Help with an Alembic inspired Fernandes MH-110 wiring

[StephenR]

If you don't want to use a TSR cable that splits to supply stereo output the cable below would be the type of cable to use with the 1/4" jack.
http://bayoucables.com/index.php?main_page=product_info&cPath=4&products_id=7

[flavofive]

For reference to anyone doing maintenance on a FAB/Masterhand:  Here is a full circuit trace of the Fernandes FAB / Masterhand circuit that I traced out from on my own FAB-170, and verified with some photos of a few other FAB/Masterhand instruments online.  It's a pretty big image, so you may need to right click and "Save image as..." so you can zoom in on the details.

https://i.ibb.co/D9yMNck/2022-08-29-Fernandes-FAB-and-Masterhand-Schematic.jpg

I know a lot of people have traditionally said that the electronics didn't copy the Series 1 circuit well, but to set the record straight - the tone controls and circuit are exactly the same as a late 70s Alembic Series 1.  Like literally, same circuit, same component values, etc.  The only exceptions tone-wise:
- Fernandes uses a 2k volume pot instead of 10k, which technically has a very slight change to the frequency response.
- I've seen some Alembic Series 1s with slightly different filter capacitors - some have only 1 cap, others have 2 in parallel.  The Fernandes matches one of these configurations.  So if you own a Series 1 and notice a different filter cap value, you may have the "other" configuration.  Very minor difference though.
Otherwise, all of the tone-producing portions of the circuit are the same.

It is true that some of the components themselves are cheaper, and the opamps use a slightly lower maximum voltage (but still way more than what you get on +/-9V battery power anyway), but none of this should affect the tone of the bass in a perceptible way.  There are some additional protection on the power side, but again, no tone impact.
Also, I can confirm that the dual batteries do produce +9V and -9V just like an Alembic Series, at least on my FAB.


All the respect in the world to Ron Wickersham / Alembic for inventing the instrument and circuit!  To be clear, I'm not saying was good or ethical of Fernandes to make such a blatant copy, but just stating facts - unethical though it may have been, when Fernandes copied it, they didn't stop at just the body, they went all out on the controls too.

[lbpesq]

Thanks Mike!  This will be immensely helpful when I get around to restoring mine.    None of mine came with working electronics, let alone a power supply.   Do you know if these work with a standard Alembic Blue Box, or do they require different voltage or polarity?   The MH-110s really are sweet guitars, though extremely rare.  And I appreciate the original body shape.


Bill, tgo

[gtrguy]

They do work on an Alembic power supply, but I think the Alembic unit is putting out twice as much juice as the original Ferbic unit which is a bit over the design limits of some of the Ferbic components.

[flavofive]

Hi Bill, my pleasure, happy to help!  Bummer about the electronics/power supplies.
David/gtrguy is correct about the power supplies.  Everything is compatible between the Alembic "blue box" DS-5/DS-5R and Fernandes electronics EXCEPT the voltage, unfortunately - at least on paper.  Specifically:

- The Alembic DS-5/DS-5 outputs somewhere around +/-20V to +/-22V.  i.e. ~40-44V full range in terms of the maximum signal voltage it can output (roughly).  I don't actually own one, so I can't check the exact value, but this is what others here on the forum have reported.  The opamp ICs that Alembic has used since at least the 80s (I think?) are NE5534xx, which have a maximum rated power supply range of +/-22V.  i.e. The DS-5 is designed to output pretty much exactly what a Series bass's opamps can handle, which makes sense.
    - The 70s Series instruments used a different opamp that is long out of production, so I'm not sure exactly what the max voltage is, but it must be at least +/-22V as well.

- The Fernandes opamps are rated at +/-18V maximum, i.e. a 36V range.

SO - if you use a DS-5 with a Fernandes, it will hit the opamps with ~+/-20-22V, which exceeds the maximum RATED +/-18V voltage of the opamps.  Will it still work?  I've always wondered that, but I'm not brave enough to try!    It might be fine, OR it might burn up the opamps either immediately or somewhere down the line.  Replacing them isn't extremely difficult, but it's time-consuming and I'd rather not.  So I wouldn't recommend it.  (Although if you do take the risk, I'd love to know if it worked!)

Side note, unfortunately I also don't own a Fernandes PS-5 power supply.  They're basically impossible to find unless you buy a FAB/MH that still includes it - mine didn't.  So I don't know exactly what an original Fernandes power supply box outputs myself.  If anyone knows, and can share, that would be awesome to know!

Instead, I just built my own power supply based on the DS-5 schematic that Alembic has freely made available (thank you Alembic!!), and used a transformer with a slightly lower output voltage.  So my power supply currently outputs about +/-16.3V (i.e. a 32.6V range).  That way, it's compatible with both Fernandes and Alembic.  I suppose technically it SLIGHTLY limits the max volume of an Alembic vs. if I used a "stock" DS-5.  But it's still way more than you can get with just using two 9V batteries, I never adjust the gain trimpots up that high anyway.  So the difference between a 32.6V power supply and a 44V power supply is moot to me.
Heck, for comparison - a Stingray bass just uses one 9V battery (+/-4.5V), and I don't recall hearing many people complaining that they're lacking in volume! 

[gtrguy]

Good info Flavo! I have used Alembic power supplies with the Ferbic and it does work, but I kinda think it is stressing it just a bit. For me, I have a bunch of Tascam units and boards that have lots of the same Ferbic chips in them (they were quite conman in stuff built back in the day) and I installed sockets in my Ferbec circuit board for the opamps, so I can always easily swap in a new chip if one should fail. Finding an original power supply for the Fernandes seems to be next to impossible.

[flavofive]

Thanks David!  Good to know.  I remember you mentioned you had "socketed" the Ferbic ICs in a separate thread - that is definitely a good idea!  I need to just make some time to do that myself...

[gtrguy]

Here's my Ferbie board alongside a couple Alembic vintage circuit boards. The Ferbic is waiting for new trimmers, hence the holes in the board. You can make out the sockets for the ICs.

[flavofive]

Nice work!!

[flavofive]

Hi all - quick followup for posterity / future reference:  I now have an actual Alembic DS5 power supply, so I opened it up and measured the output voltage.  Mine reads +21.05V and -21.05V for the positive/negative power supply voltages, respectively.  So a total voltage range of 42.1V.  It sounds like there might be a slight variation in individual units, but it falls exactly in the range of +/-20-22V that I have heard from others.
For reference, my DS-5 is from 1980, but I don't think anything has changed about the design at any point.