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Old 30th January 2012, 05:45 AM   #571
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After removing light bulb from mains, Q5's collector voltage measured as ~ -1.5V (Q6 is -0.65V). It seems voltage drop caused by light bulb produced measurements on picture. I was realised that I have to use total 30V zener with my 31V supplies when using 2x16V at previous builds. Then I switched to single 30V/1W.

Elvee: You specified Q5 and Q6 as 2Vs, but I can't see any voltage gap greater than Vs on their legs. All measurements are negative. I'm asking this because I want give a try Philips BD137's as Q5/Q6 with my 31V supplies.

Last edited by terranigma; 30th January 2012 at 06:13 AM.
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Old 30th January 2012, 08:43 AM   #572
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by terranigma View Post
If you can find an opportunity, it may involve us if you clarify with some schematic that what you mean with "cascode at output potential, rather than a zener".
Here is the cascode version.
It has not been physically tested, just simmed, but it should work without problem.

Quote:
Elvee: You specified Q5 and Q6 as 2Vs, but I can't see any voltage gap greater than Vs on their legs. All measurements are negative. I'm asking this because I want give a try Philips BD137's as Q5/Q6 with my 31V supplies.
During the positive excursions, Q6 sees up to ~2*Vs Vce. And since Q5 has to be identical to Q6, both need the 2*Vs voltage rating.
In principle, you could also try small MOSfets for Q5 and Q6. Small, low capacitance types like BSS145 should be suitable.
R6 and R7 would have to be increased to ~2.7K.
This has not been tested either.
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Old 30th January 2012, 01:23 PM   #573
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And, so does the RC, R18-C12 go on the phase inverter side as shown in this simulation?:
http://www.diyaudio.com/forums/attac...phonekpmod.gif
Or, does it go on the driver side as shown in this picture?:
http://www.diyaudio.com/forums/attac...clophone13.gif

P.S.
Maybe I need to redo my layout to put the phase inverter (and input pair) at 1cm or less distance from the drivers? That would relocate Q2/Q7, Q12/Q13 to the opposite end of the board from the drivers. However, that layout change would make the feedback and phase inverter connections direct rather than jumpered. Some of the PCB examples also show jumpers or long distance connection via circuitous traces taking the scenic route. Does that section need flipped? Turning it over makes the signal caps and input cable arrive at the center of the board which is the trade-off for not jumpering phase inverter and feedback.
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Old 30th January 2012, 05:22 PM   #574
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by danielwritesbac View Post
Or, does it go on the driver side as shown in this picture?:
http://www.diyaudio.com/forums/attac...clophone13.gif
That's the correct version

Quote:
Maybe I need to redo my layout to put the phase inverter (and input pair) at 1cm or less distance from the drivers? That would relocate Q2/Q7, Q12/Q13 to the opposite end of the board from the drivers. However, that layout change would make the feedback and phase inverter connections direct rather than jumpered.
That aspect is completely irrelevant here, this is low to medium signal level, and more importantly, it operates in current-mode, making the signal practically immune to track lengths or contortions.
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Old 31st January 2012, 07:44 AM   #575
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Here is post 1 schematic altered to modular. That took all day. I hope its right, but it needs checked out.

I also tried to decrease the occurrence of subharmonics or spurious noise causing D10, D11 misfiring by, instead, passing larger signals through a larger capacitor as needed and by doubling the switch on voltage of the diodes. There is also signal star ground arrangement in that it visually appears closer to a balanced amp. I hope this is okay.

Instead of showing a sky high gain, I decreased the operating voltage; so, now a computer might be able to push this to potential. It has about the same operating voltage as post 1 and the same gain setting. It also has a 3055, but this time, its TIP3055, supposedly the same (except PD), but it fits the PCB designs.

An additional protection that could be very useful is a diode clipper at input because, especially computers, random sources are prone to emit a spike or surge, especially at power up or power down, and this also happens if using a source selector dial. I didn't know exactly how to add the diode clipper, but would like to know.

Q14 is shown. I hope I got everything shown correctly this time. It should render tack sharp 1024x600, which fits the entire schematic onto the screen of any computer, including a netbook. There is no footnote for R21 but I was wondering if it is possible to, perhaps, use a transistor or two to facilitate wide voltage tolerances instead of changing the resistor? If not, then there is room for a handy little chart added later.
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Old 31st January 2012, 10:12 AM   #576
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Due to my location's terrific ambient RFI noise, I was in struggle by efforts of "dead silence" achievement again as like as my -blown- very first build. But it didn't happen again. I haven't any serious issue with my second build which was a powerflux pcb layout. It is comfortably silent but not "dead" obviously. I'm sure that there is something special with this topology which gains such silence but it seems I have to live with my ambient RFI noise at low levels.

Elvee: Regarding to post #261, should I use equal volume pot each side or implementation permits just one pot at positive side?
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Old 31st January 2012, 12:42 PM   #577
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I suspect shutdown of transistors and/or diodes in the quadrature loop
breaks up oscillation and squelches noise in the main loop... If you run
the quadrature loop in a shutdown-proof way too, things can get ugly.
This amp also runs at absurdly low quiescent current, considering the
smoothness of its crossing. Elvee also did his homework on PSRR.

Last edited by kenpeter; 31st January 2012 at 12:46 PM.
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Old 31st January 2012, 12:54 PM   #578
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Quote:
Originally Posted by danielwritesbac View Post
I also tried to decrease the occurrence of subharmonics or spurious noise causing D10, D11 misfiring by, instead, passing larger signals through a larger capacitor as needed and by doubling the switch on voltage of the diodes.
I do not exactly see what you mean, but there is no way the diodes could "misfire" or generate spurious noise: even when the amp is reproducing a full power 10Hz signal, the voltage seen by the diodes remains lower than 100mV, and even schottky's wouldn't have a chance to begin conducting under those conditions.

The diodes only role is as a safeguard, in case something goes wrong with the supplies powering sequence for example, to avoid excessive charge building up on C3.
Doubling them means the output voltage during unexpected transient conditions could practically reach the supply rails, which is undesirable and will almost cancel their usefulness.

Quote:
There is also signal star ground arrangement in that it visually appears closer to a balanced amp. I hope this is okay.
No problem with that.

Quote:
An additional protection that could be very useful is a diode clipper at input because, especially computers, random sources are prone to emit a spike or surge, especially at power up or power down, and this also happens if using a source selector dial. I didn't know exactly how to add the diode clipper, but would like to know.
A good clipper could be nice, but unfortunately, any simple scheme operating at a meaningfully low level will have an effect on linearity.
To avoid very severe spikes damaging the B-E junctions of Q4 and Q3, one could add a pair of back to back diodes between the bases.
This will not actually clip anything, but it will not impact the linearity, and it will make the input practically bullet-proof.
Note that the clipping of the amplifier itself is clean. It is hard, of course, but clean. Any soft-clipping scheme will have to eat up some of the output dynamic.

Quote:
Q14 is shown. I hope I got everything shown correctly this time. It should render tack sharp 1024x600, which fits the entire schematic onto the screen of any computer, including a netbook. There is no footnote for R21 but I was wondering if it is possible to, perhaps, use a transistor or two to facilitate wide voltage tolerances instead of changing the resistor? If not, then there is room for a handy little chart added later
Q14 is basically identical to Q5 and Q6: same operating voltages and currents, same dissipation.
A two-wire, 1.5mA current source could be substituted for R21. I have described some two transistors examples here and here.
Here, only a very crude accuracy is required, and a single transistor with two diodes or one LED would be sufficient.

Quote:
Due to my location's terrific ambient RFI noise, I was in struggle by efforts of "dead silence" achievement again as like as my -blown- very first build. But it didn't happen again.
Very strange.....

Quote:
Elvee: Regarding to post #261, should I use equal volume pot each side or implementation permits just one pot at positive side?
Here is a possibility, but the differential offset of your source has to be ~0 (ideally a transformer) to be able to do that.

A better option is to locate the volume pot upstream, at a place where the signal is in unbalanced form.
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Last edited by Elvee; 31st January 2012 at 12:58 PM.
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Old 31st January 2012, 02:56 PM   #579
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Here are two further possibilities for replacing R21: a plain vanilla 1 transistor CCs, and an improved one with a zener.
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Old 31st January 2012, 09:15 PM   #580
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Quote:
Originally Posted by Elvee View Post
Here is a possibility, but the differential offset of your source has to be ~0 (ideally a transformer) to be able to do that.

A better option is to locate the volume pot upstream, at a place where the signal is in unbalanced form.
I did it very quick and dirty way with two different pcb's. Either suffered serious dc-offset problem which is not a case of connect a speaker. If source connected, dc-offset beginning from five hundreds of mV then rises up to many volts step by step. I source not connected, i see at least 10 Volts for first. I'm not about to find a immediate solution, just bringing news of what happened. My source is a voltage-out dac chip's differential analogue output pins. I used 5K pot. Probably my source is not suitable for doing such thing.

Last edited by terranigma; 31st January 2012 at 09:19 PM.
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