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Interstage Mono Block 300B/2A3 SET Power Amplifier
Mono Block Single-Ended Triode Hi-Fi Power Amplifiers with interstage coupling transformers
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Peter Qvortrup
The Interstage Mono Blocks 2010 Version are back with an entirely new look and mechanical design!!!! We successfully launched the product back in 2007 with options for single and parallel triode in the same kit - we received quite a bit of great feedback from customers. Since then we have upgraded the Mains and Interstage transformers and been enhancing many of the mechanical aspects - the result being a a fantastic new compact look and amazing sound!! - Expert wiring guides and a brand new manual will ensure first time success like a true DIY pro! We supply Hi-res digital jpg files of all the manual pics with your kit so that you can zoom in on extreme detail of the build.
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Click here to check out the build manual. |
We have made several dimensional changes to the blocks based on customer feedback - They can now sit in a rack or shelf that is only 12 in deep - the rack friendly chassis also allows for very short wiring lengths.
The new version Manual (possibly our finest to date) guides you with expert wiring & layout diagrams along with extended final unit testing to assure even a first time builder a superbly working unit!
Here are some of the features of the new version MonoBlocks:
- 19.5" x 9.3" new length x width for compact locations
- increased height slightly to 2.5" total for DIY extra's
- Rock solid 3mm aluminum chassis with stainless steel insert plate
- Original insert plates fit into current monoblock
- Parallel or Single Triode Models available
- Professional wiring guide lines provided
- Higher Rated Mains Transformer (300Ma )
- Larger Core 1:1 Interstage Transformer for superb bass response
- 5AR4 rectifier tube , 6SH7 driver tube
- New 3 capacitor Power Supply
- New Manual - which you can check out by ckicking here
Here we see a parallel triode Mono Block on the left from above. On the right we see it from below.
The main power supply components are kept at the rear to isolate them from the rest of the circuitry. As you can see, signal path wiring is kept as short as possible as you would expect.
Using an interstage transformer dramitically reduces wiring complexity.
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An attractive combination with our L2 or L3 pre-amplifier (above left).
With regards to the base plate, we provide you with 6 feet – and also a number of different hole sets on the bottom. This makes it possible to arrange the feet in the best configuration to suit you - whether you are going to use it on a rack, shelf, or floor.
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Circuit Description
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The new Interstage Mono Block Kit is comprised of a 6SH7 input tube - this was selected by Andy Grove for a number of technical reasons related to input impedance and input sensitivity of the power amplifier in mating with the L3 Line.
The 6SH7 is fairly readily available and not overly expensive (yet). It comes in both a glass tube version and with a black metal case on it. NOS tubes are available in the $5 USD range and up. The 6SH7 then feeds an interstage transformer designed specially by Audio Note for use in the Interstage Mono Block Kit. We currently have IE cores available to ship with the kit but I also have a double C-core version of this transformer being prototyped (The Interstage transformer design style is currently used on Audio Note's top of the line On Gaku 211 amplifiers). Back to the circuit - The Interstage transformer drives the Triode 300B or 2A3 in single ended mode. The Triode then drives the output transformer - either the kit1 transformer TRANS-152 or the Double C-Core TRANS-300.
The input sensitivity is around 2V which is ideal for a power amplifier and ideal when mating with Audio Note's M3 Line pre-amplifiers.
We are using the top of the line Valve Bases in the Interstage Mono Block for both 8 pin and 4 pin. We are also using Audio Note Hardwire Tag Strips.
The unique design style makes use of an interstage transformer on each channel - rather than having an additional tube driver stage, the interstage transformer takes over this task for ultimate authority! The power supply and driver circuitry is all hardwired and the user has a choice of components. The power supply supports large black gate or Jensen Electrolytics that protrude through the chassis. The mechanical design of the unit is second to none using all stainless steel metric hardeware; countersunk screws and removable plates make for a truly fun build experience! Then there is the sound - In combination with an AudioNote M3 transformer coupled pre-amp the Interstage Mono Block provides a level or realism and detail that you may not have ever experienced.
This composite picture shows the internal wiring of the parallel version - Click to see hi-rez
The InterStage Mono Blocks have been designed so that you could start off with an IE core version and basic components or upgrade from a kit1 and then upgrade to double C cores or higher end power supply capacitors and other parts over time - the idea being that over time you could build up a pair of Interstage Mono Blocks of the extreme quality while not spending all your money at once!
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Standard Configurations and Pricing
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NOTE: Prices are for a pair of Interstage Mono Blocks (a Right and a Left Chassis)
| 2010 InterStage Mono Block Parallel 300B | $3,800(USD) |
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| 2010 Interstage MonoBlock Single 300B | $3,550(USD) |
| Signature Upgrade Kit | (Enquire about pricing) |
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Audio Note 2W Tantalum Resistors |
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Black Gate or Elna Cerafine Capacitors |
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Jenson Power Supply Capacitors |
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More Pictures
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Click on an image below to zoom-in or cycle through the images using the arrow buttons below.
First impressions are that they are just absolutely out of this world. The detail is incredible especially when combined with the DAC.
They look stunning with those black transformer covers and at night the tubes have a nice blue glow. The bass extends well into the low frequency range and the trebles are crystal clear.
There is nothing better out there in my opinion that even comes close to the quality of your kit. It is truly magnificent.
Vincent Gore - Parallel 300B Mono Blocks
"I must say the monoblocks are authoritative-they control the mid/bass drivers well. I can feel the bass but it is never bloated, just about right for me. At the moment the mid to lower registers shine. I hear quite a bit more details from my CDs, and the imaging is rock-solid.
Guess these are early days yet. But if things are so good now, I can't imagine what it would be like when the amps are run in. So I'll reserve full assessment until then."
Michael Cheong - single triode C-core 300B Mono Blocks
"I have to say that the M3/mono-block combination is really quite something. I am currently running them in, so I will reserve full judgement (and a write-up) for a couple of weeks... that said, there is certainly quite a difference from the Kit One. The sound is fuller, and more defined - especially when there is more going on.
I am also very pleased with my decision to get the parallel 300b's. The benefits of the extra power is very noticable. The M3-mono-block combination seems now perfectly matched with my Ariels. It's real something to hear..."
Mark Leece, USA - Parallel 300B Mono Blocks
..."But then you listen and the sound - WOW the improvement was unbelievable"...
..."The mono's control of the speakers is absolutely fantastic right through the range"...
..."The improvement in sound quality was a shock (yes jaw dropping)- I had never heard anything like this before."...
| Paul Clark UK - Single Triode 300B with IE-core output transformers |
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"I will also like to say a big thanks to Peter, Andy & Co !! for coming up with these products as I would like to call "musical time-machines" (it takes me on fantastic musical journeys to extraordinary musical happenings through the times of recorded music), and also Brian at Audio Note Kits and Upgrade Audio here in Norway !!"
Rune Saevik - Parallel 300B Mono Block owner
"First, I must tell you, that we are very happy with the Interstage-Monoblocks! The sound from both types are absolutely fantastic! Even a very deep Bass.incredible! It is a very good instruction manual.
Thank you very much for the finest Audio Kits."
From 2 customers who bought a 2A3 monoblock and 300B monoblock
..."They sail through transitions and the music sails as well. The whole presentation isn’t subdued, it’s exciting! But where there used to be a limit, the bar has been raised much higher. I can listen to The Who at near deafening levels and not want to lower it just because “I Can’t Explain” is about to open up with an onslaught of electric guitars."...
| Doug Lindley |
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| Interstage Mono Block Related Links | |||||||
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