Why the Plexsound Psychonote has no master volume control?

Guitar amplifiers were originally designed in accordance with typical audio amplifier diagrams (often hi-fi amplifier type as provided by tube manufacturers). Their designers would never imagine anyone who’d want to distort their sound. That’s why preamplifiers used to offer relatively low amplification. Guitarists discovered and fell in love with overdrive. Over time, overdrive has become the most recognizable sound of the electric guitar. But to obtain deep distortion, you needed to turn the volume control to max, which was quite comfortable from a practical point of view. So guitarists asked for an amplifier that would provide a lot of distortion even at low volume levels, and designers fulfilled this request introducing the ‘master volume’ control. It should also be noted that amplifiers got more and more powerful (the first guitar amps offered up to a dozen or so watts of power) and turning the volume knob of a 50-100W amp to max in a small room could be downright painful. Amp designs with the ‘master volume’ control provide distortion at the very beginning of the audio signal path, but controlling is generally restricted to the volume only. Unfortunately, the resulting distortion has a completely different character than the distortion in vintage amplifiers. In vintage designs the signal is only slightly distorted when it reaches the power stage, where it gets fully shaped. The resulting distortion at the power stage is affected by several factors – the mutual influence of the power tubes and the speaker being among the most important ones. On the one hand, the speaker converts electric signals to an acoustic wave, while on the other hand it is a generator of electric current (the speaker coil moving in the magnetic field of the magnet induces an electric current), which returns to the power tubes through the speaker, affecting their operation. This phenomenon becomes more and more intensive with the growing power supplied to the speaker. Speaker distortion is yet another element of vintage-type distortion and it occurs when the speaker is not able to reproduce a high power distorted signal (due to technological limitations vintage speakers had much lower maximum capacity than today’s speakers).

Designing the Plexsound Psychonote we aimed to build a vintage-style amp.

Can you replace a tube rectifier with a semiconductor rectifier?

Absolutely not. The type of rectifier significantly affects the sound of the amplifier. Changing the rectifier to a semiconductor system would also exceed acceptable output tube voltages leading to their rapid destruction.

Why the Plexsound is not upholstered with Tolex?

It is true that most of the amplifiers are finished in this way. The Psychonote Plexsound cabinet is made from selected, seasoned sycamore wood. Each Plexsound Psychonote is finished with an individual touch. It would be a waste to cover such precious material with artificial veneer.

Can I use other tubes than those pre-installed?

Yes, you can use other tubes provided that they are of the same type and you adjust the quiescent current (bias). However tubes from another manufacturer will change the sound of the amplifier. Electron tubes are complicated mechanical, electrical and chemical devices. Same type tubes from various manufacturers may differ in significant parameters for the sound of an amplifier. We do not recommend the use of tubes other than those that have been pre-installed (please refer to the Certificate for more information about the tubes in your amp).

Does the Plexsound support universal power supply (115/230V)?

Yes, the Plexsound Psychonote can operate both when connected to the European (230V) and the US (115V) power grid. We configure the power supply voltage depending on the needs of the customer. The Plexsound Psychonote features a voltage selector switch. The user can select the type of electric power supply to connect the amplifier. Selection of incorrect voltage (e.g. 115V on a 230V network) will cause damage the amplifier and this type of damage is not covered under warranty.

Why the Plexsound does not feature an automatic switch-on delay of the anode voltage?

We wanted to keep the electronic system of the amplifier as simple as possible, i.e. free of any unnecessary elements. Not because of the costs, but to preserve “vintage spirit.” Of course, it is important for the durability of the tubes to provide a high anode voltage when the tubes are hot, so we used a mechanical Play (standby) switch. In the Plexsound, the rectifier is built on an electron tube which makes the anode voltage grow relatively slowly (as opposed to when the rectifier is based on semiconductor diodes), so even if we forget to put the Play switch in the correct position, the risk of damaging the tubes is much smaller.

Can I buy the Plexsound Psychonote as a DIY kit?

Unfortunately, not. The Plexsound Psychonote is only sold as a finished product. We take full responsibility for the quality of our device. Each piece is tested against the technical specifications and sound quality. Each Plexsound Psychonote is signed and accompanied by a certificate outlining the history of its construction and measured technical parameters.


Is the Plexsound Psychonote is a copy of some cult amplifier design?

No, the Plexsound Psychonote is neither a copy nor a replica of any factory amplifier design. Naturally, as the Plexsound Psychonote is built in line with the classic tube amp design, you can spot similarities to many amplifiers offered today or in the past. We believe that you cannot build a true copy of a 1950s-60s amplifier due to unavailability of original components from those times (tubes, transformers, capacitors, speakers).