For the time being I've simply taken the two lowest value resistors out of circuit to limit the lowest load. This has improved things some although it means that my highest volume setting is now 63. After that we go back to zero and cycle through again X3. I can live with this for now but it does mean the fine adjustment at low levels is compromised quite a bit.
I've run into another issue that I can't really get my head around - when connecting a balanced input it causes the single-ended inputs to become completely distorted. The balanced source plays fine but anything single-ended is useless. Unplugging the balanced source makes the everthing fine again. Also, the source connected to the balanced input seems to 'break through' and can be heard faintly through the single-ended inputs if they're selected. This makes no sense to me as they are selected separately. The only thing is that ground for all inputs is connected together but I still can't see how this is causing this particular issue. In practical terms it means that the balanced inputs can't be used in conjunction with single-ended sources which is a major pain. John - did you come across any similar issues?
I've run into another issue that I can't really get my head around - when connecting a balanced input it causes the single-ended inputs to become completely distorted. The balanced source plays fine but anything single-ended is useless. Unplugging the balanced source makes the everthing fine again. Also, the source connected to the balanced input seems to 'break through' and can be heard faintly through the single-ended inputs if they're selected. This makes no sense to me as they are selected separately. The only thing is that ground for all inputs is connected together but I still can't see how this is causing this particular issue. In practical terms it means that the balanced inputs can't be used in conjunction with single-ended sources which is a major pain. John - did you come across any similar issues?
Now that is an interest problem. I have built 6 boards with the different revs and never encountered that issue. The inputs are completely isolated at the input relay, unless you are getting some bleed through from the relay but I have never seen that, you could try removing a relay and just to see what happens and maybe give you something to eliminate. The grounds are common but that shouldn't affect anything unless the input wires are crossed. Good luck with the troubleshooting and let us know what you find.
I have had a thought on your bleeding sound problem. I haven't seen your PCBs up close but I know running my analog traces I tried to keep them at .1" width with .050" between the traces and no sharp corners to act as antenna.With digital traces too close together they can cross talk but I am not sure on analog the best spacing but just something to look at.
Well I almost have the PCBs laid out for a redux on the preamp control. It breaks the main board up into 3 PCBs, one digital, one analog, and one power supply. The analog board stacks on top of the digital so instead of one 7"x12" board it will probably be two 6"x7" boards and one PS of 3"x4". The board will be fully balanced but can be used as single ended by only populating half the relay, it has 6 inputs. The display board has be changed from a push button up/down volume control to a rotary encoder for people who like knobs. I have to test new resistor values that will not load the input devices so much. I don't know when I will get time to test everything but now that the house is built I have a sound room to setup and play in.
Ok, here is some schematics for people to look at and pick apart for a new version with a rotary encoder for the volume up/down on the preamp. Some things moved or changed as the rotary encoder supplies the pulses so the "helper" circuit, 7555 timer, was moved to just the remote input. See if you can find any errors. BOM is 95% the same parts as previous version. Will do a new BOM when I have a chance to test the new design.
HI Samoloko,
When I turn the PCBs I will get a set of 10 each so if it works then the extra 9 sets will be available. The parts are all available if you can get Mouser delivery. Only the one rotary encoder chip is from separate source and I may buy a set of those to go with the boards.
Have a good one,
John
When I turn the PCBs I will get a set of 10 each so if it works then the extra 9 sets will be available. The parts are all available if you can get Mouser delivery. Only the one rotary encoder chip is from separate source and I may buy a set of those to go with the boards.
Have a good one,
John
I will be experimenting with volume resistors values so the minimum input impedance doesn't drop below 1k.
I am also consider separating the input select from the volume section so you can choose to put the gain section, preamp, before or after the volume section.
To soon to be sure about board sizes but the power supply should be 3"x4", the Analog and Digital Boards 6"x7", the display 6"x4".
I am also consider separating the input select from the volume section so you can choose to put the gain section, preamp, before or after the volume section.
To soon to be sure about board sizes but the power supply should be 3"x4", the Analog and Digital Boards 6"x7", the display 6"x4".
Hi Samoloko,
Not with the digital weighting resistor scheme. I have started playing with another resistor configuration that has a constant input resistance and variable output resistance. Something between a ladder resistor network and a R2R. And will test the rotary encoder the volume control. The pulse decoder chip has an interesting feature where if the mode is set one way it steps one at a time and set another way it steps 4x. The rotary encoder can be had with a momentary push button switch so you can do coarse, fast, volume adjustment by pushing in the volume knob and rotating then releasing to fine volume adjustment by just rotating the knob.
I will get back to the volume control project after I debug a DC blocker for the AC mains. I have very dirty AC power here and the DC block stops my big toriods in the power amps from humming. And I just finished setting up a new turntable, uses a Denon DP80 for the drive on a PBN Audio Plinth, a SME V tonearm, and a Koetsu Rosewood Signature. Just awesome resolution from the Vinyl.
Have a good one.
Not with the digital weighting resistor scheme. I have started playing with another resistor configuration that has a constant input resistance and variable output resistance. Something between a ladder resistor network and a R2R. And will test the rotary encoder the volume control. The pulse decoder chip has an interesting feature where if the mode is set one way it steps one at a time and set another way it steps 4x. The rotary encoder can be had with a momentary push button switch so you can do coarse, fast, volume adjustment by pushing in the volume knob and rotating then releasing to fine volume adjustment by just rotating the knob.
I will get back to the volume control project after I debug a DC blocker for the AC mains. I have very dirty AC power here and the DC block stops my big toriods in the power amps from humming. And I just finished setting up a new turntable, uses a Denon DP80 for the drive on a PBN Audio Plinth, a SME V tonearm, and a Koetsu Rosewood Signature. Just awesome resolution from the Vinyl.
Have a good one.
So I have finished building my new house with the nice sound room, 18' x 24', vaulted ceiling room, and have returned to playing with audio stuff. I have rebuilt some amps and laid out PCB for a Aleph P preamp (have spare Boards if anyone is interested, no cost) so I can use it to test my new volume control boards I am working on. I have laid out a separate Power Supply, Digital control, Analog switching, and display board. The Volume control will be a ladder style with a constant input resistance, and a rotary encoder for knob control. PCBs are laid out, hope to turn some soon and start testing the design and start listening.
In the meantime I have tested the current volume board which uses digital weighting. Some were having a problem driving the input as the original resistor values caused the input resistance to drop too low, 64 ohms. In testing, after a lot of listening, noticed a compression of the dynamics, so I tried alternate value and found that using the alternate values or 20k, 10k, 5k, 2.5k, 1.25k, 625, 312, 156 ohms, kept the input resistance above 300 ohms, worst case, which occurs only at mid volume level. Listening shows the dynamics returned to normal and neutral sounding.
So just FYI. In the amp rebuilt I found a couple good Anodize companies in San Diego. Still using the PCB shop in Shenzhen China, Seeed Studio Fusion. And currently working with a machine shop in Guangzhou China to do aluminum cabinets to my specs. They will machine, brush finish, and Black Hard Anodize finish for half the cost of any other shop I tried. Company is Runsom, will let everyone know the quality of their work when I get the parts.
Have a good one.
In the meantime I have tested the current volume board which uses digital weighting. Some were having a problem driving the input as the original resistor values caused the input resistance to drop too low, 64 ohms. In testing, after a lot of listening, noticed a compression of the dynamics, so I tried alternate value and found that using the alternate values or 20k, 10k, 5k, 2.5k, 1.25k, 625, 312, 156 ohms, kept the input resistance above 300 ohms, worst case, which occurs only at mid volume level. Listening shows the dynamics returned to normal and neutral sounding.
So just FYI. In the amp rebuilt I found a couple good Anodize companies in San Diego. Still using the PCB shop in Shenzhen China, Seeed Studio Fusion. And currently working with a machine shop in Guangzhou China to do aluminum cabinets to my specs. They will machine, brush finish, and Black Hard Anodize finish for half the cost of any other shop I tried. Company is Runsom, will let everyone know the quality of their work when I get the parts.
Have a good one.
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The new ladder resistor topology can be set to a constant input or constant output resistance. For this use will be using a constant input resistance of 10K. The ladder topology unfortunately requires twice the number of resistors from the digital weighted topology, for a 8 bit balanced stereo topology it requires 68 quality resistors, Single ended requiring half of that. For Audio sound quality I prefer the Vishay Dale RN65 series metal film resistor. Caddock might be a hair better but are way too expensive for my sensibilities. Still inputting a spreadsheet for the BOM and then will have a cost of goods to share.