Whatever is happening it is working, we have discussed the possibility of changing it to a passive RIAA filter between the two stages, do you think this would be an improvement?
DIY High or Low Ouput Moving Coil Phono Stage
- Thread starter HypnoToad
- Start date
Whatever is happening it is working, we have discussed the possibility of changing it to a passive RIAA filter between the two stages, do you think this would be an improvement?
Bill and I were discussing that earlier. What I didn't mention is that passive might cause more loss than the active/feedback RIAA EQ. I think that either passive or active will work, sound good when properly designed and used. I don't think in this case there is a strong advantage to one or the other. (and I could be dead wrong)
More for information than an answer to your question:
All RIAA EQ looses gain. In the Dynaco PAS, the McIntosh C22 and the ARC SP3-a-1 tubed preamps it was a feedback loop, active. As the tubes age the gain drops and the feedback stays constant, your EQ gets all screwed up.
Passive is great for tubes since it doesn't rely on the tube's gain for accuracy. Looking at the Bugle schematic it uses passive, and it uses 3 Op-Amp stages. The three stages might be needed to make up some losses to the passive RIAA EQ, maybe not. Not to mention that it operates only on MM, it doesn't have the gain for MC (leaving that in here but I'm wrong).
More for information than an answer to your question:
All RIAA EQ looses gain. In the Dynaco PAS, the McIntosh C22 and the ARC SP3-a-1 tubed preamps it was a feedback loop, active. As the tubes age the gain drops and the feedback stays constant, your EQ gets all screwed up.
Passive is great for tubes since it doesn't rely on the tube's gain for accuracy. Looking at the Bugle schematic it uses passive, and it uses 3 Op-Amp stages. The three stages might be needed to make up some losses to the passive RIAA EQ, maybe not. Not to mention that it operates only on MM, it doesn't have the gain for MC (leaving that in here but I'm wrong).
Last edited:
ripblade
Addicted Member
This is true for the opamp itself. However because of the opamp's high input Z , the cartridge sees only the circuit in which the opamp operates. This uses negative voltage feedback and by definition has an input and output Z approaching zero ohms. The complete circuit is referred to as a transimpedance amplifier, or a current-to-voltage converter because the input current determines the output voltage.
Fasterdamnit
Super Member
I use my Bugle with 60DB gain for use with the DL-301 II and it is an improvement over using 40db and an SUT. The "clone" pre (or HTM) is quieter by a small amount.
Pio1980
AK Member
For clarification purposes of this application, does impedance equal the resistance to match the FB resistor to the cart?
ripblade
Addicted Member
In typical applications, ac impedance (Z) is the feedback resistor divided by the opamp's open loop gain +1.
Z=Rf/(A+1)
For typical opamps, this value will approach zero.
Jim, are you using R1 = 33 ohms and R2 = 850 ohms?
I am not following that. The impedance at the input might have something to do with the feedback resistor to the output. And the output has a very low impedance. But the output is not referenced to ground, the "low impedance" is the source impedance (the source, inside the Op-Amp). So there is still an infinite input impedance to the op amp and the circuit.
Can you elaborate?
I will have to stand corrected on this one. Maybe the reason for the third Op-Amp? I hadn't realized the gain on the Bugle would go high enough for a LOMC without a step up device in front of it. EDIT: I just looked at the OPA134 spec sheet. The GBW product is 8M Hz. That is considerably larger than when I studied Op-Amps. With a gain (G) of 30 (not 30dB) that is a 266k Hz bandwidth.
Resistance is a component of impedance. The phrase DC resistance is sometimes used because it is simple with DC.
Impedance is what happens in a reactive element when AC is applied (even resistors are slightly reactive). The voltage and current waves are no longer in phase with each other. It is a complex number requiring complex algebra not really normal algebra. Every term or element is either a magnitude (vector) at an angle or (X +/-jY), where j represents the reactive component (also the square root of minus 1, imaginary).
In other words, COMPLEX algebra.
I'm not familiar with ripblade's formula. That doesn't mean it is not right, I just don't remember it if I have seen or used it.
Last edited:
FrankPA
Active Member
I don't know if it applies as I haven't really looked at this circuit (just enjoying following the discoveries) but Jung wrote about using transimpedance amps in audio circuits in 1992:
http://waltjung.org/PDFs/High_Performance_Audio_Stages_Using_TransZ_Amps.pdf
Might lead you to your answer.
I decided to try out the phono stage with a diy regulated power supply I had laying around, it's a highly filtered, regulated low noise type with Schottky diodes and large high grade filtering caps etc, much better than most commercial products with +15v, 0, -15v outputs. I put the same connector on this supply as I have on the batteries so I could change them out quickly.
I played my usual test album, Love by The Beatles, all the detail was there, the sound stage was the same, pretty much everything was the same, the noise levels were nearly non existent as with the batteries.
That's the good news, the bad news is there is a harshness to the sound. Even my wife noticed it without her knowing which supply she was listening to, she picked the linear supply every time saying it sounds harsh and the battery supply every time saying it sounds smooth.
I played my usual test album, Love by The Beatles, all the detail was there, the sound stage was the same, pretty much everything was the same, the noise levels were nearly non existent as with the batteries.
That's the good news, the bad news is there is a harshness to the sound. Even my wife noticed it without her knowing which supply she was listening to, she picked the linear supply every time saying it sounds harsh and the battery supply every time saying it sounds smooth.
Fasterdamnit
Super Member
Now that is interesting. I am listening to mine right now- just some good ol' loud rock and roll- Judas Priest, Journey and Joe Walsh. I know it is cliche', but I am hearing things I have not heard before- and my hearing is not the best. Breathing and small instrument noises I had not noticed before. I can also listen at higher volumes before discomfort sets in. All on Ray-O-Vac 9 volts. I will have to try my Bugle PS and see if I hear a similar result.
Now that is interesting. I am listening to mine right now- just some good ol' loud rock and roll- Judas Priest, Journey and Joe Walsh. I know it is cliche', but I am hearing things I have not heard before- and my hearing is not the best. Breathing and small instrument noises I had not noticed before. I can also listen at higher volumes before discomfort sets in. All on Ray-O-Vac 9 volts. I will have to try my Bugle PS and see if I hear a similar result.
These might be connected in some way.
Frank, thanks for the clip. I will read it in full when I get home mid day. I looked in my book and Transimpedance doesn't appear in the index. I guess it was about a decade too soon.
The circuit is almost the same as shown on page 39 for section 1.2.3 Errors Due To Non Zero Output Resistance except that Ri is the internal resistance of the LOMC. The optional "load matching" resistor on the + input to ground matches the suggestion that Ri be mirrored there for minimal voltage offset.
The true revelation of this circuit seems to be that Ri can be the cartridge's internal resistance. Simple but elegant!
Richard seems a really nice guy, I hope others take advantage of his generosity, it's well worth it. I just love mine.
No Affiliation.
I just basically cut of the PSU and ran it off batteries, I made my own PCB at home, with a couple of other tweaks. If you get boards off Richard you can just connect batteries to the opamp inputs or make the whole thing with his power conditioner circuit.
fasterdamnit and Big Bill just did what I did.
It works with any moving coil cart, I just calculated the values for R1 and R2. R1 is the same as the internal resistance of the cart to balance the inputs of the op amp mine was 90ohms. R2 is the gain resistor and is set by knowing the output of the cart mine is 2.5mv's so I set mine at 330ohms and the gain is perfect.
Last edited:
HT,
Just so I understand, did you get the specified resistance of your cartridge or measure? I have read (so I am not sure it is right) that you should never measure an MC cartridge with a meter since the DC might magnetize the coils.
Thanks.
Just so I understand, did you get the specified resistance of your cartridge or measure? I have read (so I am not sure it is right) that you should never measure an MC cartridge with a meter since the DC might magnetize the coils.
Thanks.
That's good to know Grainger, I got it from the spec sheet that came with it. Never even thought to measure it so I will let people know not too just in case.