A high-quality German WIMA has little to do in the wrong place. A medium-quality capacitor should be enough.
There is a risk that 0.01uF is not large enough for keeping a 5532 happy.
I always use 0.1uF. Cheap polyester is fine, they're only bypass/decoupling caps.
Thanks Douglas. I will follow your guidance and switch to a 0.1 uF cap. I'll save those WIMAs for the future.
Building the Doug Self Preamplifier
Please note the BOM calls for 0.1uF film caps. I have been buying and using a part available at Mouser as made by EPCOS/ TDK.
They work well and can be had for less than 10 cents apiece if you buy 100 or more at a time.
Description: Film Capacitors 0.1uF 100volts 5%
Manufacturer Part #: B32529C1104J
Mouser Part #: 871-B32529C1104J
Please note the BOM calls for 0.1uF film caps. I have been buying and using a part available at Mouser as made by EPCOS/ TDK.
They work well and can be had for less than 10 cents apiece if you buy 100 or more at a time.
Description: Film Capacitors 0.1uF 100volts 5%
Manufacturer Part #: B32529C1104J
Mouser Part #: 871-B32529C1104J
Measured, double measured and triple measured. The panels are in production. Hopefully will get them by the end of next week.
Meanwhile, I have got my boards assembled and connected. I get the sound alright, no noise or hum, and preamp responds to volume and line selection as expected. What I have a problem with is equalizer. If I set Low Gain to lowest frequency (80Hz) then changes to gain don't make a difference in sound. Respectfully if I set High Gain to highest frequency (10kHz) then changes to gain don't produce any noticeable difference
Frequency selection anywhere in the middle or to the other extreme in the frequency spectrum produces desirable results in the sound, although I cannot be sure that I am adjusting the correct frequency since I don't have a way to measure it.
I can see a few possibilities:
1. I messed up with resistor values
2. My music is not high enough quality to observe changes at spectrum extremes (very low or very high frequency)
3. My hearing is not that great (although this can probably only explain the 10kHz part)
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I take the view that an opamp requires to see a low impedance supply.
As most (but not all) opamps have no notion of what or where ground is, then to my way of thinking the main supply decoupling should be between the opamp supply pins themselves.
Adding a cap to ground from each supply pin effectively places the caps in series as seen by the supply pins. The available 'ground' point close to the opamp is invariably some physical distance from a reference 'star' point and so the caps now have the possibility of actually coupling rail induced noise into the audio ground relative to other points on that ground trace.
As most (but not all) opamps have no notion of what or where ground is, then to my way of thinking the main supply decoupling should be between the opamp supply pins themselves.
Adding a cap to ground from each supply pin effectively places the caps in series as seen by the supply pins. The available 'ground' point close to the opamp is invariably some physical distance from a reference 'star' point and so the caps now have the possibility of actually coupling rail induced noise into the audio ground relative to other points on that ground trace.
Pushing theory aside just for a moment - single capacitor rail to rail decoupling appears to work reliably.
But I'd say that although the 'not star ground' point is valid - it's less relevant if using a 'ground plane' approach.
Got parts ordered, I've read everything at least twice and believe I understand everything.
Time to BUILD very soon.
One thing I unsure of: Is the most recent supplied power supply board and associated KAD_ADJ_PWR_SUPPLY.pdf define the 17V setup or 15V ? Seeing how the tranfo is 18V leads me to question whether it'll be sufficient for 'adjusted' 17V rail match.
Charles
Time to BUILD very soon.
One thing I unsure of: Is the most recent supplied power supply board and associated KAD_ADJ_PWR_SUPPLY.pdf define the 17V setup or 15V ? Seeing how the tranfo is 18V leads me to question whether it'll be sufficient for 'adjusted' 17V rail match.
Charles
Well, the advantage is that you get 1.1 dB more headroom.
Not a lot, its true, but you get it at zero cost. I have been running 5532s off +/-17V ever since they became affordable.
Power supply in a separate chassis/ grounding
Hi, I'm planning my build and i have the PCB's and some of the parts. I've read the thread and that has been very helpful so i think there will be no major problems. One question i have right now is that i think i will put the power supply in a seperate box and i'm not sure what to do with the safety ground. Is it OK to use safety ground on the power supply only or does the preamp chassis need safety ground as well? IE through the power supply line? If that the case, how does one keep audio ground separate?
TIA Vincent
Hi, I'm planning my build and i have the PCB's and some of the parts. I've read the thread and that has been very helpful so i think there will be no major problems. One question i have right now is that i think i will put the power supply in a seperate box and i'm not sure what to do with the safety ground. Is it OK to use safety ground on the power supply only or does the preamp chassis need safety ground as well? IE through the power supply line? If that the case, how does one keep audio ground separate?
TIA Vincent
I've not connected safety earth (PE) under those circumstances. If you want to be certain there is no way for mains to get to the chassis, fuse the low voltage supply. The only other way it could would be via the interconnects and that would depend on the precautions taken in the connected equipment