Interstage Monoblock Power Amplifier Pair


Reference quality, single ended 300B power amps (pair), using an interstage transformer.

SKU: 300B-INT-MONO Categories: , , ,


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 wide band transformer has to offer.

Peter Qvortrup: Audio Note UK
The Interstage MonoBlock amplifier pair are the finest expression of 300B SET either in parallel or single configuration ( 8w and 15w) The magic of these monoblocks is the fact that a 1:1 interstage transformer acts as the driver for the 300b(s) rather than capacitor coupling – the insane control of the mid range is immediately noticeable along with the over all authority of the amps – If you are already a 300B fan then the interstages will take you to the next level of audiophile nirvana!

The ANK Interstage Monoblock amplifier is our highest and most extreme expression of Single Ended Amplification reserved only for the true connoisseur audiophile. The interstage transformer design style is currently used on Audio Note’s top of the line On Gaku 211 amplifiers.

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! These amplifiers provides a level or realism and detail that you may not have experienced.



The interstage Mono blocks come in 6 flavours – First you can choose between Parallel Single ended yielding 18W and uses 2 x 300B tubes for each monoblock and the other option is Single Triode so one 300B per block yielding 8.5Watts

Once you have made that choice then you go for the Top of the line range which uses both C core for the output transformer and the Interstage transformer – thats Level 3 . Level 2 would use the CCore output transformer and an EI core intertage ( rated at over 1000v) and the Level 1 would be both the EI core interstage and EI core output transformer – so these three options allow for 3 different budget levels! approx 4500, 5500 and 6500 $ versions!


Recent enhancements to the blocks have taken them to a totally new level. We have a new Mains transformer – the T-195 dedicated to the Legend & Interstage Monoblocks. We have also enhanced the Choke to a new CH-170 for 300ma capacity. The interstage transformer is bifilar wound and sits on a very large Core for maximum bass response.

The mechanical design of the unit is second to none using all stainless steel metric hardware; countersunk screws and removable copper insert plates for a truly fun build experience. Power supply and driver circuitry is all hardwired and uses the latest Mundorf Mlytic 4-pole capacitor technology.

Copper Insert Plates

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 physical size and are keyed so that the tubes can only be inserted the correct way.
The Audio Note traditional venting pattern is used.


  • 50 cm deep x 24.5 cm wide for compact locations
  • Increased lower case height to 6.3 cm
  • Ultra sturdy 3mm aluminium chassis powder coated black with solid copper insert plate
  • Parallel or Single Triode models available
  • Professional wiring guide provided
  • High rated Mains Transformer (300Ma )
  • Large 1:1 Interstage Transformer for superb bass response
  • 5U4GB rectifier tube, 6SH7 driver tube
  • New Power Supply with Mundorf 4 pole M-Lytic technology

The Circuit

The new Interstage Monoblock 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 readily available and not overly expensive. It comes in a glass tube version or with a black metal case. NOS tubes are available in the $5 USD range and upwards. This tube feeds an interstage transformer designed specially by Audio Note for use in the interstage Mono Block Kit. The interstage transformer drives the Triode 300B in single ended mode. The Triode then drives the output transformer.

The input sensitivity is around 2V which is ideal for a power amplifier and ideal when mating with our high quality Pre-amplification.

Building your Interstages in easy to follow steps

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

Using an interstage transformer dramatically reduces wiring complexity and they are easy to build.

The InterStage Mono Blocks have been designed so you could start off with the IE core version and then later upgrade to double C-Core.

Check out the Interstage Wiring Manual



The Interstage MonoBlocks are sold as pairs, and come in either the single 300B 8.5W version, or the parallel 300B PSE 18w version.

We also have upgraded transformer versions where you can select the C-Core output upgrade or the ALL C-Core version
where the Output and the Interstage transformer are both upgraded to C-Core!


Power 18 Watts Class A (Parallel)
Output Tubes 2 x 300B or 4 x 300B
1st Stage Gain 6SH7
Rectifier Tube 5U4GB
Front Insert Plate Solid Copper
Inputs 1
Outputs 1 x Stereo Pair 4, 8, 16 ohms
Recommended Speakers min 88dB
Width 24.5cm
Height 20.5cm
Depth 50cm
Weight 48kg
Chassis 3mm Aluminum with Black Powder Coat

Parts Compliment includes:

  • AudioNote Tantalum Resistors 1W & 2W
  • Mundorf’s Best Myltic Power Supply Caps
  • PTFE Silver Plated Hookup Wire
  • Elna Cerafine Signal Electrolytics
  • Shuguang 300B Tubes
  • Audio Note Speaker Posts & RCAs
  • Ceramic Hard-wiring Posts
  • PTFE Silver Plated Stranded 5U4GB EH Rectifier
  • Solid Copper Insert Plate

A great pic of a complete kit layed out by a customer!