HP filter after DSP and Stereomour?

[Kmmm]

I'd like to implement a MiniDSP to my system Running my AER BD3 from the Steremour and the bass units from two Hypex UcD400HG
The stereomour using AC filaments does give me a hum. Not much but audible. If i put a HP filter before the stereomour running the full tones from say arround 200-250Hz i will still get the hum Right?
But if I put a cap in parallel on my element (after the Stereomour), say 50uf, would this block out the hum? I might be raving here...I'm new to this...I’m thinking this wild act as a HP filter. This would maybe do some change to phase but I can deal with this on the DSP

Any thoughts on this?

 

[fullheadofnothing]

If you wire your Stereomour directly to your full ranges without connecting the bass drivers/amps, how much hum is there?

How much hum are you measuring at the binding posts of the Stereomour?

 

[Paul Joppa]

I assume this is the original Stereomour, not the current Stereomour II? And I am guessing you are in Europe, from your name?

You are correct, a filter before the Stereomour will not affect the hum, which is 100Hz when the power is 50Hz and the filament gets AC power. (In 60Hz countries, residual hum is 120Hz.)

You can create a highpass after the 2A3 by replacing the parafeed capacitor with a smaller one. If the corner frequency is 200Hz, it would attenuate the 100Hz hum by 6dB - audible but not a lot.  However, this will not attenuate the output at the driver resonance frequency where its impedance is much higher than in the midrange.

An interesting possibility is to put the driver in a very small box, around 5 liter for instance. This would raise the resonance to around 200Hz, with a QT=1.0 highpass response. In that case, you might see 12dB attenuation of the 100Hz hum without adding any filters. This would not be as simple as it sounds of course!

 

[Kmmm]

You are correct, I'm in Europe. And it is the Stereomour (not II). Replacing the parafeed capacitor sounds like something I could try. What value would you suggest?
Putting the drivers in a small box will not work. These are Front loaded horns The AER is 106dB...

Doc was suggesting to wire mye Stereomour in the lowest value (2ohm) the speakers ar 16 ohm. It's now wired in 4 ohm

Attached is a picture of how I'm thinking the set up. What would be the downside of adding a HP filter?
Where would I need the CO point, and what order, to dampen the 100Hz hum sufficiently?
Suggestions would be appreciated.

(There is also som hiss in the Eros. I hope this will sort out after I replace the LM431s)

I'll try to measure the values on the binding post soon.

Regards
KÃ¥re

 

[Paul Joppa]

Changing the parafeed capacitor relies on the output transformer being loaded with the right resistance, which complicates the design, especially when you are using the low-impedance tap with a high-impedance load.

Example: with a 16-ohm resistance loading the 4-ohm tap, the reflected impedance at the output transformer primary would be 16K. That's the value used to calculate the capacitor. About 0.050uF would give 200Hz. However, the transformer inductance is adequate for its design impedance of 4K but may prove inadequate at 16K. I can't say whether this is a real problem or not, but it's an inexpensive experiment, which will give you better information than my theoretical analysis/speculation!

I think this is becoming more a project rather than a simple design. For instance, you could put a 5.3-ohm resistor in parallel with the 16-ohm speaker, so that the combination loads the output transformer with 4 ohm that stays close to resistive and close to 4 ohms across the frequency spectrum. Then you could count on the reflected impedance to be close to 4K and close to resistive, and a 0.20uF cap would give the desired 200Hz highpass function. Again, I can't say if that would be audibly better or not.

Switching to the 2-ohm wiring would reduce the hum by 3dB - probably audible but not a big change.

The LC highpass in your circuit should give about 12dB hum reduction if designed for 200Hz. I would expect that to be adequate for 106dB sensitivity speakers.