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Prototype AKAI S612 Filter Defeat Board in Action!
Old 3 weeks ago
  #1
Prototype AKAI S612 Filter Defeat Board in Action!



Well I've just built the first pcb up... and it works!!

Designed to go hand in hand with the MIDI Front Panel Animator for the S612 here is a sneak preview of the new Filter Defeat Module (FDM) for the AKAI S612..

This is not as easy as it first might appear to undertake as the filters in the 612 are digitally clocked switched-capacitor type filters and so its not simply a question of modifying the control voltages or a simple switch...

The board takes control of the clocks for the switched capacitor filters in the 612 allowing them to be fixed wide open (in fact considerably wider open than simply turning up the filter control to max) with no tracking for maximum crunch in the lower registers, or overclocked thus giving a brighter than normal tracking characteristic or locked to the last positiion with no tracking thus allowing for very warm sounds or fixed formants across the full transposition range. Each of the 4 modes are cycled between using a push button fitted in place of the Sample Trigger socket.

In the test recording you can first hear the normal tracking characteristic where the 612 becomes very muffled in the lower registers... then the filter is defeated to wide open allowing you to hear the 612 in all its crunchy 12-bit glory... in the last part of the recording you can hear the filter locked to a very warm setting...


Last edited by EF86; 3 weeks ago at 08:16 AM..
Old 3 weeks ago
  #2
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Obviously I must have this
Old 3 weeks ago
  #3
Quote:
Originally Posted by Sir Ruff View Post
Obviously I must have this
I have to say I've really been taken by how nice the 612 sounds with its filters bypassed / brightened - to my ears it sounds really cool playing percussion and all manner of other sound sources really slow in full crunchy/punchy 12-bit slo-fi
Old 3 weeks ago
  #4
Here for the gear
 

Does it run through the same filter circuit for the 6x outputs (that go to the AX60, etc.)?
Old 3 weeks ago
  #5
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Color me interested
Old 3 weeks ago
  #6
Quote:
Originally Posted by DJFonzi View Post
Does it run through the same filter circuit for the 6x outputs (that go to the AX60, etc.)?
It will indeed make the 6 channel output on the 13 pin connector go super bright/crunchy so this does open some interesting options to AX60/VX90 owners.

Last edited by EF86; 3 weeks ago at 10:10 PM..
Old 3 weeks ago
  #7
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Quote:
Originally Posted by EF86 View Post
It will indeed make the 6 channel output on the 13 pin connector go super bright/crunchy so this does open some interesting options to AX60/VX90 owners.
Projected cost/date/difficulty level to install? Do you still sell the other mod?
Old 3 weeks ago
  #8
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acreil's Avatar
 

Quote:
Originally Posted by EF86 View Post
I have to say I've really been taken by how nice the 612 sounds with its filters bypassed / brightened - to my ears it sounds really cool playing percussion and all manner of other sound sources really slow in full crunchy/punchy 12-bit slo-fi
True of the Casio SK series too. My favorite mod is bypassing or disabling filters on cheap digital gear.

Also, I hope you're not plugging header pins into DIP sockets. That's just asking for trouble.
Old 3 weeks ago
  #9
Quote:
Originally Posted by acreil View Post
True of the Casio SK series too. My favorite mod is bypassing or disabling filters on cheap digital gear.

Also, I hope you're not plugging header pins into DIP sockets. That's just asking for trouble.
No.. other than the ROM socket - there are no DIP sockets on the 612's mainboard so unfortunately, like the FPA module, it has to come out, two chips desoldered and proper mating SIL headers fitted in their place.

If you're good with PTH rework - and especially if you have a heated solder pump its a little time consuming but not difficult to undertake. Like the FPA module, once in place, its a very neat installation.
Old 3 weeks ago
  #10
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rids's Avatar
 

I'm totally in for this. I'll be looking for the details that follow.
Old 3 weeks ago
  #11
Quote:
Originally Posted by kslight View Post
Projected cost/date/difficulty level to install? Do you still sell the other mod?
Don't panic - the FPA Modules are still proving very popular and they are still very much available to everyone who is interested.

The process to install the Filter Defeat module is very similar to the FPA in that the motherboard needs to be removed, some PTH chip desoldering and mating SIL headers fitted in their place.

Since the mainboard needs to be removed, from a labour point of view, it makes sense to install both modules at the same time.

Cost of the new module will be very similar to the FPA both as a self install kit or including fitment.

I have had a few ask me if it might be possible to leave the front panel untouched ie. not fit the Mode Switch in place of the sample trigger socket and select filter mode over midi - this was actually taken into account in the design but would require an FPA module to be fitted and a firmware upgrade for the FPA along with two wires installed between headers on the two modules. This might be a bit tricky to manage for existing FPA owners with self-installed modules - I'd need to think about that. If there is enough interest then I will make it available as an option.

The FDM module also has an output to drive an external LED indicating the filter mode - this can be wired to a new LED or drive a less used existing LED - in my case I'm driving the MONO/POLY LED which is a very simple mod.

The 612 FDM Modes are:

1. Normal stock filter operation [No LED]
2. Bright Filters (with tracking but brighter than stock filter) [LED short flash]
3. Filters Wide Open (maximum crunch!) [LED on solidly]
4. Current Filter Cutoff level locked (with no tracking) [LED long flash]

Last edited by EF86; 3 weeks ago at 08:17 AM..
Old 3 weeks ago
  #12
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acreil's Avatar
 

Quote:
Originally Posted by EF86 View Post
No.. other than the ROM socket - there are no DIP sockets on the 612's mainboard so unfortunately, like the FPA module, it has to come out, two chips desoldered and proper mating SIL headers fitted in their place.
That's actually good. Headers are fine. DIP sockets might seem like a good idea since it's hypothetically easy to revert the mods, but the header pins ruin the sockets and make the connections unreliable. You probably know that already, but a lot of daughterboard modifications end up working really badly because they use DIP sockets.

Quote:
Originally Posted by EF86 View Post
2. Bright Filters (with tracking but brighter than stock filter) [LED short flash]
How are you doing that? I couldn't think of an easy way to do it.
Old 3 weeks ago
  #13
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You're saying that other mods install DIP sockets in place of the original chips (or use DIP sockets that were already present), then mate daughterboards to the main board by press-fitting straight headers into the DIP sockets on the main board? That does sound like a bad idea.
Old 3 weeks ago
  #14
Quote:
Originally Posted by krylenko View Post
You're saying that other mods install DIP sockets in place of the original chips (or use DIP sockets that were already present), then mate daughterboards to the main board by press-fitting straight headers into the DIP sockets on the main board? That does sound like a bad idea.
Yes, many a computer and synth retrofit has worked this way including countless memory/processor upgrades for the home computers and the infamous II+ upgrade for the DK Synergy which is a lovely thing... when it works!

The main problem is that the mating pins are all too often way too large for the existing IC socket thus straining them and this is made 100 times worse as the plug and socket pins tarnish with age, or worse, corrode with age due to incompatible plating methods.
Old 3 weeks ago
  #15
>> 2. Bright Filters (with tracking but brighter than stock filter) [LED short flash]

> How are you doing that? I couldn't think of an easy way to do it.

The 612 Filter Defeat Module runs at 8MHz and features two 82C54s triple timer chips which can run twice as fast as the original 82C53s on the 612's mainboard that run at 4MHz. On careful reading up about the the Nat Semi MF6 series switched capacitor filter ICs it transpires that, although they are usually only clocked up to 250KHz, they are good for at least 1MHz and in this case are being clocked up to 500KHz thus permitting the filters to be opened considerably wider than in the stock 612s.

By clocking at twice the normal rate you still get a tracking filter effect but considerably less muffled. This is how Bright Mode works.

After some experimentation with the prototype, having both a Wide Open Mode and Bright Mode is proving useful as I've found some sounds actually sound more punchy with the tracking enabled in Bright Mode than in the Wide Open Mode.

The later sounds particularly cool playing sounds sampled in max sample rate transposed right down and percussion or anything with a short subtle embedded reverb tail can sound awesome this way.

Last edited by EF86; 3 weeks ago at 08:17 AM..
Old 3 weeks ago
  #16
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Quote:
Originally Posted by EF86 View Post
Yes, many a computer and synth retrofit has worked this way including countless memory/processor upgrades for the home computers and the infamous II+ upgrade for the DK Synergy which is a lovely thing... when it works!

The main problem is that the mating pins are all too often way too large for the existing IC socket thus straining them and this is made 100 times worse as the plug and socket pins tarnish with age, or worse, corrode with age due to incompatible plating methods.
Yeah, that’s what I would expect as well, I just didn’t realize it was so common. It’s the kind of terrible idea that sounds ok at first thought and is much easier than the alternative. Easy to see why it got chosen.

Maybe that’s why so many of the early synth retrofits/expanders are notoriously flaky?
Old 3 weeks ago
  #17
The prototype has been running nicely for a couple of days now - it won't be that long before I start to install the first few modules in friendly owner's machines for some in-field testing prior to making the modules available to all...

Incidentally - whilst one of my 612s has been open on the bench I have been experimenting with supply voltage on the Variac vs heat production and there is absolutely no question that running a Japanese spec 100V S612 at 120V produces very considerably more heat and pushes the main bulk capacitors right to the limit of what they are designed to handle. The heatsinks on the 5, 15 and -15V regulators are way too hot to touch at 120Volt operation so, once again, I reiterate my concerns that any owners of 100V Japanese spec units (and that makes up a surprisingly high percentage of the total population outside of Japan) who are currently running them at 120V should seriously consider running their units on a 100V autotransformer designed for Japanese equipment.
Old 3 weeks ago
  #18
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madtheory's Avatar
Quote:
Originally Posted by acreil View Post
True of the Casio SK series too. My favorite mod is bypassing or disabling filters on cheap digital gear.
I tried that with my SK-5 and it revealed a ton of hiss, and also data bus noise. Could be that it's missing some of the big foil screen over the PCB, but that doesn't explain the hiss.

I like how it sounds anyway
Old 3 weeks ago
  #19
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acreil's Avatar
 

Quote:
Originally Posted by madtheory View Post
I tried that with my SK-5 and it revealed a ton of hiss, and also data bus noise. Could be that it's missing some of the big foil screen over the PCB, but that doesn't explain the hiss.

I like how it sounds anyway
I didn't get any hiss or noise with mine (both an SK-1 and SK-8). But I just removed some capacitors. If you go adding wires, it needs to be done very carefully to avoid interference.
Old 3 weeks ago
  #20
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Quote:
Originally Posted by acreil View Post
I didn't get any hiss or noise with mine (both an SK-1 and SK-8). But I just removed some capacitors. If you go adding wires, it needs to be done very carefully to avoid interference.
Ya I tapped out the signal before the filter, using unscreened wire lol you're probably right.
Old 3 weeks ago
  #21
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Quote:
Originally Posted by madtheory View Post
Ya I tapped out the signal before the filter, using unscreened wire lol you're probably right.
Yeah, you definitely want to use shielded wire, and be very careful about what you're connecting to. It's better to take outputs from a low impedance source, and connect inputs to a summing node rather than a high impedance buffer. It's hard to mod these things without adding noise, which is a large part of why a lot of circuit bent stuff ends up being useless.
Old 2 weeks ago
  #22
I am hoping to setup a page on my website for both the 612 FDM and FPA modules with more details, indicative pricing and demos in the near future.

In the meantime, if anyone wants to be an early adoptor of the 612 Filter Defeat Module please PM me - especially if either you are able to install your own module (requires PTH desoldering skills/equipment) or are based in the UK (for shipment).

As I did with the first FPA Modules, early adoptors will be entitled to free firmware updates (if required) and support.

Furthermore, anyone who is also interested in an FPA Module please PM me as installing both modules together will require less overall bench time.
Old 1 week ago
  #23


The first four S612 Filter Defeat Modules are now built and working nicely ready for early adoptors to try out...
Old 3 days ago
  #24
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Gotek USB emulates Quick Disk now!
http://torlus.com/floppy/forum/viewt...Jx7hGUFALA1Y-U
Old 3 days ago
  #25
Quote:
Originally Posted by madtheory View Post
Yup.. JF emailed me yesterday about this wonderful news.

I will be having a go shoehorning a Gotek drive into one of my MD-280 drive units very soon!

I have just updated the 612 Filter Defeat Module demo to include a few more crunchy loops

Old 3 days ago
  #26
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Quote:
Originally Posted by EF86 View Post
Yup.. JF emailed me yesterday about this wonderful news.

I will be having a go shoehorning a Gotek drive into one of my MD-280 drive units very soon!

I have just updated the 612 Filter Defeat Module demo to include a few more crunchy loops

Beautiful... loving the Pacific homage (strings at end sound great too).
Old 3 days ago
  #27
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Damn, I really need to find another S-612. They’re awesome stock but with these boards and the Gotek emulation news I’m drooling again...

Nice work EF86!
Old 3 days ago
  #28
Quote:
Originally Posted by krylenko View Post
Damn, I really need to find another S-612. They’re awesome stock but with these boards and the Gotek emulation news I’m drooling again...

Nice work EF86!
Many thanks.. don't forget the 612 MIDI Front Panel Animator too...

Prototype AKAI S612 MIDI Front Panel Animator!!
Old 3 days ago
  #29
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Oh I didn't forget -- that's what I meant by "boards," the FPA and filter defeat mods together!
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