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The good, the bad, and the ugly OTL amplifiers
The good, the bad, and the ugly OTL amplifiers
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Old 4th November 2006, 06:36 PM   #11
coresta is offline coresta  France
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Hi Burnedfingers , for sure you'll realize your dream OTLs are for me the cream top of amplifiers . I did my own ones as i didn't want to use 6c33 (many failure) , 6528 (not good in OTLs) , nor 7542 (hard to find) ... king of the OTL is 6080/6as7 . With 10 per channel , you should drive 5 ohms loads without problems . Some tweaks : as previously said , make them run UNDER max rate, have a tube tester to match them , and ... heat the NEW ones 24 or 48 hours long without HV to evaporate residual dusts : 10 years long without a failure
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Old 4th November 2006, 07:05 PM   #12
ErikdeBest is offline ErikdeBest  Switzerland
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The good, the bad, and the ugly OTL amplifiers
Hi Coresta

Could you post a schematic of your OTL amplifier?

Many thanks

Erik
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Old 4th November 2006, 08:55 PM   #13
Burnedfingers is offline Burnedfingers  United States
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Are OTL amplifiers lacking in bass? Some people tell me yes and some say no.
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Old 4th November 2006, 10:46 PM   #14
vax9000 is offline vax9000  United States
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Tubes are not for OTL. Do you want NFB? If no, the damping factor is almost always bad. If you want a damping factor close to a triode SE, you need 100 6080s, not 10 or 20. No, no tube OTL.
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Old 5th November 2006, 12:56 AM   #15
Burnedfingers is offline Burnedfingers  United States
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You mention the dampening factor is bad with OTL. I haven't seen a tube amplifier with high dampening factor. As a matter of fact there was a thread here a while back that discussed dampening factors in tube amplifiers and if higher dampening factors were better than lower ones. If my memory serves me correctly I believe that lower dampening factors were favored in tube amplifiers and very high dampening factors are favored with solid state amplifiers. The higher the dampening factor in solid state amplifiers the better the amplifier. I can respect your opinion here and would just like some facts and figures to go along with your opinions because I'm still on the fence here.

What is the dampening factor of a OTL amplifier, a push pull amplifier and a SE amplifier if I may ask?

With respect to feedback...Some here surely don't want any while others feel that a small amount is needed. Naturally any amplifier will sound somewhat better with a small amount of feedback.
The solid state amplifiers absolutely need it to sound listenable and for stability. Where do we draw the line here anyway?
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Old 5th November 2006, 01:23 AM   #16
Wavebourn is offline Wavebourn  United States
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The good, the bad, and the ugly OTL amplifiers
vax9000, use impedance matching transformer and you will get your damping factor with less tubes. You may take only couple of them: one in cathode follower, one in current source, and you will get mach more damping factor than from one triode with OC and transformer in anode.

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Old 5th November 2006, 01:43 AM   #17
dshortt9 is offline dshortt9  United States
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I am presently using a Transcendent amp that uses 2 6C33C-B's per channel with quite a bit of NFB. My speakers are homebuilt with good efficiency but low impedance - around 97db and 3 ohm minimums. It is one of the best sounding amps I've had. In my top few favorites of all times.
In my opinion the NFB may not be as harmful in an OTL since it is not being used in a loop that includes a less than perfect output transformer. Just my thought as to why it does not seem to hurt the sound much.
Sometimes the best way to find out if your system will sound good with different gear is to just try it out. Not everything can be figured out with measurements, statistics, and opinions.
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Old 5th November 2006, 01:55 AM   #18
5u4 is offline 5u4  United States
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I made a Transcendent T8 several years ago. It is not a finicky amp at all, has plenty of bass, will easily drive 4 ohms, sounds really great & all that. Downside, it throws off some serious heat & the price of all those power tubes. Owning an OTL was my dream for many years & after I got one, I'd just as well listen to my little Loftin-White.
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Old 5th November 2006, 09:39 AM   #19
Giaime is offline Giaime  Italy
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Bah. Never heard an OTL amp going too good with the Cornwalls.

I would stick with a 6L6GC push pull, or 6550/KT88. McIntosh 275 would be a good candidate

McIntosh + Klipsh is something that one must hear in his life
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Old 5th November 2006, 11:34 AM   #20
Burnedfingers is offline Burnedfingers  United States
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Quote:
Never heard an OTL amp going too good with the Cornwalls.
Gamie,

Have you ever heard Cornwalls? Anyway they are Cornwall in size and that is about it. They are a highly developed design by DJK that totally kicks the Klipsch to the curb. They test almost ruler flat also. I refer to them as a Cornwall clone because they look almost the same. In terms of performance they are so much smoother and higher efficiency.

I'm interested in your opinion don't get me wrong. Have you heard any OTL amplifiers in which you could lend a opinion based on this information?

Quote:

McIntosh + Klipsch is something that one must hear in his life.

Well, heard them and wasn't impressed. Mac is ok but there are far better amps out there to be had.

Getting back to the OTL amps

So far we have established that they run hot. This is because of a large number of tubes producing mega heat. Note: Good for winter heat in home. There is considerable cost to replace the output tubes. They may or may not go up in a puff of smoke. They do require some feedback to sound halfway good. Note: Feedback
is 23db for the design I am looking at.

Safety: In checking into various designs it should be noted that some do not use transformers in their power design. No design like this should be considered or purchased. This notice is for SY and the diyaudio board and is meant to protect us so we don't fry our butts.

It shall be noted that some consider the OTL to sound quite good.
We should consider the type of speaker driven and the impedance curve of same. OTL's don't like to drive low impedance loads unless they have a massive amount of output tubes. Some claim long tube life if broken in correctly. I should mention that the 6C33 has a tube socket problem as it cannot withstand the massive heater current and this leads to problems. The 6C33 is a great tube however.

It would be of great interest to see some of the OTL amplifier designs that some of you have made in the past or are currently using.
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