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.
Another Super High End Phono Stage! No expense spared...
- Thread starter Fasterdamnit
- Start date
I think the guy that does Muffsy is a member here, I can't remember if it's Sachin or Skrodahl?
Edit: Muffsy = @skrodahl .
I believe the board from PSAudio is the same layout. My dad wanted something he could give me for Christmas and the kit was easier than a Mouser BOM, at the cost of the overseas shipping.
shelly_d
Not An Audiophool
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
Shelly_D
I believe the topology is identical, it just has provisions for selectable input loading via dip switch.
One question on this. Is this truly the distinction between active/passive phono stages? I would have thought an active stage would have had more to it than simply, "The signal goes through a cap."
Aaaaah, so if I'm understanding properly, the CNC and the Bugle basically use the opamps as impedance buffers so that the RIAA EQ in the middle can do it's thing without interaction with the cart/output device impedances, whereas others would put the RC networks in the feedback loop of the opamp, thus necessarily some of the final signal goes through the loop?
What is meant when a phone stage uses a "DC servo" topology? Is that the feedback style you're referring to?
Active EQ;
In a low distortion signal amplifier, there is typically a feedback loop from output to input to set gain, lower distortion, and stabilize operation. Aside from those things, a simple network may be used in the loop to modify it's frequency response, as for tone controls, or a RIAA compensated phono preamp stage such as this one and others similar. Most resemble this technique.
Passive EQ does it with passive EQ networks between gain elements using linear non-EQ'ed feedback loops.
In a low distortion signal amplifier, there is typically a feedback loop from output to input to set gain, lower distortion, and stabilize operation. Aside from those things, a simple network may be used in the loop to modify it's frequency response, as for tone controls, or a RIAA compensated phono preamp stage such as this one and others similar. Most resemble this technique.
Passive EQ does it with passive EQ networks between gain elements using linear non-EQ'ed feedback loops.
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So, now I've been told in the past 4 posts or so that it's a. passive and b. active. Which is it?
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.
shelly_d
Not An Audiophool
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
Makes sense. So in an active design the EQ is literally determined by the output gain of the opamps at each frequency, whereas a passive works more like a buffered line level crossover except the opamps are amplifying the signal instead of just setting it at unity gain.
Yes, thank you!
Edited my last post.
absolon
Super Member
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.
Interesting. I'd found the 49720 and OPA2134 combo recommended elsewhere. I'll add that one to the list.
I thought this was the CNC build thread.
I found one of the 0905 enclosures for sale with double aluminum end caps. Should spruce up the look a bit.
I thought this was the CNC build thread.
I found one of the 0905 enclosures for sale with double aluminum end caps. Should spruce up the look a bit.
ghazzer
Senior Member
Engineer Nate: I thought this was the CNC build thread.
It is!
The Muffsy is basically the CNC, with some minor tweaks. The basic design was created by Fasterdamnit based on circuits suggested in Application Notes for some of the popular opamps. Tweaks came in from Big Bill, HypnoToad, Pio1980, shelly_d, and a few others. MANY AKers have made contributions, and meaningful suggestions.
Skrodahl dressed it up a bit and had his own boards built. They were red, not green. He made them available commercially and tagged his product as "Muffsy", but it is basically a CNC.
Anyone is free to add or subtract anything they want to the design, and they can call it whatever they want. Bottom line is that we all owe a heap of thanks to Fasterdamnit & HypnoToad for getting all of this started.
It is!
The Muffsy is basically the CNC, with some minor tweaks. The basic design was created by Fasterdamnit based on circuits suggested in Application Notes for some of the popular opamps. Tweaks came in from Big Bill, HypnoToad, Pio1980, shelly_d, and a few others. MANY AKers have made contributions, and meaningful suggestions.
Skrodahl dressed it up a bit and had his own boards built. They were red, not green. He made them available commercially and tagged his product as "Muffsy", but it is basically a CNC.
Anyone is free to add or subtract anything they want to the design, and they can call it whatever they want. Bottom line is that we all owe a heap of thanks to Fasterdamnit & HypnoToad for getting all of this started.
