Twin OTL


Acoustat OTL amplifier tube upgrade

For the Acoustat Servocharge amplifier, which comes with the models Monitor X,III,IV, and can be also used with the models 1+1, 2+2, 2200, 6600, and with the hybrid systems Spectra with an extra woofer amplifier, we designed an upgrade which replaces the aggressive sounding Op-Amp and driver transistors by an all-tube preamp/equalizer.

The original design came form Curcio, which also published an OTL design for ESL-headphones in Glass-Audio nr 0.

In the basic design we found too many irregularities. We changed many component values in the equalizer and feedback section. To avoid unstable operation and drift we added per power tube a regulator for the quiescent current and got rid of the total DC coupled design.


We ended up with a stable amplifier with a well known tube sound: soft and silky.
In the pictures you will notice the extra thick piggy-back board with the tubes and stabilized power section.
The upgrade of your working Servocharge Amp will be done in our workshop.
As soon as we have received and tested your standard amps, we will send you an upgraded set, which is in stock.

Upgrade Price: € 2000,- per set excl. P&P

Delivery Time:  2 weeks if in stock after receiving your payment and 4-6 weeks if we ran out of stock!!

Modu cabinet OTL Twinstatic Audio

Mono OTL direct drive amplifier for ESL loudspeakers

Spin-off from the Acoustat upgrade is a complete new mono direct drive amp, based upon the Acoustat Servo-charge Amp + upgrade. The amplifier is build in a 19” inch rack with handles.

The special low capacitance cable to your ESL-speaker panels will be delivered in 2 mtr. standard length.

The amps will be tuned on your speakers: Final, Acoustat, Martin Logan, QUAD, Stax, Soundlab, Audiostatic, Innersound.
Recently we hooked the amplifiers up to a set of Quad 2905.
The delay line will be still in use, but due to the omission of the audio transformers the bass response improved a lot.

Max. signal level: 4600 Volt peak to peak

Input sensitivity: 0,2 Volt RMS at clipping point

Bias voltage: upon request 2kV-5 kV max.

Recent upgrades: XLR & Cinch input, modern enclosure, new designed pc board, all new components.
permanent bias voltage during switch-off optional (300 €/set extra)
Price per set  € 4500,- incl. VAT excl. P&P Delivery time: 12-16 weeks if we ran out of stock.