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Active Pre-Amp question


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4/18/2004 9:11 PM
Fred Hammon
Active Pre-Amp question
I've got a customer that wants to couple a set of my pickups with a J-Retro preamp system. The trouble is that my pickups have very high output and I was thinking of winding a set specially suited for this amount of gain. It would be over-kill as it is.  
Presently I'm using #43, 7,500 winds measuring at 6.5K. I'm afraid that if I under wind the pup it's tonal characteristics will change too much. Does it really matter with this type of system?  
 
http://www.j-retro.co.uk/main.htm
 
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4/18/2004 11:25 PM
Fred Hammon

maf has suggested this to me. It's called an Impedanz-Wandler made by Helmut Lemme. It's an impedance lowering device like an emitter follower I gather but I don't speak Deutsch.  
 
http://www.gitarrenelektronik.de/elektronik/a_elektronik/a_elektronik.html
 
4/19/2004 8:31 AM
maf

Bei starken Pickups kann man die Schaltung aber auch so auslegen, dass die Lautstärke nicht erhöht wird, sondern nur die Resonanzüberhöhung des Pickups. Dazu schaltet man einen sogenannten Impedanzwandler (Bild 3) zwischen Pickup und Poti. Man hat damit das Gefühl, durchaus noch mit derselben Gitarre und denselben Pickups zu spielen, aber da ist einfach mehr Farbe: charakteristischer, bissiger. Unüberhörbar.  
 
to avoid translation-mistakes (my German-language is even more worse than my English !) maybe someone on this forum can translate this decently ?  
 
with regards  
Maf
 
4/20/2004 1:53 PM
Sheldon Dingwall

If you have a customer wanting you to wind your pickups, they are looking for your familiar tone. Even 500 fewer turns will make a significant difference in tone that will force the customer to compensate with the eq.  
 
J-retros have input trimmers that I believe would be useful if the output of the pickups are clipping the inputs to the pre-amp. If not, you could do it passively.
 
4/20/2004 4:56 PM
Fred Hammon

Thanks Sheldon.  
I'm not crazy about this marriage but for some reason the customer has to have a J-retro.  
BTW the Hagstrom pickups that I'm recreating are the same ones that Alembic used on their first active bass systems around '69.  
Ron Wickersham mounted emitter followers directly onto the pickups to lower the Z. I believe the signal then went to a mic preamp system and what was essentially a channel out a recording console with some Q filters mounted inside a hollowbody bass.  
The pickup was still able to deliver it's entire frequency range to the preamp without the high end loss associated with line capacitance. They found that even 6" of harness wire was enough to cause a measurable loss.
 
4/21/2004 5:40 PM
Mark Hammer

My concern would be that the marriage of hot pickups and preamp would yield overall guitar output levels that would be rendered unsuitable for a number of tasks, such as providing a level that anything with a sidechain (noise gate, compressor/limiter, envelope-controlled filter, attack envelope modifier, etc.) is designed to anticipate, or providing a level that headroom-limited devices, like phasers, or BBD-based devices, lacking companders can't cope with. A hot guitar signal that only lets you actually use 5 degrees of pot rotation on an effect control before it turns to mush, is *limiting* options more than improving tone.  
 
If there is a means of varying gain in the preamp to turn it into more of a buffer than booster, that would be good. If the preamp does not permit that, I would think the customer needs to know now.  
 
On the other hand, if the customer is someone who anticipates using that instrument exclusively for going direct to an amp that only "behaves well" when tortured by robust input signals, then there is no problem.
 
4/21/2004 10:04 PM
Fred Hammon

Hey.  
Who ever said that musicians were logical?  
It's up to us guys to make the impossible possible right?  
However......in this case I'm going to try to talk him out if it.
 

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