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Old 17th August 2011, 12:13 AM   #801
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Thanks nAr. That works much better, but I'm still seeing some hokey voltages. I'm getting +24 / -27 from one board, and +22.75 / -27.8 on the other. I'm checking at the output pins of the regs and the ground pad.

But holy God, do these boards sound good . Mt current phono pre is a Hagerman Bugle, and the sound coming out of these Pearl boards is fantastic. I could only use one at a time, and just played a single track a few times on each, but it was obvious my analog rig is at a whole new level.

I already ordered new regs just in case. Should I change out the three that aren't putting out 24v?

Also, do you still recommend this PS for the Pearl 2? http://www.amb.org/audio/sigma22/

Mark

Last edited by McQuaide; 17th August 2011 at 12:22 AM.
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Old 17th August 2011, 03:44 PM   #802
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Quote:
Originally Posted by McQuaide View Post
Thanks nAr. That works much better, but I'm still seeing some hokey voltages. I'm getting +24 / -27 from one board, and +22.75 / -27.8 on the other. I'm checking at the output pins of the regs and the ground pad.

But holy God, do these boards sound good . Mt current phono pre is a Hagerman Bugle, and the sound coming out of these Pearl boards is fantastic. I could only use one at a time, and just played a single track a few times on each, but it was obvious my analog rig is at a whole new level.

I already ordered new regs just in case. Should I change out the three that aren't putting out 24v?

Also, do you still recommend this PS for the Pearl 2? The σ22 Regulated Power Supply

Mark
Never used it, but seems technically suitable

Quote:
Low noise, high PSRR

A constant-current source feeds a zener diode as a stable voltage reference. A low-pass filter (with a corner frequency of 1.6Hz) prevents zener noise from being introduced into the error amplifier. This is an effective yet lower-cost alternative to expensive voltage reference ICs. The low-pass filter also provides a soft-start characteristic.
The output noise (unloaded) is less than 12V at 30VDC output (measured using a Tangent LNMP (low-noise measurement preamplifier) and a Fluke 187 50000-count DMM in ACmV mode). The output noise is even less when the output voltage is lower. This is much better than the noise of an IC regulator based PSU tested under identical conditions.
The error amplifier is a discrete implementation of an opamp with a high open-loop gain of 102.5dB. The voltage supply to the error amplifier is isolated with capacitance multipliers to boost its PSRR (power supply rejection ratio). This greatly improves the line regulation performance of the PSU.
A long-tailed pair differential amplifier with current mirror and constant current source forms the first stage of the error amplifier. The second stage is the voltage amplification stage (VAS), also with constant current source load. The 3rd stage is comprised of the power MOSFET output devices configured as a source follower.

Tracking rails

The positive regulator's output voltage is based on the reference zener voltage and the gain of its error amplifier.
The negative regulator's voltage reference is the output voltage of the positive regulator. Its error amplifier has a gain of -1, so that its output voltage is the inverse of the positive regulator's output voltage. The negative regulator dynamically "tracks" the positive regulator -- any small voltage fluctuations on the positive rail also appear inverted on the negative rail, improving the CMRR (common mode rejection ratio) of the amplifier being powered.
The tracking behavior means that the voltage on both rails rise and fall equally. When used to supply a fully-complementary amplifier such as the β22, no "thump" noise is heard as the power is turned on or off.

High-current MOSFET pass transistors

Two paralleled high-current, highly reliable MOSFETs (rated at 17A each) serve as the "pass" transistor of each rail.
The high current rating provides a very high safety headroom against overcurrent damage.
The use of paralleled MOSFETs divides the heat dissipation, simplifying thermal management. Onboard heatsinks can be used which would allow the σ22 to supply up to 1A continuous (with much higher peak currents). More sustained currents are possible by using larger, offboard heatsinks.
The negative temperature coefficient of MOSFETs prevents damaging thermal-runaway conditions that may plague conventional BJT devices.

No current-limiting

The high-current MOSFETs are not normally the limit of how much current the σ22 PSU could supply, as long as they are adequately heatsinked.
The maximum current limit is determined by the rating of the power transformer, the rectifier diodes (the specified MUR820 devices are rated at 8A), and the AC line fuse.
The AC line fuse rating should be selected to protect the power transformer from overcurrent damage.
There is otherwise no current-limiting circuit in the σ22, which allows it to supply peak currents of many amperes. High transient bursts of current are always available, which some amplifiers require to avoid clipping and distortion.

Wide bandwidth

The all discrete topology allows the σ22 to be optimally tuned for the best combination of wide bandwidth and solid stability. Since the σ22's output impedance is much lower than even the best low-ESR large aluminum electrolytic capacitors, having wide bandwidth allows the σ22 to respond to fast changing current demands better than a large capacitor (or a bank of capacitors) ever would.
σ22's bandwidth extends beyond the audio band, and maintains supremely low output impedance in the Ω range. (in fact, the hookup wire will dominate the output impedance).
As such, only a 1F decoupling capacitor is used on each output rail onboard the σ22. The PSU can supply an amplifier with little additional capacitance for very fast response.
σ22 is also stable with a large capacitive load (tested to 10000F), making it suitable for use in a wide variety of applications.

Flexibility

Configurable for rail voltages up to 36V. The voltage is selected by using an appropriate reference zener diode, and choosing the value of a resistor. No further adjustment is needed.
Typical output voltages are 5V, 9V, 12V, 15V, 24V, 30V or 36V. These are popular voltages specified for many headphone amplifiers, preamplifiers, and class-AB power amplifiers up to around 20Wrms power output into 8Ω.
Multiple onboard capacitor footprint options.
Four sets of output terminal blocks.
Can be used with dual-secondary or center-tapped secondary power transformers.
σ22 is the default power supply for the AMB β22 stereo amplifier.
Other popular applications include power supply upgrades for the Kevin Gilmore Dynalo, Dynahi and DynaFET headphone amplifiers, various stereo preamplifiers, etc.

Versatile heatsink options

The default is to use onboard heatsinks for ease of building.
Offboard heatsinks for higher powered applications.
In this case I recommend you remove the onboard 78XX / 79XX, bypass the in and out board pins of said removed devices, and use the PSU directly to 24VVDC. The discrete reg seems doing a better job than integrated 7XXX

Best,

nAr
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Old 21st August 2011, 03:18 AM   #803
milosz is offline milosz  United States
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I had about a 10 dB difference in gain between L and R channels in a Pearl I built. After I got some help on this forum, I ordered 8 matched 2SK170BL JFETs from FETAUDIO out of Hong Kong, which were very reasonably priced. I replaced all the 2SK170BL JFETs with the new parts, and now channel balance is spot on. I guess my original FETs were poorly matched. Many thanks to FETAUDIO.

This is a very good sounding phono stage. It is impressively quiet. Incredibly quiet!

Thanks to NAR and others for the help.

Last edited by milosz; 21st August 2011 at 03:21 AM.
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Old 21st August 2011, 08:02 AM   #804
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Quote:
Originally Posted by milosz View Post
I had about a 10 dB difference in gain between L and R channels in a Pearl I built. After I got some help on this forum, I ordered 8 matched 2SK170BL JFETs from FETAUDIO out of Hong Kong, which were very reasonably priced. I replaced all the 2SK170BL JFETs with the new parts, and now channel balance is spot on. I guess my original FETs were poorly matched. Many thanks to FETAUDIO.

This is a very good sounding phono stage. It is impressively quiet. Incredibly quiet!

Thanks to NAR and others for the help.
Quite OK
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Old 21st August 2011, 02:00 PM   #805
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Gents ,


Can I use 47.5 k instead of 47k ... same question ! 6.81k instead of 6.8k ?
cheers , Rich
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Old 21st August 2011, 02:00 PM   #806
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I checked the voltages on my Pearl 2 boards to see how they compared with Wayne's. Everything seems reasonably close, with the exception of the collector terminal of Q3 (connects to R11). I'm seeing 14.7 - 14.9 volts there, while Wayne's drawing shows 10.1v. I'm not sure if this signifies anything.

Mark
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Old 21st August 2011, 02:12 PM   #807
Salas is online now Salas  Greece
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Has to do with pinch off voltage in different batches that give differences in DC bias. Combined transconductance of the quads should be near over a wider IDSS range, and the 10R resistors equalize a lot. I would be worried only about gain differences in the AC output and then look for problems.
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Old 21st August 2011, 02:14 PM   #808
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Quote:
Originally Posted by Salas View Post
Has to do with pinch off voltage in different batches that give differences in DC bias. Combined transconductance of the quads should be near over a wider IDSS range, and the 10R resistors equalize a lot. I would be worried only about gain differences in the AC output and then look for problems.
Thanks. How would I check for gain differences, other than by ear? The only equipment I have is a DMM.
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Old 21st August 2011, 02:20 PM   #809
Salas is online now Salas  Greece
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Run a test record with a tone 1kHz or preferably lower, put your DVM on ACV and probe the output RCA. Most DVMs will catch such tones well. HFNRR test disc has 300Hz. See that the track has not advanced to higher modulation if your disc has no lock grooves when you will do the other channel for comparison. That will include your cartridge's channel matching performance.
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Old 21st August 2011, 02:24 PM   #810
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Thanks.
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