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PostPosted: August 3rd, 2017, 10:47 am 
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Joined: January 14th, 2015, 11:15 pm
Posts: 499
My understanding is that this version of the 300B OTL is indeed single ended without output transformers. There is a photo of the insides of another build of the design at

http://www.audio-talk.co.uk/phpBB3/viewtopic.php?f=11&t=6803

The third photo shows the power supply that was used for this build.

I have not seen the circuit since I don't have the book. From my discussion with Ray P, the 300B is operated at a much lower voltage and higher current than usual and there are four 300B tubes per channel. I presume they run in parallel and as a cathode follower, but I could be wrong.

I suppose I will just order the book to satisfy my curiousity.

ray


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PostPosted: August 3rd, 2017, 11:33 am 
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Joined: July 17th, 2016, 6:24 am
Posts: 1099
Jim G wrote:
I just noticed this thread. You know David Berning is in this group, right? I'm sure he'd be happy to talk OTL amps with you.


I know David makes wonderful amps but I wanted to go DIY route. Didn't hear his amps though. Atma-sphere and Transcendent sound were the only two credible options. I remember auditioning Atma-sphere amps several years ago and not being terribly impressed.

Initially I was thinking of T8 or the Beast for bass considerations as my speakers are not "high" efficient at 93dB. Because building T8 or Beast involves considerable investment of time and $$, I was trying to listen to them before starting the project.

Bruce Rozenblit suggested I should try Son of Beast which outputs only 15w. He already obsoleted the Beast and is coming out of a new amp later this year with about 40w of power.

Anyways, built the SOB and is running as of this morning. I will burn it for a couple of days before judging it.


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PostPosted: August 3rd, 2017, 11:36 am 
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Joined: July 17th, 2016, 6:24 am
Posts: 1099
tomp wrote:
I have heard the original Futterman and atma-sphere amps. They are better than most transformer coupled amps but their output impedance is high which makes them very susceptible to speaker impedance. The advantage of the ZOTL that David uses is that there are also no iron problems that plague transformer coupled amps but the output impedance is very low compared to OTL amps, sometimes by more than an order of magnitude. There is then much less of a problem with matching to different speakers. The smoothness, clarity and transient response of his amps is superior. I have yet to hear any other tube amp that I like better than those from David but hey, that's my opinion. He has also gotten rave reviews in some of the major magazines for those same qualities of smoothness and transparency without being etched or forward.

Tom


Bruce Rozenblit also has an patent on OTL design, although Bruce and David have taken completely different approaches to solve the problem.


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PostPosted: August 3rd, 2017, 11:53 am 
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Joined: February 28th, 2013, 3:31 pm
Posts: 363
I know Dave has offered to help with diy OTL amps, and transformer coupled amps too for that matter, as well as custom one offs like Tom's VFET amp. He's a great resource, and is generous with his time. Consider contacting him.


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PostPosted: August 3rd, 2017, 1:35 pm 
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Joined: July 17th, 2016, 6:24 am
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Jim G wrote:
I know Dave has offered to help with diy OTL amps, and transformer coupled amps too for that matter, as well as custom one offs like Tom's VFET amp. He's a great resource, and is generous with his time. Consider contacting him.


I did not know David offered to help the DIY community. A class act.

Next time I will seek his advise.


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PostPosted: August 4th, 2017, 6:15 am 
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Joined: January 15th, 2015, 7:19 am
Posts: 1697
Location: Baltimore MD
TS kits are easy to build, good instructions, and reasonable decent quality parts, except for the case work. The prices reflect this. He does not believe in boutique caps or resistors, wire. One could always substitute whatever. There is always good docs, schematics. And plenty of discussions on mods.
One of the major complaints is his transformer sizing. He believes that over kill in this area is a waste of time.
When I was using the GG preamp the only mods I did was to replace the first resistor on the I put with a better quality one. I replaced the low quality pot with an Alps Black Beauty, and I reduced the feedback. This is a really god sounding preamp and would still be using it until I built a Gary Dewes design preamp which I still use.
I still use the TS phono and have yet to find a better sounding one


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PostPosted: August 4th, 2017, 7:42 am 
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Joined: July 17th, 2016, 6:24 am
Posts: 1099
Pelliott321 wrote:
TS kits are easy to build, good instructions, and reasonable decent quality parts, except for the case work. The prices reflect this. He does not believe in boutique caps or resistors, wire. One could always substitute whatever. There is always good docs, schematics. And plenty of discussions on mods.
One of the major complaints is his transformer sizing. He believes that over kill in this area is a waste of time.
When I was using the GG preamp the only mods I did was to replace the first resistor on the I put with a better quality one. I replaced the low quality pot with an Alps Black Beauty, and I reduced the feedback. This is a really god sounding preamp and would still be using it until I built a Gary Dewes design preamp which I still use.
I still use the TS phono and have yet to find a better sounding one


I finished building the Son of Beast yesterday. It took only a few hours for it to start showing what it is capable of. My initial impressions:
1. Definition in the bass is amazing.
2. Tube warmth/sweetness is reduced a little but it sounds more natural.
3. Strings sound very realistic with the full reverberations.

At about $1200 for Bruce's kit and tubes, this thing is a steal.

If you are coming to the August meet, I would like to hear how GG preaamp sounds with SOB in my system. My current preamp has Mullard E182CC which brings clarity and sweetness to the system. You can borrow SOB if you wanna try in your system.


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PostPosted: August 4th, 2017, 8:02 am 
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Joined: January 15th, 2015, 7:19 am
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Location: Baltimore MD
I'm going to try to come. I need to dig it out, dust it off, fire it up. It will be a good reality check since I've made changes to my 6ew7 preamp.


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PostPosted: August 4th, 2017, 10:28 am 
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Joined: July 17th, 2016, 6:24 am
Posts: 1099
SoundMods wrote:
Reliability can be an issue putting your speakers in harm's way of DC should you have tube failure. A friend had tried both the Futterman and Atmos-sphere amps in the past and the sound quality was "Hi-Fi" rather than musical and transparent -- and to add insult to injury the build quality was crude. He is now running SET and all the more happy for it.


Bruce's design uses fuses for each P-P pair of output tubes. Remember reading in one of his books (dont remember which one) Audio Reality or Tubes & Circuits, Bruce tested the amps for tube failure. Fuses blow so quickly in case of output tube failure, the DC never reaches the speakers.


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