Fully Discrete 400 / 700 Driver Circuit (Full Comp Only)
- Thread starter THD+N
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Thanks Glen for confirming that.
I tried to keep the PLX the same size as the original PL36, but there were just too many components in the new design to use the same size PCB and have room to comfortably layout the components without the PCB being "densely populated".
Sniffer,
The PLX will work with the WO backplane. I will make sure the documentation for the PLX clearly covers all the connections points, what they do and where they need to be connected.
I tried to keep the PLX the same size as the original PL36, but there were just too many components in the new design to use the same size PCB and have room to comfortably layout the components without the PCB being "densely populated".
Sniffer,
The PLX will work with the WO backplane. I will make sure the documentation for the PLX clearly covers all the connections points, what they do and where they need to be connected.
I am going to order boards for my new PL amp design soon. I need 15 for my heard.
Preliminary Specs (Will be finalized when PCB's come in and testing begins)
Low distortion and slew rate are not everything and the design will be tweaked for sound quality and stability as well. To my ears, if an amp is "too fast" (high slew rate), it sound cold and clinical (not warm/musical). However, since we all hear differently, this design can be easily manipulated for your listening preference(s) within reasonable limits.
Let me know if you want to participate in the PCB order, so I can get an order quantity going. It looks like unstuffed PCB's will be $64 shipped in the contiguous US.
Except for some capacitor values/types, the "amp control board" design is very forgiving and parts selection is not too critical. The drivers and outputs for a full comp version should still use MJ15024/25 or MJ21195/96 transistors.
Board features will include:
Preliminary Specs (Will be finalized when PCB's come in and testing begins)
- 100kHz power bandwidth (I don't recommend trying to get 350 Watts out at 100kHz, but it should do it, in theory)
- Slew rate - 37 V/us (Calculated. In reality, closer to 33 V/us probably)
- >100dB signal to noise
- THD+N at 20kHz <0.002% at 350 Watts/8 Ohm
- 1 Watt frequency response - 0.5Hz ~ 200kHz
Low distortion and slew rate are not everything and the design will be tweaked for sound quality and stability as well. To my ears, if an amp is "too fast" (high slew rate), it sound cold and clinical (not warm/musical). However, since we all hear differently, this design can be easily manipulated for your listening preference(s) within reasonable limits.
Let me know if you want to participate in the PCB order, so I can get an order quantity going. It looks like unstuffed PCB's will be $64 shipped in the contiguous US.
Except for some capacitor values/types, the "amp control board" design is very forgiving and parts selection is not too critical. The drivers and outputs for a full comp version should still use MJ15024/25 or MJ21195/96 transistors.
Board features will include:
- FR-4 epoxy glass board
- Top and bottom solder mask
- Top silk printing (white)
- RoHS compliant
- Double-sided, plated through holes
Nick,
Thanks for offering up some specs on your board.
Is the S/N ratio unweighted or A weighted or perhaps DIN (Audio) flat from 22-22kHz?
Is the power bandwidth (essentially) flat all the way out to 100 kHz or 3dB down at 100kHz?
Any ideas on what channel separation is at 1KHz, or 10 kHZ, or 20 KHz at rated output or at -3dB?
How about damping factor (at a given frequency)?
Phase Shift?
Rise Time?
Thanks again!
Ed
Thanks for offering up some specs on your board.
Is the S/N ratio unweighted or A weighted or perhaps DIN (Audio) flat from 22-22kHz?
Is the power bandwidth (essentially) flat all the way out to 100 kHz or 3dB down at 100kHz?
Any ideas on what channel separation is at 1KHz, or 10 kHZ, or 20 KHz at rated output or at -3dB?
How about damping factor (at a given frequency)?
Phase Shift?
Rise Time?
Thanks again!
Ed
Hi Ed,
- S/N spec is weighted, but I can certainly do un-weighted.
- The power bandwidth would be -3dB at rated power for the 700. For the 400, the power bandwidth would be a bit better due to less power and more headroom on the slew rate.
- Channel separation should be as good as the original 400 or 700, but I won't know until I get the boards for testing.
- I'll have to measure the damping factor and phase shift when I do testing. Rise time and slew rate are interrelated, so the rise time should be better than the original 400 and 700.
- S/N spec is weighted, but I can certainly do un-weighted.
- The power bandwidth would be -3dB at rated power for the 700. For the 400, the power bandwidth would be a bit better due to less power and more headroom on the slew rate.
- Channel separation should be as good as the original 400 or 700, but I won't know until I get the boards for testing.
- I'll have to measure the damping factor and phase shift when I do testing. Rise time and slew rate are interrelated, so the rise time should be better than the original 400 and 700.
I have "grafted" the latest 400-700 driver circuit onto one of my PL36 PCB's and installed a DCP (Thanks to Glen for sending an extra he had).
Before I order the PCB's, I want to get a second opinion of the amp performance, so I am sending the entire amp to Glen for his evaluation. I am getting 400 Watts out at 1kHz @ 0.2% THD+N.
The circuit is capable of better (distortion) performance than what the PL 400-700 chassis will allow. In other words, the 400-700 heat sink area is not large enough to bias the amp to the optimum setting without the heat sink getting very warm at idle. I knew this was going to be a limitation and was prepared to work within the limits of the PL chassis. This mainly affects the 20kHz THD+N. However, I have found a compromise setting and I am happy with it.
Test results of unit being sent to Glen:
Frequency Response @ 1 Watt/8 Ohm: 0.5Hz to 250kHz
Frequency Response @ 50 Watts/8 Ohm: 0.5Hz to 250kHz
Signal to Noise (Inputs grounded): <200uV's
Rise Time: 1.4uS
Slew Rate: 45V/uS
THD+N @ 1 Watt/1kHz: 0.015%
THD+N @ 1 Watt/20kHz: 0.06%
Phase Response: +3° @ 10Hz, -5° @ 20kHz
Left Channel Separation: 1kHz/80dB, 10kHz/67dB, 20kHz/63dB
Right Channel Separation: 1kHz/75dB, 10kHz/70dB, 20kHz/68dB
Have not measured damping factor. It should be the same as the PL spec since the output stage has not changed.
Before I order the PCB's, I want to get a second opinion of the amp performance, so I am sending the entire amp to Glen for his evaluation. I am getting 400 Watts out at 1kHz @ 0.2% THD+N.
The circuit is capable of better (distortion) performance than what the PL 400-700 chassis will allow. In other words, the 400-700 heat sink area is not large enough to bias the amp to the optimum setting without the heat sink getting very warm at idle. I knew this was going to be a limitation and was prepared to work within the limits of the PL chassis. This mainly affects the 20kHz THD+N. However, I have found a compromise setting and I am happy with it.
Test results of unit being sent to Glen:
Frequency Response @ 1 Watt/8 Ohm: 0.5Hz to 250kHz
Frequency Response @ 50 Watts/8 Ohm: 0.5Hz to 250kHz
Signal to Noise (Inputs grounded): <200uV's
Rise Time: 1.4uS
Slew Rate: 45V/uS
THD+N @ 1 Watt/1kHz: 0.015%
THD+N @ 1 Watt/20kHz: 0.06%
Phase Response: +3° @ 10Hz, -5° @ 20kHz
Left Channel Separation: 1kHz/80dB, 10kHz/67dB, 20kHz/63dB
Right Channel Separation: 1kHz/75dB, 10kHz/70dB, 20kHz/68dB
Have not measured damping factor. It should be the same as the PL spec since the output stage has not changed.
Attachments
Nick,
From looking at the photos, there appears to be a bunch of modifications done on the back side of the pc board. Will these mods eventually end up on the top side of the board with the next revision?
The frequency response specs you quoted are at what value? (i.e. +0/-1db with 1KHz as a “0†reference)
When you performed the signal to noise tests (with inputs grounded/shorted) what position did you also have the volume pots set at? (i.e. fully CCW, 12 o’clock or fully CW). NOTE: Even though the inputs are shorted I have seen a difference depending upon where the volume pots are set.
Can you provide me with a THD+N spec at rated power at 20KHz?
At what level did you use when you performed the channel separation tests (i.e. rated output, -3dB down from rated output)?
Ed
Ed,
The circuit is being debugged/tested before I get the PCB's made, so yes, the final PCB is coming.
I'll post more detailed test info later.
Frequency response is referenced to 0dB with 1kHz as the reference.
On this amp, I have bypassed the level controls. I never use them (on any amp) and they just get in the way (literally and from a noise stand-point). I'm sure somebody may have a need for them, but I don't.
THD+N @ 20kHz full power will be posted tonight after more testing.
Channel separation was done at 1 Watt, but I can do other levels too. Let me know the exact power levels you are interested in (1, 50, 200 or 350 watts, etc).
The circuit is being debugged/tested before I get the PCB's made, so yes, the final PCB is coming.
I'll post more detailed test info later.
Frequency response is referenced to 0dB with 1kHz as the reference.
On this amp, I have bypassed the level controls. I never use them (on any amp) and they just get in the way (literally and from a noise stand-point). I'm sure somebody may have a need for them, but I don't.
THD+N @ 20kHz full power will be posted tonight after more testing.
Channel separation was done at 1 Watt, but I can do other levels too. Let me know the exact power levels you are interested in (1, 50, 200 or 350 watts, etc).
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Nick,
I would be interested in channel separation at (100 Hz, 1KHz, 10KHz and additionally 20KHz) at rated output and -3dB (as referenced in the IHF-A-202 you provided us with).
I am assuming that the frequency response is at 1 watt and not at rated output? As was the case with old originals 700's.
The same IHF-A-202 section 3.13.1 "The frequency response rating of a set of input terminals shall be plus or minus decibel error from flat response, referenced at 1000 Hz." If my memory serves me correct, the upper frequency response of the old Phase Linear 700 was .25MHZ (250 KHz) but upon further review it was also -3dB at 250KHz.
NOTE: I have also seen frequency response of old Phase Linear 700's referenced to 1V but I think that must be a typo. Unless the spec tells us what kind of load (i.e. 8 ohm or even 600 ohms as was the case when driving a lot of test equipment.)
GENERAL COMMENTS:
In general, I like to see specs at rated output since they generally tell us worst case scenario (and typically 20 KHz). This can be difficult at times..... since the amplifiers can thermally shut down...... larger power supply and B+ and B- fuses may also need to be installed...... the resistor in the Zobel network can be destroyed, etc.
I was looking at an very old spec just yesterday where they required you perform a test at a given frequency for a minimum of 30 seconds. In which case, driving both channels at rated output into 4 ohms at 20KHz can be problematic. (Try holding it 30 seconds on some Phase amps and you are going to have problems). Many standards don't give us much guidance as to how long you must perform a given test. Or try to establish the upper (bandwidth) frequency limit on a series II amp at rated output and spec'd distortion level. I have also read that driving an amplifier into clipping into a 20KHz can be harder on output transistors in some amplifiers than shorting the outputs (HUH!).
Enough rambling for now!
Ed
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I would then suggest when performing subjective testing that one states the manufacturer, and model number of the speakers..... The speaker placement.... The size of the room.... The artist and song(s).... etc.... Better yet maybe do what many well known amplifier designers do and that is to perform listening tests at 1W with a pair of headphones. In which case you can remove the room acoustics and some of the variables. Notable designers like Dan D'Agostino, John Curl and Nelson Pass all use headphones at approximately 1W to evaluate the amplifiers they are designing. By the way, most amplifier use is between 1W and 40 Watts. Nelson Pass has a website and it is http://www.firstwatt.com. "Dick Olsher famously remarked that the first watt is the most important watt".
Perhaps we all need to also buy a copy of J. Gordon Holt's (former publisher of Stereophile) book "The Audio Glossary" which has terms and definitions.
(It will cost you around $75+ for a used copy)
Here is a link to some of the terms re-published in 1993. https://www.stereophile.com/reference/50/index.html
Did I stir the kettle enough? LOL!
Ed
Perhaps we all need to also buy a copy of J. Gordon Holt's (former publisher of Stereophile) book "The Audio Glossary" which has terms and definitions.
(It will cost you around $75+ for a used copy)
Here is a link to some of the terms re-published in 1993. https://www.stereophile.com/reference/50/index.html
Did I stir the kettle enough? LOL!
Ed
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I did not mean to infer anything... it was late when I posted. The 1 watt frequency response is -3dB on the top and bottom frequency measurements.
At 50 watts (8 ohm load), the frequency response is still the same as 1 watt because the slew rate is about 45V/uS. The power bandwidth of this design is approximately 100kHz at 350 watts output, 8 ohm load.
Of course you do not have to destroy an output stage to know the bandwidth by testing at those high frequencies, however, other measurements will confirm the bandwidth and performance.
I will post AP graphs later (with small notes) and you can extract all the info you want or need.
At 50 watts (8 ohm load), the frequency response is still the same as 1 watt because the slew rate is about 45V/uS. The power bandwidth of this design is approximately 100kHz at 350 watts output, 8 ohm load.
Of course you do not have to destroy an output stage to know the bandwidth by testing at those high frequencies, however, other measurements will confirm the bandwidth and performance.
I will post AP graphs later (with small notes) and you can extract all the info you want or need.