PSU decoupling or WE connection capacitor closing the output signal current loop. if you have any more there you simply show how it should not be done.

Quote:
Originally posted by fdegrove
Maybe I shoul also put that sticker up my bumper stating:

"My other amp is a 2A3 PP"

Which just so happens to be the absolute truth...
Mine is a 45 PP, at the moment, but I can make it 2A3 PP or 300B PP, as I please... ;-)

Sayonara
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Old 22nd March 2004, 10:36 PM   #34
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Quote:
No bashing or the like intended, but I would like to know a little more about the system context (especially speakers) and your seating preferences in the concert hall (I like "Mid-Hall" Center best), assuming you include classical music (fresh and converve) in you musical diet.
At home I use Lowther Fidelio and as you I like mid-hall center best when listening to live classical music. I have a relatively wide taste of music, including classic music, (especially piano music) jazz, classic soul and classic pop.

I also used other speakers at when comparing amplifiers including some larger Audiovector model, (that I borrowed from a friend) and Quad ESL63. Regardless of speaker, I can quite easily here details in some recordings using my OTL amp that is masked by the SE amps I have compared to, I have also been running around in the high end shops in Akihabara and elsewhere here in Tokyo and been listening to many SE amps with different speakers, by using the same CD's I am used to listening to at home I have come to the same result, i.e that SE amps hide details in some music.

I am quite surprised about the result myself as many people rave about SE amps but probably that is becaused SE amps make almost all recordings sound good, with an OTL amp you get to hear everything including bad recordings.

Regards Hans
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Old 22nd March 2004, 10:48 PM   #35
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Hi,

Quote:
No, I happen to know. For the output stage one transformer (hopefully a good quality one - in which case it presents no material sonic problems), one Valve and one PSU decoupling or WE connection capacitor closing the output signal current loop. if you have any more there you simply show how it should not be done.
Well if you jump to the conclusion that the PSU is in the direct signal path of the OTL circuit then it's just as easily said that the PS is in the signal path of a SE amp...

After all, DC has to be stopped somewhere and with most OTL/OCLs I know of it's the opposing +/- rails that allow the extraction of the AC signal without DC riding along with it.

BTW, I may have said this before, a very close friend of mine owns a set of AN Baransus and Lowthers.
They sound fine even though I hear them humming on quiet passages but I'd never dream of using them in my system as they really don't offer anything the OTL can't do better.

This, regardless of cost which let's face it, skirts the absolutely ridiculous.

Cheers,
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Old 23rd March 2004, 12:21 AM   #36
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Hi,

Quote:
The 6080/6AS7 ones I heard had only 4 valves per monoblock and where very recent, about a year back, maybe a little longer. They where some of the last ones with the ugly wooden frontpanels and bog standard stock.
Looks aside, can you honestly imagine an OTL with just 4 6080s that can drive a modern 8 Ohm speaker adequately?

I sure have a hard time with that one...

Quote:
Mine is a 45 PP, at the moment, but I can make it 2A3 PP or 300B PP, as I please... ;-)
I know you do, the 45 are my favourites but my speakies (86 dB two ways) need a little more beef than that, I'm afraid.

Cheers,
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