saturnaal
Member
Looking for a sanity check and some circuit design guidance here.
This one might be better suited to one of the more DIY-focused audio forums which I've long been an active lurker on, but lately I've seen most of the DIY engineers I've come to respect most posting here regularly. So, I'll save myself the account creation process for now.
Like many of you, I've consistently failed to keep my desktop audio setup simple and manageable. I really appreciate a well organized and tidy desk, and with two headphone amps, two computers, and a pair of speakers in scope shuffling equipment around and switching cables became frustrating quickly. Searching for a product that would let me use my equipment in the way I want on demand without doing this proved fruitless.
There's no shortage of switch boxes and passive pre-amplifiers on the market, but none of them quite fit my needs. So what am I trying to accomplish?
- Analog audio signal from a single source. A DAC fed by S/PDIF from my personal desktop and USB from my work laptop dock.
- Outputs to three different amplifiers. A Koss "energizer" for my usual headphones, a hybrid tube headphone amp for "fun with distortion", and a speaker amplifier.
- The ability to optionally pass the source signal through the tube amp (which has pre-outs), to muck up the nice clean signal with distortion on demand.
- A single, high quality, nice feeling volume control. The volume control on the DAC works well, but leaves much to be desired where the user experience is concerned.
To illustrate:
There are plenty of products out there across a wide range of prices that will provide lots of inputs with a single output, a few with multiple outputs, and most of them have a volume knob in the form of a potentiometer or occasionally a stepped attenuator. As far as I could find however, nothing that would allow one to easily toggle sending the signal through an external device before routing it to whatever amplifier it's destined for.
I find this curious, as I remember in the not too distant past lots of home audio equipment came with "EQ output and input", which would allow you to send the signal through your choice of equalizer or other signal processing component before it made it to the amplifier section. Often times there was a "direct" button that would bypass this, or sometimes just a set of jumpers you'd place across the terminals if you weren't using one. This was pretty radical if you had something like one of those fancy Sony SEQ-555ES (R.I.P.) like I used to.
So, how would I accomplish this with commercially available products while keeping the form factor small? After some shopping around, the JDS Labs OL Switcher seemed like the best fit. Two inputs, two outputs, all switchable and with a potentiometer. Solving my problem seems to require two of them, but at $45 each that isn't too painful.
So what would that look like?
Ok, well... That does appear to meet the requirements, if not in a particularly elegant way. Switcher 1 provides unified volume control and a toggle to route either through the tube amp or directly to switcher 2. Switcher 2 volume knob would stay at 100%, and you'd need to also toggle the input depending on how SW1 was set.
It works, but I'm not crazy about it for a few reasons. Now there are up to three potentiometers in the signal path incl. the one on the tube amp, two of them at all times. Assuming the OL Switcher uses the same pot as the JDS O2, it measures ok but not perfectly for channel matching. Best case scenario any imbalance cancels out, worst case it stacks. Any other objections I have are purely subjective. For one, setting the four toggle switches into the right configuration (well, three, one would be unused) wouldn't be the best UX. The JDS Switcher seems like a great product, but at 12 ounces I don't expect it to stay in place very well, and I need all the functionality to be one-hand friendly.
So, looks like my requirements are specific and odd enough that I'm in "custom solution land". Time to build my own! I haven't done any circuit design since I was about 12, with a radio shack learning lab and Forrest Mims "Getting Started in Electronics" books, but this has to be about as simple as it gets right?
As with any type of engineering, requirements first!
- Minimum one source input.
- Minimum one "EQ" input.
- Minimum three outputs.
- Output selector.
- Toggle for routing signal through one of the outputs, and passing the "EQ" input to another output.
- Volume control.
- Minimize sources of noise, distortion, crosstalk, and channel imbalance.
- Shouldn't explode, catch on fire, or risk damage to any connected component.
Let's try...
Ok, this gives me three selectable outputs, with optional routing through the tube preamp for output 1. It only represents one channel, but a second channel is implied.
Probably painful to look at for a serious DIY'er or any professional. Simple software has gotten me this far, but I think it's time to move to some sort of SPICE editor (probably KiCad) to improve the quality and readability of my diagram which will be a learning experience for me. I think I'll also add an input selector and another input or two, just in case I want to add another source in the future. I'd also like to allow any of the outputs to be routed through the "EQ" path, rather than just one of them. Besides of course the output to the tube amp. Time for some refactoring!
In the meantime, I'd be extremely grateful for any feedback, ideas, or suggestions. I'll take anything into account and post my updated diagram here for "peer review" when done.
This one might be better suited to one of the more DIY-focused audio forums which I've long been an active lurker on, but lately I've seen most of the DIY engineers I've come to respect most posting here regularly. So, I'll save myself the account creation process for now.
Like many of you, I've consistently failed to keep my desktop audio setup simple and manageable. I really appreciate a well organized and tidy desk, and with two headphone amps, two computers, and a pair of speakers in scope shuffling equipment around and switching cables became frustrating quickly. Searching for a product that would let me use my equipment in the way I want on demand without doing this proved fruitless.
There's no shortage of switch boxes and passive pre-amplifiers on the market, but none of them quite fit my needs. So what am I trying to accomplish?
- Analog audio signal from a single source. A DAC fed by S/PDIF from my personal desktop and USB from my work laptop dock.
- Outputs to three different amplifiers. A Koss "energizer" for my usual headphones, a hybrid tube headphone amp for "fun with distortion", and a speaker amplifier.
- The ability to optionally pass the source signal through the tube amp (which has pre-outs), to muck up the nice clean signal with distortion on demand.
- A single, high quality, nice feeling volume control. The volume control on the DAC works well, but leaves much to be desired where the user experience is concerned.
To illustrate:
There are plenty of products out there across a wide range of prices that will provide lots of inputs with a single output, a few with multiple outputs, and most of them have a volume knob in the form of a potentiometer or occasionally a stepped attenuator. As far as I could find however, nothing that would allow one to easily toggle sending the signal through an external device before routing it to whatever amplifier it's destined for.
I find this curious, as I remember in the not too distant past lots of home audio equipment came with "EQ output and input", which would allow you to send the signal through your choice of equalizer or other signal processing component before it made it to the amplifier section. Often times there was a "direct" button that would bypass this, or sometimes just a set of jumpers you'd place across the terminals if you weren't using one. This was pretty radical if you had something like one of those fancy Sony SEQ-555ES (R.I.P.) like I used to.
So, how would I accomplish this with commercially available products while keeping the form factor small? After some shopping around, the JDS Labs OL Switcher seemed like the best fit. Two inputs, two outputs, all switchable and with a potentiometer. Solving my problem seems to require two of them, but at $45 each that isn't too painful.
So what would that look like?
Ok, well... That does appear to meet the requirements, if not in a particularly elegant way. Switcher 1 provides unified volume control and a toggle to route either through the tube amp or directly to switcher 2. Switcher 2 volume knob would stay at 100%, and you'd need to also toggle the input depending on how SW1 was set.
It works, but I'm not crazy about it for a few reasons. Now there are up to three potentiometers in the signal path incl. the one on the tube amp, two of them at all times. Assuming the OL Switcher uses the same pot as the JDS O2, it measures ok but not perfectly for channel matching. Best case scenario any imbalance cancels out, worst case it stacks. Any other objections I have are purely subjective. For one, setting the four toggle switches into the right configuration (well, three, one would be unused) wouldn't be the best UX. The JDS Switcher seems like a great product, but at 12 ounces I don't expect it to stay in place very well, and I need all the functionality to be one-hand friendly.
So, looks like my requirements are specific and odd enough that I'm in "custom solution land". Time to build my own! I haven't done any circuit design since I was about 12, with a radio shack learning lab and Forrest Mims "Getting Started in Electronics" books, but this has to be about as simple as it gets right?
As with any type of engineering, requirements first!
- Minimum one source input.
- Minimum one "EQ" input.
- Minimum three outputs.
- Output selector.
- Toggle for routing signal through one of the outputs, and passing the "EQ" input to another output.
- Volume control.
- Minimize sources of noise, distortion, crosstalk, and channel imbalance.
- Shouldn't explode, catch on fire, or risk damage to any connected component.
Let's try...
Ok, this gives me three selectable outputs, with optional routing through the tube preamp for output 1. It only represents one channel, but a second channel is implied.
Probably painful to look at for a serious DIY'er or any professional. Simple software has gotten me this far, but I think it's time to move to some sort of SPICE editor (probably KiCad) to improve the quality and readability of my diagram which will be a learning experience for me. I think I'll also add an input selector and another input or two, just in case I want to add another source in the future. I'd also like to allow any of the outputs to be routed through the "EQ" path, rather than just one of them. Besides of course the output to the tube amp. Time for some refactoring!
In the meantime, I'd be extremely grateful for any feedback, ideas, or suggestions. I'll take anything into account and post my updated diagram here for "peer review" when done.
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