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Steve's OTL Amplifier (Read 2999 times)
Steve Deckert
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Steve's OTL Amplifier
04/14/18 at 01:48:24
 







This is my own personal OTL amplifier prototype that I built as a possible Decware flagship product several years back. It uses the 6C33C output tubes, two per channel to give 20 watts into 8 ohms.  

The design turned out to be far too difficult to put into production without circuit boards, in fact I remember the two weeks of bench time when I built it almost put me in the hospital with a stuck vertebra in my neck. That was a big deciding factor, but more importantly was the price. This would have been a 20K amplifier in a slightly more dolled up chassis and our market wouldn't have supported it.

It has always exceeded the fidelity of all other Decware amplifiers as you would expect and still does with the possible exception of our new Anniversary amp, but that amp is only 2 watts and no direct comparisons have been made since the applications are so different.

I have always only listened to the things I sell because if it's not good enough for me, I shouldn't be selling it. The only exceptions are amps, like this, which were built with the intension of putting into production. Since I know for a fact that this amp won't be going into production I find no pleasure in seeing it set on a shelf and not doing what I created it for.  It would be best to sell it.  I could always make another one someday if I had to.

The R&D on this was a lot. It is the only one that exists like it in the world.  I firmly believe it to be the best sounding OTL amp ever made because there are no tubes in parallel. In fact it is basically a single tube per channel with the second tube being used as a constant current source.  

This amp is fan cooled with dual quiet slow running fans built into the base.

Price is 10K OBO

Terms are personal check or money order made out to Steve Deckert, amp ships when cleared. Shipping is included at the 10K price, although it would be advisable to drive here and pick it up. This way we know it won't get broken in shipping, and you can hear it before you hand over the check, and I can give hands on lesson on how to use it. I will warranty it against defects for 1 year, after that any repairs are parts and labor.  A functioning set of tubes will be supplied, however the buyer will be expected to have at least four output tubes on hand. The tubes cost about $50 each from ebay and if your not familiar with them, you are also expected to do some research as these are not normal audio tubes and by their nature can not be tested with any constancy in 99% of all tube testers. The only way to test them is in the amp and see how they behave. The amplifier has meters for each channel to show the tube bias and watching how it warms up and balances out is how test and match the tubes. The current draw idles at 200 mA per channel and should be limited to 400mA per channel when playing music.

While the tubes get hot, the amp stays cool to the touch so long as the fans are on.  The fans must never not be used else the amp will melt down in less than 20 minutes.

If you're new to tubes don't even ask about this amp, it's not for sale to you at any price.  


Steve
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Archie
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Re: Steve's OTL Amplifier
Reply #1 - 04/14/18 at 02:02:59
 
Come on LR, step up!!!     Grin
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Re: Steve's OTL Amplifier
Reply #2 - 04/14/18 at 13:34:16
 
Plus it has the cool skull with ruby eyes volume knob. Worth at least $2k by itself.
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Steve Deckert
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Re: Steve's OTL Amplifier
Reply #3 - 04/14/18 at 17:37:04
 
I can be reached by email - steve  @   zenamps  .    com


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Re: Steve's OTL Amplifier
Reply #4 - 04/15/18 at 15:34:34
 
What an amp. I'm sure it sounds spectacular. I've spent more than enough on Decware over the years to have bought this if I hadn't spent the money before, but look at all the great listening I would have missed in the meantime! I hope this finds a great home!
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Jeff of Arabica
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Re: Steve's OTL Amplifier
Reply #5 - 04/15/18 at 16:19:22
 
I had the pleasure of hearing this amp play for hours at Decfest last year.  It sounded phenomenal!!  

There is a part of me that is so tempted to snatch this amp up.  But right now, my ZMA is sounding so incredible that I can’t justify the expenditure..... at least at this moment (Saturday April 15, 2018 at 8:18am PST)
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Re: Steve's OTL Amplifier
Reply #6 - 04/15/18 at 17:00:48
 
Justify?   What does that mean?    ;D
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Jeff of Arabica
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Re: Steve's OTL Amplifier
Reply #7 - 04/16/18 at 04:13:45
 
Please.  Somebody buy this amp so I can get it off of my mind. Thank you.
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Lonely Raven
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Re: Steve's OTL Amplifier
Reply #8 - 04/16/18 at 20:55:59
 
If I had the money, I would absolutely get this amp. This amp (probably literally) rewired my brain when it comes to listening to music.

Thankfully, a CDApS member is putting in an offer so we can keep in the family. And being local, it looks like he would drive down to learn from Steve how to feed and water his new pet and pick up the amp.

I've always loved this amp, I just can't see me being able to afford it without selling my ZMA - and that's not happening anytime soon. (unless Steve wants a straight up trade!?  :D  )
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Re: Steve's OTL Amplifier
Reply #9 - 04/17/18 at 03:02:52
 
My offer has been accepted!
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Lonely Raven
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Re: Steve's OTL Amplifier
Reply #10 - 04/17/18 at 03:45:13
 

(Virtual High-Five)

Next CDApS meet at your house!!

Or feel free to bring it down south and we'll do an OTL tour. We just need to rent a Brinks security truck to transport it.  ;)

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Re: Steve's OTL Amplifier
Reply #11 - 04/17/18 at 20:38:01
 
Next CDApS at my house sounds great. If you still have some portable room treatments bring them along as I have not made much progress in that area. Although I plan to make some if the weather ever improves.
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Lonely Raven
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Re: Steve's OTL Amplifier
Reply #12 - 04/18/18 at 17:42:10
 

I had to put my spare bedroom build on pause due to being sick constantly since like late November. So I still have all my foam diffusers piled up and not yet mounted to the walls. I'll see what I can bring along. We just need to plan the When!

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Steve Deckert
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Re: Steve's OTL Amplifier
Reply #13 - 04/19/18 at 00:55:53
 

Well I have spent the day with the amplifier on the QC bench going through it with a fine tooth comb.  Put new tubes in and cleaned it up inside and out.  Having made its way back into the listening room I am able to swap it in where the 25th Anniversary amp was, same source and same speakers.

I am going to write down the operation notes here, that way we can't forget them, myself included.

During testing of the amp's new tubes (and understand the 6C33 can handle lots of mills in exchange for long life) I biased it up to 500 milliamps per side just to see what would happen (5 times higher than a ZMA) and it put out 42 watts at 0.03% distortion into 8 ohms, and could have gone farther no doubt.  That said it is biased at 200 milliamps per side so that the tubes last a very long time and can be called a solid 25 watt amp. When the volume is pushed up to the point where the meters dance you're in the 5 watt range.  When the meters dance up to 400+ milliamps, you're in the 10~20 watt range.  Unlike most amps, when the meters dance there is no distortion in fact distortion goes down with current in this amp.

The amp is fan cooled, the fans run as long as the amplifier is plugged in.  The input stage and driver tubes also stay on continuously if the amplifier is plugged in.  This is so they are fully warmed up prior to turning on the output tubes.  The power switch turns on and off the output tubes.  If the amplifier's power tubes are turned off, be sure to wait at least a minute before turning them back on and be sure the volume control is set to zero. 

Other tidbits about the amp - even biased at the recommended 200 milliamps the amplifier can put out 40 watts of class A power into a 16 ohm load.  Probably close to 100 watts into a 50 ohm load or higher.  The output impedance is 0.5 ohms. Even though this amp uses a 100K volume control, the input impedance is around 25K.  The DC offset for each channel has been set to .100 milliamps.

This amplifier has 7 independent power supplies with a 2000 milliamp high voltage main supply.

I will say this; this is the first time I've heard the amp with the DNA2 speakers and if I had heard this before I posted the ad, I wouldn't have been able to sell it. At least it's going to a great home where I know it will be well appreciated.  

It has a unique sound, which I have figured out what to call:  Majestic transparency.

Enjoy!

Steve
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Re: Steve's OTL Amplifier
Reply #14 - 04/19/18 at 21:40:24
 
Quote:
Majestic transparency.


I like the sound of that.

Going to a good home indeed!
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Steve Deckert
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Re: Steve's OTL Amplifier
Reply #15 - 04/20/18 at 03:28:34
 

Amplifier is sold.

You can hear it in the following 13 minute video demonstration of the DNA2 speakers.

https://www.facebook.com/Zenamps/videos/434481140306619/


Steve
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BadWolf
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Re: Steve's OTL Amplifier
Reply #16 - 04/22/18 at 20:11:56
 
Here’s an infrared picture of the OTL. This helps show just how much heat this puts off as this picture is entirely illuminated by the infrared radiation from the tubes.
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DSC00341-2.jpg

Zen OTL, Mini Torii II and III, “El Camino” MTM speakers, Tang Band 1808s used with SVS Sub, Schiit Gungnir Multibit, DIY "Zbit", dedicated circuits.
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Archie
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Re: Steve's OTL Amplifier
Reply #17 - 04/22/18 at 20:40:11
 
So what's the current draw of this amp?  Does it dim your lights when you turn it on?
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BadWolf
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Re: Steve's OTL Amplifier
Reply #18 - 04/22/18 at 21:48:13
 
Steve said 200 to 400 watts depending if it’s sitting idle or being driven. Far less than I expected actually. It takes it a long time to warm up and a long time to cool down. When it’s been used for a few hours it really puts off a lot of heat.

Since I've redone the wiring nothing dims lights. Though I doubt this amp would in any normal situation. Sometime I’ll measure its inrush current.
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Zen OTL, Mini Torii II and III, “El Camino” MTM speakers, Tang Band 1808s used with SVS Sub, Schiit Gungnir Multibit, DIY "Zbit", dedicated circuits.
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Archie
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Re: Steve's OTL Amplifier
Reply #19 - 04/23/18 at 00:26:39
 
That's a lot of heat though if you think of a 400 Watt light bulb.  I was joking about the lights dimming.   Wink
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Steve Deckert
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Re: Steve's OTL Amplifier
Reply #20 - 04/27/18 at 02:30:59
 

Well the infrared picture is just cooler than shit!  

So how does it feel to be listening to tubes designed for Russian ICBM's that were intended specifically to kill you?

Steve
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BadWolf
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Re: Steve's OTL Amplifier
Reply #21 - 05/01/18 at 15:33:52
 
Thanks Steve! I thought you might enjoy that.

It feels pretty awesome! I’ve always enjoyed the history some of these tubes have. I have some tubes that were made for WWII I particularly enjoy as well. There aren’t many things that can sit around for decades with no maintenance or attention and work just like the day they were made. This unique quality invites all manner of unintended uses as the world changes around them.
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