ashpool
Head-Fier
- Joined
- Oct 16, 2005
- Posts
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I've made it a project to rebuild a Grado PH-1 and (hopefully) improve its sound. I've ordered the parts to build a +/- 12V Dynahi PSU and now I'm looking into replacing the components inside. I know the PSU is a little overkill for this application, but I've never built a power supply with opamps in it before and I thought I'd give it a try...
I've taken the PH-1 apart and have attempted to draw a circuit diagram of one of the channels so that I can plan a parts order:
I have quite a few questions that, hopefully, somebody can help me with:
1. Does this even look right? I've checked the diagram against the pcb, but I could have made a mistake. Once upon a time, I understood the basics of RC networks. These days, however, the RIAA equalization portion of this circuit just makes my head hurt.
2. How do I calculate gain of this circuit? How much will I have to pay attention to the ESR of C6 and C4 when I choose replacement parts? The current gain on the "high" setting is too low for low output moving coil cartridges and I'd like to make sure the gain will be high enough before I order parts.
3. I assume R14 is there to bring down the input resistance for proper cartridge loading. 47k seems like a pretty standard input impedance for moving magnet cartridges, but totally wrong for just about any moving coil cartridge. I think the input impedance for my current phono stage is around 500 Ohms on the moving coil setting. I have to admit that I don't really understand the principles behind what makes for a "good" cartridge loading. Can anybody explain the black art of cartridge loading to me?
4. What are some good brands/types of resistors and capacitors for this application? This is the first project I've had that involves anything that looks like a crossover or filter.
5. Are the 100nF power rail capacitors necessary with a high-quality power supply and is there any benefit to removing them? I think the ones I pulled out are ceramics. Do they have to be ceramics?
Any help I could get would be great. I only know enough about electronics to get myself in trouble. This project is an attempt on my part to remedy that...
I've taken the PH-1 apart and have attempted to draw a circuit diagram of one of the channels so that I can plan a parts order:
I have quite a few questions that, hopefully, somebody can help me with:
1. Does this even look right? I've checked the diagram against the pcb, but I could have made a mistake. Once upon a time, I understood the basics of RC networks. These days, however, the RIAA equalization portion of this circuit just makes my head hurt.
2. How do I calculate gain of this circuit? How much will I have to pay attention to the ESR of C6 and C4 when I choose replacement parts? The current gain on the "high" setting is too low for low output moving coil cartridges and I'd like to make sure the gain will be high enough before I order parts.
3. I assume R14 is there to bring down the input resistance for proper cartridge loading. 47k seems like a pretty standard input impedance for moving magnet cartridges, but totally wrong for just about any moving coil cartridge. I think the input impedance for my current phono stage is around 500 Ohms on the moving coil setting. I have to admit that I don't really understand the principles behind what makes for a "good" cartridge loading. Can anybody explain the black art of cartridge loading to me?
4. What are some good brands/types of resistors and capacitors for this application? This is the first project I've had that involves anything that looks like a crossover or filter.
5. Are the 100nF power rail capacitors necessary with a high-quality power supply and is there any benefit to removing them? I think the ones I pulled out are ceramics. Do they have to be ceramics?
Any help I could get would be great. I only know enough about electronics to get myself in trouble. This project is an attempt on my part to remedy that...