Synthi 100 (Mk1) Dual High Pass Filter Rack Module

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papz
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Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by papz » Mon Feb 17, 2020 3:14 pm

Hi

We're proud and happy to announce this "new" EMS product.

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This is a new 19” rack module built under license from EMS (Cornwall) by Digitana Electronics (UK/Italy) and PORTABELLABZ (Belgium). It is a 100% faithful reproduction of the Dual High Pass Filter (DHPF) section found on early versions of the legendary EMS Synthi 100 synthesiser. An original spare ‘Mk1’ DHPF PCB from a Synthi 100 was kindly loaned by Robin at EMS and then faithfully reconstructed using the same trace artwork/layouts, via modern PCB design software. The PCBs are very high quality with ENS gold plated card edge contacts and traces. The same components as found in the original circuit are used throughout.

The DHPF rack case was deliberately chosen to be the same design as those found in the classic EMS rack instruments from the 1970s such as the Random Voltage Generator, Pitch to Voltage Converter, Octave Filter Bank etc. These were created in CAD from original engineering drawings kindly made available by Robin at EMS. The 1U high chassis is formed from 3mm silver anodised front/rear panels which are connected by solid aluminium side blocks and then 2mm anodised aluminium top/bottom covers. This allows the rack to be safely mounted in standard 19” rack enclosures. The panel graphics use anodic digital printing technology which is far more resistant to wear than silk screened graphics. Original control knobs/coloured inserts/jack sockets made by Cliff Plastics are also used to meticulously maintain authentic EMS design.

An optional beautiful wood rack sleeve is available with the exact same design as found in vintage units. These are made from Afrormosia hardwood (now on the protected species list) just like the original. The wood is ethically sourced from existing historical stock.

Inside the DHPF, the only change compared to 1970s rack modules has been to use a modern (and safer) switch mode PSU. This also has the advantage of allowing a wider range of operating mains voltages (from 98v–220v AC).

The Synthi 100 was designed by David Cockerell and the high pass filter design itself is rather unusual compared to other high high pass filters found in synthesisers. It has CV control of frequency cutoff but also has a response control which can control feedback of the output, creating a resonant peak that at extremes pushes the filter into self-oscillation. The use of diode ‘strings’ in the CV control section of frequency is quite unusual and is reminiscent of the same principle he used in his (later) Synthi Hi-Fli design, although there the filters sections are used to phase shift the input signal.

The high pass filter is capable of easily removing the fundamental in any audio passed through and then the first harmonic as the cutoff frequency is increased. By increasing also the response, the higher frequencies are boosted in a mix and eventually the filter will self-oscillate.

The two filters in the module are identical and a central three-way toggle switch has positions series, off and parallel.


A single square wave tone fed into 1 of the 2 filters and frequency swept with a repeating ramp CV. Some echo added for fun. Response pot turned slowly to self oscillation. Pushing beyond the point of 1st self oscillation creates large amplitude heavily distorted sound in the High Pass Filter. So you can certainly get sweet or very nasty filtering.


This is a test on audio fed into filter 1 only. CV is a sine wave gradually increased in level to give vibrato effect. Also playing with frequency and response pots ..to demonstrate removal of fundamental and higher harmonics from the mix.


Price is £800 or £1000 in the nice wooden sleeve (no, the sleeve is not available standalone for now) + shipping.

To order, please contact Steve @ Digitana
http://www.synthi.co.uk/synthi-100-mk1- ... ck-module/
http://www.synthi.co.uk/contact/
Last edited by papz on Tue Feb 18, 2020 7:09 am, edited 2 times in total.
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I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Re: Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by Graham Hinton » Mon Feb 17, 2020 7:07 pm

papz wrote:
Mon Feb 17, 2020 3:14 pm
Original control knobs/coloured inserts/jack sockets made by Cliff Plastics are also used to meticulously maintain authentic EMS design.
Synthi 100s had Elma collet knobs.
Inside the DHPF, the only change compared to 1970s rack modules has been to use a modern (and safer) switch mode PSU.
How exactly is that safer?
You do realise that this is illegal to sell in the EU without having a CE mark and the appropriate LVD certification, don't you?
The Synthi 100 was designed by David Cockerell and the high pass filter design itself is rather unusual compared to other high high pass filters found in synthesisers.
It is just the same as the Moog modular high pass filter that it was based on, changing transistors to diodes to avoid infringing the Moog patent--just like the low pass filter.

Is it as noisy as the original?

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Re: Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by tobb » Tue Feb 18, 2020 4:53 am

Graham Hinton wrote:
Mon Feb 17, 2020 7:07 pm
Inside the DHPF, the only change compared to 1970s rack modules has been to use a modern (and safer) switch mode PSU.
How exactly is that safer?
You do realise that this is illegal to sell in the EU without having a CE mark and the appropriate LVD certification, don't you?
I guess less heat producing?

But out of experience with vintage gear (the very few pieces that use one)i found out a switched PSU is less safer when its getting aged.

So my worries buying new gear with switched PSU's is that in 99% of the case a cheap version of the brand switched PSU is used.

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Re: Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by Llouwelyn » Tue Feb 18, 2020 5:24 am

Papz can add more informations about that?

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Re: Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by digitana_electronics » Tue Feb 18, 2020 6:57 am

well as said SMP are more efficient..less ohmic heating. The original rack units had a transformer crammed into a very small space. With top and bottom aluminium covers fitted (as needed for safe use in a rack case if a wood case is not needed ) the spacing between a transformer and the cover is uncomfortably small. The advantage of the SMP is also the wide range of operating input voltages. I am sure we can argue until the cows come home on the point of linear vs SMP.. I don't have the time personally... :hihi:

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Re: Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by papz » Tue Feb 18, 2020 7:04 am

Demos added :tu:
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Re: Synthi 100 (Mk1) Dual High Pass Filter Rack Module

Post by MindMachine » Sat Feb 22, 2020 1:30 am

Graham Hinton wrote:
Mon Feb 17, 2020 7:07 pm
papz wrote:
Mon Feb 17, 2020 3:14 pm
Original control knobs/coloured inserts/jack sockets made by Cliff Plastics are also used to meticulously maintain authentic EMS design.
Synthi 100s had Elma collet knobs.
Inside the DHPF, the only change compared to 1970s rack modules has been to use a modern (and safer) switch mode PSU.
How exactly is that safer?
You do realise that this is illegal to sell in the EU without having a CE mark and the appropriate LVD certification, don't you?
The Synthi 100 was designed by David Cockerell and the high pass filter design itself is rather unusual compared to other high high pass filters found in synthesisers.
It is just the same as the Moog modular high pass filter that it was based on, changing transistors to diodes to avoid infringing the Moog patent--just like the low pass filter.

Is it as noisy as the original?
All good questions for someone in the know.
:guinness:
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