Shipping was kind of expensive though since it came from overseas. I did get it with the PSU board as well to get cleaner power into it.
So this is the same as the CNC board from Sachin?
If it is the same circuit as the start of this thread, then the equalization is done passively. What that means is that one leg of the eq caps is grounded, causing some of the power at selected frequencies to drain to ground. The signal that you listen to is what doesn't pass through those caps. The circuit is a high quality one and as long as the caps are in spec, relatively low tolerance (i.e. accurate to their rated value), and don't exhibit excessive esr, swapping caps should have little to no influence on the output sound quality.
Shelly_D
If it is the same circuit as the start of this thread, then the equalization is done passively. What that means is that one leg of the eq caps is grounded, causing some of the power at selected frequencies to drain to ground. The signal that you listen to is what doesn't pass through those caps.
Afaik, the Hagerman Bugle is passive EQ, most other chip based phono stages are feedback loop active EQ.
It looks to me like per the OP, the equalization is passive but there's some feedback designed into the opamp circuits. The opamp circuits are free of caps though, just resistive dividers, so I don't think the opamps are involved with the equalization, just signal amplification.
Yes there is feedback around the opamps. That is the only way to set the gain on an opamp gain stage. The feedback is resistive only, no equalization done. There are many designs where the equalization is done as part of the feedback loop. When doing that, what happens is that the gain of the opamp stage changes with frequency. In this circuit, the gain is flat over the entire listening band. The resistive capacitive networks between the two opamp stages are the equalization network. Once again, I am referring to the circuit that the OP started out with.
Does this help?
Shelly_D
Yes, thank you!Yes there is feedback around the opamps. That is the only way to set the gain on an opamp gain stage. The feedback is resistive only, no equalization done. There are many designs where the equalization is done as part of the feedback loop. When doing that, what happens is that the gain of the opamp stage changes with frequency. In this circuit, the gain is flat over the entire listening band. The resistive capacitive networks between the two opamp stages are the equalization network. Once again, I am referring to the circuit that the OP started out with.
Does this help?
Shelly_D
The CNC and the Muffsy were based on the circuit published by National Semi in the LME 4562, 49720, 49860 and other datasheets. National identifies it as passive EQ and a glance at the data sheet schematic would support that. As was noted in this thread and also in the build thread for the CNC, the EQ values in that schematic are incorrect and should be revised. The CNC thread is long but has a lot of info worth seeing. I found OPA 627 in both places to be my preferred choice.So, now I've been told in the past 4 posts or so that it's a. passive and b. active. Which is it?