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count
Intermediate Member
Username: count

Post Number: 140
Registered: 10-2003
Posted on Thursday, February 27, 2014 - 5:43 am:   Edit Post

When I play around with the pickup selector on 73-44 I notice a difference in volume when I change from only running one pickup, say the neck pickup, and switch to running both.
Is this normal on Series instruments.?
It's only a slight difference, but it's still audible if you listen for it.
keith_h
Senior Member
Username: keith_h

Post Number: 1970
Registered: 2-2005
Posted on Thursday, February 27, 2014 - 7:04 am:   Edit Post

That's normal for the V-V-F-F setup. With this configuration the pickups are additive when combined.

Keith
count
Intermediate Member
Username: count

Post Number: 141
Registered: 10-2003
Posted on Friday, February 28, 2014 - 6:37 am:   Edit Post

You lost me....
V-V-F-F..?
lbpesq
Senior Member
Username: lbpesq

Post Number: 5668
Registered: 7-2004
Posted on Friday, February 28, 2014 - 7:33 am:   Edit Post

Volume Volume Filter Filter

Bill, tgo
mica
Moderator
Username: mica

Post Number: 8135
Registered: 6-2000
Posted on Friday, February 28, 2014 - 12:56 pm:   Edit Post

Yes, it's normal for the Series I, II, and Anniversary models. Think of it like a mixing board, you are adding something (another pickup).

We used to make the Tribute and Further guitars like this as well, but the newest version of those electronics uses a zero sum amplifier to make the volume not change when you have one, two, or three pickups selected.
count
Intermediate Member
Username: count

Post Number: 142
Registered: 10-2003
Posted on Saturday, March 01, 2014 - 3:15 am:   Edit Post

Ah.. Allright.. You learn something new every day!
Is this also the reisen I hardy hear any harmonisk when using both pups?
When I only have one of them engaged it sings, but with both I can almost only get the harmonics for tuning.. (5th and 7th fret)
I donít have a master volume pot btw.
count
Intermediate Member
Username: count

Post Number: 143
Registered: 10-2003
Posted on Sunday, March 02, 2014 - 8:07 am:   Edit Post

Did a little troubleshooting last night, and it appears I have faulty pickup selector. Need to get me one of those..
So for now I just bypassed the switch all together, but I swear the output of the bridge pup is lower than the neck pup.
I have them both runding into completely different amp, and I have the neck pup running a 10 dB cut to make them level out.
Tried swapping the connections around, and it changed to the neck pup.
Gonna try switching around the volume pots tonight or tomorrow to see if that makes any difference, but they're supposed to be the same impedance.. (10k)
Hope It's not the case, but it seems I've got a huge signal loss somewhere in the circuit.. :-(
keith_h
Senior Member
Username: keith_h

Post Number: 1972
Registered: 2-2005
Posted on Sunday, March 02, 2014 - 9:14 am:   Edit Post

Have you tried adjusting the volume balancing pots on the PC board? If not it is worth a try.

Keith
jimmyj
Senior Member
Username: jimmyj

Post Number: 502
Registered: 8-2008
Posted on Sunday, March 02, 2014 - 11:09 am:   Edit Post

Whoa Nicolai, slow down and step away from the soldering iron. Ha!

This is a Series-1 correct? Power supply, stereo or mono out, etc...?

As Keith said, the first thing you should do is try adjusting the preamp trimpots accessible through the small holes in the brass cover plate which has the board mounted to it. See the pic below (stolen from an old Mica post).

Issue # 2: Harmonics and overtones in general will be more prevalent from the bridge pickup. I can't explain the physics of that (smaller divisions of the vibrating string, something, something...) but when you add the neck pickup to the signal some of these harmonics and overtones are cancelled because that pickup is seeing the string at a different location.

#3: Level differences. Technically speaking, if the preamps were set to identical gain, the neck pickup would seem louder simply because at that point the string is moving farther and thus generating more voltage. More low frequency power is captured by the neck pickup. But your description of "swapping the connections" and the volume difference "following" means the two preamps are not set to the same gain and you need to adjust the trimpots. I run my basses with more gain on the bridge pickup than the neck pickup but you should set your levels to blend (in mono) the way YOU want to hear it.

#4: What makes you think you have a bad pickup selector switch and how did you bypass it? Again, trim pots first (did I mention the trim pots?) then you can continue to investigate the other components.

Jimmy J

count
Intermediate Member
Username: count

Post Number: 144
Registered: 10-2003
Posted on Monday, March 03, 2014 - 7:08 am:   Edit Post

Hi guys, thanks for replying!

No worries, I'm more than competent with the soldering iron, but I rely on it as a last resort.. Hehe.. Troubleshooting always comes first!

First of all I have the PF-5 electronics. So my trimpots are on the front. And yes, I've adjusted them as much I can. The neck pickup on min and bridge on max, still there's a difference. Plus when I have it on this setting it sounds really wimpy, so definitely not the way to go..

Also, mine doesn't have any master volume, and my powersupply (DS-2) is stereo only (no mono output) so in essence the signals never "meet" on their way out to the speakers.

After some reconsidering (and investigation) I found out that my pickupselector is good after all, I misunderstood the sequence of options it puts out. False alarm there. Puh!

Gonna measure the resistance over the volume pots tonight, as I suspect one of them is playing tricks on me..
OR: I've wired them backwards..? If the pups are out of phase this could explain the lack of harmonics. (?)
adriaan
Moderator
Username: adriaan

Post Number: 3095
Registered: 6-2002
Posted on Monday, March 03, 2014 - 10:10 am:   Edit Post

Out of phase is mostly noticeable in the low-end - you won't hear too much of it.

For the harmonics, there's a different type of cancellation going on, between the pickups. You get the same with a pan pot near the middle position. I wonder if it's any different if you run the instrument in stereo.
jimmyj
Senior Member
Username: jimmyj

Post Number: 503
Registered: 8-2008
Posted on Monday, March 03, 2014 - 11:06 am:   Edit Post

Could you post a small picture of your preamp board? I'm curious about the PF-5 and can't remember - flat pack op amps, microwave coaxial p/u connectors, etc...

Something is definitely wrong if you have one trim pot all the way up and the other all the way down and it's not responding as expected.

Since you're handy with the soldering iron (you know I was only teasing) you should look into using summing resistors for a mono mod. Are you sure your power supply doesn't have the mono/stereo switch built into one of the 1/4" jacks? If it does, even that could be part of your current problem...

Post a pic or two if you can and we'll help you sort this out.

Jimmy J
count
Intermediate Member
Username: count

Post Number: 145
Registered: 10-2003
Posted on Tuesday, March 04, 2014 - 10:39 am:   Edit Post

I'll see if I can get a shot of it for you Jimmy.
To my knowledge it's only slightly different to the PF6, but don't quote me on that.. ;)
Like I thought, the resistance values of the neck pickup volume pot were WAY off, almost up to 1 Mohm. This explains the wimpy low output.
I installed one of the old ones as a temporary solution, while I wait for a new one to arrive.
Still can't agree with myself if I should order two to have them "matched".
count
Intermediate Member
Username: count

Post Number: 146
Registered: 10-2003
Posted on Tuesday, March 04, 2014 - 11:20 am:   Edit Post

Some pics of the preamp board:


And one of the pups:
jimmyj
Senior Member
Username: jimmyj

Post Number: 504
Registered: 8-2008
Posted on Tuesday, March 04, 2014 - 6:37 pm:   Edit Post

Wow Nikolai, that is a historic bit of Alembic gear you have there! Thanks for posting the pics (now I want to see the instrument). I recognize the coax pickup connectors and the flat pack op-amps, but I am unfamiliar with the layout of this PF-5 board. I guess I didn't join the party until PF-6. So I may not be much help but Mica and others can speak of any known issues specific to this vintage rig...

I will however make a couple suggestions......

Alembic has always used sealed pots and switches but with gear of this age you occasionally need to exercise all of the moving parts. And I mean really sweep the pots through their full range and throw the switches back and forth 50 - 100 times. I don't mean the trim pots, although I've never thought about those - but the volume, tone controls, cue boost switches for sure. I've found this to be true particularly for controls which I don't normally move - when I DO move them they complain. (Kind of like me - HA!).

Also, I think it would be unusual for one of these volume pots to "go bad" in the way you describe. Again, be sure to exercise it many times to be certain it's not just temporarily gone out of spec. Did you take the pot out of the circuit to measure it's value? And does the resistance change as you turn it?

You said you tried swapping pickup connectors and the louder output also changed, yes? So we know the pickups are OK but one channel of your preamp board appears to be acting up. Be aware that the "middle" input (top of the board in your pic) for the hum canceling coil is purposely out of phase when compared to the main pickup inputs. The hum balance trim pots control the amount of that out-of-phase signal which is introduced to the main outputs. I could explain that better but you probably already understand the concept.

It could be a failed op-amp but I hope not because that would make it a fairly complicated repair. Maybe the board needs a vacation in California?

Jimmy J
count
Intermediate Member
Username: count

Post Number: 148
Registered: 10-2003
Posted on Tuesday, March 04, 2014 - 11:37 pm:   Edit Post

A spa in northern california is definitely in the long term plans.! It has a bizarre "squeezing-piglet-squeel" with the Q's in the max position and the tone pots at about 12 o'clock which is beyond my comprehention. I won't even TRY to explain it.. It need's to be looked at by an (even..) more competent person.. Hehe..
The only thing holding me back from sending the electronics is the lead time on the work, price (believe it or not..) and the fact I've not had that much actual playing time on it since I started refurbing it back in August.

The reason for changing the volumepots is a looong loong story...
Short version is I broke one of the Q-switches while reassembling it, the replacements weren't a direct fit (old one's out of production), old volume pots (you can get a glimbse of them on the top picture) also different from the new one's, had to change these for the Q's to reach their holes, and the rest you know..

I had the pots out of the bass when measuring them, yes. Now I have one of the new ones (@10.3 ohms) and one of the old ones without it's baseplate (@11.4 ohms) and the levels aren't that far from being level. Which is easy to bias out with the trimpots. This tells me two things:
1. my preamp board is working fine. (Yay!!)
2. need to get new volume pots...
(3. ma'bass is ready to groove!)

I made a thread when starting my refurb promising alot of pictures, and I'm just about ready to start uploading them. Stay tuned for the piccies there. ;)

I've been in contact with Mica, and indirectly the Ron-someness himself ever since I started, and they've been OUT OF THIS WORLD helpful. I even got a handwritten complete schematic of the circuit from Ron. Without it it would have been next to impossible for me to work on it.
I mean, the circuitry is more complicated than alot of instrument amplifier circuits up until the solid-stage-age..!
flpete1uw
Advanced Member
Username: flpete1uw

Post Number: 273
Registered: 11-2011
Posted on Wednesday, March 05, 2014 - 4:03 am:   Edit Post

Wow! Those switches and Pots mounted directly to the main board. If you already haven't tried, this almost sounds like it could be a cold or loosened up solder joint at the Pot?
Thanks for sharing this nostalgia
~Pete
jimmyj
Senior Member
Username: jimmyj

Post Number: 505
Registered: 8-2008
Posted on Wednesday, March 05, 2014 - 10:09 am:   Edit Post

OK, thanks for the background story and we look forward to your refurb thread. Also glad to hear the Wickersham's are already on the case. Alembic's direct tech support is the greatest! If your pickups and board are working then you are very close to getting that machine back to spec.

I'm familiar with the "squealing pig" Q knob situation, a shockingly LOUD oscillation! Again I think this can be resolved by exercising the pots and switches - though I'm not 100% sure.

Good luck with your project. please keep us in the loop!

Jimmy J
count
Intermediate Member
Username: count

Post Number: 150
Registered: 10-2003
Posted on Thursday, March 06, 2014 - 12:07 pm:   Edit Post

Wow, wouldn't you know.! Tonight I decided to give it a go, and "exercised" the tone pots what seemed close to 667 times, each.. (the pig squeal nearly drove my dog up the wall..)
It worked!! Now the tone pots are as quiet and smooth as the rest of the electronics. Unbelievable! I imagined this a proper ghost in the machine, but now it seems the spa-trip to sunny cali is even further away. Because the blonde (La Güera) is now pretty darn close to a Marilyn Monroe..!

Thanks for the tip Jimmy..!
edwin
Senior Member
Username: edwin

Post Number: 1719
Registered: 5-2002
Posted on Thursday, March 06, 2014 - 10:34 pm:   Edit Post

Nice pickups! Are they trapezoidal inside the rectangular shells? The set in my Starfire look very similar.
count
Intermediate Member
Username: count

Post Number: 158
Registered: 10-2003
Posted on Wednesday, April 02, 2014 - 3:49 am:   Edit Post

To my knowledge they're perfectly "ordinary" inside.
Don't know when they stopped making or providing the trapezoidal ones, but I'm it was well before mine was made.

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