Double Bass 1/4" Attenuator for Piezo

[bassically_eli]

So, I've noticed an issue with my Headway EDB-2 H.E. and was looking for a 1/4" attenuator (signal pad) adapter, but I can't find such a thing anywhere. XLR pads are around everywhere, but no 1/4" versions.

The problem I'm having is that the output from my Lifeline pickup distorts the harmonic enhancer if I really dig in hard on an open E or if I play a loud double stop with the bow. It doesn't happen if I turn off the H.E. or if I put something before the Headway to trim the signal a bit. I have various other preamps and pedals I could use that way--I could put fdeck's HPF-Pre behind the tailpiece for instance--but the whole reason I got the Headway was to have a single preamp that could do everything. So, I am hoping to find something cheap, simple, and passive. I know a passive attenuator or volume control will lower the impedance the pickup sees, but since the Headway has a 6.8 M-Ohm impedance and the Lifeline seems happy with anything over 1M, I think I have a little wiggle room. I don't think I need much attenuation, maybe just 3-6db. Any suggestions? Am I stuck with a DIY adapter or a custom cable? If so, I could use some advice on specific components and schematics. Doesn't Yamahiko sell some kind of custom jack that pads the signal?

I also thought about the Realist Docking Station, but I'm not sure how that affects the signal quality, and at $90 it's actually more expensive than my HPF-Pre. I was hoping to sell off a good amount of gear soon, not buy more

 

[bassically_eli]

I should probably add that I really like what the harmonic enhancer does for my Lifeline. I don't want to keep it off. So far the solution is to just not dig in super hard, which is okay pizz., but it's a bit of a problem when playing double stops with the bow. Or I can use a mic only, but that's not always possible....

 

[Martin Spure]

This would be the perfect attenuator match for your Lifeline:

Link Removed

EDIT: Sorry, hadn’t seen your last paragraph in the first post. My bad..

On another note - but you’ve probably already tried that - wouldn’t lowering the gain on the input of the Headway achieve a similar result as putting an attenuator in front of it? In lowering the gain I assume that the Harmonic enhancer isn’t driven as hard? At least that’s how most - if not all - tube/saturation plugins/hardware units are operated.

 

[Wasnex]

Are you sure you can't resolve the problem with gain staging? Gain down/Master up.

I believe you can solder a small capacitor across the piezo to drop the level. This is something you can probably add in the shell of a 1/4" jack or plug. I don't remember if the capacitor should be on the pickup side of the cable, or the downstream side (or if it matters). I also don't know the value. It may vary depending on the characteristics of your pickup and how extreme you want to go.

Perhaps @DoubleMIDI has some insight.

 

[Wasnex]

Found the post I was thinking of. Take a look at this and post 22:
Yamahiko: Single sensor too hot!

Keep in mind these capacitor values were recommended for a specific pickup. Different values may work better for your particular pickup.

 

[Earl]

I thought David Gage sold a cable that did this.

 

[DoubleMIDI]

Found the post I was thinking of. Take a look at this and post 22:
Yamahiko: Single sensor too hot!

Keep in mind these capacitor values were recommended for a specific pickup. Different values may work better for your particular pickup.

That’s it.
Get several capacitors with different values, since their value depend on the capacitor value of the piezo. I would get five or six with a factor around 1.5 from value to value and start with the values for the Yamahiko and get two below and one or two above these values.

Experiment to find the best value for your pickup preamp combination.
For testing you could use two crocodile clip cables to connect the capacitor to an open plug. When you found the best value make a short adapter cable with a plug/jack and solder the capacitor inside. Make sure to isolate the capacitor/leads against any possible shorts.

BTW, 1000 pF =1 nF, so you might want to get values in the low nF range.
My recommendation: 1.5 nF, 2.2 nF, 3.3 nF, 4.7 nF, 6.8 nF, maybe also 1.0 nF.
Use polyester film capacitors, avoid ceramic capacitors. You might want to stick them between the plug leads, since there is some room and you can bend the capacitor leads to the plug leads to solder.
Get the lowest voltage (typically 50 or 65 volts, but at least 16 volts) as they get bigger with higher shortage voltages. Not every value might fit into the plug, even with 50 volts.

 

[Ric Vice]

David Gage had a cable that attenuates the Realist. You should contact Sam Findlay at Findlay and Gage to see if their still available. I couldn’t
find them on their website,

 

[bassically_eli]

Oh great! I have an assortment of capacitors on hand already.

I thought it was gain staging at first, too. Then I thought it was the combination the enhancer and EQ making the EQ clip, but here's the block diagram from the Headway manual. Makes it pretty obvious why turning the gain down doesn't help.

Edit: looks like all the capacitors I have are much too large. I'll have to order some smaller values.

 

[bassically_eli]

@DoubleMIDI I'm looking at Digikey.com. Do these look like the right capacitors?

 

[james condino]

That’s it.
Get several capacitors with different values, since their value depend on the capacitor value of the piezo. I would get five or six with a factor around 1.5 from value to value and start with the values for the Yamahiko and get two below and one or two above these values.

Experiment to find the best value for your pickup preamp combination.
For testing you could use two crocodile clip cables to connect the capacitor to an open plug. When you found the best value make a short adapter cable with a plug/jack and solder the capacitor inside. Make sure to isolate the capacitor/leads against any possible shorts.

BTW, 1000 pF =1 nF, so you might want to get values in the low nF range.
My recommendation: 1.5 nF, 2.2 nF, 3.3 nF, 4.7 nF, 6.8 nF, maybe also 1.0 nF.
Use polyester film capacitors, avoid ceramic capacitors. You might want to stick them between the plug leads, since there is some room and you can bend the capacitor leads to the plug leads to solder.
Get the lowest voltage (typically 50 or 65 volts, but at least 16 volts) as they get bigger with higher shortage voltages. Not every value might fit into the plug, even with 50 volts.

Exactly. I'd wire them all up together on a temporary motherboard (even cardboard would work) and use something like a six way toggle switch so you can rapidly switch between them to see what results you like. I do the same thing wiring pickups on electric instruments. I'd almost guarantee that you'll find a good thread over on the slab side detailing this.

 

[bassically_eli]

Why does the capacitor across the leads attenuate the signal? If I understand the wiring correctly (which I might not), then it's wired like a LPF. I take it the capacitor interacts with the piezo differently than it would with magnetic pickups or preamplifier signal?

 

[DoubleMIDI]

Why does the capacitor across the leads attenuate the signal? If I understand the wiring correctly (which I might not), then it's wired like a LPF. I take it the capacitor interacts with the piezo differently than it would with magnetic pickups or preamplifier signal?

First:
the capacitors you have shown should work.

Second:
It took me a while to understand why the capacitor works as an attenuator.

The key is that the piezo acts as a capacitor itself (together with an AC source), so you have an AC source and two capacitors (one the piezo and the other the external one) in series.

Since you grab the voltage at the junction of the two capacitors to ground, the voltage is divided between the two.
I‘m not completely sure this is correct, but this is how I explained it to myself.

The piezos I have measured have a capacity from 8 to 45 nF (with some exceptions).
If you want to be sure not to order again since the parts are cheap, you might want to get values up to 47 nF.
I have never tried myself to attenuate a piezo with a capacitor, so I cannot speak from experience.
You can grow the values by factor 2 if it gets too expensive to order by factor 1.5.

 

[bassically_eli]

I ended up ordering 10 each of 1200, 2200, 3900, and 5600 pF. Those values were based largely on just what was available. If there is room, I can combine two caps to get an in between or greater value. I emailed Headway as well as Gage and Findley about this, but decided to just go ahead and order the caps without waiting to hear back. I'll update this thread once I put something together or hear something interesting, which might be couple of weeks because I'm traveling next week.

 

[bassically_eli]

So I finally got around to playing with these this week, and I'll need to use the either the 3.9 nF or 5.6 nF. Alligator clips were cumbersome and picked up loads of noise. I ended up unscrewing a 1/4" lead and using painters tape to hold the capacitor in place. I could hear the difference in high frequency noise, so it was evident that this circuit is both a pad and an LPF when used with a piezo pickup. The cut off frequency is probably high enough to not matter though.

I would like to make a custom cable where the capacitor is switchable, but I'm not sure how to add a switch to an instrument cable. Even better would be a 3-way switch with mute, pad (capacitor), and normal mode. That way I can mute the cable, switch to BG, and switch to normal mode. Any ideas where I can get the parts? I don't even know what to search for.

I did come across Neutrik's Timbre Plug, which has a knob and 3 different capacitor values meant for tone shaping passive magnetic pickups. Unfortunately, I couldn't find out what the cap values are, only that they are in the single digit nF range.

I've only been playing acoustically lately, so fortunately there's been no rush. But I do have some amplified gigs coming up, so I should probably finish this project.

Also, DigiKey was great. My stuff was cheap and showed up right away. All the caps I measured where right at the claimed value

 

[Jefenator]

I keep trying to retire my HPF-Pre, but everything I've ever tried just sounds that much better with it patched in.
For the time being, I have surrendered. Until that happy day when I find that amp head (or combo!) that sounds as rich without the 10M buffer & HPF, I will deal with one extra cable and a 9V every 6 months. (It helps my OCD to have the right length cables. 10' from the bass & 5' to the amp is usually perfect.)

 

[bassically_eli]

Sorry for taking so long to update this thread. I made a custom cable. I had a cable on hand that was already slightly high capacitance, so after adding a cap the total capacitance is 3.5nF. I don't like it. It's way too dark, and it renders the presence and treble control on the Headway almost useless, even with the harmonic enhancer cranked all the way up. I'm still wondering if there is a simple RC combination that would work better--without introducing a bunch of noise. I do believe my Lifeline could stand to benefit from a lower impedance input; it has way more than enough low end.

 

[Ryan in PDX]

If I'm reading this correctly, it's only your lowest note(s) causing the problem. The block diagram shows the "bass/guitar/violin" switch - which I assume is the unit's HPF - coming after all the gain/exciter/eq. My first thought would be to put a separate HPF before the Headway. I acknowledge that you explicitly said you don't want to do that, but it seems like less work in the long run than trying to figure out a cable solution, especially since you've been unhappy with that process for months now. Sort of a "pick your battles" situation, I suppose.

 

[bassically_eli]

If I'm reading this correctly, it's only your lowest note(s) causing the problem. The block diagram shows the "bass/guitar/violin" switch - which I assume is the unit's HPF - coming after all the gain/exciter/eq. My first thought would be to put a separate HPF before the Headway. I acknowledge that you explicitly said you don't want to do that, but it seems like less work in the long run than trying to figure out a cable solution, especially since you've been unhappy with that process for months now. Sort of a "pick your battles" situation, I suppose.

This is what I've been doing--putting my Fdeck HPF-Pre in front of the unit if I want to use the HEAT feature. Either that, or just not using the enhancer, which is totally fine if the situation allows for a little gain on the mic channel. It's just a bit frustrating because I bought the Headway as an all-in-one box to replace my more complicated signal chain, and it comes so close!

As for unhappy, yes, I'm unhappy with the results of the cable mod, but I enjoy the process. This thread (and many of my other gear interests) are largely an excuse to tinker.

 

[Ryan in PDX]

This is what I've been doing--putting my Fdeck HPF-Pre in front of the unit if I want to use the HEAT feature. Either that, or just not using the enhancer, which is totally fine if the situation allows for a little gain on the mic channel. It's just a bit frustrating because I bought the Headway as an all-in-one box to replace my more complicated signal chain, and it comes so close!

As for unhappy, yes, I'm unhappy with the results of the cable mod, but I enjoy the process. This thread (and many of my other gear interests) are largely an excuse to tinker.

In that case, carry on! It seems odd to me that Headway would put the HPF so late in the signal path.