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Interstage Mono Block 300B/2A3 SET Power Amplifier
Mono Block Single-Ended Triode Hi-Fi Power Amplifiers
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Peter Qvortrup
Interstage Mono Blocks pictured with our L3 Line Pre-Amplifier and L3 Phono Stage
We are pleased to announce the new Mono Block kits available from AudioNote Kits. A lot of thought, planning, and careful design has gone into this product and we think it provides a wonderful opportunity for a kit builder, or extreme audiophile, to have the best in Mono Block Technology.
The features are numerous:
- Power Amplifier design with 2V input sensitivity (an ideal match for L3 Line Pre-Amplifier).
- Can be configured for 300B, 2A3, Parallel 300B, or Parallel 2A3.
- Removable front and rear plates for configuration of triodes and power supply capacitors.
- Power supply and triode/input tube are all hard-wired.
- Input stage using 6SH7 followed by Audio Note designed Interstage Transformer.
- Supports the standard Kit1 output transformer AND the Trans-300 Double C-core output transformer.
- The interstage transformer available as an IE core but upgradeable to C-core.
- 25" in length and 8.5" width.
- Using mains transformer and choke configuration from Kit1.
- Large Black Gate/Jensen Power Supply caps can be used or standard electrolytics for power supply.
- No film caps used in the design.
- No AN-cable required as we hardwire from input RCA to tube valve base via resistor.
- High quality mechanical design using all metric hardware.
- Using high quality WE 8 pin valve bases and the AN 300B valve base.
- Upgrade path available from kit1 to mono Block.
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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 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 power supply uses the CHOKE-165 (also used in the Ongaku) along with the H301067 mains transformer designed for both 2A3 and 300B use. I wanted the amplifier to be able to supply both a single triode as well as a parallel. Cleverly, we are using a 5Y3 tube rectifier for single triode operation and a 5U4G for parallel - both tubes using the same power supply circuit!
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 Mono Block for both 8 pin and 4 pin. We are also using Audio Note Hardwire Tag Strips.
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Here we see the configuration for parallel operation where two output valves are used instead of one.
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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.
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 mono blocks of the extreme quality while not spending all your money at once!
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Parallel vs Single Triode
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We have here the two different configurations of front insert plates - single triode and parallel triode.
In single triode mode for 300B - each channel of the mono block has 8Watts of Single Ended Power. In parallel 300B mode the output is double that or 16Watts. If you are using a 2A3 tube as a single triode the mono block channel will provide 3.5 Watts of power. In parallel 2A3 mode the mono bock will provide about 7 Watts. If you were to build a 300B single triode and you wanted to go up to parallel triode 300B you would need to request a front insert plate, along with a new Output transformer for parallel triode operation.
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How does it sound?
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The Mono Block was designed in the UK by Andy Grove after listening to the requirements of the many audiophiles who have wanted a Mono Block product. He suggested that using an interstage transformer (as used in the highest level AN finished products) was the ideal solution. An IE core interstage transformer was built specifically for the product.
The constraints that I put on Andy were that I wanted to support both 2A3 and 300B which was easily done as he had designed the new Mains transformer and filament section that we have been using recently in the Kit1 2a3/300B.
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We built the first prototype in the UK last fall and then I built two prototypes in Canada for testing over the winter - the results were very impressive! When the prototype chassis arrived and the first pair was put to the test I have to admit I was blown away by the results. Coupled with an M3 line pre-amplifier, the level of sound quality astonished me - almost like the first time I listened to SET.
If you are interested in one of the ten available mono blocks and helping us with the initial launch let us know via email audionotekits@rogers.com and we can discuss your ideal configuration.
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Up close
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The point-to-point hardwiring is made easy by concise, easy to follow wiring diagrams.
Below are examples of the front plate and power supply wiring.
We are making available a fast download / low resolution copy of the instruction manual so you can see for yourself the quality and detail of the build instructions. You will, of course, recieve a high resolution printed manual of the latest version with your kit. A CD containing all high resolution manual pictures is also supplied with each kit.
Click here to view the manual.
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Testing the Mono Blocks
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With each Mono Block kit pair comes a Testing Kit where we provide:
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1. A dummy 8 ohm load
2. Test CD
3. grounded RCA input cable
Upon building the Mono Block you will go through a series of wiring checks outlined the manual - then you will follow the turn on procedure. If all is well you will do some key voltage checks and finally an audio signal amplification test with dummy load and a hum test (the kit is extremely quiet).
Once all those tests are complete, you will be all set to plug into your speakers and listen to music!
If there are any hiccups along the way we are here to support you all the way to your successful build!
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Standard Configurations and Pricing
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NOTE: Prices are for a pair of Mono Blocks (a Right and a Left Chassis)
InterStage Mono Block - IE Core - Single Triode (specify 2A3 or 300B)
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Level A - $2,899 USD - Our entry level Mono Block kit allows you to build this unique amplifier at a cost effective price with the allowance for easily installed future upgrades. The kit will use 1W Beyschlag Resistors, Good quality Electrolytics, Jensen PS caps, PTFE silver plated copper wire, Western Electric and Ceramic Valve Bases, AN Hardwiring Tags.
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InterStage Mono Block - Double C-Core - Single Triode (specify 2A3 or 300B)
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Level C Signature - $5,549 USD - We assume that if you are ordering the TRANS-300 double C-core output transformers for the mono blocks then you will want all the component upgrades - this kit will include 2W tants throughout the driver and power supply sections - Black Gates on the filament circuits and tube cathodes.
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InterStage Mono Block - Double C-Core - Parallel Triode (specify 2A3 or 300B)
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Level C Signature - $5,799 USD - We assume that if you are ordering the parallel triode TRANS-305 double C-core output transformers for the mono blocks then you will want all the component upgrades - this kit will include 2W tants throughout the driver and power supply sections - Black Gates on the filament circuits and tube cathodes.
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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.
"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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