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Old 14th September 2012, 07:37 PM   #821
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Quote:
Originally Posted by bambadoo View Post
Houston we have sound..

I have not checked bias..
How to do this?
Stop listening to music through the amp and before you go further with anything, set to appropriate bias current through the output stage and check for output offset.
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Old 14th September 2012, 07:47 PM   #822
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Nice pic. Big speakers. How many mV did you use of bias ? Yes it is possible you might need bigger sinks

Set bias by having 23mV across R14.
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Last edited by OnAudio; 14th September 2012 at 07:50 PM.
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Old 14th September 2012, 08:05 PM   #823
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No sensitivity control...

Thanks ... Hmm I think I have read that before

Hmm - Which one of the big whites is R14 again?... Unable to see the printings on the pcb.....after completed and brainmalfunctioning...

Last edited by bambadoo; 14th September 2012 at 08:11 PM.
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Old 14th September 2012, 08:58 PM   #824
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Measure any of them
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Old 14th September 2012, 09:03 PM   #825
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Thanks

Approx 3-5mv was it.. on one channel. Have to check with 2 multimeteres I guess.... Will disconnect all and do some bias adjustements.

To turn from tube stuff to transistor stuff is a bit new for me..
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Old 14th September 2012, 10:29 PM   #826
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I do hope you like your excursion into transistor stuff . Do give us a thorough review once you set the bias and are just relaxing enjoying some classics . You do own some pretty pieces from those speakers to the preamps.
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Old 15th September 2012, 07:18 AM   #827
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by bambadoo View Post
................ Which one of the big whites is R14 again?... ..............
Quote:
Originally Posted by OnAudio View Post
Measure any of them
measure the Vdrop on all of them. Compare the readings to see how good the matching of the source currents are.

One device that passes more current will run hotter. This could be too much if you run the amp hard.
You should be aiming for the same source current for all the amplifier output devices. That's why you match the resistor resistances and match the output transistors.
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Old 15th September 2012, 10:33 AM   #828
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EDIT:: Since all of this is quite new for me some basic questions will come from this fellow..

If wee look underneath the board - counting from left to right we got 4 measurepoints. Call them 1-4

A pic is added.

My measurements. (after a bit adjustement)
Right channel:
1 - 21.5mV 2 - 25.8mV 3 - 23.4mV 4 - 23.8mV


Left channel:
1 - 22.1mV 2 - 25.6mV 3 - 22.4mV 4 - 25.9mV

Is this ok or not?... Which value should I settle on...
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Last edited by bambadoo; 15th September 2012 at 10:55 AM.
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Old 15th September 2012, 11:37 AM   #829
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Originally Posted by evette View Post
Make r18=1.8k watch your swing into the drivers. Your hum problem could be you might have to lift the input gnd by a 10 ohm resistor. Evette

Hi there. Has anyone experience with this? Lifting the input gnd by 10ohms. What is the meaning of this?

Where in the schematics should a 10ohm resistor be placed then?

http://www.harrisonaudiolabs.com/Amp...YMEF/SYMEF.pdf

hmm - feels like I have endless with tiny questions

It is natural since this amp plays ridiculously good and I would like to be able to use it with my setup..

So it needs to be hum free and I really need to lower the gain in a way or the other...

Tumbs up soundwis..

Burn in time..It has played about an hour now.. Only new unused components. Can I expect something regarding that issue also?
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Old 15th September 2012, 02:54 PM   #830
alex mm is offline alex mm  Europe
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@bambadoo...... just a hint , place C5 and C12 between B and C of transistors not between B and ground like it is in schematic ....
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