2 years ago I started a project for a phono preamp, that can be completely controlled remotely (incl. input resistance, capacitance and amplification) and can be used for all kinds of systems (LO-MC, HO-MC, MM). Unfortunately the project was on hold for a long time, but now it's time to to it finally.
The planned features:
- amplification, input capacitance and input resistance selectable during operation with remote control
- integrated volume control, no need for an external preamplifier
- based on platINA design, but with SMD ICs (that are still large enough to be soldered with a good soldering iron)
- 1-4 inputs
- optional digital output and USB output
If you're looking for the ultimate "comfort" RIAA stage - are there any features that you would like to see?
I do not plan to implement different equalization curves, because this will be a stereo preamp.
The planned features:
- amplification, input capacitance and input resistance selectable during operation with remote control
- integrated volume control, no need for an external preamplifier
- based on platINA design, but with SMD ICs (that are still large enough to be soldered with a good soldering iron)
- 1-4 inputs
- optional digital output and USB output
If you're looking for the ultimate "comfort" RIAA stage - are there any features that you would like to see?
I do not plan to implement different equalization curves, because this will be a stereo preamp.
Hi,
Similar to the PlatInA, I'd offer assistance. I've some ideas about the input stage up to a fully differential circuit, orientating at the PlatINAs basic topology, but with uC controlled comfort.
Just one Q: do you intend to go commercial as with the PlatINA? Or will it be bare PCBs only?
jauu
Calvin
Similar to the PlatInA, I'd offer assistance. I've some ideas about the input stage up to a fully differential circuit, orientating at the PlatINAs basic topology, but with uC controlled comfort.
Just one Q: do you intend to go commercial as with the PlatINA? Or will it be bare PCBs only?
jauu
Calvin
Hi Calvin,
it's always good to get help. I'm planning to use low-resistance analog switches (<2 Ohm) in the input stage to change the input capacitance and resistance. There will be also 2-3 analog switches to change the gain of the input stage (CN0146 from AD shows a similar setup).
Every input gets it's own input stage, switching takes place after the first stage amplification (if there is more than a single input).
I have to test some analog switches to find out which work best.
I do not plan to sell finished comfortINAs, but PCBs to interested people. That might change if there is a huge demand. Circuit diagrams will be available to everybody free of charge.
it's always good to get help. I'm planning to use low-resistance analog switches (<2 Ohm) in the input stage to change the input capacitance and resistance. There will be also 2-3 analog switches to change the gain of the input stage (CN0146 from AD shows a similar setup).
Every input gets it's own input stage, switching takes place after the first stage amplification (if there is more than a single input).
I have to test some analog switches to find out which work best.
I do not plan to sell finished comfortINAs, but PCBs to interested people. That might change if there is a huge demand. Circuit diagrams will be available to everybody free of charge.
I've checked several options for the input gain stage. The original platINA design used DIP switches to select the amplification of this stage. Unfortunately for a high gain, an external resistance of down to 10 Ohm is needed. Switching this with analog switches with some tolerance, can result in gain variations between the two channels. Also ultra-low Ron analog switches from ADI are only available in TSSOP packages. That would require a 4 layer board (I'm still trying to get the circuit on a two layer board).
Therefore I will try another approach: I accept minor balance errors in the input stage and adjust them later. The error in the input stage should be <1dB, therefore correction should not be a problem.
This makes it possible to use higher resistance switches like the ADG451 that are available in SOIC packages (and even DIP, but I think I will go for SOIC).
Therefore I will try another approach: I accept minor balance errors in the input stage and adjust them later. The error in the input stage should be <1dB, therefore correction should not be a problem.
This makes it possible to use higher resistance switches like the ADG451 that are available in SOIC packages (and even DIP, but I think I will go for SOIC).
Hi,
I wouldn´t rule out the TSSOp and TQFN- Packages and also not a 4-layer board. Ok, the boards would have to be populated at least in part by a professional, but that shouldn´t be a prob in a group buy, even at lowest device number counts. And it certainly is no real cost problem.
It´d allow for improvements due to devices only manufactured in those SMD-casings.
Extremely low on-value and tightly tolerated analog switches would only be required for the gain setting resistor in a INA-stage. For the impedance setting switches one could well use low-ohmic switches around 10Ohm.
The first could be omitted with completely with a 2-chip chipset in TQFN-casings, thereby also eliminating zipper noise and other issues of a discrete solution.
jauu
Calvin
I wouldn´t rule out the TSSOp and TQFN- Packages and also not a 4-layer board. Ok, the boards would have to be populated at least in part by a professional, but that shouldn´t be a prob in a group buy, even at lowest device number counts. And it certainly is no real cost problem.
It´d allow for improvements due to devices only manufactured in those SMD-casings.
Extremely low on-value and tightly tolerated analog switches would only be required for the gain setting resistor in a INA-stage. For the impedance setting switches one could well use low-ohmic switches around 10Ohm.
The first could be omitted with completely with a 2-chip chipset in TQFN-casings, thereby also eliminating zipper noise and other issues of a discrete solution.
jauu
Calvin
Hi Calvin,
I haven't decided yet. I think, TSSOP is still an option. The main problem for me is prototyping will become much more expensive.
Another option for a pure MC stage might be the PG2505. Its 10k input impedance is a problem for MM, but not for MC. The 0.5dB gain variation would also not be a problem, because it would be corrected later.
I'm thinking about the concept to have a balanced MC input stage and a different unbalanced input stage.
Daniel
I haven't decided yet. I think, TSSOP is still an option. The main problem for me is prototyping will become much more expensive.
Another option for a pure MC stage might be the PG2505. Its 10k input impedance is a problem for MM, but not for MC. The 0.5dB gain variation would also not be a problem, because it would be corrected later.
I'm thinking about the concept to have a balanced MC input stage and a different unbalanced input stage.
Daniel
Ok, I did some calculations now based on the ADG451. With a 0.1Ohm tolerance between different ICs, the final tolerance in the gain would be max. 0.05dB. With maximum tolerance of the ADG451 of 0.5Ohm, the channel tolerance would be 0.25dB. In the highest gain setting I will use two parallel switches.
I will test some of these ICs to see how big the tolerances are in reality.
I will test some of these ICs to see how big the tolerances are in reality.
Hi Calvin,
Can you please elaborate? Some of the ICs that appeared during the last couple of years come to mind.
What fully differential ICs can compete with INA163 in this application?
Cheers,
Sebastian.
Can you please elaborate? Some of the ICs that appeared during the last couple of years come to mind.
What fully differential ICs can compete with INA163 in this application?
Cheers,
Sebastian.
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