I assumed that Aleph 1.7 is also a balanced pre-amp and therefore for two channel operation, it would require either two conventional double-decker-VR or two 4-layer-attenuator. I prefer one 8-layer attenuator because there is only one knob to adjust both channel. I believe this is regardless of whether you're attenuating the input or output and me too I'm not sure about the impedance Aleph 1.7.
I used a 8-layer 10K attenuator for my BOSOZ - as I have posted several time on this forum - and it works wonderfully.
I used a 8-layer 10K attenuator for my BOSOZ - as I have posted several time on this forum - and it works wonderfully.
The input impedance on the Aleph P is 10K so the attenuator should be perfect. I don't understand why I would need an 8 section attenuator if I am just attenuating the input? I would think Russell is correct that only a 4 section would be needed. If the input and outputs were attenuated, then I would need 8 sections.
Russel,
Now I am totally confused. If I want to attenuate the input only on a stereo balanced preamp. I would need an attenuator section for each (-) input and each (+) input. So that would be 4 sections. If I wanted to attenuate the input and outputs I would need 8 sections total because I would need 4 more sections, one for each (-) and (+) output as well as the 4 for the inputs. I assume this is correct? I would go with the 8 section attenuator but the output impedance is on the Aleph P 1.7 is 5K ohms. Do you think the 10K sections on the output would be a real big deal? If not I will buy the 8 section attenuator. Sorry for all the confusion. While I am not new to electronics, it has been a long time and just getting back into it. I got my EE degree 27 years ago and have not used it much since.
Now I am totally confused. If I want to attenuate the input only on a stereo balanced preamp. I would need an attenuator section for each (-) input and each (+) input. So that would be 4 sections. If I wanted to attenuate the input and outputs I would need 8 sections total because I would need 4 more sections, one for each (-) and (+) output as well as the 4 for the inputs. I assume this is correct? I would go with the 8 section attenuator but the output impedance is on the Aleph P 1.7 is 5K ohms. Do you think the 10K sections on the output would be a real big deal? If not I will buy the 8 section attenuator. Sorry for all the confusion. While I am not new to electronics, it has been a long time and just getting back into it. I got my EE degree 27 years ago and have not used it much since.
My understanding is that if you do intend to hook up your pre-amp for BALANCE operation, you'll need 8-layers attenuator regardless of whether you install it on the input or output.
Of course my memory could be failing because the last time I read the NP construction article was about 2 years ago.
Of course my memory could be failing because the last time I read the NP construction article was about 2 years ago.
Russell,
This is just going to be a volume control similar to the one pictured below in the bosoz schematic. The input and output attenuators must be ganged together I assume? Is there a reason why the input and output attenuators can not be ganged together? I also assume on your eight section attenuator it is just 8 different 10K attenuators ganged together. Is that correct?
This is just going to be a volume control similar to the one pictured below in the bosoz schematic. The input and output attenuators must be ganged together I assume? Is there a reason why the input and output attenuators can not be ganged together? I also assume on your eight section attenuator it is just 8 different 10K attenuators ganged together. Is that correct?
An externally hosted image should be here but it was not working when we last tested it.
Gee this is fun.
If you gang the input and output so they sum you get twice as much gain change per step. If you gang them opposing you get no gain change at all.
From looking at the schematic IHMO it seems that one device is for volume control and the other is to pre-set a relatively fixed output level so the volume pot operates over a "correct" range.
Operating both seems to add a lot of cost and little benefit.
The design looks like it might tolerate a fair amount of impedance variation so it could be possible to use a circuit that modifies either a fixed series or shunt element or both. Now only one layer (two per channel for balanced) is needed. You can afford a better switch and better resistors. The attached schematic (proud papa posted this once before) is not really the 10K average but illustrates the idea.
It's easy to scale the impedance, I wrote a spreadsheet that does it. Note that after building this I think 1 dB steps are overkill, 1 1/2 are probably about right.
If you gang the input and output so they sum you get twice as much gain change per step. If you gang them opposing you get no gain change at all.
From looking at the schematic IHMO it seems that one device is for volume control and the other is to pre-set a relatively fixed output level so the volume pot operates over a "correct" range.
Operating both seems to add a lot of cost and little benefit.
The design looks like it might tolerate a fair amount of impedance variation so it could be possible to use a circuit that modifies either a fixed series or shunt element or both. Now only one layer (two per channel for balanced) is needed. You can afford a better switch and better resistors. The attached schematic (proud papa posted this once before) is not really the 10K average but illustrates the idea.
It's easy to scale the impedance, I wrote a spreadsheet that does it. Note that after building this I think 1 dB steps are overkill, 1 1/2 are probably about right.
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