Minute MM Phono Stage Pre-amplifier

Design Concept

The only phono pre-amplifier with pure Class-A all vacuum tube design with zero negative feedback circuit that allows user to customize gain and experience variety of tonal characteristic simply by just changing the vacuum tube (tube rolling). Famous 12AU7, 12AY7, 12AT7 and 12AX7 are all compatible and will produce different gain/character which greatly enhance flexibility and enrich musical experience in any analog turn table system.

Adjustable Gain

Nowadays we enter resurrected era of analog playback, turn table, system because it offers unsurpassed musical expression although the difficulty in operation/set up, the cost of maintenance and the cost of associated equipment are higher than digital media. But it comes with its own price. Unlike current digital media industry where standard output level of source component has been realized by equipment manufacturers, the phono cartridge manufactures produce their own specification with so many different cartridge's output level and impedance that confusing and complicating the matter of selection to match cartridge and phono stage to the end user. Some clever phono stage designs offer solution by adding adjustable gain to their phono pre-amplifier, but not realize that typical gain adjusting circuit work against the fidelity that user strive for. Popular methods to adjust gain in circuit are
1) adjust negative feedback level. The higher dB in negative feedback, the lower the gain. This works like a dream, a nightmare dream. Not only it changes the gain, but it also change the output impedance, frequency response, harmonic distortion, phase shift etc, but because it only requires a few resistors (or trimmer pot) to implement, the cost saving is abundance, thus utilize in many phono stages nowadays.
2) attenuate the signal path of the circuit. This strategy is "Lazy Man" solution that works very much like first method but instead of intruding NFB circuit, it just like adding potentiometer to signal path. Dumping signal away from the next stage and add unwanted impedance into the signal path. Increasing signal impedance means increase noise, reduce bandwidth, reduce current drive.
The new Minute Phono Stage offers variation in circuit gain to cope variety of cartridge different signal output level by using the purest gain control of all, that is the gain of different type of tube. Each tube design can result in different signal gain by the pitch of control grid wire, the dimension & distance & shape of internal construction etc, and this is the true intrinsic property of each type of tube. By using the gain of tube there is no need to add extra component (attenuator) or NFB to control the overall gain of the circuit maintaining the simplicity and allow user to hear the inner details of each tube that usually lost by other design.

12AX7 + 12AU7 combination in Minute Phono Stage provides +40dB of gain suitable for high output MM cartridge with +4mV output.. This can be called "Standard MM gain phono stage" that usually requires user to connect to another line pre-amplifier (with +10dB to +20dB gain) before feeding the signal to power amplifier. 12AU7 are famous for its linear/ well balance sound. Popular NOS or old production are still easily accessible.


12AX7 + 12AY7/6072A combination in Minute Phono Stage provides +47dB of gain suitable for most MM cartridges. This is our standard combination. Suitable cartridge output is from 2.5mV to 4mV. This set works great with our MC-step up transformer. With additional +7dB gain from 12AU7, this combination can be used with passive pre-amplifier or with simple integrated amplifier with passive pre-amp. 12AY7 has very warm and smooth character.


12AX7 + 12AT7 combination in Minute Phono Stage provides +51dB of gain suitable for low output MM cartridges, or couple with our MC-step up transformer to low output MC cartridge. It can also work directly with some MC high output cartridges of +1mV. 12AT7 are famous for fast dynamic sound with punchy bass.

12AX7 + 12AX7 combination in Minute Phono Stage provides +56dB of gain suitable for ultra-low output MM cartridges. It also works directly with some MC high output cartridges of +1mV. 12AX7/ECC83 Telefunken are one of the most famous tube that is hard to find these days. We use current production Sovtek 12AX7LPS that offers great sounding quality/reliability and value.
Zero Negative Feedback topology
Minute Phono Stage uses simple one way feed through circuit arrangement to preserve simplicity in design. By not aiming to lower the distortion with negative feedback we instead design the tube circuit to work into pure class-A and let this linear spot bring out the best no manipulating sound. The harmonic distortion is less than 0.1% at 4mV input (about the highest singal from normal MM cartridges) and distortion figure will reduce nicely in linear proportion to the input signal level.
Although it costs much cheaper to outsource power transformer making to other supplier, we only use our own transformer design & production that we create for each individual circuit arrangement to meet the goal of high performance, low noise and high reliability.
Internal construction of the new Minute Phono Stage is very simple, elegant and carefully laid out for symmetrical signal between left and right channel. Each component is high audio grade like Kiwame carbon film resistors and at some point Dale precision resistor as well as all capacitors that are matched for improving RIAA accuracy. The internal design has minimize the use of wiring cable, but where it needs to be, we use highest quality silver plated/teflon wire.

The complete illustration of the new Minute Phono Stage's own frequency response characteristic range from 20Hz to 20,000Hz. Reference to RIAA standard the maximum error is less than +/-0.5dB (typical +/- 0.1dB). The new Minute Phono Stage achieves this astonishing accuracy without the use of any negative feedback. Only the well design / implementation and pure class A circuit that we use.
This figure shows response of 100Hz with respect to the reference marker at 1KHz. The response is +13.079dB (RIAA standard is +13.088dB) which correspond to only -0.009dB error)
This figure shows response of 10KHz with respect to the reference marker at 1KHz. The response is -13.93dB (RIAA standard is -13.734dB) which correspond to only +0.196dB error)
We design the new Minute Phono Stage with proprietary pure class-A circuit to allow the tubes and its circuit component to work into their most linear part of their transfer characteristic, consequently generating very low harmonic distortion without the need to use any kind of negative feedback. This figure derives from 1KHz sine wave input at 4mV level(which is typical from MM cartridge). The harmonic distortion level produced by Minute Phono Stage is only 0.09%. Therefore during normal music playback when cartridge generates less output signal, the harmonic distortion will be even lower. Due to the fact that there is no negative feedback, harmonic distortion almost directly relates to the signal level in this pre-amplifier.
We publish all these test results documented during our design R&D of the circuit and component selection to demonstrate the FACT of our product. The aspect of our listening test or feeling that we spent together with technical details are hard to capture into pictures and would be meaningless to put them here.

We use waterfall plot to fine tune our design to eliminate any abnormal noise (from FM/AM radio interference) that happen randomly through long period of time. Random spikes, if exist, will be observed evidently in waterfall plot.



Frequency Response according to RIAA standard
+/- 0.5dB from 20Hz to 20KHz
Total Harmonic Distortion with 4mV input signal
less than 0.1%
S/N ratio (SINAD 20mV input, 400Hz & 30KHz filter on)
Input Impedance
47K ohm
Output Impedance
600 ohm
+40dB to +56dB adjust by changing output tube (standard +47dB from 12AX7 + 12AY7)
Circuit arrangement
All vacuum tube 2 x 12AX7 (input), 2 x 12AY7 (output)
RIAA network
R/C zero negative feedback type
Bias Operation
Pure Class-A
Maximum input level
20mV from 20Hz to 20KHz

Introductory Price of $695USD (standard 12AX7 + 12AY7) + Shipping.

* Extra tested/matched set of other combination tube available at additional cost.
*New Minute Phono
(Dimension 19 x 26 x 10.5cm (W x D x H) weight 3.5kg (4.0kg packed)
* All specification are subject to change without prior notice.