RE: What does that cap do becase I already have a resistive load

Posted by Steve O (A) on August 30, 2016 at 21:09:32

In Reply to: What does that cap do becase I already have a resistive load posted by Michael Samra on August 30, 2016 at 20:30:51:

The cap adds a reactive component to the load that more closely approximates a real world speaker, especially an electrostat. Most feedback amps will exhibit overshoot and ringing to some degree or another when presented with a reactive and esp a capacitive load. The overshoot and ringing are indicative of overall amp stability. The less the overshoot and more damped the ringing, the more likely the amp is stable under typical operating conditions. Some amps will spontaneously oscillate w/o applied signal at some ultrasonic frequency when presented with a reactive load.

I always check for stability when working with a vintage amp to be sure it won't blow something up if high cap cable or estat type speaker is anticipated.

Looking at that 10KHz waveform again, it looks suspiciously bandwidth limited. Next time you check sq wave perf, I suggest you put the scope in dual trace mode and show both input to amp as well as output.

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Follow Ups Full Thread

Topic - Bone stock Fisher 55a mesurements. All original as far as power supply. - Michael Samra 17:19:33 08/30/16 (14)

How about a10KHz sq wave w/1uF across the load R? (nt) - Steve O 18:19:26 08/30/16 (10)

Here is a 1uf cap across the load with a 10khz sq wave injected. - Michael Samra 19:35:20 08/30/16 (9)

That's excellent performance... - Steve O 19:44:45 08/30/16 (1)

Here is a McShaned Mc225 at 22khz sq wave - Michael Samra 20:36:10 08/30/16 (0)

I'm sure Steve meant 100uF, that's a REAL test - Triode_Kingdom 19:43:28 08/30/16 (6)

I most certainly did not ;-) (nt) - Steve O 19:47:17 08/30/16 (5)

What does that cap do becase I already have a resistive load - Michael Samra 20:30:51 08/30/16 (4)

RE: What does that cap do becase I already have a resistive load - Steve O 21:09:32 08/30/16 (3)

RE: What does that cap do becase I already have a resistive load - Michael Samra 22:17:24 08/30/16 (2)

RE: What does that cap do becase I already have a resistive load - Triode_Kingdom 06:49:21 08/31/16 (1)

RE: What does that cap do becase I already have a resistive load - Michael Samra 10:04:28 08/31/16 (0)

show pics of the amp too Mike! (nt) - vinnie2 17:26:33 08/30/16 (2)

RE: show pics of the amp too Mike! (nt) - Michael Samra 18:40:14 08/30/16 (1)

RE: show pics of the amp too Mike! (nt) - vinnie2 03:20:52 08/31/16 (0)

Follow Ups

RE: What does that cap do becase I already have a resistive load - Steve O 21:09:32 08/30/16 (3)

RE: What does that cap do becase I already have a resistive load - Michael Samra 22:17:24 08/30/16 (2)

RE: What does that cap do becase I already have a resistive load - Triode_Kingdom 06:49:21 08/31/16 (1)

RE: What does that cap do becase I already have a resistive load - Michael Samra 10:04:28 08/31/16 (0)

RE: What does that cap do becase I already have a resistive load

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