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F5 power amplifier
F5 power amplifier
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Old 7th August 2016, 03:16 PM   #15191
EUVL is offline EUVL  Europe
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Pictures of our matching setup, MOSFET heater block (insulation removed), and a special heater block for TO92 JFETs.
And the FET tester of our own design.


Patrick

.
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File Type: jpg 121228 Matching Station.jpg (138.3 KB, 1116 views)
File Type: jpg MOSFETHeater Block.jpg (58.5 KB, 1099 views)
File Type: jpg TO92 Heater Block 2.jpg (91.0 KB, 1079 views)
File Type: jpg 120528 SFT w Hsg.jpg (878.4 KB, 1090 views)
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Old 7th August 2016, 09:13 PM   #15192
jackinnj is offline jackinnj  United States
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F5 power amplifier
My test setup:
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Old 16th September 2016, 01:01 PM   #15193
Joca is offline Joca  Portugal
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hi, any help is welcome

My recent build of the F5 has this simptoms:

Cold start - bias rises to 0.7v on both channels and stays there for 3 to 5 seconds and then go low to 0.60v after a while. this voltage is my bias setup after thermal equilibrium (1 hour) but i have flutuation between 0.595v and 0.625v
my dc offset is stable on both channels at 1mv

i have little hum on the speaker when i have my ear very very close. This hum seems to be related to the hum or noise i have inside the case near the rectifier bridge. I have the ixys diode and they get really hot. i can't touch them more than 2-3 seconds
https://www.digikey.pt/product-searc...DPG60C200QB-ND

thank you.
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Old 16th September 2016, 01:59 PM   #15194
ColinA is offline ColinA  United Kingdom
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Have you got anything connected to the input while testing?
Try re-arranging your wiring to see if it affects the hum.
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Old 16th September 2016, 02:12 PM   #15195
Joca is offline Joca  Portugal
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nothing connected to the input. i am going to do the bias procedure again with the inputs shorted. My problem here is the inrush at cold start. Is it a common behavior?

so, it is normal the noise (mechanical?) inside the case?
if i can't reduce hum with wire arrangement, what else can be done?

thank you
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Old 16th September 2016, 02:18 PM   #15196
qwertyl is offline qwertyl  United Kingdom
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Quote:
Originally Posted by Joca View Post
nothing connected to the input. i am going to do the bias procedure again with the inputs shorted. My problem here is the inrush at cold start. Is it a common behavior?
Do you have thermistor in series with transformator?

Quote:
Originally Posted by Joca View Post
so, it is normal the noise (mechanical?) inside the case?
Big toroids can buzz a bit. It helps to have 2 separate rectifier bridges...
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Old 16th September 2016, 02:21 PM   #15197
labjr is offline labjr  United States
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IXYS diodes or bridges can fail easier than cheapo bridges. You have to limit inrush current.
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Old 16th September 2016, 02:34 PM   #15198
Joca is offline Joca  Portugal
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I have two thermistors in series with the primary.

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Old 16th September 2016, 02:40 PM   #15199
sangram is offline sangram  India
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It is normal for bias to start off little higher and back off as the thermistors start reducing the gate drive once the amp warms up.

It is normal for diodes to run hot. A heatsink is absolutely needed as the standing current is pretty high. You can expect about a watt for every ampere of standing current through the diodes, which makes them run hot. Add to that the temperature inside the case, and they could be quite toasty. If your fingers are not blistering, it's under 80 degrees which is okay for the diode, if not your fingertips.
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Old 16th September 2016, 04:52 PM   #15200
ColinA is offline ColinA  United Kingdom
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Try turning the transformer a bit and re-tighten.(Not too tight.)
Try some rubber or cork sheet under the transformer.

By the way, nice tidy build.

A suggestion from my troubles.
Take the power from the rectifier board via connector blocks to the amp boards.
Then you can take one out of circuit without de soldering wires.
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Last edited by ColinA; 16th September 2016 at 04:55 PM.
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