Different volume output Series1

[count]

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]

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

[count]

You lost me....
V-V-F-F..?

[lbpesq]

Volume Volume Filter Filter
 
Bill, tgo

[mica]

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]

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 don?t have a master volume pot btw.

[count]

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]

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

[JimmyJ]

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]

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]

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]

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]

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]

Some pics of the preamp board:

 

 And one of the pups:

[JimmyJ]

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