Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Return to Tube DIY Asylum

Message Sort: Post Order or Asylum Reverse Threaded

How to model this? (LTSpice)

62.163.171.12
Posted on November 14, 2014 at 02:22:51
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005




Further to the thread below about the DC path to ground and the influence of its resistance on the AC behavior of the amp (especially the Coupling Cap and Grid Choke combination before the driver), I now added the bias supply in the simulation (above).

When doing an AC analysis on this, the AC behavior is completely different (compared to the version without the bias supply posted earlier).





It seems response is highly dependent on the Series Resistance of V7. In the simulation it's now set to 1meg, giving the result above.

These 'odd' results I always get are the reason I always maintain separate versions for AC and for Transient simulations. For some reasons my model of the power transfomers always seem to screw up AC analysis.

(by 'odd' I mean the 'dip' in the response around the very 'suspicious' frequency value of 100Hz).

Please help.

NC

 

Hide full thread outline!
    ...
RE: How to model this? (LTSpice), posted on November 14, 2014 at 03:24:25
jazbo8
Audiophile

Posts: 70
Location: Europe
Joined: January 16, 2012
 "It seems response is highly dependent on the Series Resistance of V7. In the simulation it's now set to 1meg, giving the result above."

Is this a typo? Why would you have a 1M series resistance for the mains voltage source?

 

Because..., posted on November 14, 2014 at 03:26:32
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 With that value the response is more or less resembling would I would expect.

Choosing another value make the response only look more odd.

Do you have a suggestion for the value?

 

Bias supply, posted on November 14, 2014 at 05:11:39
Chip647
Audiophile

Posts: 2652
Location: The South
Joined: December 24, 2012
 Try modeling the bias supply as a simple Full Wave Bridge with the positive side grounded and the negative side supplying the negative bias and the center tap floating. Use 500uf - 5K - 500uf - 5K - 500uf as the filter, (bin the 20H choke for now). See if that takes care of the weirdness.

 

RE: How to model this? (LTSpice), posted on November 14, 2014 at 05:28:59
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001
 FWIW... the ac voltages in spice are all peak so the 230V on tour bias supply primary is actually 161Vrms.

dave

 

RE: How to model this? (LTSpice), posted on November 14, 2014 at 06:13:57
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 Yes, correct... I keep forgetting that.

Thanks.

NC

 

RE: How to model this? (LTSpice), posted on November 14, 2014 at 07:20:54
jazbo8
Audiophile

Posts: 70
Location: Europe
Joined: January 16, 2012
 The series resistance of the mains power source is very low and typically omitted from the simulation.

 

RE: How to model this? (LTSpice), posted on November 14, 2014 at 08:06:37
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 I almost never combine power supplies and amplifier circuitry in one model. I sim the supplies separately to verify their operation, then I substitute simple voltage sources with their "AC amplitude" blank or zero in order to power the active circuitry. If the goal is to determine how the amplifier interacts with the bias supply, simplify it first. Drive the two last filter components in the bias supply with a negative voltage source. Avoid installing more than one AC source unless absolutely necessary.

 

Yes, I do that too..., posted on November 14, 2014 at 08:09:22
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
 But its tedious and should actually not be needed,

NC

 

RE: Because..., posted on November 14, 2014 at 08:11:17
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 I would think an impedance of zero would be closer to reality but then I don't understand how spice works.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

That gives..., posted on November 14, 2014 at 08:13:28
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005



This result :-/

NC

 

Odd, posted on November 14, 2014 at 08:19:09
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 Someone smarter than me will have to explain that one.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: How to model this? (LTSpice), posted on November 14, 2014 at 14:25:11
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001
 Is the voltage source for the bias supply also sweeping?

look at the waveform of the CT of the bias transformer seconday

dave

 

What I see is this..., posted on November 15, 2014 at 04:01:31
Nickel Core
Audiophile

Posts: 870
Joined: February 11, 2005
The response on the CT is this...




 

RE: That gives..., posted on November 15, 2014 at 12:31:54
jazbo8
Audiophile

Posts: 70
Location: Europe
Joined: January 16, 2012
 Are we still looking at the same simulation? Why is the gain so much higher than the one you posted eariler? I did a quick sim and could not duplicate your results, i.e., the AC response looked pretty normal to me...

 

Page processed in 0.020 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]