PL2000 preamp square wave ringing.
- Thread starter George S.
- Start date
Joe, you did it. Results look very good.
The PL has appx 1/2 dB rise over the Acurus at 4 Hz.
I ran the frequency response out to the Nyquist Limit, appx 90 kHz.
The PL is down appx 1/2 dB at 45 kHz, the Acurus is down appx 1/2 dB at 75 kHz.
Thank you! This is going to help a lot of people who want to run a PL preamp with their WOPLs.
C18, C20, 15pF or 7pF silver mica (I used 7pF, got slightly flatter high frequency response)
C42, C43, 100uF electrolytic
C21, C22, 2.2uF film
The PL has appx 1/2 dB rise over the Acurus at 4 Hz.
I ran the frequency response out to the Nyquist Limit, appx 90 kHz.
The PL is down appx 1/2 dB at 45 kHz, the Acurus is down appx 1/2 dB at 75 kHz.
Thank you! This is going to help a lot of people who want to run a PL preamp with their WOPLs.
C18, C20, 15pF or 7pF silver mica (I used 7pF, got slightly flatter high frequency response)
C42, C43, 100uF electrolytic
C21, C22, 2.2uF film
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Those op-amps have phase shift...and so some can be unstable driving the capacitive DC blocking circuit.
Easy fix...put a 50 to 100 ohm resistor in series with the back-to-back DC blocking caps on both channels to isolate the capacitive loading.
I have a new design on this website for a cleaner new design, if your interested in building one. I have a 2000 that I upgraded with new 40 MHz op-amps..,. much cleaner and distortion less. The switches are a bit noisy, so I derided to do a ground up re-design to replace this preamp. Clean square waves and triangle waves with very very sharp peaks also.
Easy fix...put a 50 to 100 ohm resistor in series with the back-to-back DC blocking caps on both channels to isolate the capacitive loading.
I have a new design on this website for a cleaner new design, if your interested in building one. I have a 2000 that I upgraded with new 40 MHz op-amps..,. much cleaner and distortion less. The switches are a bit noisy, so I derided to do a ground up re-design to replace this preamp. Clean square waves and triangle waves with very very sharp peaks also.
Thanks GeorgeP
I've been following your thread on the new preamp when you posted, haven't seen anything lately and didn't know if your still at it.
I want to take the original board as far as possible.
The PL2000 is a learning tool for me as I have no background in electronics.
Does your board drop into a original chassis? You should post some photos.
I and I'm sure others are interested in what your doing.
You'd probably sell some boards.
I've been following your thread on the new preamp when you posted, haven't seen anything lately and didn't know if your still at it.
I want to take the original board as far as possible.
The PL2000 is a learning tool for me as I have no background in electronics.
Does your board drop into a original chassis? You should post some photos.
I and I'm sure others are interested in what your doing.
You'd probably sell some boards.
Which OPAMPs are you referring to? The OPAMPs we use are the Texas Instruments, Burr-Brown Division, OPA134 or the dual channel OPA2134. These are 8MHz Gain Bandwidth, 20V/us Slew Rate, 0.00008% @ 1kHz THD+Noise, 100db Common Mode Rejection Ratio, 120db Open Loop Voltage Gain, FET Input unity-gain stable devices that provide excellent dynamic behavior over a wide range of load conditions including high load capacitance. They can be driven from +/-2.5V to +/-18V Rails and will swing the output to within 1V of the Rail Voltage for maximum headroom in audio circuits.
From the Texas Instruments Datasheet:
"The OPA134 series of operational amplifiers are free from output phase-reversal problems. Many audio
operational amplifiers, such as the OP176, exhibit phase-reversal of the output when the input common-mode
voltage range is exceeded. This can occur in voltage-follower circuits, causing serious problems in control loop
applications. The OPA134 series operational amplifiers are free from this undesirable behavior even with inputs
of 10-V beyond the input common-mode range."
And it's worth noting that phase shift is meaningless in itself. A constant delay (which delays all frequencies equally) results in a consistent phase shift, in which all frequencies arrive at the same time. And this will be the case as long as the phase shift is linear with frequency.
Viewing the "Open Loop" Phase vs. Frequency chart on the datasheet, the Phase Shift is a linear -90.0 degrees from 100Hz to 200kHz. Of course, our OPAMPs are used in a closed loop (with feedback), so the chart is a worst case scenario.
See the Datasheet, page 8:
https://www.ti.com/lit/ds/symlink/o...l=https%3A%2F%2Fwww.ti.com%2Fproduct%2FOPA134
If this sounds like an advertisement, it is. I believe this is the best AUDIO OPAMP available today.
From the Texas Instruments Datasheet:
"The OPA134 series of operational amplifiers are free from output phase-reversal problems. Many audio
operational amplifiers, such as the OP176, exhibit phase-reversal of the output when the input common-mode
voltage range is exceeded. This can occur in voltage-follower circuits, causing serious problems in control loop
applications. The OPA134 series operational amplifiers are free from this undesirable behavior even with inputs
of 10-V beyond the input common-mode range."
And it's worth noting that phase shift is meaningless in itself. A constant delay (which delays all frequencies equally) results in a consistent phase shift, in which all frequencies arrive at the same time. And this will be the case as long as the phase shift is linear with frequency.
Viewing the "Open Loop" Phase vs. Frequency chart on the datasheet, the Phase Shift is a linear -90.0 degrees from 100Hz to 200kHz. Of course, our OPAMPs are used in a closed loop (with feedback), so the chart is a worst case scenario.
See the Datasheet, page 8:
https://www.ti.com/lit/ds/symlink/o...l=https%3A%2F%2Fwww.ti.com%2Fproduct%2FOPA134
If this sounds like an advertisement, it is. I believe this is the best AUDIO OPAMP available today.
The OPA1611 is a Bipolar input device and the cost (from Ti) is $4.10 each. But the downside for me is the SOIC surface-mount package.
The OPA134 is a FET input device and the cost (from Ti) is $2.47 each. These are PDIP packages and make replacement (and OPAMP rolling) easier.
Maybe Joe can chime in with advice, technical difference, advantages, and other opinions.
The OPA134 is a FET input device and the cost (from Ti) is $2.47 each. These are PDIP packages and make replacement (and OPAMP rolling) easier.
Maybe Joe can chime in with advice, technical difference, advantages, and other opinions.
I understand the surface mount chip apprehensions, but this is easier to do than I thought. Easy "touch-and-go", and its down, holding it in place carefully on the first pin with tweezers, then the rest is easy. I also have seen SMT to PDIP with pins as interface boards for sale. I used them on my 2000, then I decided to redesign a new preamp with newer chips and love it. The Bipolar technology is now better, since the bias points are better controlled, better than the VGS variations... so I guess that's why the newer chips are made this way, and achieve very low input currents, very high input impedances, and NO distortion at all.
Try the interface boards, they are expensive for a chip already mounted on one... but, its a one time test anyway, or you can leave it that way. My 2000 has them. Pin for pin compatible. I'm getting ready to post the sale of the boards on EBAY. I'm cleaning up the parts lists, so I'll have them ready soon.
Try the interface boards, they are expensive for a chip already mounted on one... but, its a one time test anyway, or you can leave it that way. My 2000 has them. Pin for pin compatible. I'm getting ready to post the sale of the boards on EBAY. I'm cleaning up the parts lists, so I'll have them ready soon.