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Interstage Mono Block PSE 300B / SE 300B SET Power Amplifier
Mono Block Single-Ended Triode Hi-Fi Power Amplifiers with interstage coupling transformers

“ It is becoming increasingly obvious that applying transformers at every stage of an amplifier yields a great benefit in sound quality, provided of course that the transformer in question is of an appropriate quality and design. Replacing any coupling capacitors with a well designed and correctly matched driver or interstage transformer yields an almost shocking improvement in sound and should be tried to fully understand what a good wideband transformer has to offer. 

Peter Qvortrup

Introducing our new Interstage MonoBlocks!

Welcome to the web page for the ANK Audiokits Interstage MonoBlock Power Amplifiers.

These amplifiers are our highest and most extreme expression of Single Ended Amplification reserved only for the true connoisseur/audiophile.

Recent enhancements to the blocks have taken them to a totally new level. We have a new version Mains transformer - the T-195 dedicated to the new Legend & Interstage MonoBlocks for both parallel and single Triode configurations. We have enhanced the Choke to the new CH-170 for 300ma capacity. The Interstage transformer is bifilar wound and sits on a very large Core for maximum bass response!

Along with all this, our latest version of the Interstage MonoBlocks includes a stunning new set of solid copper Insert Plates and black Teflon valve bases now standard with both our single and parallel configurations! A newly enhanced power supply completes the Interstage MonoBlocks.

These amplifiers are simply our highest and most outrageous expression of single ended amplification!

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:

Copper Insert Plates and Teflon Valve Bases Now Standard


The latest version of the Interstage MonoBlocks now ship with the new copper insert plates for both single and parallel 300B configurations!

Along with that, we have standardized on the new high quality black teflon valve bases for both 4 and 8 pin. The sockets are the same phyical size and are keyed so that tubes can only be inserted the correct way!

The Audio Note traditional venting pattern is used. The plates are coated in a high gloss clear coating so they are protected from scratches and will never change color!


A stunning addition to these phenomenal amplifiers!


Circuit Description

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 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 can support 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 picture shows the internal wiring of the parallel version - Click to see hi-rez

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.

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!
We provide easy to follow, step-by-step wiring instructions with the manual.

Check out the detailed wiring Guide for the 300B PSE version of the Interstage MonoBlock by clicking on the wiring image on the right.


Click to view

Standard Configurations and Pricing

NOTE: Prices are for a pair of Interstage Mono Blocks (a Right and a Left Chassis)

InterStage Mono Block Parallel 300B $4,500(USD)

20W of pure single ended 300B power. We have configured the MonoBlocks as a top of the line version with Audio Note 2W tants, Mundorf Mlytic Power Supply caps and ELna Cerafine Electrolytics.

3mm black powder coated strong aluminum chassis
Audio Note 2W tantalum resistors for signal path
(1W & 1/2W for other positions)
Mundorf's Best Myltic Power Supply Caps
ELNA Cerafine signal Electrolytics
Shuguang 300B tubes
Audio Note speaker posts & RCA's
Ceramic hard-wiring posts
IE core transformers - custom designed by Andy Grove
PTFE silver plated stranded copper wire
5U4GB EH rectifier

Interstage MonoBlock Single 300B $4,350(USD)

Same as above configuration but delivering 8.5W

C-Core Transformer Upgrade $2,500(USD)

The C-Core Transformer Upgrade includes:
One pair of Audio Note Hi-B C-core transformers

More Pictures

Click on an image below to zoom-in or cycle through the images using the arrow buttons below.

What customers are saying about the Interstage Mono Blocks

Hi Brian,

Completed both the mono blocks, and oh boy, just them playing into some cheap speakers and using the volume off the cd player, it already sounds amazing. Just think what it will sound like when I have them with the rest of the gear playing………………..can’t wait………………..

Just magic……………


I recently had the privilege of listening to a pair of the AudioNoteKits Interstage Mono Block Single SET at a friends house. I was completely blown away from what I heard. The Interstage Monos exhibited an incredible control over the music, and yet retained a delicacy to the nuances that make music, music!

Everything came from a pitch black back round and from the first notes I was drawn INTO the sound stage. This was the most emotionally involving evening I have ever had spinning tunes. Familiar songs sounded new again, old discs that I had written off as bad, were brought back to life.

Chris Rodgers

I'm listening to the 300B monoblocks as I write this.... and I have to say (as a frequent listener to live music) that the resolving power of these amps is unbelievable. Music that I know well was previously a caucophony.... now I hear every detail and it's all perfectly placed.... who would have thought?

So... where from here.... the Ongaku?


I recently replaced my Kit1 with a pair of Interstage monoblocks and am really impressed with the results. I built the parallel version which of course has more power than the Kit1.

I found the monoblocks in a whole different league than the kit1, a weightier presentation of the music and greater dynamics. Bass presentation is more precise and there's just more to the music. I lack the vocabulary to describe it fully so I'll never make a reviewer but I just find I'm more emotionally drawn into the music, probably due to a more lifelike sound-stage and more flowing presentation of the music.

Rick Ford

"My Audio Note Parallel 300B monos have done only 100 Hours against 500 Hours. But I can tell you that I observed a big difference between my EL34 based - 50 Watts Six Packs and AN Monos. The sound is much more open in the MID and High Band. Surprisingly, they produce astonshing Bass which may be due to Insterstage design and Double C Core Output TX. There is NO hum - even within 4 inches from the woofer after connecting with Multiwave Option in PS Audio's Premier Power Plant. Output level can be compared with 50 Watts Push-Pull Six Pacs amplifier. I am curious to know, how will it sound when it completes 500 hours of Break-In"

Abbhijit Dey

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-Rowe - 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

"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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