69. Not Helios/Phaeton. Pics/schematics/building support thread.

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Well-known member
Jul 17, 2006
Hi to all!

Finally, I got time to move with this EQ project.

Inspired by Helios. It is not a clone (to avoid debates :)

It started here:


Let me introduce cynically called 69-EQ.


This can be excellent project for beginners, very simple assembly,
simple electronics, output part of BA-283 used for makeup stage.
(This is IMHO best makeup amp for Helios inspired passive EQ circuit sound-wise).
From the other side, all controlls are stepped...
This way EQ can be used for mastering as well, if precision high quality comp's used.

Inductors: Carenhills layout done exactly by .pdf on their webside. Not tested yet.
(If someone want to get free pair of EQ pcb's, he/she can test them with
the Carenhills and post the results).

I can offer inductors which are wound locally and tested. Soundwise, very, very nice
(all you know, I hate "punchy crispy big" sound talks, better to hear once).

The passive EQ itselves can be used with virtually any dual stage pre-amp,
like 1072 clones, DC servo'ed Jenssen's circuit (like on JLM website), etc.
Just insert it in between first and second stage, and use more gain on second stage.

There's no need of expensive ELMA switch. Solution with the use of cheap Lorlin
is worked out. (BTW, Lorlins are cheap but very reliable).

There are two output options on makeup card, choke or 1166-like transformer.
It is possible to use 2:1 input transformer, stay unbalanced
at the input (I don't like this idea) or use kinda THAT line receiver,
"breadboard" holes reserved at the "input transformer" part of
make-up PCB.

People who like an idea, write here if you want the kits will appear on my WM tread,
more people-less price.

I think experienced person can finnish this EQ within a day, and beginner within
a week....


EQ is tested, PCB layout polished, final version of inductors wound and
whole thing was listened. I have to put all things inside the rack,
and here you can see some preliminary photos, schematic, EQ pcb stuffing.




Links to updated front panel layout, schem/pcb:


Inductors comes with the dot at one side:


Installing the inductors on PCB:


Make-up boards:

Output half of BA-283, place for input transformer reserved:

Hel*os inspired amplifier:

BOM's, etc-here:


For panels, you can ask Dan or Purusha, or make your own
(Fell free to ask for Corel file if you ordered the kit/pcb).

Some notes.
I got hum at -67 dbV induced by quiet toroidal transformer from right channel
(closer to power supply) when low boost was at the maximum (+16db) at 60Hz freq.
Nothing unexpected (huge 10H inductor picks up the hum).
I aded mu-metal shield to toroid, and hum gone to -78dbV (total noise of channel).
However, I'd recommend external 24V power supply or place power transformer far as possible from inductors (in this case, when operated from lab power supply, total noise of channel was about -86 dbV
when all controls are at max.)
Of course, this is UNWEIGHTED level, which gives not so bad S/N.

IMHO, input transformer's best ratio is 2:1, all equivalents to LO31267 will work,
anyway, you can try other transformers.

Sound-wise: I hate punchy-crispy shit talks. For me, it sounded simply great.
We did some tests at friend's studio, I liked this EQ very much on drums and distorted guitars.
Very good EQ for BD, snare, drum bus before compressor,
bass, even can go good on vocals.
I saw video where folk screwed all controls of EQ up...fun, but at 2-3 db boost/cut
this eq  worked best for me. Again, this is my taste.
This is not full BA-283, only the output part.

I think to make 69 modular as possible.
I.e. EQ PCB's, makeup boards, bypass boards will be offered separately.
This way you can use makeup boards with your Pultecs, and EQ pcb's with
preamp's...or use your make-up boards, the limit is the fantazy.
I can offer limited qty (like 20-30) of EQ kits by very low price,
it will be cheaper than buy everything from different suppliers and pay shipping.
Interested in estimated pricing for complete EQ kits and just boards with inductors.  Thanks Igor!  Project looks great!
hey igor! looks great :)

i'd be down for 2 channels of the EQ boards & parts kits. possibly 4 channels if i'm flush at the time it all goes down.

do you have any plans for a 500 series version? that would be very handy to me (and i imagine most of the other 51X rack owners!)

did you try the EQ with the original helios gain cards circuit? when i make mine i might try breadboarding the original input card... compare that to the neve style... also the TG style gain stages could sound good too. i like the modular approach!

Hi Igor,

AWESOME! Again, amazing work!

Keen on 4-10 sets, it all depends on costs. I'd like to see options for a FULL kit, a PCB + Inductors and PCB only prices.


i have been avoiding this EQ ever from the start, but looks very handsome...

after checking the sound with BA, i think i will use pair of tubes for gain stage  ;D