Passive 6dB EQ

[ruffrecords]

I just did a quick sim and the R is half what I said because it is the parallel combination of the  the 10K and the 11K from the centred treble control. Bottom line is 2H give a 3dB point of about 300 Hz and the ultimate shelf is at 100Hz. I think the 0.22uF of the original must be wrong because it gives a shelf at 1KHz. If you use 22nF you get a shelf at 10KHz as expected.

I have attached the LTspice sim file so you can play with it yourself. You will need to change the extension to .asc to be able to load it into LTspice.

Cheers

Ian

 

[bernbrue]

I've got this in my RIM Musikant de Luxe. Sounds sweet. Definitely something to test.
Bernd

 

[DerEber]

ok cool, very good explaination.
That realy helped me!
So the boost/cut pot resistance is also determining  the shelfing and the output pot plus the rest over there is fixing the actual frequency.

So the frequencies take the shortcut through the cap and see another pot.
Wait, but only those that are boosted or cutted by the bass controll.
But a  0,22 uF at 400Hz has a 1800 Ohm impedance by itsefe and a 22nF has 18kOhm at 400Hz.

Thanks again Ian, this was very helpful to me.
I do not have Spice, but maybe it is time to check it out.
I just know I get lazy thinking when the program starts doing it.

 

[abbey road d enfer]

I've got this in my RIM Musikant de Luxe. Sounds sweet. Definitely something to test.
Bernd

That's a "standard" 20dB James, that requires 10% log pots. In the neutral position, the frequency response error can be up to 3dB.

 

[PRR]

> a "standard" 20dB James, that requires 10% log pots

Yet the plan says "Linear".

Also the 100K over the Bass is 200K, and there is a 200K 10K pair around the Treb pot which is not classic James.

I threw it at Duncan TSC before I realized the extra (missing in TSC) Treb parts. I'm not excited enuff to throw it to SPICE.

 

[abbey road d enfer]

I've got this in my RIM Musikant de Luxe. Sounds sweet. Definitely something to test.
Bernd

Please find attached sim graphs.
Green is with controls in center position, quite far from linear.
Blue is with controls at 10% as they would be with 10% Log pots. Not very linear, but reasonably compared to teh response of speakers.

 

[abbey road d enfer]

I've got this in my RIM Musikant de Luxe. Sounds sweet. Definitely something to test.
Bernd

Looking at the complete schemo, I see that the input channels have exactly the same EQ.
Simulation shows that whatever you do with the Höhenregler und Bassregler (except when Bass is fully CCW), there is always a 7-8 dB dip at ca. 3.2 kHz. When both input and output EQ's are cascaded, it results in a 15dB dip of offensive nasal frequencies. No doubt you find it sweet... ;D.
The flattest response is when the Bass pot is between 5% and 10% of its rotation.
I suspect this is intended to compensate the deficiencies of the speakers.
I have no info on the particular speakers that were intended for the Musikant, but I remember at the time German PA loudspeakers often used a mid-hi horn that would have sounded very nasal.

 

[ruffrecords]

Now I am properly moved into my new home I have started work on a set of PCBs for the 600 ohm version of this project. There will be three types.

1. A common switch board. This holds two Grajhill  1 pole 12 way switches. One is the level control (plus or minus 10dB in 2dB steps for example) and the other is the frequency select switch. Both are connected to 12 way Molex connectors.

2. EQ board which hold  the LCR required for a particular band. Not sure how many variations of this there will be. We may need one dedicated to bass because it will need a larger inductor than the other. A second would use a smaller inductor for low mid and a third might use axial leaded inductors for high mid or high. Any of the boards could be used for shelving high just by shorting out the inductor posistion. This board will connected to the 12 connector from the frequency select switch. I am toying with the idea of this board piggy backing onto the switch baord if only to keep frequency  selective connections as short as possible.

3. Interconnect board.  Tbhis has the EQ in and out connectors, the single resistor ladder used by all bands and a bunch of 12 way Molex connectors that connect to each band.

I will post layout pics as they become available.

Cheers

Ian