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Old 5th April 2012, 02:13 PM   #81
dadod is offline dadod  Croatia
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Quote:
Originally Posted by greenm01 View Post
Hi, Dado.

The amp is sounding worderful: punchy bass, smooth mids, and aggressive highs. I'm looking forward to completing the second channel.

A few questions in regard to the TT-Triple:
  1. Do you happen to know the input sensitivity?
  2. Have you been able to measure real-world THD?
Also, an unrelated observation/question not specific to this amplifier. On most of my amps, I can hear very low level Johnson Noise (white noise) with no input signal, and my ear pressed up to the speaker. I'm not sure if this is from the speakers themselves, noise from amplifier RC components, or a combination. It's definitely not a ground loop, but low volume white noise. My living space ambient noise is MUCH louder, but I'm just curious about the source of the white noise.....

With headphones I don't notice white noise with line level portable media players and computer audio output.

/Mason
Hi Mason,
I hope, when you say aggressive hights, it does not mean something bad as aggressive could be.
This amp has the gain = R5/R4+1 and this is 26.6 times or 28.5 dB (20 log(gain))
R5 = 10k and R4 = 390 ohm
As Andrewt said, with the input shorted there should not be any noise from normal sensitive loudspeaker.
If you have some noise from this amp, wait until it is wired properly (shielded input cable, star grounding) and then you should have no noise at all.
dado
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File Type: pdf DADO-TT-triple-d.pdf (53.9 KB, 117 views)
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Old 5th April 2012, 03:02 PM   #82
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Quote:
Originally Posted by dadod View Post
I hope, when you say aggressive hights, it does not mean something bad as aggressive could be.
Aggressive in a good way: very nice highs. The amplifier faithfully reproduces material with no audible distortion.

Quote:
Originally Posted by dadod View Post
This amp has the gain = R5/R4+1 and this is 26.6 times or 28.5 dB (20 log(gain)) R5 = 10k and R4 = 390 ohm
By input sensitivity, I mean the max input signal voltage that drives the amp at max output power.

Quote:
Originally Posted by dadod View Post
As Andrewt said, with the input shorted there should not be any noise from normal sensitive loudspeaker.
If you have some noise from this amp, wait until it is wired properly (shielded input cable, star grounding) and then you should have no noise at all.
dado
This question is not specific to your amplifier. I can hear a little white noise even on the commercial amplifiers I own, if I place my ear a few mm close to the speaker with no active input signal. It's not audible more than a few inches away. I'm just wondering about the source of this noise, if it's a limitation in the speaker itself or some other result. I will try as Andrewt suggested. Or maybe my amplifiers are amplifying white noise from my source.

/Mason
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Old 5th April 2012, 03:34 PM   #83
dadod is offline dadod  Croatia
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Quote:
Originally Posted by greenm01 View Post
By input sensitivity, I mean the max input signal voltage that drives the amp at max output power.


/Mason
At 3 V pp or 1.06 is a max before clopping, it is 100W on 8 ohm. This of course deppents on the power supply voltage, here is +-45V.
dado
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Old 5th April 2012, 10:25 PM   #84
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Originally Posted by AndrewT View Post
With the Power Amplifier input shorted you should not be able to hear any noise from the connected speaker. If you can then the amp has too high a noise level for that speaker.
I grounded the input and the speaker is dead silent with my ear a few mm from the driver...

For some reason I assumed that my audio sources are clean: computer output and portable players. The noise is inaudible for practical purposes, but it's there none the less if I put my ear to the speaker, with content paused or silent moments between songs. Definitely something for me to consider in component selection.

/Mason
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Old 2nd May 2012, 02:51 PM   #85
dadod is offline dadod  Croatia
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Here is a new TT amp with diamond triple OPS. All CCS are with deplation mode mosfet DN2540 and this simplified a quite this amp and 20k THD is still low as 3ppm at full power.
The question is how to make a bias current temperatute stable enough.
I simulated the case when predrivers and drivers are mounted on a separete small heat sink and suppose to canceled temperature drift in that way. The bias spreader is a small transistor not in thermal conntact with output transistors but uses two TT diodes feeding the base. R24 and R7 are trim pot used to set the bias current. I can set those two trimer and simulate output transistors temperature change and it is quite stable. This is first simulation where predrivers/drivers temperature is set to 50 degree centigrade and output transistors/TT-diodes temperature was swept from 20 to 150 degree centigrade.
Next simulation is with output tansistors set to 50 degree centigrade and predrivers/drivers temperature was swept. Here I have a problem as the bias current drift is to high not canceled as expected.
Any idea way and how to solve that?
dado
Attached Images
File Type: jpg DADO-TT-diamond-triple-temp1.jpg (176.6 KB, 333 views)
File Type: jpg DADO-TT-diamond-triple-temp2.jpg (179.2 KB, 319 views)
File Type: jpg DADO-TT-diamond-triple-sch.jpg (149.0 KB, 317 views)
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Old 2nd May 2012, 03:13 PM   #86
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Hey there.

Connect R18 across the B-E of Q12, this will increase the VAS gain.

If you do some work, you can do something close to real-time thermal simulation. It involves putting a behavioral voltage source in series with the emitter which adds the 2.2mV/C tempco. But you must have realistic thermal models. There are thermal models for the FJP5200/1943. Here is the bias drift for such a simulation. Very bad! Yes, it is this way in real life too. This can be observed with an ordinary scope if you know how.
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Last edited by keantoken; 2nd May 2012 at 03:30 PM.
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Old 2nd May 2012, 04:35 PM   #87
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Hi keantoken,
With R18 connected as you suggest there is no difference in 20kTHD, it is exactly the same.
Your simulation picture is unreadable.
dado
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Old 2nd May 2012, 04:38 PM   #88
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I did a pretty detailed analysis of this with LTspice a while back, details, models, etc. are here: Another look at Thermal Trak biasing. This shows using behavioral voltage sources as keantoken mentions above.

Basically if you take the approach that there are two different slopes that need to be compensated - the pre-drivers plus drivers, and the final outputs, then you can compensate very well.
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Old 2nd May 2012, 05:09 PM   #89
dadod is offline dadod  Croatia
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Quote:
Originally Posted by mightydub View Post
I did a pretty detailed analysis of this with LTspice a while back, details, models, etc. are here: Another look at Thermal Trak biasing. This shows using behavioral voltage sources as keantoken mentions above.

Basically if you take the approach that there are two different slopes that need to be compensated - the pre-drivers plus drivers, and the final outputs, then you can compensate very well.
Thanks mightydub,
You are stepping a temperature for whole circuit and I do it for separted transistor groups, so I can simulate predriver/driver independetly of output transistors and its TT diodes.
If you look this thread a bit back you can see that I use similar Vbe multiplier.
Here, as this triple predrivers are connected in diamond connection, Vbe multiplier need to be different and that is what I tried to simulate.
I use Cordel's models too.
dadp
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Old 2nd May 2012, 05:16 PM   #90
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I haven't seen anyone else doing the simulation in real time though, as opposed to temperature operating points. It is not much harder. I've gotten the sim ready, I think it will work if you unzip all the files to the same directory, but I've been wrong before.

The subcircuits are just a more compact way of doing what could be done on the schematic with behavioral sources. There are some flaws with this thermal simulation:

1: Transistor models haven't been updated since when I first drew it.

2: Hfe tempco hasn't been implemented.

3: The heatsink has only thermal resistance, no thermal capacity. This gives an unrealistically fast time constant for the case temperature of the outputs.

4: There is no thermal resistance or capacitance between the outputs. Meh.

5: There is no way to vary the BJT temp parameter in real time so this simulation cannot benefit from accurate temperature modeling in the transistor model. This modeling must be applied manually as a subcircuit adapted for real-time simulation. It is difficult to do this without causing simulation issues.

My conclusion so far is that there is no point in simulating output bias tempco, because it's faster and less complex to build the amp and skip simulation altogether. The exception is when you're testing out different bias generator concepts, just to see if they can work at all.
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File Type: zip 4-27-12_PowerBJT_Temp.zip (5.3 KB, 46 views)

Last edited by keantoken; 2nd May 2012 at 05:25 PM.
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