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Retro Amp 50W Single Supply
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Old 22nd June 2018, 09:43 AM   #421
prasi is offline prasi  India
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Quote:
Originally Posted by thimios View Post
Crossover distortion visible.
This start to disappear at 14mA bias setting.
Very nice, so anywhere between 20 to 50 mA should be good to go, depending on one's wish.
Thanks for posting this.
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Old 22nd June 2018, 12:25 PM   #422
thimios is online now thimios  Greece
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Quote:
Originally Posted by avtech23 View Post
I found some spare time to clean up the sim files.

Attached is a relabelled spice file that reflects the most recent schematic in terms of component designators. This should alleviate confusion between the sim and the schematic when refering to specific components.

This version has the output silicon that I am currently working on, so change these devices to match whatever you are using.

I am using a .step command for voltage input to find the clipping point as well as one set up for RBias to help with finding appropriate values. Set these to ;.step and reactivate the .param with your desired values once you have identified them.

----------------


Just for your viewing pleasure, I have also uploaded another version with gain set to around 25 and (I think) global feedback altered via R6. This drops the simulated THD from around 0.055 to 0.027.

This was done by reducing the 6k8 R6 to 3k6:

Gain = 1+(R6/R4) = 1+(3600/150) = 25.
Ηι avtech23,Please if isn't a big effort for you can you simulate this using R15=33R(INSTEAD OF 27R). AND bias near to zero.
I can't understand why i had measured 18v out before clip when 33R for R15 AND zero bias was used.

Last edited by thimios; 22nd June 2018 at 12:31 PM.
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Old 22nd June 2018, 12:51 PM   #423
avtech23 is online now avtech23  Australia
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Hi Thimios, no problem:

I altered the schematic for the MJL4281 and 2sc/2sa drivers.

R15 and R8 to 33R.
R5 to 15K for symmetrical clipping.
Load to 6R

The sim shows:
450mV max input before clipping.
Output of 19.38V max output at max input across 6 ohm load.
R18 Current ~900uA
R19 Current ~130uA
R15 Current ~1.77mA
R9 Current ~1.76mA
THD 0.0758% @1KHz

This is with 'ideal' components so 19.38v ideal simulated versus ~18v real life is pretty close I think.
Attached Images
File Type: jpg Capture2.JPG (122.4 KB, 157 views)
Attached Files
File Type: asc AX6_3_2sc5200_Relabelled_2_Thimios.asc (6.2 KB, 6 views)
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Old 22nd June 2018, 01:08 PM   #424
thimios is online now thimios  Greece
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Thanks dear avtech23.
Now look what real life THD is and what is the THD profile.
Attached Images
File Type: png 1W.PNG (88.1 KB, 150 views)
File Type: png 1W 10K.PNG (84.0 KB, 150 views)
File Type: png 13.6V.PNG (86.6 KB, 146 views)
File Type: png 13.6V 10K.PNG (85.1 KB, 149 views)
File Type: png STEPS.PNG (65.3 KB, 33 views)
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Old 22nd June 2018, 01:41 PM   #425
avtech23 is online now avtech23  Australia
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Looks quite different. I may be doing something wrong. I use the Hann window when doing FFT and reduce the scale to the audible range usually. But I have played around and can't get similar results to what you have measured.

Your 13.6v, is that RMS? If it is, then 13.6*1.414 = 19.23v peak into 6 ohms which is very close to the 19.38 the simulator came up with.

Is your bias resistor (R8) set at 33R? And do you have 6.8k for R6?
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Old 22nd June 2018, 01:48 PM   #426
thimios is online now thimios  Greece
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Quote:
Originally Posted by avtech23 View Post
Looks quite different. I may be doing something wrong. I use the Hann window when doing FFT and reduce the scale to the audible range usually. But I have played around and can't get similar results to what you have measured.

Your 13.6v, is that RMS? If it is, then 13.6*1.414 = 19.23v peak into 6 ohms which is very close to the 19.38 the simulator came up with.

Is your bias resistor (R8) set at 33R? And do you have 6.8k for R6?
It is at 13.6V RMS/6R
No, R8 is a 220R multiturn trimmer.ADJUSTED for 10mv/0.47R.
R15=10R+15=25R.
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Old 22nd June 2018, 02:19 PM   #427
thimios is online now thimios  Greece
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Yes R6=6K8.
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Old 22nd June 2018, 02:26 PM   #428
avtech23 is online now avtech23  Australia
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Sim gives: 19.26v (13.62v RMS) which agrees with what you got. THD doesn't agree but there could be many reasons for that.

R8 will be in the region of 57 ohm to get 10mV (~21mA bias).

Using Kaiser7, linear Hz scale to emulate your ARTA screenshots, I get the attached FFT. I've not used the K7 before and it gives different results to the Hann or Blackman windows that I tend to use.
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File Type: jpg Capture3.JPG (83.2 KB, 29 views)
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Old 22nd June 2018, 02:47 PM   #429
thimios is online now thimios  Greece
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If you want i will repeat this using hanning or what other you want.
What is the input voltage when out is 13.6v?
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Old 22nd June 2018, 03:10 PM   #430
thimios is online now thimios  Greece
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Quote:
Originally Posted by ivanlukic View Post
I found an older Mile's post at the local Serbian forum, where he gave a short explanation of AX6 circuit, and translated it. This is what he said:

AX6 has two global feedback circuits, one DC circuit before series output cap that keeps output at the half of supply voltage, and second AC feedback circuit that is taken after the output cap to lower distortion produced by the cap. VAS transistor has local feedback using emiter resistor (220R) and 100uF cap. Input transistor is compensated with 47pF to prevent ingress of ultrasonic noise at the input of amp. 27R resistor at the emiter of 2SA1837 driver helps stabilizing bias current.
ivanlukic, thank you!
You help us understanding this topology.
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