Hi all:
I am having a very strange thing happening:
Started with a simple VSPS using an NE5532 op amp fed by a ClearAudio MM cartridge on an Oracle Delphi. This into a $50 class D chi-amp then into a pair of Dave's Minifonken speakers. Overall, very satisfactory performance from a truly minimalist system.
Enter the Aikido... I had an itch to build a remote controlled preamp with 4 inputs and an Aikido line stage using 6DJ8s. I used an Arduino Nano to control the input relays and built a nifty volume control driven by a small stepper motor. This piece turned out well and when fed into the chi-amp there is absolutely no noise or hum at all.
Playing the CD player through the Aikido/chi-amp sounds great - exactly what we have come to expect from the Aikido topology.
Here comes the problem - when I play the record player through the Aikido/chi-amp the sound is heavily distorted - crackly, edgy and thin. Plug the phono stage back directly into the chi-amp and it sounds fine.
My first impression is that the phono path is over-driving the Aikido, but that makes no sense as it works fine directly into the class-D.
Anyone have any suggestions as to what might be going on here?
I am having a very strange thing happening:
Started with a simple VSPS using an NE5532 op amp fed by a ClearAudio MM cartridge on an Oracle Delphi. This into a $50 class D chi-amp then into a pair of Dave's Minifonken speakers. Overall, very satisfactory performance from a truly minimalist system.
Enter the Aikido... I had an itch to build a remote controlled preamp with 4 inputs and an Aikido line stage using 6DJ8s. I used an Arduino Nano to control the input relays and built a nifty volume control driven by a small stepper motor. This piece turned out well and when fed into the chi-amp there is absolutely no noise or hum at all.
Playing the CD player through the Aikido/chi-amp sounds great - exactly what we have come to expect from the Aikido topology.
Here comes the problem - when I play the record player through the Aikido/chi-amp the sound is heavily distorted - crackly, edgy and thin. Plug the phono stage back directly into the chi-amp and it sounds fine.
My first impression is that the phono path is over-driving the Aikido, but that makes no sense as it works fine directly into the class-D.
Anyone have any suggestions as to what might be going on here?
Impedance mismatch??
Aikido line stage here...
VSPS Phono stage here...
*Note: phono stage is exactly as shown except using NE5532 op amp instead of OPA127
Any thoughts gratefully received
Aikido line stage here...
An externally hosted image should be here but it was not working when we last tested it.
VSPS Phono stage here...
An externally hosted image should be here but it was not working when we last tested it.
*Note: phono stage is exactly as shown except using NE5532 op amp instead of OPA127
Any thoughts gratefully received
Sorry, but I can't open any of the 3 "Click the image to open in full size." items you posted. Maybe try using the Manage Attachments facility on the Advanced posting screen to try uploading a JPG or PNG, rather than a URL to another site. (Suspect I don't have 'permission' to dabble on it.)
Is the phono stage perhaps lacking an output coupling capacitor? If the chi-amp input has one and the Aikido input does not, that might explain it.
When the phono stage is connected directly to the chi-amp, where/how is gain controlled?
Cheers
Is the phono stage perhaps lacking an output coupling capacitor? If the chi-amp input has one and the Aikido input does not, that might explain it.
When the phono stage is connected directly to the chi-amp, where/how is gain controlled?
Cheers
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sorry about the images - stored them on Amazon AWS S3 storage, but permissions are definitely an issue. I'll try to fix them.
The chi-amp has an input gain control on it, which I usually leave cranked wide open (or nearly).
However, your suggestion about the possible absence of coupling caps on the output of the phono stage is a great thought. I will open the 'lil bugger up and see.
Thanks for the input.
Jess
The chi-amp has an input gain control on it, which I usually leave cranked wide open (or nearly).
However, your suggestion about the possible absence of coupling caps on the output of the phono stage is a great thought. I will open the 'lil bugger up and see.
Thanks for the input.
Jess
Err .. Ummm .. I hope you didn't build the preamp exactly as in the schematic .. There's no connection between the 1st and 2nd stage of the Left channel. In fact, it looks to me like it has 4 inputs and no outputs!
Even guessing past some possible/likely drafting errors, I don't see any way for it to work. Maybe it's just me .. o:
Regarding the phono stage -- the posted schematic shows two mounting locations for output coupling capacitors: Pad21/Pad22, and Pad23/Pad24.
Cheers
Even guessing past some possible/likely drafting errors, I don't see any way for it to work. Maybe it's just me .. o:
Regarding the phono stage -- the posted schematic shows two mounting locations for output coupling capacitors: Pad21/Pad22, and Pad23/Pad24.
Cheers
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Phono amps like this have large DC offsets unless you use JFET opamp(s). Perhaps just substitute something like OPA1642/1652 (on a SOIC8 breakout, alas).