Author Topic: Picked up a ?? [Fernandes] ...trying to figure it out.  (Read 627 times)

gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #15 on: August 22, 2020, 10:32:11 AM »
Yes, the saddle is not cut to the same profile as an Alembic saddle and is set correctly. There are various other subtle and not so subtle changes as well. BTW, I can tell anyone that wants to know that an Alembic 5 pin cable and power supply do work with these instruments.

BeenDown139

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #16 on: August 23, 2020, 08:25:33 AM »
[BTW, I can tell anyone that wants to know that an Alembic 5 pin cable and power supply do work with these instruments.]

hope ya didn't let the smoke outta something finding that out! 🤯
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gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #17 on: August 23, 2020, 10:45:06 AM »
18 volts is pretty low

HyAlembicK

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #18 on: August 23, 2020, 02:01:41 PM »
Nice one, Dave!

BeenDown139

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #19 on: August 24, 2020, 09:57:40 AM »
Quote
18 volts is pretty low

actually, you'd be surprised what you can trash if you get this backwards across something that's delicate like a guitar pre-amp circuit.  you're pretty much guaranteed to take out an op amp, some discreet transistor circuits might survive it, signal diodes probably not.  just because you didn't let the smoke out doesn't mean you didn't kill it.
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gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #20 on: August 25, 2020, 10:33:00 AM »
That's true. It has what were just OK op amps for back in the day (RC4558P) but not for these days. Can anyone suggest a better drop in replacement that does not use a ton of power? I will be using this with a power supply though.

lbpesq

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #21 on: August 25, 2020, 11:02:45 AM »
David, I’d be curious to see what you come up with.   I restored my first Fernandes with non-series Alembic guts, converting the hum canceller into a middle pickup ala Stratocaster.  I have a couple more Masterhands that are projects-in-waiting, on which I will have to do something about the electronics.

Bill, tgo

gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #22 on: August 25, 2020, 11:34:12 AM »
I am beginning to think the fernandes circuit is designed to run on 9 volts total from their power supply and not 18. I just measured the op amp inputs and with two 9 volt batteries I get 8.93 volts dc and with the Alembic power supply I get 19.6vdc. I do not know if this is how a the Alembic circuit works, but could measure one as well. Right now I am thinking that the excessive hum might be from a dead middle PUP or transistor or something in that part of the circuit, but I don't know. I am unsoldering the PUP leads next to measure the PUP output.

BeenDown139

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #23 on: August 25, 2020, 01:07:34 PM »
disclaimer:  I spent many years as an analog circuits engineer, but i've been out the mix for a while.

i pulled up the spec sheet for RC4558P and its recommended supply voltage is +/- 5V.  its max is +/- 15V, so be careful if you're using a +/- 18v alembic supply.  Its current consumption rises fairly significantly at supply voltages above 5V.  I would trade performance over power consumption in this case.  You can definitely tell when you've put a crappy (i.e. low quality) op-amp in a pre-amp circuit, so battery usage be damned IMHO.

interesting discussion about this subject here: https://www.diyaudio.com/forums/analog-line-level/135546-rc4558p-replacements.html

putting a bypass cap right across the supply pins at the op amp is an old trick, pretty effective if you keep your leads short and use a good quality low ESR cap.  It doesn't take much, maybe a 0.1 uF.  ya gotta have a good hand with a soldering iron, because you gotta tack the cap leads right to the IC pins.  I don't recommend doing this unless you're experienced soldering delicate electronic components and have the right equipment to do it, because you *will* cook the op amp if you can't get it done in under ~ 2 seconds.  The intent behind this is to decouple power supply noise from the op amp and to prevent oscillation due to a high impedance power supply path.  it doesn't take too much softness in the supply path to wreak havoc on the output, especially if there are rapidly changing signals with high frequency components.

i had to replace one one the op amps in my series II years ago, i don't remember what it was other than a dual op amp in an 8-pin DIP.  You might poke around and see what alembic is using in their circuits, i'm pretty sure they've done their homework on these.

if you have access to a scope (i'm thinking this is a lost art these days.  i work in an electrical shop and i can't think of anybody i know who knows how to drive one anymore except for me.  when i draw a waveform on a piece of paper to illustrate a point, people's eyes glaze over...  but i digress), it's pretty easy to trace out a hum.  a good first step might be to get the op amp power situation straightened out and then go from there.  if there's something funky going on there, you can spend endless hours chasing your tail trying to find it in the signal path.

good luck and happy hunting.

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lbpesq

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #24 on: August 25, 2020, 02:30:56 PM »
Your middle pickup isn't a pickup.  It is a "dummy" hum canceller - essentially wound wire with no magnet in the middle.  It is part of the Alembic-designed hum-cancelling system.

Bill, tgo

mario_farufyno

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #25 on: August 26, 2020, 10:50:12 AM »
David, please read this before messing with your guitar's hum cancelling system.

http://club.alembic.com/index.php?topic=269.0
« Last Edit: August 26, 2020, 10:57:50 AM by mario_farufyno »
Not just a bass, this is an Alembic!

gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #26 on: August 26, 2020, 11:20:32 AM »
Thanks for the help. First thing I tried when I got the guitar was the hum canceling procedure, but it would not eliminate a fairly loud consistent hum.
Right now for fun I am installing IC 8 pin sockets on the board so I can swap in and out the op amps. I found 3 of the same op amp chips on an old Peavy amp circuit board I keep around for parts.
Eventually after figuring out the hum I want to try swapping some better newer chips in there.

gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #27 on: September 04, 2020, 04:53:41 PM »

Can any electronics experts help me with any knowledge about the transistors this thing uses? There are 4 marked K66 P .99 and 2 marked K66 R 88
I think they might be vintage Panasonic FETs but that is about all I can find.
Thanks,
Dave

BeenDown139

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #28 on: September 08, 2020, 09:44:54 AM »
did you ever get any enlightenment on this?  if not, i was gonna do a quick lookabout to see what i could find out.  i did a lot of discreet transistor design work back in the days of my youth, so i may be able to shed some light on it.  maybe.
just so that i don't reinvent the wheel, what searching have you already done?
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gtrguy

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Re: Picked up a ?? [Fernandes] ...trying to figure it out.
« Reply #29 on: September 08, 2020, 09:58:59 AM »
I have just searched the web and found some info that makes me think they are vintage Panasonic FETs. I also have an old vintage Shin-E Four in the Floor drum stomp box (MIJ) that uses transistors with the same logo marking, which makes me think they are vintage Japan made parts. I would love to find an equivalent that I can swap in so I can test the originals. Right now I have finished soldering in the chip sockets and swapped in some identical op amp chips to test them (works the same).