O2 amp CRC, diode, cap, and heatsink mods - Page 12 - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 27th November 2012, 02:25 PM   #111
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
coolhead: interesting! The two major things the different power supply would probably affect are output impedance vs. frequency (looking back into the power supply output pins) and noise generation.

The MC/LM7xxx regulators are fairly noisy vs. some other regulators, but both RocketScientist with the O2 and opc with the Wire amp said they found it made no difference on their dScope/AP testers.

The output impedance of the MC/LM78xxx goes up a bit with frequency, but RocketScientist has the supplies bypassed with the 220uF caps.

So I'm not sure what is making the difference. But I'm always of the mindset that measurements are great, and important, but in the end it is how something sounds that matters!
  Reply With Quote
Old 28th November 2012, 01:39 AM   #112
diyAudio Member
 
Join Date: Mar 2010
Worth a try if you have a hard to drive headphone like HD650. I forgot to mention, remove the 9v battery and connect the +ve, Gnd and -ve accordingly, it is that easy, all components stay as it is. If you don't like just remove the wires and put back the battery.
  Reply With Quote
Old 12th December 2012, 06:13 AM   #113
diyAudio Member
 
availlyrics's Avatar
 
Join Date: May 2011
Default Any ideas for adding upc1237 for DC protection?

Any ideas for adding upc1237 for DC protection? I'm not sure if +ve thresh hold 0.7V & -ve threshold of -0.2V would be of any use in h/p as its basically a spk. protection IC or will it require some sort of DC instrumentation amp (to amplify few mV DC offset to couple of V for upc1237 to detect).
Ragards,
availlyrics
  Reply With Quote
Old 12th December 2012, 04:54 PM   #114
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Quote:
Originally Posted by availlyrics View Post
will it require some sort of DC instrumentation amp (to amplify few mV DC offset to couple of V for upc1237 to detect).
The thrshold levels in that IC at 700mA are too high for headphones, but like you say a 10x amp circuit that would bump 70mA DC at the phones up to 700mA DC for the chip would work. That is essentially what AMB's e-12 protection circuit is doing

The ε12 Muting / Protect Circuit

so that 70mA DC input gets amped up 10x to 700mA DC to turn on the B-E junction of the pulldown transistors.

A couple of years ago I whipped up a schematic for a "super e-12" that had separate low pass filters for each channel. The filters were upgraded to 3-pole active for a very sharp cutoff. I think I lowered the corner frequency from 1Hz to 0.1Hz as I recall, and since there were two stage of gain on each channel (for the filters), was able to lower the trigger voltage to 7mV at the phones (100x gain) instead of 70mA.

I'll poke around and see if I find that over the holidays and post, in case someone wants to give it a try. I've never posted it before but have sent AMB a copy. He is trying to keep the e-12 to a certain size to fit in a chassis and this version would wind up substantially larger physically.
  Reply With Quote
Old 12th December 2012, 05:25 PM   #115
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Default O2 amp dual-rail voltage doubler and quadrupler for +/-15Vdc rails and beyond

This modification of RocketScientist's O2 amp adds a few diodes and capacitors to the power supply to create a dual-rail voltage doubler and dual-rail voltage quadrupler using the same AC input transformers. The net result is that a 9Vac transformer with 2A secondary will produce +/-18Vdc rails going into the regulator chips (120mA load per channel), allowing for the use of 15V regulators and supply rails (MC7815 and MC7915).

A note on terminology first. RocketScientist's power supply in the O2 is already a voltage doubler if you look at it just right. It all depends on where the ground reference is placed (negative DMM lead for the discussion here). If the ground reference is in the middle, at one end of the transformer secondary as in the O2, you get dual rail 1x, which is 9Vac rms X 1.414 for sine = 12.7Vdc. Subtract a couple of volts ripple for the half wave rectification and another volt for AC line fluctuation you get +/-9.7Vdc into regulators. If however you move the ground reference to the negative rail being produced, the result is a single ended votlage doubler of 9.7V x 2 = 19.4Vdc.

So the "dual rail voltage doubler" circuit presented here is really a "single ended voltage quadrupler" if the ground reference is moved from the middle to the negative rail. Similarly the "dual rail voltage quadrupler" here is a "single ended 8x" with the ground reference moved.

Another note is in order on currents and voltages. Anyone building these circuits should pay close attention to the ripple currents needed in the capacitors at each stage and make sure cap voltage ratings around around 20% higher than the peak voltage, including line voltage fluctuations, at each stage. And finally, a voltage doubler or quadrupler can produce some high DC voltages if higher AC voltages are used on the input. Use caution! 24Vac into a dual rail voltage doubler will produce around +/- 60Vdc.

The first circuit and plot below show the dual rail voltage doubler. As shown a 9Vac rms transformer with a 2A secondary, like this one

9 Volt 9V AC 2000mA Adapter for Line 6 PX 2 US Pod Power Supply Cord Charger PSU | eBay

will produce around +/-18Vdc rails going into the regulators with a 120mA load on each channel. 15V regulator chips can then be used, along with appropriate resistor value changes in the PM circuit and clip on heat sinks on the output chips (as shown in the first couple of posts in this thread).

Green and blue in the plot are the voltage outputs of the voltage doubler, going into the regulators. Red is the AC input voltage. Volt scale is on the left. The aqua and magenta current plots using the righthand scale are the currents through the input capacitors, C2 and C6. Half the current waveform looks distorted since these caps charge on one half cycle and discharge on the other. The grey plot is the current spike through the input transformer, showing the need for the 2A secondary.

The second circuit is less of an O2 modification and more of a separate DIY project for someone with high impedance (600R) low efficency cans. The plot shows the result of 12Vac into a dual rail voltage quadrupler circuit, producing +/-60-Vdc going into the regulator. Regulator chips are not available at these voltages, so a simple discrete regulator pair as in the next attachment would have to be used. This one is a simple capacitance multiplier fed with a current sourced zener. The high voltage +/-60Vdc rails here can be used with amps such as opc's "wire class A/AB" amp based on the LME49830 chip and mosfets that goes up to +/-90V rails

"The Wire AMP" Class A/AB Power Amplifier based on the LME49830 with Lateral Mosfets

In both the dual rail doubler and dual rail quadrupler the circuit just replaces D3 and D4 on the O2 PCB, as shown. In the case of the voltage doubler the parts cold be built up on an upside down PCB slid into the top slot on the taller B3-080 case, with wires going to the 4 holes where D3 and D4 would have gone, plus the one ground connection on the AC input jack.

Last edited by agdr; 12th December 2012 at 05:33 PM.
  Reply With Quote
Old 9th January 2013, 01:45 AM   #116
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Default O2 amp dual rail power management modification

Here is a dual-rail version of RocketScientist's power management circuit in the O2 headphone amp for anyone into some DIY modding work. This circuit essentially takes RocketScientist's design and just applies a copy to each power supply rail individually rather than measuring the two rails summed together.

One benefit is the ability to detect a single supply failure that doesn't add up (both rail voltages added together in the original O2 PM circuit) to less than 14Vdc where the original PM O2 circuit would trip. An example from a recent post in the O2 thread is using a DC power supply instead of AC. One rail is on AC while the other is one battery, allowing the battery to discharge too low to about 3Vdc. The dual rail circuit here would catch that condition - or any unbalanced rail condition like a battery with partially shorted cells inside - and shut down the O2.

The circuit adds reversed biased diodes across each rail to ground to take care of a situation where one rail is left floating and held up to the opposing rail by rail-to-rail parts, like using a DC supply with no batteries installed.

The circuit incorporates the latch modification earlier in the thread to latch the PM circuit off once it trips. This eliminates any chance of the circuit oscillation when the battery runs down, original PM circuit trips, then the battery recharges a small amount and turns the PM circuit back on. I've left off RocketScientist's hysteresis resistor R25 since it isn't needed with the latch circuit. With the latch the O2 will remain off until the power is switched off and left off for about 15 seconds to reset the latch circuit.

I've also left off the capacitors on the mosfet gates to slow turn on, the "turn on thump" preventer. I'm assuming that a headphone relay cutout circuit like posted earlier in this thread would be used instead to lockout turn on thump. But the caps can be added back if needed.

This dual-rail circuit has two power leds, one for each rail, which also act as voltage references for each rail just as with RocketScientist's original design. The LEDs would also help diagnose missing power supply inputs on one rail or the other.

The output uses a mosfet optical solid state relay, an Omron G3VM-62C1 to improve the syncronization and hence quality of the PM switch-on and switch off. RocketScientist's original design tries to keep the gate switching of the two individual mosfets synchonized so both rails switch at exactly the same time. But in actual practice a lot of posts have noted that turn on thumps are solved by replacing one mosfet or the other, meaning manufacturing differences (and possibily installation static damage) are causing switching time differences with the mosfets.

The Omron SSR is an integrated DIP-8 unit so the two mosfets will be highly matched. Easily replaced, too, since the whole thing fits in a standard DIP8 socket. The mosfets are optically triggered by two LEDs in the package that are placed in series between the outputs of the voltage comparators on each rail, fed with two mosfets in a similar fashion to RS's original design. So now the mosfets don't supply the power rails directly, but rather together turn on the SSR control LEDS and simultaneously switch both SSR mosfets. If one comparator chain or the other is slightly off in time it doesn't matter since the SSR LEDs are in series. First one wins. The constant current source maintains the datasheet recommended 7.5mA current through the SSR LEDs through the whole power supply range of 12Vdc to the trigger point of 7Vdc on each rail. The downside is 7.5mA of additional current draw, about the same as one of the op amps, which will run the batteries down slightly sooner. Another external LED is included in series with the SSR LEDs as a PM trigger indicator that comes for "free" in terms of current draw. The PM "on" LED indicator should help with diagnosing problems.

The LEDs in the schematics for the voltage reference are just something that was living in LTSpice. For the actual circuit use the LED in the O2 and adjust the series resistor accordingly for the same current from one rail rather than rail to rail. The voltage divider resistors get adjusted for the 1.7Vdc of the O2 LED.

The first plot below shows the positive battery (green trace) discharging from from +9.5Vdc intial down through the +6.5Vdc trip point of the comparator and down to +6.3Vdc. The orange trace is the current through the SSR LEDs, showing the switch at the trigger point. The battery then recharges back up through the trigger point to +7.5Vdc, but the SSR remains off due to the latching circuit.

The second plot shows the same thing for the negative rail (blue trace). The negative rail circuit has an extra comparator to make an inverted copy of the output signal for the negative rail latch circuit. The third plot shows the effect of a sudden complete disconnection or failure of one supply (loose battery terminal, one battery removed, AC voltage regulator failure). The SSR switches off as it should.
Attached Images
File Type: png O2 V2.0 PM circuit A.png (53.4 KB, 46 views)
File Type: png O2 V2.0 PM plot A.png (20.1 KB, 35 views)
File Type: png O2 V2.0 PM circuit B.png (53.2 KB, 25 views)
File Type: png O2 V2.0 PM plot B.png (21.2 KB, 23 views)
File Type: png O2 V2.0 PM circuit C.png (52.1 KB, 24 views)
File Type: png O2 V2.0 PM plot C.png (18.6 KB, 24 views)

Last edited by agdr; 9th January 2013 at 02:07 AM.
  Reply With Quote
Old 12th January 2013, 04:59 AM   #117
diyAudio Member
 
availlyrics's Avatar
 
Join Date: May 2011
Quote:
Originally Posted by agdr View Post
I'll poke around and see if I find that over the holidays and post, in case someone wants to give it a try. I've never posted it before but have sent AMB a copy. He is trying to keep the e-12 to a certain size to fit in a chassis and this version would wind up substantially larger physically.
It would be very helpful indeed if you can post your design here.
My plan is to build desktop ver. of O2 with stepped attenuator+ DC offset amp ( preferably opamp based over discrete design)+upc1237 with mute relays.
Thanks,
availlyrics.

Last edited by availlyrics; 12th January 2013 at 05:08 AM.
  Reply With Quote
Old 13th January 2013, 01:24 AM   #118
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Quote:
Originally Posted by availlyrics View Post
It would be very helpful indeed if you can post your design here.
My plan is to build desktop ver. of O2 with stepped attenuator+ DC offset amp ( preferably opamp based over discrete design)+upc1237 with mute relays..
Here you go, below.

I found my old design with the single 3rd order filter but I had done it in a schematic editor rather than LT Spice. While entering it in I had a better idea. Instead of a single piece circuit, here is an "e-12 booster" that could simply be added in front of (electrically, before the e-12 inputs) existing AMB e-12 board(s) stacked vertically with spacers between the screw holes. I'm a big one on not re-inventing the wheel. Most of parts needed are just the existing e-12 (power supply, relay and relay driver, and now-secondary filter on each channel). This modification just adds a front-end on each channel that does several things:

  • Separate filters for each channel all the way to the pull down transistors to prevent the (highly unlikely, granted) chance of the two channel's DC offsets summing to below the trip point. For example, if one channel DC offset is +90mV and the other -30mV the existing e-12 would sum those to +60mV, below the 70mV trip point, and not trip. This modification treats each channel separately and compares each independently against the (new, lower) 7mV trip point.
  • Added an additional cascaded filter stage on each channel to convert the filter from second order to 3rd order. The original e-12 has a first order active low pass followed by a discrete low pass (the 1K and 100uF) to make a cascaded second order LP filter. The higher 3rd order filter increases the roll-off slope from -40dB/decade in the original e-12 to -60dB/decade here for an even more definite cut-off.
  • Filter feedback caps increased from 1uF to 10uF XLR MLCC to drop the corner frequency from about 1Hz in the original e-12 to 0.1Hz. This helps with handling very low frequency inputs like 10Hz. The filter gain and phase plots won't drop smoothly if the corner frequency gets too close to the minimum signal frequency.
  • The added filter stage on each channel has a gain of 10x, increasing the total cascaded gain from 10x to 100x, and thus dropping the DC offset trigger voltage being detected on the headphone amp output from 70mV to 7mV. The O2 typically runs at 3mV DC offset per channel, less than the new 7mV trip voltage, so it would not erroneously trigger the circuit in normal operation. In conjunction with this the op amps specified for the new stages are very low inherent DC offset OPA627 units. The OPA627 is a precision DC op-amp which has about 0.1mV (100uV) of offset vs. 3 - 15mV for the TL082. This becomes especially important both with the small DC offset being detected (7mV) and with cascading gain stages. A 0.1mV input offset voltage become a 10x0.1 = 1mV output offset on the first stage, and 1x10 = 10mV after the second cascaded stage. The larger DC offset of the TL082 makes a smaller difference in the second stage. However, another change, I'm also specifying TL082B chips with have a maximum input offset of 3mV, vs up to 15mV for the base TL082 to help keep the second stage input offset under control. The OPA627 is also extremely expensive, about $30 each for the high grade part (lowest offset) and $20 each for the low grade part, meaning each op amp costs about as much as all the basic O2 amp parts combined. That would probably make RocketScientist bang his head against a wall if he were still around, since his goal was always low cost and affordability. There are some (much) lower cost chopper stabilized op amps out there with even 10x better offset numbers, but I wanted to keep yet-another filter out of the filter circuit here and wanted something that didn't chop as was all through hole for easy DIY.
In the schematic below the parts in the outline called "AMB e-12 #1" are one e-12 board fully stuffed with the regular parts except all 10K input resistor left out but one. The second stacked e-12 board labelled "AMB e-12 #2" is a short-stuffed board with the power supply and relay parts left off. The power and ground lines are jumpered over from board 1. Just the filter and open collector transistor are used here, with the open collectors tied to those on the first board to form a wire-OR circuit.

All of this can just be DIYed too, of course. The new parts with the OPA627s could probably be laid out on a board sized to stack vertically with the other two e-12 boards. If someone were laying out a PCB with the two new OPA627 filter stages it might be easiest just to add the parts shown for the second e-12 PCB, the TL082B and open collector transistors, reducing things to just the one new board and the one existing e-12 board.

And a link to AMB's e-12: The ε12 Muting / Protect Circuit
Attached Images
File Type: png e-12 booster for AMB's e-12 protection circuit.png (65.9 KB, 34 views)

Last edited by agdr; 13th January 2013 at 01:54 AM.
  Reply With Quote
Old 13th January 2013, 02:52 PM   #119
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Default e-12 booster relay protect - part 2, applied to O2 amp

Here is some more info on the "e-12 booster" above. If used with the O2 amp the O2's power supplies can be used, as shown in the circuit below. Just don't populate the power supply and virtual ground parts on e-12 PCB #1. Wire the +12Vdc, -12Vdc, and ground over from the power switch on the O2.

Also a typo warning on the circuit I attached above - it has the negative rail attached to ground in the top half when I did a cut and paste. The negative rail should attach as shown here.

I've added the device models for the OPA627 and TL084 in the LT Spice sim below. The first plot is the AC response from 0.01Hz to 200kHz, showing the 0.1Hz corner frequency and 20dB/decade, 40dB/decade, and 60dB/decade rolloffs for the output of the 3 cascaded filter sections. Green, blue, and red respectively. Labels are at the top of the plots.

The second plot shows the transient response when a fault of 20mV occurs at the 1 second point (20mV of DC shows up on one headphone output). The circuit takes about 2.3 seconds to switch the relay, which is the transient delay through all the filters. The the input signal is in green (2.5khz so it looks nearly solid here) and relay current is in purple. The output of filter section 3 (1K in series with the 100uF), the aqua plot, clamps at 0.7Vdc since it is feeding a transistor B-E junction, of course. Voltage scale on the left and relay current scale on the right.

The final two transient plots show the more "difficult" cases for the filters of lower signal frequencies at 150Hz and 20Hz. The filter delay at 150Hz is still about 2.3 seconds until the relay switches off, while at 20Hz it shrinks down to about 1.5 seconds.

Last edited by agdr; 13th January 2013 at 03:17 PM.
  Reply With Quote
Old 13th January 2013, 05:50 PM   #120
diyAudio Member
 
availlyrics's Avatar
 
Join Date: May 2011
Thanks for your detailed reply
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Reduced diode switching by placing a cap across Goetz Power Supplies 10 19th December 2011 12:38 AM
DC blocker diode/cap orientation Glen B Solid State 4 22nd August 2011 05:46 PM
Mounting a small signal diode on heatsink - need suggestion IG81 Solid State 14 3rd November 2009 04:12 PM
diode bridge - 10000uF cap - diode tube - small cap - HV+ engels Tubes / Valves 5 29th January 2008 10:16 PM
Diode Heatsink dmk Tubes / Valves 8 9th September 2007 04:03 PM


New To Site? Need Help?

All times are GMT. The time now is 03:21 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2