So, I put some more work into it, rechecking the whole Gardo PH-1 clone . Completely removed the rest of the PSU / screw terminals, touched up the solder joints for the gain resistors, the dip switches and gave it a final cleaning. Totally forgot that I hadn't soldered in the LED before, put in a wire bridge instead of leaving the spot open.
Something was fishy about the LME49720NA. As I had the issue that on the L+H setting for a total of 58dB gain the left channel didn't worked. After these changes it isn't working on the high setting for the left channel. It's definitely not the resistors or the switches as the correct resistances arrive at the socket / input legs. So either I fried the OP-AMP... or it isn't genuine. As there is no serial number on the underside of the package ... I tend to say that it's a fake one. My fault, as I sourced it via eBay to save a few instead of purchasing it from a reputable seller Won't buy again from that seller.
Thus I switched back to the JRC 5532 D and as of now and put both channels into low gain with 40dB. Level matched everything to my usual listening volumes. And I'm happy to say that I finally achieved a state which I would consider as : useable as a phono stage to me. Only the usual noises you would expect from a record that should be cleaned.
Thanks again for your input up up so far !
Something was fishy about the LME49720NA. As I had the issue that on the L+H setting for a total of 58dB gain the left channel didn't worked. After these changes it isn't working on the high setting for the left channel. It's definitely not the resistors or the switches as the correct resistances arrive at the socket / input legs. So either I fried the OP-AMP... or it isn't genuine. As there is no serial number on the underside of the package ... I tend to say that it's a fake one. My fault, as I sourced it via eBay to save a few instead of purchasing it from a reputable seller Won't buy again from that seller.
Thus I switched back to the JRC 5532 D and as of now and put both channels into low gain with 40dB. Level matched everything to my usual listening volumes. And I'm happy to say that I finally achieved a state which I would consider as : useable as a phono stage to me. Only the usual noises you would expect from a record that should be cleaned.
Thanks again for your input up up so far !
Yesterday I recieved a Dual OPA1642 OpAmp with a DIP8 adapter and switched out the JRC 5532 D from the Gardo Clone. The last bit of line noise / interferences is more or less completely gone now.
Nevertheless, as I did some readings about the OG Gardo PH-1, I'm also a bit more aware of it's sound characteristics. E.g. it seems to amplify crackling noises a bit more than other phono stages. Which I can totally confirm. I'll look into that at a later point. As this project is still at a beginner level and I want to learn more about it.
Therefore I'm going to document the whole thing in its current stage, take some pictures and do some reverse engineering. At least to document the actual circuitry which was included in the kit. I guess I will overhaul the initial post once I'm done with this and once I'm at the point to revisit the actual components / resistor values and capacitances. And I'll dive into the datasheets of both, the JRC 5532 D as well as the OPA1642 to look for recommendations, especially in terms of the RIAA equalizations.
Currently I'm just a bit busy to make some custom knobs and input selector switches. And will have to add an EMI filter stage for the mains as the Gardo clone at least is sensitive to major loads being switch in my home.
Nevertheless, as I did some readings about the OG Gardo PH-1, I'm also a bit more aware of it's sound characteristics. E.g. it seems to amplify crackling noises a bit more than other phono stages. Which I can totally confirm. I'll look into that at a later point. As this project is still at a beginner level and I want to learn more about it.
Therefore I'm going to document the whole thing in its current stage, take some pictures and do some reverse engineering. At least to document the actual circuitry which was included in the kit. I guess I will overhaul the initial post once I'm done with this and once I'm at the point to revisit the actual components / resistor values and capacitances. And I'll dive into the datasheets of both, the JRC 5532 D as well as the OPA1642 to look for recommendations, especially in terms of the RIAA equalizations.
Currently I'm just a bit busy to make some custom knobs and input selector switches. And will have to add an EMI filter stage for the mains as the Gardo clone at least is sensitive to major loads being switch in my home.
Very nice. The OPA1641/1642 are a really good choice for MM phono circuits because of their low current noise. Douglas Self in his Small Signal Audio Design evaluates it as being slightly noisier than the venerable NE5534A but better than almost anything else. Obviously, you can't use the 5534A in the Grado PH-1 clone because it calls for a dual opamp.
Hopefully, you will be able to finish your preamp build to your complete satisfaction.
Ah, literature recommendations. Always welcome. Unfortunately that read would be hard to get a hold off, as I'm from Germany. At least on the used market to safe a few.
Well, I'm currently on the cheapskate track, so to say. There is much room for improvements. But my next priority would be a DSP module as I'm currently running my room correction for my speakers through an convolver, PC based.