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Simple, no-math transformer snubber using Quasimodo test-jig
Simple, no-math transformer snubber using Quasimodo test-jig
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Old 7th February 2018, 01:21 AM   #1311
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Has anyone ever measured the inductance of a fuse? Specifically, a slow-blow fuse such as "F1" in the schematic below, placed in series with the transformer secondary. The inductance of F1 directly adds to the self-inductance of the secondary.

Conventional wisdom (D. Self et al) suggests that F1's job is to protect the transformer in case the bridge rectifier fails as a short. While F2's job is to protect the power supply in case the output transistors fail as a short. The transistors are destroyed of course; F2 is simply trying to prevent further damage inside the PSU.

Thanks for any measured data or laboratory results!

_
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Old 7th February 2018, 02:48 AM   #1312
PH104 is offline PH104  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
I just got a new LCR meter and had a box of fuses handy as the result of a shop cleaning up: Type 313 1.5A SB measures 2 uH.
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Old 7th February 2018, 03:41 AM   #1313
alexkosha is offline alexkosha  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
I used DER EE DE-5000.
100kHz Test frequency.
5x20 fuses:
T10A - 0.011uH
T6.3A - 0.010uH
T5AL - 0.019uH
2A - 0.027uH
T1A - 0.022uH
F100mA - 0.048uH

6.35mm fuse:
T10A - 0.011uH
T10A-
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Old 7th February 2018, 09:25 AM   #1314
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Mark Johnson View Post
Has anyone ever measured the inductance of a fuse? Specifically, a slow-blow fuse such as "F1" in the schematic below, placed in series with the transformer secondary. The inductance of F1 directly adds to the self-inductance of the secondary.

Conventional wisdom (D. Self et al) suggests that F1's job is to protect the transformer in case the bridge rectifier fails as a short. While F2's job is to protect the power supply in case the output transistors fail as a short. The transistors are destroyed of course; F2 is simply trying to prevent further damage inside the PSU.

Thanks for any measured data or laboratory results!

_
F1 and F2 are both unnecessary, if one fits a close rated fuse to the primary.
Any significant overload that lasts for any significant period will blow the close rated mains fuse.

A power amplifier that is not abused will run forever from a close rated fuse.
It's when someone tries using two pairs of speakers to get more volume during a drunken party that the two significants add up and save the equipment.
Similarly when one accidentally shorts the output wires when doing a hot swap, the primary fuse comes to our aid.
__________________
regards Andrew T.
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Old 7th February 2018, 12:26 PM   #1315
jackinnj is offline jackinnj  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Quote:
Originally Posted by Mark Johnson View Post
Has anyone ever measured the inductance of a fuse?

_
Here's a 3AG -- 20nH and 6A Slo-Blo
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File Type: png 3AG_Z.png (51.9 KB, 324 views)
File Type: png Fuses.png (41.6 KB, 314 views)

Last edited by jackinnj; 7th February 2018 at 12:33 PM.
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Old 7th February 2018, 01:46 PM   #1316
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
I used Quasimodo (naturally) to measure a 5mmX20mm 5 ampere slow-blow fuse.

With Cx=10.1nF {measured on a DER EE 5000 and also on an AADE LC-meter II}, and two 12-inch crocodile clip jumper wires between the fuse and the bellringer jig
  • Fuse shorted: Osc_Freq = 1.43 MHz ... thus L_total = 1.24 uH
  • Fuse intact: Osc_Freq = 1.37 MHz ... thus L_total = 1.34 uH
Subtracting the two gives L_fuse = 0.1 uH which is in rough agreement with other people's measurements.

The good news for audio equipment builders is: the inductance of the fuse "F1" is a tiny, tiny addition to the self-inductance of the transformer secondary. Even if you omit the fuse from your wiring harness when you tune your secondary snubber(s) with Quasimodo, the difference will be small. Aaaah.

_
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Old 7th February 2018, 04:14 PM   #1317
jackinnj is offline jackinnj  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Quote:
Originally Posted by Mark Johnson View Post
I used Quasimodo (naturally) to measure a 5mmX20mm 5 ampere slow-blow fuse.

With Cx=10.1nF {measured on a DER EE 5000 and also on an AADE LC-meter II}, and two 12-inch crocodile clip jumper wires between the fuse and the bellringer jig
  • Fuse shorted: Osc_Freq = 1.43 MHz ... thus L_total = 1.24 uH
  • Fuse intact: Osc_Freq = 1.37 MHz ... thus L_total = 1.34 uH
Subtracting the two gives L_fuse = 0.1 uH which is in rough agreement with other people's measurements.

The good news for audio equipment builders is: the inductance of the fuse "F1" is a tiny, tiny addition to the self-inductance of the transformer secondary. Even if you omit the fuse from your wiring harness when you tune your secondary snubber(s) with Quasimodo, the difference will be small. Aaaah.

_
“golden ears” claims to be able to hear the fuse!
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Old 7th February 2018, 04:38 PM   #1318
Mark Johnson is offline Mark Johnson  United States
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Simple, no-math transformer snubber using Quasimodo test-jig
Quote:
Originally Posted by jackinnj View Post
“golden ears” claims to be able to hear the fuse!
An especially easy claim to test. Experiment 1: (double blind) someone's wife installs either the fuse, or a solid copper rod of the same diameter, into the fuse holder. Takes a few digital photos with timestamp. Listening panel, listens. Experiment 2: same person swaps them, replacing fuse with copper rod or vice versa. Takes a few more digital photos with timestamp. Listening panel, listens. Experimenter asks panel, which did you prefer? After votes are tallied, wife shows digital photos with timstamps.

Be sure to wipe the fuse and the copper rod, with your favorite contact cleaner (Cramolin? DeOxit? Unicorn tears?), before installation. If you believe in burnishing, burnish.
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Old 12th February 2018, 08:30 AM   #1319
audiomusica is offline audiomusica  Germany
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I just discovered this thread and wonder if anyone has a Quasimodo PCB left or if there are any group buys planned?

I would like to build one but ordering a single PCB only is much too expensive because of the fixed cost.

Best regards

Michael
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Old 12th February 2018, 12:48 PM   #1320
dsolodov is offline dsolodov  United States
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I still offer complete kits for the through hole version. Please my earlier posts here. Please drop your e-mail for PayPal invoice.
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