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Old 30th January 2013, 07:51 PM   #101
tomchr is offline tomchr  United States
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I don't think the spikes you pick up are 192 kHz. That should not come through like that. That looks more like RF interference. Is it present with zero input signal? Does its signature change when you change the sampling rate of the sound card?

Try making some scope shots of the amp output with its input grounded. Also, ensure that you use the ground clip on the scope probe rather than the grounding plug on the front of of the o'scope. It's quite likely that the smearing of the trace that you see is caused by poor grounding of the o'scope probe (measurement error) or supply ripple feeding through to the output. If it's caused by supply ripple, then a good B+ regulator would eliminate this.

Recall that inductance is proportional to loop area. Hence, if the loop area formed by the input impedance of the o'scope, the probe cable, probe, circuit under test, and back through the measurement ground is large, you'll have a lot of inductive pick-up. Perfect for 50/60 Hz to get in.

Nice scope, by the way. I remember using those in college...

~Tom
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Last edited by tomchr; 30th January 2013 at 07:55 PM.
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Old 30th January 2013, 08:35 PM   #102
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You might enjoy this practical reference:
http://www.designers-guide.org/Design/bypassing.pdf
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Old 31st January 2013, 09:39 AM   #103
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Thanks guys,i am glad you haven't lost interest

Tom ,
I think the spikes are introduced by a cheap signalgen/supply on my bench

i followed your recomendation with the wiring and i took a pic of the trace on amp output with input grounded, set to 10mV,5uS (and the signalgen switched off.)

IMG_7503.jpg



maybe the blurry lines on my previous posts are leading in the wrong direction.
I also need to explain the sound i am chasing.
its an audible noise produced by the output tube of the amp, i called it squeeging before. Possibly this is the wrong term for it, sorry about my english here.
its more like a whistle produced by the tube even if only a resistive load is connected. it varies with the frequency i feed from 8khz to 17khz, and it varies with the volume setting. since it is also audible when i feed the signal directly into the driver stage i am thinking now its either produced in the driver or output stage of the amp.
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Old 31st January 2013, 06:48 PM   #104
tomchr is offline tomchr  United States
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Your scope shot looks pretty decent. The last bit of trace blur may be from local FM radio transmitters. You can investigate by reducing the time scale.

On my 400 MHz scope I get about 20 mVpp of 91.7 MHz from a local transmitter. Hence, I tend to have the 20 MHz bandwidth limiter enabled when I perform low-level measurements.

~Tom
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Old 7th February 2013, 08:25 AM   #105
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remove R56-R61 and the 1n4007's out of the output circuit.
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Old 11th February 2013, 08:28 AM   #106
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Quote:
Originally Posted by DavesNotHere View Post
remove R56-R61 and the 1n4007's out of the output circuit.
i tried this before, didn't change anything.
i also removed C31.
still the same problem.
i looked at the powersupply circuit again and simplified the heater circuit.
i doesnt change the sound i am hearing though
all the schematics are attached so everyone can see it as built.
Attached Images
File Type: gif MY5050-1ch-integrated-amp-kt90-032012.gif (26.7 KB, 361 views)
File Type: gif MY5050-protect-bias-bal.gif (19.7 KB, 357 views)
File Type: gif MY Powersupply5050 13.01.2013.GIF (21.7 KB, 356 views)
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@Audio Asylum: your paralleled Bias resistors = 666.6r
is there some improvement in sonics when using satanic valued resistors?
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Old 11th February 2013, 09:05 AM   #107
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i also tried grid stoppers on V3/V4 as suggested earlier in this thread,
isn't a cure either.
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@Audio Asylum: your paralleled Bias resistors = 666.6r
is there some improvement in sonics when using satanic valued resistors?
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Old 17th March 2013, 04:00 AM   #108
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regarding motorboating....
Are the powersupply-caps connected close to the respective amplifierstages or are they somewhere miles away?
Did you try to damp possible ringing of the powersupplies pii-filter, or even better substitute the choke with a resistor?
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Old 27th November 2013, 12:16 PM   #109
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Looking at the earliest schematic in this post, is a SEPARATE R10 resistor used for each grid or did you tie the grids together and use a single R10?

If not, please use a SEPARATE R10 resistor for each grid and tell me if this solves it.
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