looking for a 2A3/45 SET amplifier for my Open Baffle speakers ~

-Richard- · « **on:** 15 Sep 2011, 03:29 am »

I designed and built my own Open Baffle speakers... each panel has 2 drivers that are crossed over with a simple coiled inductor... both are 97db sensitive. I write quite a bit on the Open Baffle forum here on AC.

I have had extensive experience with 2 different 45 SET tube amplifiers with my OB's... I liked them both but moved on for various reasons. I would like to enter once again the rarefied atmosphere of the 2A3/45 world.

I have owned the Korneff... very interesting sound but too physically heavy for me.

Does anyone on this forum have experience with 2A3/45 SET tube amplifiers?

I need one that does bass very well (OB's lose bass because there is no box)... has that mid-range magic... and is very refined on the top end (for a convincing transparent portrayal of violins for example).

I would deeply appreciate your observations and insights. So thanks in advance for any help you can give me with this.

With Warmest Regards ~ Richard

InfernoSTi · « **Reply #1 on:** 15 Sep 2011, 04:28 am »

I have Hawthorne Audio SSI Trios (OB) and run a Bottlehead Stereomore 2A3 amp with them. I know Edgar4 has the same amp but different OB speakers, too. The Stereomour can be configured as either a 2A3 or a 45 amp (and you can play 2A3 tubes in the 45 configuration but not the other way around). I've upgraded to Mundorf Silver In Oil coupling and parafeed caps (and Ed has upgraded to another flavor of caps) as well as tube rolled.

The Parafeed circuit is known for deep bass as a rule and it holds with the Stereomour. The cap upgrades made the upper end silky and extended (at least with the Mundorf SIO). The tube rolling has settled down to a couple of modern tubes, but I do have some older RCAs (grey, black, and single plates and several drivers including Telefunken and Mullard). I finally left the JJ Telsa 2A3-40 and Pavane 12AT7-T tubes in and am really pleased.

I'm pretty much content and have no "amp envy" at this time. Just enjoying the beauty of the music...

John

wilsynet · « **Reply #2 on:** 15 Sep 2011, 05:13 am »

I'm waiting to receive a Transcendent Sound Mini Beast. 4 watts into 8 ohms, almost 8 into 16 ohms, and a SE OTL. Supposed to have the best qualities of both SET and OTL.

lonewolfny42 · « **Reply #3 on:** 15 Sep 2011, 05:19 am »

Richard...

Do you have a budget ?

And....how heavy is TOO heavy ?

-Richard- · « **Reply #4 on:** 15 Sep 2011, 07:54 am »

Hi John ~

I am digesting your well-thought out post on the Bottlehead Stereomore 2A3 amp. Thanks so much for sharing so much detailed information, John. I did go to the Bottlehead site and saw that the Stereomore is their latest 2A3 design... this time using one chassis instead of 2 monoblocks... which was their last 2A3 model.

Plate voltages and the size of the power transformer determine which tubes can comfortably be used. My limited understanding is that 2A3 tubes like to see the plate voltages around 300 volts... too high for the 45 tube. The 45 likes to see a plate voltage at around 275 volts... possibly lower would be even better. So at a 275 plate voltage the 2A3 would not be stressed... making the 45 version adaptable for both tubes... perhaps using different rectifier tubes like Don Garber uses on his Fi monoblock 2A3 SET amplifier.

My only concern with the Bottlehead Stereomore 2A3, is the size of the power transformer, which appears quite modest compared to the "traditional" very large power transformers used on many 2A3 circuit designs. Perhaps here is where the Parafeed circuit makes a very big difference, as you suggest, in that it might allow for a greater range of frequency response without needing a huge power transformer. Bottlehead has an impeccable reputation and a very loyal following. It does look like fun to put together ones own amp... and I like that you can feel comfortable trying out different caps. Hawthorne also has an impeccable reputation... I had an early version of their speakers and they were fun to listen to.

Hi Wilsynet ~

What speakers are you using with your soon-to-arrive Transcendent Sound Mini Beast and what is the sensitivity rating? Best of luck to you with your new amp... sounds exciting.

Hi Lonewolf ~

It has been quite awhile sense we last posted with each other. I hope you are well and enjoying autumn.

The Korneff amp was around 40 + pounds as I recall... quite a challenge for me with my less than enthusiastic hips (aging). I need something much lighter and more friendly. Budget... ah yes... an important question. I would like to spend less than $2000... which I know limits me. Less would be even better. $1000 would be wonderful!! So used would be a nice alternative for me.

Thanks everyone for your help. With Warmest Regards ~ Richard

sebrof · « **Reply #5 on:** 15 Sep 2011, 10:48 am »

Check out Tube Audio Labs website. Min in California makes custom amps. I have one of his amps, I assembled it myself but the vast majority of his product he builds himself. My amp is based (loosley) on the Western Electric 91A Radiotron linked below.
His prices are in your range.
I use JJ 2A3-40 tubes and the bass is very good and tight. I haven't heard a lot of 2A3 amps, and none other in my system so I can't compare a whole lot.

Good luck with your search.
http://members.myactv.net/~je205d/6c62a3.htm

wilsynet · « **Reply #6 on:** 15 Sep 2011, 11:15 am »

Speakers are Zu Superfly, 101 db efficient and 16 ohms. Although some folks say it behaves more like 97 or 98 db.

Poultrygeist · « **Reply #7 on:** 15 Sep 2011, 01:54 pm »

Richard,

You have been an inspiration for me and without your many insightful posts I would not have discovered the magic of OB.

I drive my Tang Band 1808 OB's ( over H-frame Alphas ) with 2a3 Bottlehead Paramour mono-blocks. I also have a Dared 2a3c integrated amp which I rotate in this set up. I believe the Tang Bands are around 93 db but both amps have lots of headroom and will drive the TB's louder than anyone would ever need.

These amps work extremely well with my OB's as does my Miniwatt S1. I can't decide which of the 2a3 amps I prefer but I do like the big Shuguang 2a3c's better than RCA gray plates.

FWIW I use no passive crossovers or filters on the Alphas but drive them separately with two Dayton APA150's amps which have built in crossovers.

Regards,
Paul

morganc · « **Reply #8 on:** 15 Sep 2011, 01:58 pm »

I would throw out a recommendation that goes in a different direction.....a Decware amp.....they fit your desire for lightness and the Mini Tori I have fits your budget perfectly. They also sound quite nice. The Tori is the bigger brother and would also provide you with much more bass, but the Mini Tori does tone, timbre, and vocals amazingly well. It is not a 2A3 but it compares favorably to the Melody 2A3 that I had in the past.....and it also gives my much more expensive Coincident Frankenstein 300 a serious run for the money.......especially for vocals, acoustic, folk, etc.......but maybe not quite the headroom for rock, electronica, etc.......

ebag4 · « **Reply #9 on:** 15 Sep 2011, 02:32 pm »

Hi Richard,
I am the "Ed" John refers to in his post. He has it right, I am loving the Bottlehead Stereomour 2a3 (I haven't tried the 45 alignment yet) which I have driving the coaxes of my GR Reseach V1 speakers (97 dB efficient).

What struck me about the Stereomour was it's ability to resolve the full spectrum of music at low volume levels, I have never heard another amp make music at 60dB like this amp does. Regarding your concern about the "heft" of the power transformer, it is my undertanding that the parafeed design is what makes the smaller size of the iron possible, just as you have speculated.

Another quality of this amp is it's ability to recreate the dynamics of the music, my V1s are incredibly dynamic speakers and this amp simply sounds fantastic driving them.

I do have to mention that the Stereomour is only driving my coaxes from 200 Hz and up, and although the bass textures and tone of my system improved greatly (bass harmonics?) when I inserted the 2a3 into my system, the bass is primarily carried by the 4 12" servo drivers and servo amps. I can't explain the improvement in bass response (compared to other amps used for the coaxes), but it was there and quite obvious.

John and Jim Rebman are the two individuals who shared their respective Bottlehead experiences with me and I am very grateful they did. In the past I always felt that amps were the bottlenecks in my systems, I no longer feel that way, the pairing of the Bottlehead and the V1s have great synergy.

John's amp is configured very similar to mine (although I built mine as a power amp and John's is an integrated), we have both shared our experiences with various tubes and capacitors and in the end we found that the same lineup of tubes and coupling caps fit our systems, the one area they differ I believe is in the parafeed caps where John is using Mundorfs and I am using AmpOhms. Of course the similarities far outweigh the differences I am certain.

A little OT, I too have been around long enough to enjoy your posts, specifically in the Dark Star thread. I have always appreciated your input to the community.

Best,
Ed

acresm22 · « **Reply #10 on:** 15 Sep 2011, 02:44 pm »

Richard, you might want to consider a pair of Wright WPA3.5 monos. George Wright passed away several years ago, but these amps show up on Agon from time to time and are very nice. The last several pairs I've seen on the used market have been priced around $850.
I owned a pair about 10 years ago, and they had some of that low end muscle you're looking for due to George's design. As I recall, these are class A amps that move into Class A/B when pushed hard, giving them some extra juice compared to other 2A3 designs.
Rather industrial looking, but very nice 2A3 SET amps.

-Richard- · « **Reply #11 on:** 16 Sep 2011, 07:50 pm »

Your very kind and very helpful responses contain a great deal of important information that will take me time to digest and research with some depth.

Hi John and Ed. Thank you Ed, for you very kind words. It sounds like your Bottlehead Stereomour SET 2A3's are bringing a great deal of magic to your music. I deeply appreciate that have included some important details in how you worked out the circuits to perfectly match your listening pleasure. I once owned a 45 SET that used a small transformer... perhaps wound much like the one used on your Stereomour SET's. It had the most delicate textural and tonal presentation I ever heard. I think there is a great deal of experimentation designers can still explore with SET amplifiers that may shed light on its performance. The early engineers were incredibly good... someone recently told me that the best engineers in the 1930's and 40's either went into aircraft design or audio... so the level of their work was incredibly high.

Hi Sebrof ~ Thank you so much for suggesting Min. I love Min's website... he seems like a very nice person and amazingly knowledgeable. I am trying to contact him to see what his thinking is. His work is impeccable looking. I have heard of JE Labs... but I never came upon his website until I clicked on your hot link... thanks so much for including that in your post. He appears to be a very accomplished musician and his writing is incredibly informative and funny... quite amazing.

Hi Morgonic ~ Decware amps have always been on peoples minds and they have a wonderful reputation... I will look into it... thanks.

Hi Paul ~ Thanks for your very kind words. The Dayton APA150's amps sound like a great idea! That way you do not stress your SET amps by having to work the bottom end. I will look into that... I like not using a crossover... even if it is passive... conductors probably do extract some of the magic from the SET amp and certainly lower the sensitivity of the drivers. When I was researching dedicated SS drivers with built in crossovers, I found they did not cross over above around 150 Hz... or possibly 200 Hz, and at the time I was experimenting with higher crossovers for my set-up. However, I need to take a fresh look at all of this... your suggestions have encouraged me to look again at how I implement the bass driver in my OB's. Thanks.

Hi Acresm22 ~ The reputation of Wright Audio was always right up there with the best. Thanks.

I have a new question for our SET amp community: What differences have you heard/observed between the 2A3 tube and the 45 tube. Yes... I know that this question is fraught with dangers in every direction... it is so subjective and then there is the rest of the equipment to consider... speakers, source/media, and the circuitry of the amp. Still... if anyone in our tube AC community has had some experience between these 2 tubes I would deeply appreciate any feedback/suggestions that might help me to understand their differences (if there are any)... your feedback will help me decide which SET amp I finally purchase.

Thanks in advance for your kindness and help.

With Warmest Regards ~ Richard

sebrof · « **Reply #12 on:** 16 Sep 2011, 08:05 pm »

Quote from: -Richard- on 16 Sep 2011, 07:50 pm

Hi Sebrof ~ Thank you so much for suggesting Min. I love Min's website... he seems like a very nice person and amazingly knowledgeable. I am trying to contact him to see what his thinking is. His work is impeccable looking. I have heard of JM Labs... but I never came upon his website until I clicked on your hot link... thanks so much for including that in your post. He appears to be a very accomplished musician and his writing is incredibly informative and funny... quite amazing.

With Warmest Regards ~ Richard

Here's the link to Min's website. I linked to the schematic he uses in my previous post I think.
http://www.tubeaudiolab.com/

Regarding Decware (morganc mentioned), check out Tone Audio's review:
http://www.tonepublications.com/blog/the-decware-zen-torii-is-simply-amazing/

-Richard- · « **Reply #13 on:** 18 Sep 2011, 04:26 am »

Hi Sebrof ~

Thanks so much for the links... I deeply appreciate it.

I put a call into Min and sent an email. So far no response. I know he has a full-time job with lots of interesting hobbies and a steady production of tube amps, as well as being a family man... so he must be extremely busy.

I am very interested to hear what his thinking is... his suggestions... and of course his prices.

I am wondering if a double 2A3 SET amplifier per channel, with 2 x 2A3 tubes hooked up in parallel might not be exactly what I am looking for. That should yield around 6 or 7 watts per side. I am not certain if doubling up on the 2A3 tube will sound less "fast"... less resolving, compared to just one 2A3 tube per channel (?).

Vu of Deja Vu makes one if I remember correctly, but it is a push-pull circuit... although when I spoke to Vu (a very nice guy) he said that no one could tell the difference between his push-pull 2A3 (or was it a 45?) compared to a SET circuit in blind auditions. I should contact him again to hear what his thinking is.

I want to take my time with this... I am hoping this will be my last amp for the Open Baffle paradigm (wishful thinking encouraged by a shrinking budget).

With Warmest Regards ~ Richard

mytubes211 · « **Reply #14 on:** 18 Sep 2011, 11:29 am »

Hi, if you ever think of buying 811/572 SET amp (perfect match bout words 300/2A3) I'm selling this unique monos

http://www.audiocircle.com/index.php?topic=97757.msg980822#msg980822

But they are very heavy.I guess nothing is perfect in this word. Ritchie

Poultrygeist · « **Reply #15 on:** 18 Sep 2011, 09:16 pm »

Bottlehead 2a3 Paramours driving Tang Band W8-1808 OB's over H frame Alpha bass drivers powered by Dayton monoblocks.

Poultrygeist · « **Reply #16 on:** 18 Sep 2011, 09:20 pm »

canzld · « **Reply #17 on:** 19 Sep 2011, 12:22 am »

Hi Richard

You may want to look at the MP-428 from Musical Paradise here in Canada

http://www.musicalparadise.ca/mp/index.php?main_page=product_info&cPath=6&products_id=69

definitely under your budget - but is on the heavy side. I have one of their smaller amps that I am very happy with. The talk on canadian audio sites about the 428 has been full of praise.

-Richard- · « **Reply #18 on:** 19 Sep 2011, 01:04 pm »

Hi Poultrygeist ~

Cool looking OB's!!!! Your Tang Band drivers with the whizzer and phase plug is similar to the Dayton drivers I am now using. But I love the white paper cones... really elegant. I like the grey and black "outlines"... minimalist in the best sense and very nicely designed.

You have to admit that driving ones (full-range top) speakers with a 3 watt amplifier is the ultimate "cool"... while most of the audio buying public has been convinced that more watts means more music, you and the whole eclectic SET culture know that less = more... more sonic bliss.

With Warmest Regards ~ Richard

Poultrygeist · « **Reply #19 on:** 19 Sep 2011, 01:26 pm »

Richard,

I couldn't agree more.