2230 bias adjustment?

savv

Super Member
I read in an earlier post that the 2230 are cap-coupled so that there is no DC offset adjustment. Just curious if anyone can share the spec sheet for the bias adjustment for the 2230? I suspect that mine are off spec since they don't sound as good as they have been reputed to be.

Thanks!
 
I'm actually looking for the same info right now, I see the two trim pots on each of the amp boards but I don't know which is what and where to place the multimeter leads! I have an owners manual and a (crappy quality) schematic but no service manual, and I am reluctant to spend the $$ on a service manual to make one simple adjustment....

The 2230 sure is a nice little receiver though.
 
Bump - Hoping someone will chime in!

Can anyone confirm whether there is a bias adjustment for the 2230?
 
Two trimpots/channel: one is for the bias setting, the other is for the symmetrical clipping at maximum output power (the 2230 has assymetrical output stages with just a positive feeding voltage and is cap-coupled to the speaker outputs).

Locate the low resistance (0.2-0.5 Ohm range) high wattage (2-5 Watts) wirewound emittor resistors (two resistors per channel) next to the output transistors on the amp board, and note their value (normally printed onto the resistor body).
Set volume potmeter at minimum, no signal connected to the inputs, and connect a digital voltmeter (mVDC range) in parallel over one of the resistors and measure the voltage (let the 2230 warm up for half an hour).
I (Amps) = U (Volts) / R (Ohms) gives you the bias current through the output transistors.
Example: R=0.47R, measured voltage = 7.5mVDC -> bias = 0.0075/0.47= 0.0159A = 15.9mA
In absence of the Service Manual specs for the correct bias, better is to have a little too much bias than too less (crossover distortion).

Set the correspondant bias trimpot (remember the physical position of each trimpot till you found the right trimpot) for a suitable bias current (everything in the 10-30mA range should be OK (or maybe a AK-member with the 2230 SM should be able to tell you the correct bias setting), recheck the setting several times as the trimpots are mostly quite 'jumpy'.
Ofcourse, do this for both the channels, and check if the output heatsink doesn't heat more than handwarm at idle.

The symmetrical clipping setting is less important, to do this setting you need a sine wave oscillator at 1KHz, an oscilloscope and two 8 Ohm dummy loads with a sufficient power rating.
Connect the dummy loads to the speaker terminals, feed the 1KHz sine wave to the left and right AUX or tuner inputs, connect the scope probe to one of the speaker outputs.
Increase the oscillator output voltage/volume potentiometer till the sine wave form on the scope display starts to clip (maximum output power).
With the above mentionned 'clipping' trimpots, trim for a symmetrical clipping on both the positive and negative side of the output signal.
Again, do this for both channels.

CD :)

Edit: The service manual of the Marantz 1060 (30Watts/channel) advises a bias setting of 7.5mV over the 0.24R emittor resistors, which gives 0.0075/0.24=31mA.
 
Thanks Turbokeu!

I will try the bias adjustments first!

Now if someone with the 2230 SM can give us the correct bias setting this post should be a sticky!
 
5 mV.

Someday i will scan the manual and uplaoad to HiFi Engine with the others.
 
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