EMG Active Pickup Circuit?

ansil · Post by **ansil** » 23 Sep 2009, 04:46

Ben N wrote:I had heard that the SPC was more like the Anderton Frequency Booster than the EC.

you are correct i traced this out years ago but the schematic died with my first computer. but it was part for part the same schematic later models changed the freq curve via changing your rc network dont remember the values but they weren't that far from the originals. my old one died and it was generation 1 they are on gen 4 or 5 now.

ansil · Post by **ansil** » 23 Sep 2009, 07:33

ok it wouldn't let me edit my post but check this out.

javascript:openreq('http://www.datasheetcatalog.org/datashe ... 009300.PDF')

page 6 its the datasheet's recomendation for a basic comparator circuit look familiar

Ben N · Post by **Ben N** » 23 Sep 2009, 15:03

Hi, Ansil, long time no "see". You might have been who I heard this from in the first place, back at Aron's. Thank's for the datasheet link.

ansil · Post by **ansil** » 23 Sep 2009, 22:55

Ben N wrote:Hi, Ansil, long time no "see". You might have been who I heard this from in the first place, back at Aron's. Thank's for the datasheet link.

well hello yeah i was a big poster over there sadly lack of internet and using a public computer system got me in not so friendly terms so i walked away and concentrated on playing and building. found i make more money and have more fun just building my crazy stuff and playing. still people come up to me and want to know how i got that tone. i just made a 6x profit on my hughes and kettner blue 30r {well i only paid 25 for it} i tricked out clean channel and the eq closer to a mixer than the stock amp. sorry for rambling about that. as far as emg goes i watched the video online like someone suggested and it was cool learned some neat things.

bajaman · Post by **bajaman** » 27 Sep 2009, 09:24

Hello again
Does anyone want to build an active preamp humbucking pickup

I wound two of the Stewart McDonald alnico humbucking pickups last week and attached two EMG style differential preamps on the bottom nickle silver base of each pickup. I soldered the through hole components on the copper track side of the PCB, then filed the leads flush with the plain side of the board. I inserted a small sheet of mylar overhead transparency film between the board and the baseplate to avoid shorting anything to ground. I soldered the earth bus at each end of the PCB to the baseplate of the pickup and ran a small bead of glue to hold it firmly in place. I laid the film caps and the electrolytic on their sides to keep as low a profile as possible and to assist soldering to the PCB.
I wound around 8000 turns of 42 gauge enamelled copper wire (.050) on each bobbin and connected the start of each coil to the metal baseplate. The finish of each coil winding was fed to the non inverting and inverting inputs of my active preamp boards.
I wanted to retain the sound of a high output side by side humbucker, so I used a resistor in series with the non inverting input, unlike the EMG 81 which has no resistor fitted and consequently has a more single coil resonance. I used larger biasing resistors (330k each) unlike the 170k resistors fitted to the EMG 81, because i did not want to damp the resonance and shift it's frequency too far down - i suppose I could have used 1M resistors for an even brighter and higher resonance, but in practice the pickups sound very nice. I tried them out with my band mates at practice in the weekend and they were most impressed with the lack of noise and the smooth sound I was getting without any pedals.
It should be possible to fit the active preamp boards to most un-encapsulated humbucking pickups. All that is required is to separate the wire connecting the two coils in series and bring each coil winding out to the non inverting and inverting terminals of the differential preamp board - the existing output is simply grounded by connecting it to the baseplate.
I hope the above makes sense!!!
I purchased some black plastic pickup shells and lined them with self adhesive copper foil - should prevent any static electrical charges or computer generated rf etc from being induced in the coils.
Here are some pictures and PCB layouts for a through hole Active preamp board and for the more adventurous DIYers - a SMT design for 1206 size (although 0805 will also fit!!)
Please feel free to ask any questions
cheers
bajaman

members/bajaman/Baja/Active%20preamp%20 ... er%201.jpg
members/bajaman/Baja/Active%20preamp%20 ... er%202.jpg
members/bajaman/Baja/Active%20preamp%20 ... %20PCB.png
members/bajaman/Baja/Active%20preamp%20 ... verlay.png
members/bajaman/Baja/Active%20preamp%20 ... posite.png
members/bajaman/Baja/Active%20preamp%20 ... %20PCB.png

bajaman · Post by **bajaman** » 27 Sep 2009, 10:12

the overlay!!!
members/bajaman/Baja/Active%20preamp%20 ... verlay.png
cheers
bajaman

all PCB images are 1200dpi

bajaman · Post by **bajaman** » 27 Sep 2009, 11:05

Here is the guitar with the active humbuckers fitted.
members/bajaman/Baja/Active%20preamp%20 ... uckers.JPG
cheers
bajaman

ansil · Post by **ansil** » 27 Sep 2009, 11:11

very well done i am stoked seeing that is really nice. question why not go ahead and make it smt since you were doing it? or were u just going with on hand parts. my ole business partner messed up the order and got us a ton of misc smt stuff for our pedals but i couldnt' use any of it because the boards were for full size parts. i managed to utilize some of it now thought

bajaman · Post by **bajaman** » 27 Sep 2009, 11:58

Yes - most of my stock parts (99.9%) are through hole, but I am getting into SMT more and more as a neccessity - so much product these days is SMT - I have to find some SMT LM4250 opamps for my next project, although the through hole/pseudo SMT board worked out very nice for this project.
cheers
bajaman

ansil · Post by **ansil** » 27 Sep 2009, 12:45

so is the chip in question here a must have or could it be replaced with another one

bajaman · Post by **bajaman** » 27 Sep 2009, 19:49

The LM4250 is a programmable current op amp with a specific pin out configuration. You set the operating current (and slew rate

) with one external resistor - in this instance a 1M value sets the current draw to 80 uA for a very long battery life.
I suppose other single op amps could be used with the pin out changed on the PCB, but most of the low current variety (TL061, LF441 etc.) draw 200uA at least which will shorten the battery life. One thing I have noticed with the LM4250 (as used in the ORIGINAL Music Man Stingray onboard preamp) is a smoothing of the high frequency response - probably due to the low slew rate at low current consumption. However, this is not necessarily a bad thing, particularly with ceramic magnet pickups

cheers
bajaman

chicago_mike · Post by **chicago_mike** » 27 Sep 2009, 23:43

any changes needed for a bass pickup preamp?

EDIT: I always thought the weakest part of emg bass pickups was the pickup itself, not the buffer/preamp.

bajaman · Post by **bajaman** » 28 Sep 2009, 06:16

You could increase the 22n coupling capacitors to 47n, OR check out the musicman preamp thread

bajaman

bajaman · Post by **bajaman** » 28 Sep 2009, 09:59

.......but wait - there's more

I am really getting into SMT - I modified an Ibanez SD9 Sonic Distortion pedal today and it was relatively easy with SMT capacitors and resistors, to turn the redundant op amp unity buffer into a recovery gain stage between the tone control and output level control. I have found it very easy to obtain SMT resistors and capacitors locally and they are much cheaper than the through hole passive components - the 1uf 50v ceramic capacitors are just too funky for words and are MUCH smaller than the eqiuvalent value in polarised electrolytics.
BUT - SMT active components are not so easy to obtain locally for me - in particular the LM4250 programmable current op amp used in this design, SO -------
I designed a board to accomodate the through hole DIP8 package op amp and SMT passive components.
members/bajaman/Baja/Active%20preamp%20 ... verlay.png
members/bajaman/Baja/Active%20preamp%20 ... posite.png
members/bajaman/Baja/Active%20preamp%20 ... %20PCB.png

The component values can be altered to tone model your pickup to your taste.
I would encourage reducing the 33k in series with the non inverting input - possibly with an external trim pot to dial in the brightness of the pickup - reducing this to zero should give a more single coil like sound perhaps while still retaining the noise cancelling properties of the differential gain stage.
ALSO - the 22n capacitors can be decreased for less bottom end response OR the two 330k resistors can be reduced or increased in value - this will alter the pickups resonance - lower values should lower it's effect and possibly shift the resonst peak down in frequency - higher values (say 2.2M) should give a much more pronounced resonance at a higher frequency for a brighter sounding pickup.
The 1M resistor can be increased for still lower current drain but reduced top end response, or increased for a brighter top end but lower battery life - check out the Musicman preamp thread for more information.
These are by no means the only mods possible - have fun

You are encouraged to share your findings in this thread - happy DIY experimenting

cheers
bajaman

once again - all images are 1200dpi

gnognofasciani · Post by **gnognofasciani** » 28 Sep 2009, 10:10

Thanks a lot Bajaman! This circuit is in my "To do list" and since I'm building 3 guitars, I think I will try it at least on one!

CHEEZOR · Post by **CHEEZOR** » 28 Sep 2009, 19:56

Wow. Nicely done! Thanks for all the detailed pictures. Makes me want to try it sometime. I think it will be a while though.

ansil · Post by **ansil** » 01 Oct 2009, 11:55

at 1:25 or so you see them talking about how many turns and what guage wire they used for each coil. it is labeled on the sheet right in front of the camera.. and emg 81 85 gets two coils with 42awg wire 57 turns per coil

ed

bajaman · Post by **bajaman** » 01 Oct 2009, 20:35

emg 81 85 gets two coils with 42awg wire 57 turns per coil

they show their turns # in 100s
So that makes them 5700 turns per coil of 42 guage wire (or 47 swg for British wire size) or .056 diameter.
I use .050 and wind 8000 turns per coil for a fat Les Paul / 335 humbucker.
The lower turns count used by EMG in their 81 pickups and the deliberate gain unbalance in their differential preamp coupled with a ceramic and steel magnet system is what gives the EMG 81 such a clear top end that will cut like a knife through butter - you won't get that Gibson "squark" from these pickups - they are almost single coil sounding, but with zero hum and noise.

bajaman · Post by **bajaman** » 02 Oct 2009, 09:31

Further to my last post, I have made some small changes to my active humbucker preamp (AHP)
I noticed that the high frequency end of the pickup's response was a bit restricted (perfect for jazz guitar players

) but not enough "bite" for my liking. As mentioned in my last post i wound two pickups (4 coils), each coil wound with 8000 turns of .050 wire on Stewart McDonald alnico humbucking pickup kits.
Most Gibson pickups used in Les Pauls and 335s etc. use 500k volume pots which load down the coil and tame it's high frequency resonance. if you have ever fitted a humbucker in a Strat style guitar with 250k pots you will know what I am talking about - the resonance and "bite" of the pickup is nowhere near as bright sounding with this lower resistance in parallel damping the coil's response.
Well - i took another look at my differential preamp design - I was using two 330k resistors to bias the non inverting op amp input to 4.5v dc. These resistors are effectively in parallel if one ignores the low impedance of the battery supply - or 165k, which is a very low resistance in parallel across the pickup coil, and here is the problem!!
For the differential amplifier to work correctly the feedback resistor from the op amp's output to the inverting input also needs to be this value ( 150k + 15k = 165k

).
So how do we load the coils with 500k - simple, we use two 1M resistors as the bias resistors and two 1M resistors in parallel with each other for the feedback resistor. We do get a little more gain from the higher value resistors which is not necessarily a bad thing as it turns out because the sound is now a lot better with an almost identical "bite" to a genuine Gibson high output (not an SG

) Les Paul pickup when the volume control is set to 7.
the extra output gives a really nice fat response that easily overdrives most clean channels on tube amps etc.
I have A B tested my guitar fitted with this pickup and preamp configuration and another guitar i have fitted with two EMG81 pickups and it makes the 81s sound very thin and lifeless in comparison.
The humbucker "squark" is their in spades with no discernable noise whatsoever - even in front of a computer monitor.
When I turn the guitar volume from 0 to 10, I cannot hear any increase in noise whatsoever, which is eerie to say the least.
My next project is going to be similar to the EMG 89 which incorporates three coils (2 stacked on top of each other for a single coil humbucking sound and a further coil next to this for a traditional Gibson side by side humbucker).
It will incorporate two completely independent differential active preamps tuned for the "perfect" strat response and "les paul" response - both totally noiseless - the best of both World's.
i will make some sound samples when I finish this one and post them either in this or a separate baja active guitar preamp thread.
please do not hesitate to ask any questions, if there is anything you do not understand.
I shall do my best to try and answer them

cheers
bajaman

ansil · Post by **ansil** » 02 Oct 2009, 12:34

you know i would probably like to check out your darker pickup if you were say wanting to let someone test one out for you. i actually need something darker in my bridge. my duncan in bridge is way to bright for my liking. my neck is ok though i run a .005uf cap in series with the output of the pickup to the switch so when its engaged it rolls off a little of that useless lowend from the neck pickup. ie the mud freq.

i dont' have a coil winder you interested in a custom project???????