Good afternoon people. I have been interested in Audiox's version of the Studer 169 EQ (See below for schematic!) for some time now but wanted to modify a few features to better suit my needs:
1: Swap the cut/boost switches for normal potentiometers
2: I need a compact stereo version for a specific application. I can't afford any more front panel space.
Point 1 is easy. Point 2 is pretty easy too but means that for the High band you need to source a 4 pole 6 way or more switch, unless you use a 4 pole 3 way lorlin, which only gives you 3 frequencies which is too few for my tastes.
So here is my question. I have devised a way of using a Lorlin or similar 2 pole 6 way switch for the High frequency circuit. My knowledge of the circuit isn't quite up to the point where I can be sure it will work.
In Audiox's original version, the switch switches two sets of capacitors, one connected to the input side and the other to the (inverted) output of the opamp. Only 2 capacitors are engaged at any time.
In the modified version, the arrangement is changed so that all the input side capacitors are wired to their counterpart on the output side and the switch chooses between each wired up pair.
The potential problem might be that we now have all these HF band caps wired permanently in parallel to the low frequency selection capacitors. My instinct is that they do not cause a problem in the HF band because they only come into play when the HF pot is not centred, and then the signal only passes through the 2 selected capacitors.
But! They will all be in parallel with the Low frequency selection capacitors. This makes me think that they will shift the pole of the low frequency band downwards. In fact this must be an issue with the original Audiox design that changed as you select different frequencies on the HF band, but in this case it would not change. But in the new version the effect is larger.
In the original design you could have for instance 10nF selected on the low EQ and between 100nF and 6.8 nF (two lots and in series, so effectively half that value) in parallel with it.
So my question for discussion is: Will this circuit work, but shift all the low frequency poles by a certain amount? Or will some other problem scupper it? Will I have to settle for an unmodified circuit and 3 HF frequencies?
Thank you in advance for any help and advice!
-Mike C
I have attached a modified schematic for you to view. The altered area is outlined in blue.
1: Swap the cut/boost switches for normal potentiometers
2: I need a compact stereo version for a specific application. I can't afford any more front panel space.
Point 1 is easy. Point 2 is pretty easy too but means that for the High band you need to source a 4 pole 6 way or more switch, unless you use a 4 pole 3 way lorlin, which only gives you 3 frequencies which is too few for my tastes.
So here is my question. I have devised a way of using a Lorlin or similar 2 pole 6 way switch for the High frequency circuit. My knowledge of the circuit isn't quite up to the point where I can be sure it will work.
In Audiox's original version, the switch switches two sets of capacitors, one connected to the input side and the other to the (inverted) output of the opamp. Only 2 capacitors are engaged at any time.
In the modified version, the arrangement is changed so that all the input side capacitors are wired to their counterpart on the output side and the switch chooses between each wired up pair.
The potential problem might be that we now have all these HF band caps wired permanently in parallel to the low frequency selection capacitors. My instinct is that they do not cause a problem in the HF band because they only come into play when the HF pot is not centred, and then the signal only passes through the 2 selected capacitors.
But! They will all be in parallel with the Low frequency selection capacitors. This makes me think that they will shift the pole of the low frequency band downwards. In fact this must be an issue with the original Audiox design that changed as you select different frequencies on the HF band, but in this case it would not change. But in the new version the effect is larger.
In the original design you could have for instance 10nF selected on the low EQ and between 100nF and 6.8 nF (two lots and in series, so effectively half that value) in parallel with it.
So my question for discussion is: Will this circuit work, but shift all the low frequency poles by a certain amount? Or will some other problem scupper it? Will I have to settle for an unmodified circuit and 3 HF frequencies?
Thank you in advance for any help and advice!
-Mike C
I have attached a modified schematic for you to view. The altered area is outlined in blue.
