Adding a Fishman Piezo tune o'matic bridge to my Les Paul.

[oliverday]

Is this something relatively easy?

www.thomann.de/gb/fishman_powerbridge_lp.htm

I would like to change to a stereo output jack L R for the two signals (pickup and piezo). I don't want any fancy controls.

ideally, if a mono jack is plugged in it acts as a regular les Paul (no piezo). if a TRS is plugged in it puts the Les Paul electric pickups to the L or R and then the piezo to the other side? Is that possible for it to act as a normal guitar when a mono jack cable is plugged in? Doesn't one of the channels get ignored anyway when you plug in a mono cable into a stereo jack? Would it just be as simple as soldering the extra wire from the piezo to the extra connector on the stereo socket?

I would deal with volume blend / pre-amping the piezo though a line 6 helix helix once the signal is split into it.

How do you deal with the wire from the peizo bridge? is making a gap for it in the bridge pickup plastic required?

Been playing for 20 years, just clueless about electronics though. Else I will get someone to do it for me.

Thanks.

[newey]

oliverday-

Hello and Welcome to G-Nutz2!

I don't really have any answers for you, because the Thormann link you provided just shows the pieces. I suspect the Fishman website would have installation instructions and a wiring diagram which might answer some questions. I doubt the instructions wouldtell you run the cable through the cover of the bridge HB; I suspect one is supposed to drill a hole. They do show a TRS jack as being suppplied with the kit, so presumable you're correct about plugging in a mono versus stereo cable.

Does this not include a preamp for the piezo? If it's strictly passive out to a splitter box of some sort to separate the mag and piezo signals, then I wouldn't expect that putting a passive piezo signal and a mag pickup signal together with a mono cable would work very well.

[mikecg]

Aug 22, 2023 12:53:06 GMT -5 oliverday said:

Hello Oliver,

Have you found a satisfactory solution to your requirements - yet?

If not - I may be able to offer something of interest, as my current project is to convert a MIK gloss black Epi Special I bought secondhand on 'Reverb' into a poor man's Godin A6 Ultra, so it will involve a 'piezo-ectomy' - at some point. However, at the moment, I am considering an intermediate step that will involve converting some replacement Donlis pickups to work through onboard buffer opamps - in other words to convert them to active pickups. So - the path I am planning with this project guitar is - EMG - Godin A6 - in that order.
If I understand your requirement - it is to fit a Fishman Powerbridge piezo TOM bridge to a LP, but without making any (major?) modifications, and to run the output through a TRS jack to your Line 6 Helix audio processor guitar input jack socket?

[sumgai]

{I see now that I should've replied to this sooner.}

Oliver, your real problem here is two-fold - 'what is the width between the two mounting posts?' and 'what is the mounting post diameter?'.

I looked at Fishman's site and found no specifications on the mounting-post width or diameter, so I can't answer your question directly - will it mount up without some major woodworking, or will it require such efforts, that's the real question.  The rest of it, installing the electronics, is dirt simple.

However, I must note that Thomann wants the price of a small car for the product, and that's unconscionable. Moreover, for that price, or much less, you can obtain a Graphtech Ghost system that will do what the Fishman does, only better, and with more options. I recommend that you check out graphtech.com for more info (and they have specifications for their stuff) before you lay out your money.

(Addendum: if you want to order directly from Graphtech in Canada, be aware that shipping costs might be larger than you wish.  If so, one of us can buy the unit and have it shipped to our home in the USA (or perhaps a Canadian Nutz?), then send it to you privately for much less money.  Several have done this before, so just ask.)

HTH





sumgai

Full disclosure:  I have used Graphtech products for years, and in fact I live only about 3 hours driving time from their factory and offices.  JFrankParnell lives about half that distance from them!

[mikecg]

Sept 3, 2023 12:17:38 GMT -5 sumgai said:

Hello sumgai & Oliver,

Fishman describes their TOM Powerbridge as a 'Nashville' style bridge and provides a template showing that the posts are 2.935" centre to centre, with post hole diameters of 0.272". My guess is that the Fishman bridge will be a drop in fit for Stewmac's 'Nashville' TOM bridge with 2.930" centre to centre, and 0,271" post holes.
If Fishman have done their homework, all the other critical dimensions for their LP TOM bridge should be in compliance, and so Stewmac's dimensioned drawing for their Nashville bridge may well be a useful representation of the Fishman product? With regard to retail prices here in the UK - the Fishman and Graphtech products are level pegging at around £200 or $250 inclusive of postage and VAT.

[ashcatlt]

If it is just a passive piezo in the guitar, then yes. Use the T as the “hot output” from your magnetic pickup circuit just like whatever wiring you’re doing wants. Connect the piezo’s hot wire to the R. Both grounds to the S. When a TS plug is inserted, you’ll only hear the normal magnetic circuit. The piezo will be shorted, but that won’t hurt anything. When a TRS is inserted, the magnetic circuit is on the T (usually used for the left side of stereo) and the piezo will be on the R. A simple TRS to dual TS splitter cable (sometimes called an insert cable) will do the job to separate them out. There might be a tiny amount of crosstalk, but I’d be kind of surprised if it was actually noticeable in practice.

The piezo probably wants a very large impedance in order to pass all the lowest frequencies. A typical “high impedance” input intended for magnetic pickups might work, but these things often want more like 10M, which is why they usually have dedicated preamps. It’s worth a try straight into the Helix, but you might end up wanting something in between.

[mikecg]

Sept 4, 2023 13:06:00 GMT -5 ashcatlt said:

Hello again - Oliver,

Are you still interested in installing a piezo tom bridge in your LP?
You have some useful information from newey, sumgai, and ashcatit, and I hope I can fill in a few more of the 'blanks' for you.
Sumgai points out that your first job is to double check if the bridge will be a drop-in fit for your guitar. You will need to use a vernier caliper to check the post spacing and post diameter. The post spacing you measure will tell you if you have an inch (imperial) or metric (mm) bridge fitted to you guitar. If it is an inch bridge - it will likely be 2 15/16" post spacing between centres. If it is a metric bridge fitted, it will likely be very close to 74.0 mm. Inch post diameters could be 5/32", 15/64", and metric post diameters will be very close to 4.0 mm, and 6.0 mm. If you prefer not to have your guitar modified in any way, you will be forced to choose the Fishman or Graphtech bridges based on the post spacing and diameter of your existing bridge. If you have an 'inch' bridge with 5/32" diameter posts, then the Fishman bridge may fit, and if you have a 'metric' bridge with either 4.0 mm, or 6.0 mm diameter posts, then the Graphtech bridge may fit. The Fishman bridge has one mini-coax output lead and no plug, whereas the Graphtech has six leads with plugs. The standard installation method for the LP is to file a gap (or gaps) in the bridge pickup surround, and route the cable(s) into the bridge pickup cavity. You will need to check that you have enough cable length to reach the TRS jack socket that will be supplied with these bridges. For your installation, the Graphtech will require a Graphtech 'summing connector', that wires all 6 signal cables in parallel, and routes them into a single cable. You should also check that the TRS jack will fit, if not you will need to enlarge the jack socket cavity, using the appropriate tools.

Now, both newey, and ashcatit, have already raised the important issue of the requirement for a high impedance load for piezo pickups. Your Line 6 Helix has a programmable input impedance, with maximum of 1 Megohm - not nearly high enough for a piezo pickup - it needs to be around 10 Megohms. So, you will need an externally mounted preamp with a 10 Megohm input impedance. Lucky for you,  Marc Brenner, (Brennerusa.com) makes and sells his pedal board mounted 'Piezo Pro V' preamp, and this is probably just what you need!

To demonstrate the importance of the requirement for a high impedance load for piezo pickups, I have simulated frequency response curves, with and without the preamp, so that you can see the difference the preamp makes. The following circuits, marked (a) through (f) represent the following hook-ups:

(a) Fishman bridge through TRS jack into 2 metres low capacitance figure 8 twin microphone cable (Mogami 3106/Sommer Onyx 2025), Y split to 4 metres low capacitance instrument cable to Helix guitar input jack.
(b) As (a) but with onboard Fishman passive volume control.
(c) As (a) but with Graphtech bridge.
(d) As (c) but with Graphtech passive volume control.
(e) Fishman bridge through TRS jack into 2 metres low capacitance figure 8 twin microphone cable (Mogami 3106/Sommer Onyx 2025) to pedal board mounted Brenner preamp, Brenner preamp piezo output through 4 metres standard instrument cable to Helix input jack
(f) As (e) but with Graphtech bridge.






And here are the corresponding frequency response plots, Fishman in red, and Graptech in blue.
The uppermost red plot is for hook-up (e), and the next, in blue is for (f).
Then there is a big drop in output without the preamp to the hook-up in (a), notice how the bass response is severely attenuated.
Next is the hook-up in (c), with the same attenuated bass response.
Finally (d), and (b), showing that the addition of the (recommended?) passive volume controls just results in a significant drop in overall amplitude.





So, I think you will agree that the Brenner preamp is definitely worth having.

And since you have the Helix - you will be able to control the piezo volume and tone using the Helix foot-switch. You will also be able to invert the piezo signal phase using the appropriate Helix command(s) to obtain the correct phasing with the magnetic signal.

P.S. I have no connection with the Brenner Guitar company.

[mikecg]

Sept 7, 2023 14:51:37 GMT -5 mikecg said:

Sept 4, 2023 13:06:00 GMT -5 ashcatlt said:

Addendum: Oliver, If you have the Helix Floor model (not the Helix LT) you will have an XLR input with phantom power implemented, so you should be able to connect a Triton Bigamp Piezo preamp between the piezo output cable and the Helix XLR input, and this should give you a similar frequency response to that shown for the (e) or (f) hook-ups, above. However, the Triton has a set gain of +3 dbV, and since my simulation reference level for both piezo bridges was -3db, the output level to the Helix is estimated to be around 0 db, or 2.8 V peak to peak, but with the benefit of an unbalanced to balanced signal conversion. The Brenner preamp has a variable gain, with a typical maximum of around +18 dbV, and a maximum output level of around +9 dbV, or 8 V peak to peak. Frequency response plots for hook-ups (e) and (f) were simulated with a -3 dbV reference level and with preamp gain set to around 11 dbV, giving an output level of around 8 dbV or 7 V peak to peak. The Brenner preamp is powered from a standard pedal board 9 V supply, includes a 3 band EQ, and has an unbalanced to unbalanced signal routing. The Triton and Brenner preamps have input impedance's  of 7.5 and 10 Megohms, respectively.

[Yogi B]

Sept 7, 2023 14:51:37 GMT -5 mikecg said:

Finally (d), and (b), showing that the addition of the (recommended?) passive volume controls just results in a significant drop in overall amplitude.

For (b), Fishman state:

This network will attenuate the Powerbridge so that it better matches levels between magnetic and piezo pickups. You can expect a 14dB (nominal) decrease in Powerbridge output with this circuit

In order to get a simulated result to agree with that 14dB figure I had to adjust the piezo to around 680pF rather than the 300pF (+ 50pF) you used — where did you get that number?

But speaking of capacitance, opting for low capacitance cable isn't necessarily the best course of action: the extra parallel capacitance will add to the piezo's own capacitance, lowering the cutoff of the HPF formed between that capacitance and the input impedance of the following stage, thus extending the range where the bass response is still flat. Yes, this additional capacitance will lower the overall signal level, but since (according to Fishman) we have around an extra 14dB than what a typical magnetic pickup provides, I don't see some loss as a huge issue.

That being said, having a system wherein the output level is determined by the cable capacitance feels inherently inelegant. Thus, chasing high impedance — both for the preamp's input and in the form of low capacitance cables — seems like barking up the wrong tree. A low impedance (current based) solution may prove better, that way the signal should only suffer negligible losses from the division of current between the cable's very low series resistance and very high parallel elastance (reciprocal of capacitance). Therefore, perhaps something like the following charge amplifier should be employed:

[mikecg]

Sept 8, 2023 21:06:00 GMT -5 Yogi B said:

Sept 7, 2023 14:51:37 GMT -5 mikecg said:

Hello yogi, and thanks for your comments.
Fishman don't provide capacitance specs for their powerbridge - and I don't have one to hand - so I made some assumptions. I do have a Fishman matrix piezo and that measures at around 350pF at the cable end. Experience tells me that the screened cable will account for about 50pF of that, leaving about 300pF for the piezo element in the matrix piezo. Now, I make another (big!) assumption that the powerbridge consists of 6 individual elements that together, when connected in parallel, would be physically similar to my matrix piezo, i.e. each powerbridge element assumed to have a capacitance of around 50pF, hence 6 in parallel giving around 300pF. So, to answer your question - 300pF is just my rough estimate. Note that I have assumed, for the sake of comparison, that the Graphtech piezo elements have the same capacitance. However, the Graphtech has 6 individual screened cables so the associated cable capacitance, as shown in the simulations, is 6 x 50pF=300pF, whereas it is 1 x 50pF for the Fishman. I think it is important to point out that my intention in this, was to simply demonstrate, in a generic way, how load impedance affects the frequency response of piezo pickups, and to guide Oliver - who freely admits to having no electronics skills - to a practical 'off the shelf' solution to his stated requirement.

With regard to your comment on the applicability of a trans-impedance (current to voltage converter) design - yes, I agree - this is probably a better solution for a piezo preamp, but I am not aware of any commercial 'off the shelf' or 'plug and play' preamps that use this topology, at the moment, and I don't think Oliver will be too keen on making and testing a preamp from scratch?

[mikecg]

Aug 22, 2023 12:53:06 GMT -5 oliverday said:

Is this something relatively easy?

www.thomann.de/gb/fishman_powerbridge_lp.htm

I would like to change to a stereo output jack L R for the two signals (pickup and piezo). I don't want any fancy controls.

ideally, if a mono jack is plugged in it acts as a regular les Paul (no piezo). if a TRS is plugged in it puts the Les Paul electric pickups to the L or R and then the piezo to the other side? Is that possible for it to act as a normal guitar when a mono jack cable is plugged in? Doesn't one of the channels get ignored anyway when you plug in a mono cable into a stereo jack? Would it just be as simple as soldering the extra wire from the piezo to the extra connector on the stereo socket?

I would deal with volume blend / pre-amping the piezo though a line 6 helix helix once the signal is split into it.

How do you deal with the wire from the peizo bridge? is making a gap for it in the bridge pickup plastic required?

Been playing for 20 years, just clueless about electronics though. Else I will get someone to do it for me.

Thanks.

Hello Oliver, I have discovered another manufacturer of high input impedance pre-amplifier/buffers, namely, the 'Creation Audio Labs' 'Redeemer' range. These are available in a number of different formats, but the best ones to use for your application would probably be the 'belt pack', or 'inline' option.
So, now you have three high-z external buffers to choose from, the Brenner, Triton, and Redeemer. That is probably enough for the time being! 

[ashcatlt]

We’re aware that we can reply without quoting, yes?

If there’s a specific (shortish) part of a post that you want to zoom in on, especially maybe if it was few posts back, go ahead and quote just that part. If you’re replying to the most recent post, or really just continuing the conversation, we don’t need a quote. We currently have like half the thread quoted several times. We’re scrolling past the same thing over and over again to try and find the new contributions. I’d really appreciate it if y’all would go back and edit those posts, but if nothing else let’s stop this exponential expansion please.

[mikecg]

Hello ashcatit, I have edited out most of my quoted posts, as requested.

[sumgai]

Mike,


Thanks for those edits. ash is correct, reading and re-reading entire quotes gets a bit tedious after the umpteenth time.

But beyond that, your contributions are having a positive effect here in The NutzHouse, and for that we all thank you.






sumgai

[mikecg]

No problem - and thanks -