Author Topic: My rare "Alembic" (Read 767 times)

keith_h · « **Reply #30 on:** October 25, 2010, 08:56:33 AM »

Have you tried performing the hum canceling procedure?

Keith

gtrguy · « **Reply #31 on:** October 25, 2010, 03:14:10 PM »

Cool bass!!! I got one with 9 layers!

sscastro · « **Reply #32 on:** October 28, 2010, 01:51:53 AM »

Hi Dave
thanks for your patience. Here is one of the pictures of the cavity. Still puzzles me why the top of the bass EQ pot chassis does not show being to ground. I mean, you test from the earth connection to the bottom top and it blips, as well as with the bridge pick-up switch, but there is no contact with the top EQ pot.

sscastro · « **Reply #33 on:** October 28, 2010, 01:54:06 AM »

this is a closer look of the same.

sscastro · « **Reply #34 on:** October 28, 2010, 01:58:16 AM »

these are switch connections on pins 10, 1 and 2

sscastro · « **Reply #35 on:** October 28, 2010, 02:02:08 AM »

Switch connections 3, 4, 5 and 6. I'm sure the ground to the switch is lost too, as I found a little piece of rotten copper, painted aluminium, like the ones crossing the cavity. But as it was smashed I removed it.

sscastro · « **Reply #36 on:** October 28, 2010, 02:14:38 AM »

Finally positions 8,9, 10 (I believe I've missed 7, but it's linked to 6 with no other connection. 4 and 5 are also linked, with 5 connecting across to 10. 2 and 3 are linked with pin 2 receiving brown wire. 1 and 10 are linked receiving black wire on pin 10. 8 and 9 are linked receiving grey wire on pin 8.
the internal pin close to pin 3 receives violet wire, and the other pin close to pin 8 receives orange wire. These are the connections as they were when the original switch got broken.

mica · « **Reply #37 on:** October 29, 2010, 08:48:35 PM »

For checking the ground, you sometimes have to scrape away some clear epoxy on the back of the pot to get contact to conductive metal.

The switch is not a part we supply, as we use Grayhill rotary switches. That it rotates all round doesn't indicate there is a problem with the switch you have, as some switches are designed to operate that way. Also, many rotary switches are non-shorting, and you will hear clicks and pops when changing positions. Our pickup selector switch has 10 terminals.

Your description matches normal operation for a mono cord and a stereo output - 2 positions will sound the same and the other positions will have no output.

Let's work on the noise. When you hear the noise, turn the volume controls on the bass completely down - does that make it silent and without noise?

Also, can you give any description of the noise? I mean, is it high frequency hiss or low frequency hum or some other sound?

We'll keep conversing one step at a time until we figure out the noise issue (and I will probably move this over to Troubleshooting soon).

sscastro · « **Reply #38 on:** October 30, 2010, 04:35:12 AM »

Thanks Mica
I will be back home on Monday and I will do all tests you propose. I don't remember any clicks when changing positions so I would guess this switch works fine. Regarding the pots, they do not seem to have any epoxy on top. Only some make contact and others don't. I would have imagined that a dual concentric pot like the EQ ones should have both chassis to ground, like the bridge pick-up does, but not the neck pick-up (I sometimes refer to as bass pick-up).
thanks again. Regards

sscastro · « **Reply #39 on:** November 01, 2010, 04:07:10 PM »

Hi Mica
today I tried some of your recommendations. Yes, turning both of the volumes down, will make the noise disappear. Both pick-ups seemed to have the same kind and amount of noise. It's definitely a ground noise. I tightened all the pots to the bass body and surely the bridge pick-up volume knob started making ground contact to the chassis of the pot. Then I picked a piece of stranded shield and got it into the screw hole of the main Switch, forcing ground contact with the switch plate. This piece of wire went down the body of the bass, inside a plastic sleeve and, after a hard work, I finally got it to solder to the chassis of both the EQ pots.
After that I had the bridge pick-up silent and sounding good and the neck pick-up, noisier than ever. The neck EQ switch still does not make any contact with the ground. I was using the stereo jack with two 11k resistors. I will try to use the IN-2 tomorrow in the hope of finding some different results. Maybe I need to get ground independently from the common point on the stereo jack, to each one of the contacts: Switch, EQ switch and the EQ pot. Or as Dave suggested, maybe I need to repaint the cavity.
Thanks for your patience and your help.
Sergio

keith_h · « **Reply #40 on:** November 02, 2010, 05:11:12 AM »

Sergio,
You may have missed my post above. Have you tried the hum canceling procedure? It is here. The FAQ explains the procedure and why.

Keith

sscastro · « **Reply #41 on:** November 02, 2010, 01:24:20 PM »

Hi Keith
Yes I tried it, but the problem was indeed no sound from one of the pick-ups. I found since that the internal coaxial connectors are very fragile indeed and probably there was a contact problem. Right now both pick-ups sound fine with the IN-2 unit although there's not a very high output from the bass into an Apogee preamp mic input. After, I tried with the stereo jack in one instrument channel of theApogee and there's quite a lot more output, but a bit more noise also. Anyhow this noise seems to be inherent to the electronics. With the hum canceling procedure I got it a bit better. The gain of both pick-ups is somewhere in a mid position. I have to try the bass in a real situation now. There are still some odd ground links as I mentioned in my last post to Mica, so I probably need to spray the cavity with the conductive painting.

mica · « **Reply #42 on:** November 02, 2010, 02:11:55 PM »

I have to dash out and vote, so my answer is a little abbreviated, but unless there is a breach in the shield under one or more of the pots that is blocked from view, the shield looks intact - it's pure silver, and does not break down over time.

When you say ground noise, can you try to describe it a little more? Is it 50Hz hum? If it's high-frequency or directional, there's only a little we can do about it remotely since the bass will be in need of an electronic upgrade. Replacing all three pickups will help in the absence of an upgrade (and is the first step in the upgrade actually).

Do set the gain controls on the pickups where they give you the output you prefer - there is no impact on tone when you adjust them.

The 1/4 jack is still wired in stereo?

sscastro · « **Reply #43 on:** November 02, 2010, 04:26:53 PM »

Hi Mica
the noise was definitely like 50Hz hum, but as you may have noticed in my previous post, I found that most of the problem was in the neck pick-up coaxial connector and by gently squeezing it and re-connecting it again, the noise disappeared and the pick-up started sounding fine. Now there is still a bit of electronics noise, but only with the stereo to mono jack lead, with the 11k resistors. Using the IN-2 it sounds pretty clean. The screen is still soldered to the neck EQ bottom pot and doing contact with the rotary switch plate.
best regards

sscastro · « **Reply #44 on:** November 12, 2010, 12:42:13 AM »

Hi
I would like to thank Dave, Mica and Keith for all your great help. The bass is now working almost fine, with a little bit of electronics noise, which I believe to be inherent to this design. It's more noticeable using the jack output, then when using the IN-2. I still would like to give it an Alembic Logo on the peghead, if possible. It looks like it will soon be used for recording a few tracks.
thanks again
regards
Sergio