NEVE HPF to 1290 preamp

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dmp

Well-known member
Joined
Oct 28, 2009
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Madison, WI
I'm trying to add a HPF to a Neve 1290 project I'm building. I built the BA182 circuit using the 9043 inductor, and put it between L and P on the BA183.
A CLC high pass filter.
I triple checked connections but it looks wrong when I swept the freq response. The bass bump is noticeable in listening. 
Frequencies are appx correct.
The base of the inductor is definitely connected to audio ground.
Any ideas?

This thread has a little background that I followed for this:
http://www.groupdiy.com/index.php?topic=42623.0
 

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you gotta tweak the C's (or the L) and/or  add a series r.

I used 1k8r  2u2  3.5H(shunt)  2u2 between stages of ba283 for roughly 3db down at 60Hz
and 1k8,.47u, .9H, .47u  for roughly -3db@160 Hz

with 50 ohm series to 2u2, 3.5H, 2u2 there is a nice peak (6-12db) at 50Hz

I don't have the rmaa in front of me, but my sweeps seemed to have a steeper attenuation-- hand wound L on pot core.
 
See resistors R32-10K, R37-1.2K and R70-5.1K (1073). The EZ1290 schematic shows R99-5K pot to ground between P and L but you may not have this in place, if not add a 5.1K resistor there for correct loading of the filter. R20-51K (BA183NV), add a resistor in parallel to equal 10K or replace with 10K followed by R37-1.2K if not already in place.
 
MatthisD said:
See resistors R32-10K, R37-1.2K and R70-5.1K (1073). The EZ1290 schematic shows R99-5K pot to ground between P and L but you may not have this in place, if not add a 5.1K resistor there for correct loading of the filter. R20-51K (BA183NV), add a resistor in parallel to equal 10K or replace with 10K followed by R37-1.2K if not already in place.

Yes, all this for proper impedance path.

(And, R71 (39k) keeps it all tied down between switch positions. You can probably omit this if you use a MBB switch.)

 
Here is a diagram for the circuit:
L and P are on the EZ1290 PCB
The BA 182 schematic can be looked up. Here showing just one position of C-L-C.
I did 5 positions (20,50,80,120,300 Hz) plus off.
I used a grayhill rotary switch. Not sure if it is MBB or BMM, but it switches without pops without the tiedown resistors, so I didn't bother installing them (4.7M etc..)
 
 

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If you can see the switch, the last letter in the part number will tell you if it is MBB or BBM.

S = MBB
N = BBM
 

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