Hello!
Hoping you all can help me understand this circuit and what/where are the critical components in the signal path. This is a 90's Aragon 47k/Acurus P10 phono stage one channel shown in the schematic. My goal is 'simple project' to practice my soldering skills, to try some resistor upgrades, and see what can be can be gained.
I understand R1-R6 are loading resistors, R10 is the input resistor, and Q1, Q2, Q3, and Q4 are transistors. I'm confused how the signal flow seems to split between C9 & C8 (which seem to implement the RiAA curve) and Q5 & Q6. I think R21 & R20 are the feedback resistors in this circuit? Q8 & Q7 seem to be output mosfets? Is R25/R26 in the signal path or just R27? I'd like to make a few part upgrades as the board and components are easy to work with and I have moderately competent soldering skills. Your help/feedback in identifying which resistors are in the signal path that would benefit from upgrading is greatly appreciated.
Happy Audio!
Hoping you all can help me understand this circuit and what/where are the critical components in the signal path. This is a 90's Aragon 47k/Acurus P10 phono stage one channel shown in the schematic. My goal is 'simple project' to practice my soldering skills, to try some resistor upgrades, and see what can be can be gained.
I understand R1-R6 are loading resistors, R10 is the input resistor, and Q1, Q2, Q3, and Q4 are transistors. I'm confused how the signal flow seems to split between C9 & C8 (which seem to implement the RiAA curve) and Q5 & Q6. I think R21 & R20 are the feedback resistors in this circuit? Q8 & Q7 seem to be output mosfets? Is R25/R26 in the signal path or just R27? I'd like to make a few part upgrades as the board and components are easy to work with and I have moderately competent soldering skills. Your help/feedback in identifying which resistors are in the signal path that would benefit from upgrading is greatly appreciated.
Happy Audio!
Everything is in the signal path, including R25 and R26.
That's a standard RIAA eq feedback circuit.
R20, R21 are for HF stability or ringing.
Start with replacing C3, which is probably bad by now.
Don't replace C8 or C9. They are critical.
All resistors should be precision metal film.
That's a standard RIAA eq feedback circuit.
R20, R21 are for HF stability or ringing.
Start with replacing C3, which is probably bad by now.
Don't replace C8 or C9. They are critical.
All resistors should be precision metal film.
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There is no direct signal path. All series and shunt impedances, and devices, affect the signal.
R7/8/9 is an critical RIAA gain setting resistor, with C3 being a large series electrolytic capacitor, to set the DC gain to unity.
Both components are part of the RIAA network and are very important.
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Well yes, C12 is currently a 10uf NP mylar capacitor. I plan to upgrade that output capacitor. But R23 & R24 look just voltage reduction resistors to power the output mosfets no?
Yes, but R7, R8, R9 are just going to gound. I understand a resistor going to ground can still introduce noise into the circuit but these are already dale N60 MF so not so critical to replace IMHO but thank you!
Well educate me! How does the concept of a voltage divider apply to this circuit? Are you referring to R25 & R26?
Those source resistors are for output stage quiescent current biasing, and are within the overall nfb loop.How does the concept of a voltage divider apply to this circuit? Are you referring to R25 & R26?
For this reason, they do not present a significant output impedance to R27, and so there is no signal drop
at the output node due to their presence when a load is connected.
The RIAA network, comprised of C8/C9/R28/R29/C2/C3/R7/R8/R9, is a voltage divider, and sets the
closed loop signal voltage frequency response. See feedback theory in EE101 texts.
They bias the two paralled input stages, improve their balance, and reduce their gains.
So Im I to understand there are effectively three gain stages in this circuit? The two paralleled input stages, then feeding Q6 & Q5, and then the output (FETs?) Q7 & Q8 with a closed loop RIAA network?
Similar topology and operation.
Any three terminal active device must have one element in common between the input and output.
So the source/cathode can be common, or the gate/grid, or the drain/plate.
The source follower/cathode follower have the drain/plate in common between their input and output.
The gate/grid are inputs and the source/cathode are outputs.
Any three terminal active device must have one element in common between the input and output.
So the source/cathode can be common, or the gate/grid, or the drain/plate.
The source follower/cathode follower have the drain/plate in common between their input and output.
The gate/grid are inputs and the source/cathode are outputs.
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Values of C1 and R1-6 will be very important to the sound you get from the cartridge.
The R25/R26 often drift or become damaged from heat, and may need replacement, with noninductive parts.
The stability related R21/R22/C4/C5 should be low inductance parts, but are unlikely to benefit from replacement.
Nonpolar or bipolar C12 is outside of the nfb loop, and can impact the sound directly.
Resistors closer to the input will tend to make more output noise than later ones, and should be metal film.