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I design and build my own equipment but I also repair and restore vintage solid state and valve studio gear such mic preamps, EQ compressers, limiters, spring reverbs etc. I usually take them as modules, repair them and put them in 19" rack enclosures. The repair of these units can be complicated because they are also very small and I do change all of the electrolytic capacitors (a common fault is dry capacitors). I sometimes design and custom build power supplies for these modules. Power supplies for the solid state modules are mostly 24V DC plus 48V DC phantom power, and they are pretty much straightforward.
For the valve modules the power supply design is a bit more complicated because they usually work on 300V DC and they operate a lot quieter if the heater voltages are rectified and DC voltage regulated.
A recent example involved Telefunken V672 pre amps, configured for mic and/or line use. These are the customers comments :
"Thick, creamy and extended with accentuated mids and smooth high end. Unbeatable on electric guitar, drums, and rock vocals. Just add an SM57 for a world-class signal path. Options such as output gain boost (and extra 6db of clean gain by using both output transformers), variable input impedance, phantom power, stepped switching, phase, pad, and custom options. Neumann V472-2 (stereo pre amps), similar to the V672, but more 'hifi' and open in the top-end. An undiscovered gem - options are as for the V672"
I recently started repairing and restoring passive EQ modules (from the US) such as the 9 Langevin EQ-251

ALL Valve Stereo Spring Reverb & Distortion Unit/Amplifier

spring reberb


A very different sound from digital reverb, valve-driven spring reverb is one of the trademarks of the dub reggae sound, giving a very organic, 'springy' sound; still unattainable with software plug-ins or digital processing.

This unit has a selectable triode/pentode driver, able to drive all types of springs. This driver can also be used as a 'valve conditioner' to liven-up drum loops or drum machines before being processed by digital recording equipment. For more information take a look at the detailed user guide READ ME


Spring Reverb Driver/Parametric Equalizer

Alternative use: distortion unit, or low power valve amp for guitars etc.

A pre amp with a switchable gain and an output level control. The inputs are unbalanced i.e. jacks and XLRs. So it can accept balanced outputs but in unbalanced mode. If necessary it can be modified to accept fully balanced signals.

Two equalizers in parallel: A three way active low mid high EQ + a variable shift (parametric) EQ.

The two EQs are mixed and then through a master drive control are applied to a mini power valve amp; this drives the reverb tank or a load if it’s to be used as a distortion unit or a small speaker if it’s to be used as a instrument amplifier. This single ended output amplifier can be switched into three modes of operation: triode, ultra-linear, pentode. Each mode contributes a different flavor to the sound.

A phono output socket for the reverb tank send.
A jack socket output for a load or a speaker
An output impedance selector switch so able to connect different tanks/loads/speakers.
A phono socket for the reverb tank return, that produces a line level signal for mixers/amps etc.  
A return level control
Choice between: An unbalanced jack output and a fully balanced XLR output

Extra unique facility: if it is built in stereo an extra switch is provided so as one channel can drive the other i.e one reverberated signal can drive a second. Read detailed guide....READ ME
Also Mono Modular EQU Reverb Driver READ ME

A.A.E Distortion BOX 

distort box

• Switchable Triode and Cascode input stage. Cascode stage produces more harmonics, resulting in a more complex distortion sound.

• Switchable 'load' - this changes the amount of resistance in the output stage. At a high setting, subtle distortion is possible. At low settings, very harsh metallic distortion is possible.

• Also available is the 'naughty' setting with no load - this produces a very lively, punchy sound which seems to emphasize peaks in the signal.  

AAE Modular System - Equalizers Distortion Unit & Pre amp

(Includes sends/returns facility and reverb driver)

The distortion unit is a mini-amplifier, producing about 1 watt of output. It can therefore be used to drive a spring reverb.

Although there are many valve pre amps available on the market which can give a gentle overdriven sound when pushed hard, the sound is often mushy and indistinct. This is because the input stage is only half the story… An output stage is required for a really powerful distortion sound; this is what produces the distortion in valve guitar amplifiers.
mod system
mod system
From gentle warmth and fatness, to searing, grinding distortion. Switchable between pentode and triode output stages. Pentode offers a gritty, dry, distorted tone; whereas triode gives a smoother, more 'musical' effect, going from a clean to a large overdriven sound.

Active or Passive Equalizers

Analogue graphic or parametric filters of various types can be built.

In terms of sound, the most harmonically-interesting valve circuit designed is a high-Q variable shift frequency booster, between 40-400 Hz (for bass boost effects). The frequency and amount of boost can be adjusted.

Midrange and treble boosters can also be built, to cover the full frequency range. Sweeping the frequency point with high boost results in a sweet, wah-like effect, with a distinct warm and musical sound.

Another newly-designed-and-built circuit is a variable cut-off frequency high-pass filter, which drives a variable cut-off frequency low-pass filter. These two filters (both of the 2nd order type) can also be connected in parallel. The high-pass is a little sharper than the low-pass. There are many possible sound effects with this circuit.

EQU specifications..READ ME



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