© 2013 Benden Sound Technology

Made by Serif

Background

A regular client was unfortunate enough to have his newly-acquired Crumar Performer destroyed by the parcel carrier bringing it to him. One of the few parts left unscathed was the triple-BBD chorus/ensemble unit, and he asked whether this could be transformed into a standalone effects unit.

Technology

The Performer ensemble is virtually identical to that used by some versions of the Solina string machine. The schematic can be found on Juergen Haible's website, surrounded by his own fantastic achievements, including a modern clone of the Solina chorus.

Three identical small PCBs each carry a TCA350Z 185-stage BBD, its associated clock driver circuit and anti-aliasing filters. A further, larger PCB contains the modulation generator. The first BBD is modulated with the sum of two LFOs running at different frequencies; this signal is then phase-shifted for the second BBD and again for the third.

Apart from the TCA350Zs, there are no other ICs present - everything else is built with discrete transistors. Supply voltage is +/-24V, and for anyone thinking of performing a similar exercise, beware the current drain! It's easy to assume that higher-voltage circuitry draws correspondingly less current, but all the class-A discrete circuitry on these boards demands nearly 200mA from the positive rail and 75mA from the negative.

Construction

I mounted the four Crumar PCBs into an all-aluminium 1U rackmount case from Holt Broadcast Services (www.holtbs.com). A conventional linear-regulated mains power supply was added along with input and output buffers (+/-10dB gain trim on the input) and a relay-based true bypass circuit.

Of more interest is the way in which the three BBD outputs were combined. I decided to make several optons available:

1. Roland-style (stereo)

Here, a stereo output is generated by summing the outputs of BBDs 1 and 2 for the left channel and BBDs 2 and 3 for the right output.

2. Solina-style

The Solina sums all three BBD outputs, equally-weighted, to form a monophonic output.

3. Performer-style

Inspection of the mildly confusing schematic shows that, although the Performer also sums all three BBD outputs, they are not equally weighted. Rather, they are cascaded through a series of passive mixers with the last signal added carrying more weight than the first.

These three outputs were each generated, buffered and made available simultaneously on separate jacks.

Sound

I auditioned the ensemble using a humble Roland Juno-6 (with internal chorus switched off). All the output options thickened the DCO sound in a delightfully "vintage" way, but the big surprise was the difference between the two mono outputs. The equally-weighted Solina-style output was brash and, for want of a better term, instantly "cheesy". However, the unequally-weighted Performer-style output was rich yet more subtle; the description which came to mind was "classy". Had I to choose just one output, it would unhesitatingly be the Performer-style.

Front view of the Crumar ensemble.
The two switches are for power and hard bypass.

Rear view of the Crumar ensemble showing individual jack outputs for the three different ensemble modes.

Top view of the Crumar ensemble. The three small PCBs carry the BBDs and the larger board is the modulation circuit.

Overall view of the Crumar ensemble.