Quick Pure Western Mini PADI Impedance fix!

[heylow]

I don't know if this has been passed around before but I haven't seen it if it has. I thought a few people might find this info fun to experiment with.

As many of us know, there is an impedance mis-match between the K&K Pure Western stuff and the Baggs PADI. Someone on the Larrivee board emailed Baggs and was kind enough to post the response.

I emailed lr baggs concerning the para di being a mismatch for the pwm.

Here's what they replied.

The Para D.I. has a 10MegOhm input impedance. You can place a 1MegOhm resistor between signal and ground, anywhere between the pickup and the Para D.I.'s input. It can be in the output jack of the guitar or in either end of the cable. The 1MegOhm resistor will interact with the 10MegOhm input resistor and cause the input impedance to drop to just below 1MegOhm. This should address the extra bass caused by the Para D.I.'s stock imput impedance bring so much higher than that of the pickup signal.

Many thanks to the original poster. I thought this bit of info was best passed around.


For the record, I haven't tried it yet.....could be interesting and well worth the hassle. Could just be a hassle.

heylow

[sdelsolray]

That would certainly work. Result would be about 980k Ohms, if I did the math right. You can mod the PADI inside too, by swapping resistors (the one nearest the FET). It's probably a good idea to do the mod with a cable, or perhaps an inline connector (e.g., 1/4" female to 1/4" male). Use the special cable for a K&K and use an otherwise normal cable for passive pickups wanting a 10 megohm input impedance (which most other acoustic guitar passive pickups like).

[heylow]

Originally Posted by sdelsolray

That would certainly work. Result would be about 980k Ohms, if I did the math right. You can mod the PADI inside too, by swapping resistors (the one nearest the FET). It's probably a good idea to do the mod with a cable, or perhaps an inline connector (e.g., 1/4" female to 1/4" male). Use the special cable for a K&K and use an otherwise normal cable for passive pickups wanting a 10 megohm input impedance (which most other acoustic guitar passive pickups like).

Yeah, I was thinking more of the possibility of something in-line for the sake simplicity and versatilty. Small hammond boxes are cheap and plentiful and so are jacks and resistors. Drill a couple holes, tighten a couple of nuts, drop a little solder and the whole deal should maybe cost you 6-10 bucks.

This way you don't have to deal with special cables or whatever at crucial times. It's one extra small box....good deal for those wanting to try it.



On another note, Sdelsolray......

You seem to have the math straight...maybe you can answer a little question for me. Looks like I will be installing the K&K Trinity system which will use the K&K pre. BUT! This pre will be feeding the Baggs PADI just the same. Does this change change anything regarding the mis-match? Better? Worse? Same? If it's anything like the original Pre, it's probably 10kOhm at the output going into the PADI's 10MOhm. Just curious.

And...I see you on Gearslutz from time to time, no?


heylow

[sdelsolray]

There are good discussions about impedance around the web. The rane.com site has a very good dictionary of audio terms (in their reference section).

Passive acoustic guitar pickups are high impedance transducers. They output a rather low level signal (in voltage). Impedance is akin to resistance, in large part. It is measured in ohms. The higher the value, the lower the resistance.

Two things have to happen to the pickup's signal to allow it to work with (or be compatible with) a power amp and speakers. First, the impedance of the signal needs to be lowered. Second, the voltage of the signal needs to be increased.

Nearly all modern audio gear (past 30+ years or so) is designed so that the input impedance of the device has a high value (low resistance) and the output impedance has a low ohm value. That way, you can hook things up, output to input, over and over, without any problems. The K&K Trinity preamp does provide separate eq for each pickup...BUT the controls are not accessible unless you take the cover off. That's a significant (i.e., fatal) design flaw in my book.

The K&K preamp takes the high impedance of the K&K pickup and changes to a low value (dunno what it is, but perhaps 600 ohms). So does the PADI. So does any DI. This is commonly called buffering.

Many of these units also increase the voltage of the signal (i.e., adding gain to the signal). This is the "gain stage" or "preamp" part of the unit. Besides the proper values of impedance between two devices, the strength of the signal must be known. Why? Because each device is designed to handle (as an input) a signal within a certain range of strength (i.e., voltage). A signal that is too weak will remain anemic even after running through a gain stage that is expecting to see a stronger signal in the first place, plus the signal to noise ratio suffers. Similarly, a signal that is too "hot" (more voltage) will overload a gain stage that can't handle that strong of a signal.

To your question, the K&K preamp buffers the signal and adds gain to the signal. The output signal will be within a certain voltage range, say 900 millivolts to 1 volt (I'm making those numbers up because K&K doesn't publish them, nor does Baggs, nor does ...). The PARI DI will have a spec - a voltage range at its input that it can safely handle. If the K&K's output voltage range and the PARI DI's input voltage range overlap, then yes, you can plug one into the other and use that gear together (how it will sound together is another topic). If they don't overlap, or don't overlap very much, then no, you can't (or shouldn't) use the two devices in series. The impedance issue is a non issue when connecting these two devices together, as the original pickup signal's impedance has already been buffered by the K&K preamp.

Yeah, I visit Gearslutz from time to time. Good and interesting info. Those folks are pretty passionate, and I've learned quite a bit over there.

Regarding the Trinity, consider something a bit different. Install the K&K mini and their internal mic (other someone else's internal mic) I think K&K calls this the "Trinity Solo" (sans preamp). Wire the pickup to the tip, mic to the ring. Run a good TRS-TRS cable to an outboard dual source blender, like a D-TAR Solistice, K&K Quantum, Rane AP-13, Highlander PAMDI or Pendulum Audio SPS-1. Lose the PARI DI, it's not designed to be used with dual source setups.

[selectortone]

I have mounted a 1meg audio potentiometer in a small box that I attach to my strap with velcro. The box has a short cable with a jack that plugs into the guitar and a jack socket for the output cable.

The purpose of the box was to provide a volume control for my two K&K equipped guitars but since it presents around a 1m ohm load (I use it at 90% to full on) to my PADI it has the extra benefit of providing the above mentioned quick 'n' dirty impedence matching.

The box sits on the strap close to the strap-jack, right by my right hip and gives me the control over volume I'm used to as a (primarily) electric guitar player. It's main purpose is to knock the volume down in case of feedback.

Here's a pic. This little gizmo literally cost me a couple of pounds ($4) as I had all the bits in my parts boxes (I'm a guitar tech). That (nice big) knob is off a '50s radio

Presumably the John Pearse JPV1 would have the same effect depending on the value of pot they use.



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[moo cow]

heylow,
i have the trinity system in my GS and i run in into the k and k blender then into a baggs padi as my d.i. box. sounds great!!! last night i bypassed to mic and ran just the mini western straight into the padi and it sounded good too. but not as good as the dual system/blender combo. i know nothing about imp. matching. i just let my ears tell me what sounds best.

[heylow]

Wow....

Lots of great stuff from everybody! That volume box is a really practical way to get the resistor in-line....well done there!


Hey Moo Cow....

Glad to hear that. My Trinity system is actually on it's way. My theory was that I would use the K&K pre/blender for basic tone shaping, which would leave the Baggs' controls open for dealing with the differences from stage to stage. In theory, this seems like a great way go.....the other pre/blenders on the market are great but it's SO hard to beat the Baggs' EQ options for fighting feedback. I haven't been on a stage yet that didn't involve me reaching for the notch filter.

Out of curiousity, how are you setting gain controls on the Trinity and the Baggs to avoid overloading the Baggs? How much mic are you using typically? I'm pretty psyched to try this setup as I already LOVE the Pure Western Mini by itself!


heylow

[moo cow]

heylow,
i keep the gain on the pre/blender at appx. 25% and use the baggs to pump the signal to the board. in a band settings i'll turn the mic up 30% and the SBT up to 75% with NO feedback ever! i could probably use a little more mic but i'd rather not push my luck. in a solo or quieter gig i'll go 50/50 with the mic and mini. you WILL NOT be disappointed with the trinity. i put them in all my guitars.

[KMHaynes]

Originally Posted by selectortone

Presumably the John Pearse JPV1 would have the same effect depending on the value of pot they use.

I have one of the John Pearse JPV1, and I have only tried it on my son's amplifier using all the flat settings, and the JPV1 is very clean, no noise at all. I'm going to probably velcro it onto my strap as well. Looks very similar to your volume box, but with a black knob.

[hann]

does anyone have any updates regarding this mod?

I just got someone to mod my cable at the guitar end of the cable but haven't had a chance to try it.

When he was doing the mod, he then tested the cable with some devive ( i think some current/volt test) and there were all these beeping sounds.. he said one jack had a short somewhere.. is there even such a thing as a short in a jack?

So he got a new jack for me and used that gadget again..explainin in non layman term about ground, etc etc.. beep here and there.. not sure if he was just out to cheat me into paying more for parts.. I used the same cable the day before and had no problems.. mmm

anyway, i'm hoping the mod does help with my guit in my church system... some days there's no problem, some days there's a bass overload.. so I figured might as well try the mod...

[66strummer]

Originally Posted by heylow

I don't know if this has been passed around before but I haven't seen it if it has. I thought a few people might find this info fun to experiment with.

As many of us know, there is an impedance mis-match between the K&K Pure Western stuff and the Baggs PADI. Someone on the Larrivee board emailed Baggs and was kind enough to post the response.



Many thanks to the original poster. I thought this bit of info was best passed around.


For the record, I haven't tried it yet.....could be interesting and well worth the hassle. Could just be a hassle.

heylow

Hi. Pardon me for being a bit Dumb about this idea...Are we talking about soldering a resistor into the inline cable somehow or is there an actual resistor (device) that can be put inline between the pickup and the Para DI box (not requiring soldering)that will cause the impedences to match? I hope my question makes sense.

[BuleriaChk]

The resistor is across the output (across tip/sleeve, or signal/ground), NOT in series with the tip.

I use PUTW and Brian at LR Baggs told me about this when I was still having overbass problems with my new A-Ref. The solution fixed EVERYTHING, and the A-Ref sounds gorgeous, along with all the other devices/software solutions I've tried.....

I told PUTW about it, but apparently they are still in denial....:-) In any case, I no longer need the PowerPlugs, since the input gains of most of the devices are more than enough to give a clear sound.

[Seagull Lover]

I mod'ed one of my cables with the 1meg ohm resistor and it sounds much better all around. I plug into a 7-band EQ (1meg ohm), into my Bellari Tube preamp, then into my keyboard amp or a PA. None of those inputs are have a higher impedance than the K&K but the resistor still rolls of the bass and low mids making the sound a lot less muddy. I have not been able to achieve the same with just EQ. I have the standard sized K&K which I believes needs more roll off of the bass and mids than the mini K&K's. Here is a somewhat fuzzy picture of the mod. It's really very simple if you are handy with a soldering iron.

[hann]

oh dear mine doesn't look like that at all.. it has to be soldered ACROSS the 2 points?

not sure if mine's correct.. basically he soldered the resistor along with the inner wires of the cable... and soldered that onto the upper part of the jack. The outer ring of wires he just soldered normally to the lower part...

is there gonna be a difference?

[DMZ]

I sucessfully modded my cable tonight as well, thanks to your pic and Radio Shack, plus 99 cents. Seems to help some of the bass, but I'm not sure if I lose just a smidge of everything else. I kept switching cables to compare. Will see what it does thru the big sound system Wednesday nite. Need to test it with my K14c PUTW Tues nite.