Introduction
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Audio Note Kits are pleased to announce the new InterStage Monobloc Power Amplifier Kits. The Monoblocs have been designed by Andy Grove and are matched perfectly to work with the K3 or K2 Audio Note Pre-amplifier kits. Various options and upgrades are available.
This amazing kit boasts a number of design features that provide the ultimate solution for all tastes of Triode amp lovers:
- Firstly it can use the 300B or the 2A3 triode valve in the output stage, without changing transformers, (just a 10 minute wiring procedure). These output valves can be configured in either single-ended(SE) mode, pushing out 8 watts(300B) or 3.5 watts(2A3) or parallel single-ended (PSE) mode, providing 16 watts(2x300B) or 7 watts(2x2A3). As you can see from pic.6 &9, the chassis has a opening at the front of the chassis, this is where the stainless steel front insert plate is fitted, hole punched either for SE mode or PSE. You tell us what you need upon ordering and we will send the correct plate.
- "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
To the delight of the interstage lover this kit uses an IE interstage the C-core version is being prototyped and will be available soon.
- One of the most essential components of any valve amp is its output transformer, for the monobloc you have two options. The Single-Ended version can be purchased with either the standard IE type of the upgrade double C-core type, these are the same type as used in the Kit1 and the Kit1 PQ Edition respectively. For the Parallel Single-Ended version only the double C-cores are available.
- The other valve complement: Cleverly, the 5Y3 valve is the rectifier for single ended operation and a 5U4G for parallel single ended - both tubes using the same power supply circuit! The input valve is the 6SH7, 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 M3 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. The 6SH7 feeds the interstage transformer perfectly.
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External view of the Interstage Monobloc 300B/2A3 SET Power Amplifier in SE Configuration (pic.8)
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Other design features of the Interstage Monobloc 300B/2A3 SET Power Amplifier
- Power Amplifier design with 2V input sensitivity (an ideal match for M3 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.
- 635mm(25") in length and 216mm(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 monobloc.
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Parallel vs Single Triode
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pic.9 - Front view of Audio Note Interstage Monobloc 300B/2A3 showing the differing front insert plates, left chassis is wearing the Single Ended front inset plate and the right the parallel single ended plate.(pic.9)
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You will see from the diagrams below that the signal circuits are similar, all that has changed is the addition of another output triode in parallel in the output part of the parallel single-ended version, thus is the versatility of this amazing kit.
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pic.10  Signal circuit of the Interstage Monobloc 300B/2A3 Single-ended configuration
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pic11 Signal circuit of the Interstage Monobloc 300B/2A3 Parallel Single-ended configuration
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Down to the design:
The new Monobloc Kit uses a 6SH7 input valve feeding the interstage transformer rather than having an additional valve driver stage - (The Interstage transformer design style is currently used on Audio Note's top of the line On Gaku 211 amplifiers) The transformer the drives the Triode 300B or 2A3 in single ended mode. The Triode then drives the output transformer - either the TRANS-152(IE version) or the TRANS-300 (double C-core). Alternatively if you go for the Parallel single ended it drives the TRANS-305 (double C-core). All output transformer have 4 and 8 ohm secondary windings.
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 valve rectifier for single triode operation and a 5U4G for parallel - both valves 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.
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pic.10 Wiring diagram of the signal section of the Interstage Monobloc 300B/2A3 Single-ended configuration kit
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pic11 Wiring diagram of the psu section of the Interstage Monobloc 300B/2A3 Single-ended configuration kit
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Available Options and Prices
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InterStage Monobloc - IE Core - Single-Ended Version
- Level A:Our entry level Monobloc kit allows you to build this unique amplifier at a cost effective price with the allowance for easily installing future upgrades. The kit will use 1W Beyschlag Resistors, Good quality Electrolytics, Jensen power supply caps, PTFE silver plated copper wire, Western Electric and Ceramic Valve Bases, AN Hardwiring Tags. The interstage and output transformers are IE types. Please specify 300B or 2A3 tubes.
Price (a pair) - £1500.00 + vat + carriage
InterStage Monobloc - IE Core - Single Ended Version
- Level B:As Level A and including 1W tantalum resistors on the driver circuit and power supply sections. We also provide Black Gates on the cathodes of the 6SH7 and 300B. Please specify 300B or 2A3 tubes.
Price (a pair) - £1605.00 + vat + carriage
InterStage Monobloc - IE Core - Single Ended Version
- Level C Signature:As Level A and including 2W tantalum resisitors on the driver circuit and power supply sections. We also provide Black Gates on the filament circuitry and valve cathodes and provide an optional power supply plate to max out the Power supply capacitors.
Please specify 300B or 2A3 tubes.
Price (a pair) - £1765.00 + vat + carriage
InterStage Monobloc - Double C-Core - Single Ended Version
- Level C Signature:As Level C Signature and including the amaizing Audio Note TRANS-300 double C-core output transformer.
Please specify 300B or 2A3 tubes.
Price (a pair) - £2875.00 + vat + carriage
InterStage Monobloc - IE Core - Parallel Single Ended Version
- Level A:Our entry level parallel 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.
Price (a pair) - £1765.00 + vat + carriage
InterStage Monobloc - IE Core - Parallel Single Ended Version
- Level B:Level B version upgrades components to 1W tantalum resistors on the driver tube and power supply sections. We also provide Black Gates on the cathodes of the 6SH7 and 300B.
Price (a pair) - £1865.00 + vat + carriage
InterStage Monobloc - IE Core - Parallel Single Ended Version
- Level C Signature: This version upgrades the resistors to 2W tants on the power supply and tube driver sections.We also provide Black Gates on the filament circuitry and tube cathodes and provide an optional power supply plate to max out the Power supply capacitors
Price (a pair) - £2020.00 + vat + carriage
InterStage Monobloc - Double C Core - Parallel Single Ended Version
- Level C Signature:Includes the Audio Note TRANS-305 double C-core output transformers for the monoblocs, including 2W tantalums throughout the driver and power supply sections - Black Gates on the filament circuits and tube cathodes.
Please specify 300B or 2A3 tubes.
Price (a pair) - £3000.00 + vat + carriage
SPECIAL OFFER: 10% off all upgrade components used on your Audio Note kit purchased through us. See the www.hificollective.co.uk shop. To take advantage of this discount orders must be called through on 01908 217202.
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Related links
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Low resolution/fast download Monobloc Build Manual
General upgrade information
The Audio Note Transformer Design Philosophy
Why Does Audio Note Choose Double C-Cores Rather Than I-E Core?
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