Hi,
I've been looking for an easy, quick way of reducing bass amount when watching/listening late at night. I don't need an eq or full tone controls, just a switch that activates a fixed high pass filter. Problem is I want the signal completely untouched when the filter is bypassed (aka source direct on some systems).
I came up with this schematic for a simple circuit to build into my preamp. I'm worried that even when the filter is bypassed the R and L channels will still be connected to common ground through R2 and R4, thus "touched". Even if I cut the ground as well with a 3-pole switch, R and L are still connected to ground via the connectors in the output end. See red markings. Do I need to find a 4-pole switch to cut R and L in both the input and output ends? Or would you consider the bypassed signal "untouched" in this scematic?
I'm planning to put the filter after the amp section, directly before the output to powered speakers.
BTW, I used CircuitLab, very nice: http://www.circuitlab.com/
I've been looking for an easy, quick way of reducing bass amount when watching/listening late at night. I don't need an eq or full tone controls, just a switch that activates a fixed high pass filter. Problem is I want the signal completely untouched when the filter is bypassed (aka source direct on some systems).
I came up with this schematic for a simple circuit to build into my preamp. I'm worried that even when the filter is bypassed the R and L channels will still be connected to common ground through R2 and R4, thus "touched". Even if I cut the ground as well with a 3-pole switch, R and L are still connected to ground via the connectors in the output end. See red markings. Do I need to find a 4-pole switch to cut R and L in both the input and output ends? Or would you consider the bypassed signal "untouched" in this scematic?
I'm planning to put the filter after the amp section, directly before the output to powered speakers.
An externally hosted image should be here but it was not working when we last tested it.
BTW, I used CircuitLab, very nice: http://www.circuitlab.com/
please attach your pics.
Makes for a faster download of the page and allows rescaling of the pic so that the text wraps properly on to the available screen width.
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The disadvantage you see is simply a 11k of extra loading on the source.
If the source has a low output impedance and the receiver has a highish input impedance then the extra 11k in parallel across the receiver should make no audible difference.
Check you source and receiver impedances.
Another unhelpful post?
Makes for a faster download of the page and allows rescaling of the pic so that the text wraps properly on to the available screen width.
If I "back" out of the page and then "forward" to reload the page the text will wrap for me, but attaching avoids us Members having to load a page twice.
The disadvantage you see is simply a 11k of extra loading on the source.
If the source has a low output impedance and the receiver has a highish input impedance then the extra 11k in parallel across the receiver should make no audible difference.
Check you source and receiver impedances.
Another unhelpful post?
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Sorry, I was looking for an attachment button but I couldn't find one, but now I see it clearly. Must have been tired...
I don't have any way to measure output / input impedance at this moment, but let's assume they are fairly matched. How can I design the filter to not increase the pre's input impedance when bypassed? (When activated it will of course, since it's passive.)
would a 4-pole switch do it? Like this (all SW1 switches are assumed the same physical panel mount switch)
I don't have any way to measure output / input impedance at this moment, but let's assume they are fairly matched. How can I design the filter to not increase the pre's input impedance when bypassed? (When activated it will of course, since it's passive.)
would a 4-pole switch do it? Like this (all SW1 switches are assumed the same physical panel mount switch)
Johan,
You're over-thinking this too much.
You really should measure (or find out) the input resistance of your power amp and output resistance of your preamp. Once you know the power amp input resistance you can get rid of R2(R4) and scale the values of C1/R1(C2/R3) to provide the shelf you're looking for. Then just put a switch across the combination to disable/enable the filter.
Cheers,
Dave.
You're over-thinking this too much.
You really should measure (or find out) the input resistance of your power amp and output resistance of your preamp. Once you know the power amp input resistance you can get rid of R2(R4) and scale the values of C1/R1(C2/R3) to provide the shelf you're looking for. Then just put a switch across the combination to disable/enable the filter.
Cheers,
Dave.
start by putting a fixed test signal through the Source.
measure the source output with the output open.
Then attach your normal receiver
Now measure the source output with the receiver connected.
The difference in the two output measurments gives an indication of the "ratio" to the source output impedance to the receiver input impedance.
If the measurement drops by 1% then the receiver:source is ~ 100:1
If the measurement drops by 10% then the receiver:source is ~ 10:1
The actual calculations can be given if you know the actual resistance of one of them.
If you have a spare resistor somewhere in the range 10k to 200k, then you will have a receiver and know the receiver resistance.
measure the source output with the output open.
Then attach your normal receiver
Now measure the source output with the receiver connected.
The difference in the two output measurments gives an indication of the "ratio" to the source output impedance to the receiver input impedance.
If the measurement drops by 1% then the receiver:source is ~ 100:1
If the measurement drops by 10% then the receiver:source is ~ 10:1
The actual calculations can be given if you know the actual resistance of one of them.
If you have a spare resistor somewhere in the range 10k to 200k, then you will have a receiver and know the receiver resistance.
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Hmm. This may be a little off topic, but, how do I know that my source, pre, and power (active speakers) aren't already completely unmatched for each other. I never measured them, didn't look at the specs, didn't knew about input/output impedance when I bought them (except at speaker level). They sound good though. The preamp is a diy project from China wich currently is disconnected. Argon DAC1 to active Audioengine 5. I just found out that the A5 has an input impedance spec of 10k. The DAC's specs doesn't say - isn't that strange, since it lists dac-chip, OP-amp, and even comes with a small torx driver in case you are curious to see how it looks inside...
These are your speakers?
Audioengine 5 - Tech Specs
A 10k input resistance fits nicely with your proposed circuit above. Just get rid of R2 and R4 in your circuit since the 10k input resistance of your A5 becomes R2/R4.
You can enable/disable the filter by attaching a switch across the RC combination.
Dave.
Audioengine 5 - Tech Specs
A 10k input resistance fits nicely with your proposed circuit above. Just get rid of R2 and R4 in your circuit since the 10k input resistance of your A5 becomes R2/R4.
You can enable/disable the filter by attaching a switch across the RC combination.
Dave.
10k input impedance is low, but ideal for this purpose.
Source documentation sometimes does not give source impedance, or specifies minimum load impedance but calls it output impedance. In most cases you can assume that ordinary gear will have a low output impedance so can drive most other ordinary gear. Problems are more likely with very cheap stuff (they can't be bothered to design it) or very expensive stuff (they think the normal rules don't apply).
Source documentation sometimes does not give source impedance, or specifies minimum load impedance but calls it output impedance. In most cases you can assume that ordinary gear will have a low output impedance so can drive most other ordinary gear. Problems are more likely with very cheap stuff (they can't be bothered to design it) or very expensive stuff (they think the normal rules don't apply).
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