I've got two Yamaha APX8 guitars in right now that have problems with the newly-fitted Artec transducers. These were fitted by the owner, who then had subsequent problems with very low output on the low E string and electrical buzzing. The buzzing was a straightforward fix - the connectors didn't make good contact and I've replaced them with correct type.
The low E string has me stumped. It's an identical problem with both guitars. Additionally, I discovered the B strings on both instruments is way louder than is acceptable.
Both guitars just had noise issues before the transducers were replaced - no issue with output or string balance. The foil on the original pickups had broken down and made them noisy. I thought the problem would just be down to uneven saddle pressure, or maybe a problem with the slots, though the chances of the same fault with both guitars seemed unlikely.
A thorough check on the slots shows them to be level, with no bumps or dips. The saddle is a nice fit and doesn't bind. I also used engineer's blue to mark the transducers and evaluate the contact area. There are six, even contact areas that show on the underside of the saddle and the transducer sits flat in the slot. I'm happy that the contact is as good as it can be.
The only major difference is that the transducers are much shorter than the OEM ones, though the string spacing is correct. The height of the Artec units is the same as the originals, so the break-angle is unaffected.
Each transducer appears to have good output from each element when tapped. There are no problems with the saddle tipping and losing contact and the transducer maintains alignment with the strings - the owner glued a little tab on the underside of the saddle to positively locate the transducer. Experimentally I later removed this to see if it was having any bearing on the problem. No change, though.
I've tried shimming the transducer to apply more or less pressure to the low E element and this didn't make any difference. Additionally I swapped the E and A strings and the problem remains.
The transducers have 6 individual raised active elements and these are in alignment with the strings. I did try moving the transducer in either direction to see if there was any difference, but no success. After swapping the strings the A string moved to the E position had low output. So it's location specific. I've even tried shimming right under the E piezo element (so that its the only one in contact with the bottom of the slot) and just stringing that position. Output is still low, even though this arrangement ensures that pressure is being applied.
There's something peculiar that both guitars do the same thing, and both have excessive B string volume - to the extent they will seriously overdrive the amp, but only on that string.
Artec PG-607 is designed for 55 mm distance between the lowest and the highest string. Have you checked it? Other pickups are designed for other dimensions, see: ARTEC for details. Since both guitars have the same problem, I would say that either both transducers are broken (in exactly the same way), or both guitars have uneven bridge surfaces, or the size of the transducers is not correct for this guitar. You can build a test jig to test the transducers.
The spacing is correct at 55mm.
I've spent a lot of time checking and re-checking the contact surfaces to make sure they're correct. After critical re-listening to both guitars there's an unevenness in string volume that's identical to both instruments. Unfortunately the owner needs them for a gig, but I'll resume investigating the discrepancy when I get hold of them again.
Am update on the transducers;
I got one of the guitars back for further investigation. I tried using the polymer clay technique to ensure the pickup was 100% in contact with both surfaces and the results were the same. A further check was done by sandwiching the transducer between two machined alloy surfaces and locating the sandwich on a piece of MDF towards the bridge side of the soundhole and so it could be repositioned towards either the bass or treble side. No change in response.
Another problem that's surfaced is when the pickup/mic mix is at 50-50 the two outputs cancel and gives a hollow, out of phase sound. I can't see how this could happen unless the Artec is out of phase compared to the OEM transducer. It doesn't do this with the original transducer.
Anyhow, the owner is ordering a genuine replacement. £80 compared to £12 for the Artec. Buy Cheap, buy twice, as they say.
And the preamp does not have a phase switch? In such cases I record two signals separately (if this is possible) and verify the phase. Maybe this is just a problem caused by reverted phase and it is audible just for the lowest string?
Last edited by MarkusBass; 01-25-2016 at 12:17 PM.
No phase switch. I'll rig up Audacity and record the separate signals to see what's going on.
The easiest and the quickest test is to discoonnect the microphone. Does the problem still occurs in this case?
The E string problem still occurs with the mic disconnected. I think there could be a phasing issue anyhow because with only the bridge transducer connected the volume is greater in the 50/50 mix position.
Seems unlikely that a transducer would have a different phase relationship, though
It's been a while, but I thought I'd update this thread to close it off;
Recently I had an Ovation guitar with similar problems - a replacement transducer with no real low E output plus a weak A and through a Loudbox Mini needed the bass turning right up to get any depth. The fundamental just wasn't there though. Also, there was a real imbalance in the rest of the strings - in this case the G and B were far too loud. I took a lot of time to make sure the bridge slot was flat and made a new saddle in bone to perfectly match the transducer. Still no luck. Just out of interest I put together a simple FET buffer and used this as the first thing the transducer 'sees'. This completely fixed all of the problems - vastly different in every respect. Also, louder, much less hum and an even string response.
Does it mean that either low input impedance of the Loudbox Mini amp, or problems with jack-jack cable caused the problem and there was nothing wrong with the transducer?
I now don't think there was anything wrong with the transducers, but perhaps the impedance characteristics are different and maybe the Artec needs to see a much higher impedance than that offered by the internal preamps. The Loudbox input impedance isn't an issue because the piezo doesn't connect directly to the output socket. I just wonder if there's a construction aspect to the Artec transducer that's different to the OEM devices.
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