CM-50 mono module.
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CM-50 is a mono module for people who want to assemble their own top-of-the-line hifi ampifier.

One important reason for the easy-to-listen-to sound of a well designed tube amplifier is the kind of stabilization used, frequency feedback. The input stage has a feedback loop that limits its ampification at high frequencies. So, when the amplifier at very high frequencies reaches a high degree of phase shift (which would cause oscillation) the total amplification is below one, preventing oscillation from taking place. This feature makes tube amplifiers free from TIM (Transient InterModulation distortion), the most common reason why you tend to turn down the volume of your amplifier after a while – Even if it sounds good, you get irritated after a while and want to lower the sound level or simply turn it off.
If you have a ”normal” amplifier you probably recognize the symptoms.
If you have a tube amplifier you probably don´t have this problem.
However, the tube amplifier has drawbacks: Tubes degrade rather quickly, so the sound quality will degrade, too. Also, almost all tube amplifiers need output transformers to drive modern low impedance loudspeakers, and transformers produce harmonic distortion. Still, the frequency feedback makes the sound more enjoyable than that from normal solid state amplifiers using transistors or / and integrated circuits.

For some reason, almost all solid state amplifier achieve stability through slew rate limitation instead of frequency feedback.
The good thing (for the producer) is that this is easy when mass-producing amplifiers.
The bad (really bad!) thing is that you risk TIM (Transient InterModulation distortion).
When a sharp pulse reaches the maximum slew rate of any part of the amplifier, all other sounds dies momentarily.
As the pulse is over the other sounds are back again.
Your brain will compensate for these short bursts of silence, so you can´t really hear this distortion.
But constantly having to compensate for lost information, your brain gets tired.
After half an hour (or even less) you start feeling a bit uncomfortable, and want to turn the volume down, even if it is your favourite music. Do you recognize this? Then your amplifier probably suffers from TIM – transient intermodulation distorsion. And so do most transistor and IC amplifiers.

This is where CM-50 differs from other transistor amplifiers:

The design is similar to tube amplifiers, but using solid state devices. The resulting sound quality is exceptional. The cleanness and fine detail of reproduction far exceeds normal commercial amplifiers. There is only one balanced input stage, followed by a single voltage amplification stage and then a current amplification using very fast MOS transistors.
There is no capacitor limiting the slew rate. Only frequency feedback in the first stage is used to acheive stability.
This way the CM-130 combines the TIM-free sound of a tube amplifier with the long-time stability of transistors.
So, you get the easy-to-listen to and detailed sound of the tube amplifier, combined with the stable long time performance of a solid state amplifier in one product.

Except for the CM-50 modules you need a case, a power supply (se below), cables, input and output sockets, maybe volume controls et.c. and you should also have some basic knowledge in electronics as well as experience in soldering.
If you don´t fully understand the information on this webpage, this product is not for you.

The output power is about 50W at 8 Ohm load. The recommended power supply consits of a 24 V or 2 x 24 V transformer + four 6A diodes + two 10000 uF/40V electrolytic capacitors, and two quick 2A fuses for short circuit protection.

You will need some experience from electronics assembly. You must know how to solder (cables, fuse holders et.c.) and it is also important to take action against static discharge, as static discharge directly into the MOS components may result in irrepariable damage.

The case should be made of metal, and the coolers screwed onto/into the case to prevent static discharge from getting into the modules via the coolers.
If you want a wooden case, cover the inside with metal and make sure that all metal parts are connected to each others and to the point between the electrolytic capacitors where the three yellow cables from each CM-50 are connected. We don´t take any responsibility for damage due to static discharge or incorrect connection.

If you feel unsure about the security issues for a built-in power supply, don´t put the transformer inside the case. It is then much safer to use an external transformer, delivering 24V or 2 x 24 V to the case in which the power modules are built-in.

Click here for more info about power supply, connection and volume control.

The CM-50 is exactly the same power amplifier that is used in our high-end stereo power amplifier, CM-130.

The module is protected against overload by normal fuses (2 A quick).

We do not recommend lower load impedance than 8 Ohms at +/- 32 V or higher. If 4 Ohm speakers are used, the power supply should deliver +/- 20V and the fuses be changed to 2.4 A (quick). The power will then be about 40W at 4 Ohm load.

Cooling: CM-50´s maximum power dissipation is about 30W at 50W output power (sine wave, 8 Ohm load).
Maximum recommended operating temperature is 70° C, so if the module is outputting a continous sine wave at full power (unrealistic) a cooling of 1.3 °C / W or better would be needed at 25°C room temperature. However, when playing music, 2.5°C / W is quite sufficient per module, even at full peak power.

We recommend that the input is equipped with a volume control, a normal potentiometer 10k or 22k log is suitable.

The size of the module is about 65 x 75 x 30 mm (2.4 x 3 x 1.2 inches). It consists of a PCB and aluminium L-profile. Mounting holes are 40 mm (about 1.6'') apart. Wire connections are about 12'' long.
Connection instructions are included.

Price: 82 Euro each plus shipping costs

Shipping cost within EU is 12 Euro for two CM-50 modules. Do NOT pay until we have confirmed your order, we don´t always have the CM-50´s in stock.