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Old 31st May 2011, 04:10 AM   #1
PB2 is offline PB2  United States
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Default SWTPC Tigersaurus 250W Amp Simulation

Here's the LtSpice simulation .zip file for the SWTPC Tigersaurus using Bob's SPICE models, substituted semis but trying to be as close as possible to the original. I did not do the series output stage because the MJLs will take the voltage and I was too lazy. Others are welcome to do it if needed. I also just used zeners that were in the library. Run the sim to see the reverse Vbe issue on the drivers - good reason not to build this as is.
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Old 31st May 2011, 05:24 AM   #2
davada is offline davada  Canada
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Originally Posted by PB2 View Post
Here's the LtSpice simulation .zip file for the SWTPC Tigersaurus using Bob's SPICE models, substituted semis but trying to be as close as possible to the original. I did not do the series output stage because the MJLs will take the voltage and I was too lazy. Others are welcome to do it if needed. I also just used zeners that were in the library. Run the sim to see the reverse Vbe issue on the drivers - good reason not to build this as is.

Hi Pete,

Indeed the same problems.

I seem to remember that it was only the outputs that would blow with the Tigersaurus kit.
I know you say your scratch build didn't have this problem.
Funny that the amp would work for a few months then not.

Some friends and I back in 79 rented a pair of JBL 4560 loaded with 2225 and some horns for a party driven by the Tigersaurus. Not only did it sound bad but the Tigers couldn't controls those 15" drivers. I've never seen excursion like that since then.

Maybe we should just get the Tiger UN working first.

David.
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Old 31st May 2011, 05:44 AM   #3
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1971 Plastic Tiger

remember these?
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Old 31st May 2011, 05:48 AM   #4
PB2 is offline PB2  United States
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Mine ran on slightly lower supplies of +/-65 and I upsized the drivers to MJE243/253 with large heat sinks, other than that it was the same. I never really pushed this amp that hard, well I say that then there were all the parties that it got dragged to. I think I was careful knowing how the UT fried so easily and not wanting to have to replace all those outputs.
Perhaps the drivers were being damaged over all those months and then finally gave up. The reverse voltage causes a shift in the parameters, lower beta, more noise and I believe final death. But interesting that you say they didn't fail, when I looked at the design I was worried that they would fail and so the substitution.

Here's a page with the original article in case anyone is interested:
Tigersaurus | TigersThatRoar

I agree David, I have no plans to do much with this other than to point out the problems.
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Old 31st May 2011, 05:50 AM   #5
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Quote:
Originally Posted by digits View Post
1971 Plastic Tiger

remember these?
It is a lower voltage/power version of the UT and will have all the same problems.
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Old 3rd June 2011, 06:08 PM   #6
PB2 is offline PB2  United States
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Quote:
Originally Posted by davada View Post
Hi Pete,
Some friends and I back in 79 rented a pair of JBL 4560 loaded with 2225 and some horns for a party driven by the Tigersaurus. Not only did it sound bad but the Tigers couldn't controls those 15" drivers. I've never seen excursion like that since then.

David.
I have a theory regarding the excursion that you saw, note that the protection just essentially turns off the transistor with excessive current and does not pull the output to zero. So, the output hits max current and then the output turns off allowing it to slam back to zero or the other rail if the other side turns on. I think a more traditional protection that clamps the VAS output would be better.
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Old 3rd June 2011, 07:13 PM   #7
davada is offline davada  Canada
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Originally Posted by PB2 View Post
I have a theory regarding the excursion that you saw, note that the protection just essentially turns off the transistor with excessive current and does not pull the output to zero. So, the output hits max current and then the output turns off allowing it to slam back to zero or the other rail if the other side turns on. I think a more traditional protection that clamps the VAS output would be better.

Hi Pete,

I think you're referring to Q14 and Q15?

It's funny where the ground is place on the emitter of Q10. I would think between R28 and R29 would make more sense intuitively. Is this a mistake in the drawing of the schematic?

I'm looking at the original promotional write up on the Tigersaurus.

http://www.tigersthatroar.com/wp-con...-Article-2.jpg

David.
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Old 3rd June 2011, 07:24 PM   #8
davada is offline davada  Canada
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Default Tiger un

Hi Pete,

I was considering suggesting a current limit approach like this in the Tigersuarus for the Tiger un except rather than limit at the base of the output TR, connect the collectors of the limiter TR to the bases of the VAS TR and current sink TR respectively.

I saw this done in a similar way in an old Motorola power amp app note in the 70s. I think they called it robbing the current from the VAS.

David.
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Old 3rd June 2011, 07:39 PM   #9
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Quote:
Originally Posted by davada View Post

It's funny where the ground is place on the emitter of Q10. I would think between R28 and R29 would make more sense intuitively. Is this a mistake in the drawing of the schematic?

I'm looking at the original promotional write up on the Tigersaurus.

http://www.tigersthatroar.com/wp-con...-Article-2.jpg
It's a drawing error. Ground should be between R28 and R29.
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Old 3rd June 2011, 09:19 PM   #10
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Yes it is a drawing error and several component values are wrong right at the output, see the parts list for the correct values.
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