Long shot but if anyone has suggestions on locating a service manual for the B&K Reference 2220 amplifier I would appreciate it.
Mainly looking for idle and DC adjustment procedures.
Mainly looking for idle and DC adjustment procedures.
There is not a service manual specifically for that model, however B&K used mainly two/three versions of a similar topology in all their amplifiers, just adding more voltage and outputs to increase the wattage or a servo to control offset.
Attached is the generic bias setting procedure, which is 200mA for the smaller amps (100-150W) and 250mA for the large 200W+ amps by monitoring the current through the negative rail fuse.
Also included the three versions of their schematics, likely one is very close to or exactly what you have.
Attached is the generic bias setting procedure, which is 200mA for the smaller amps (100-150W) and 250mA for the large 200W+ amps by monitoring the current through the negative rail fuse.
Also included the three versions of their schematics, likely one is very close to or exactly what you have.
Thanks! Hard to find many references to the 2220. Also interesting they just have an 'all our amps are basically like this' schematic.
When is says Supply an input signal of 100 mV RMS @ 20 Khz., is that done with a scope?
The procedure makes sense but I'm not comfortable following it without more info.
When is says Supply an input signal of 100 mV RMS @ 20 Khz., is that done with a scope?
The procedure makes sense but I'm not comfortable following it without more info.
First thing to understand - input signal is AC voltage. Bias current is is DC voltage across a resistor. Don't get AC and DC confused on these.
You would input a 20kHz signal from a signal generator - you can find free apps that will do this from your phone.
First - measure the output from your phone using a DMM RCA plug, with ring as negative and center pin as positive. Adjust you phone's volume until you measure 100mVac on your DMM, or 0.100 Vac. I suggest you write down the volume level to get 100mV, i.e. is it one volume + click from 0 or 3 volume+ clicks from zero, so you know later.
Turn off the signal generator - by either pausing or closing the app.
Hook up the RCA from your phone to the RCA input of the amplifier and play that exact same volume of 20kHz tone into the amplifier.
Then you will use your DMM to measure the 200-250mA across a resistor you have placed instead of the negative rail voltage fuse.
Very easy process and I typically use a 10-ohm 5-10watt resistor in place of the fuse. That way 2.5Vdc across the resistor is your 250mA (2.5/10=0.250)
I would highly suggest you used a Dim Bulb Limited/Tester (google it), until you are comfortable taking the measurements. One slip of the probe, or error on the connections of the resistor and you can very quickly cause damage to the amp.
EDIT - suggest you google setting BIAS on youtube and be familiar with the multiple ways to measure BIAS - B&K is only suggesting one way to do it.
You would input a 20kHz signal from a signal generator - you can find free apps that will do this from your phone.
First - measure the output from your phone using a DMM RCA plug, with ring as negative and center pin as positive. Adjust you phone's volume until you measure 100mVac on your DMM, or 0.100 Vac. I suggest you write down the volume level to get 100mV, i.e. is it one volume + click from 0 or 3 volume+ clicks from zero, so you know later.
Turn off the signal generator - by either pausing or closing the app.
Hook up the RCA from your phone to the RCA input of the amplifier and play that exact same volume of 20kHz tone into the amplifier.
Then you will use your DMM to measure the 200-250mA across a resistor you have placed instead of the negative rail voltage fuse.
Very easy process and I typically use a 10-ohm 5-10watt resistor in place of the fuse. That way 2.5Vdc across the resistor is your 250mA (2.5/10=0.250)
I would highly suggest you used a Dim Bulb Limited/Tester (google it), until you are comfortable taking the measurements. One slip of the probe, or error on the connections of the resistor and you can very quickly cause damage to the amp.
EDIT - suggest you google setting BIAS on youtube and be familiar with the multiple ways to measure BIAS - B&K is only suggesting one way to do it.
Thank you! I've done bias but only on amps that had clear procedures for test points, expected measurement, and adjustment. I am in the 'first do no harm' camp so unless I'm sure I am not going to make anything worse I'll leave it alone.
I'll do more reading on bias and walk through the procedure a couple times. Your explanation could not be more clear and easy to follow, that should be a sticky!
I'll do more reading on bias and walk through the procedure a couple times. Your explanation could not be more clear and easy to follow, that should be a sticky!
Did you make some repairs and need replace either the drivers or outputs? If not, then your bias should not drift out of spec. I have a 200.2 that's over 20 years old and was still within 10mA of spec. so i left it.
Nope, as far as I know it's never been opened. When I get a new amp, especially 20+ years old, I like to check it over just for piece of mind. Again that's usually a very straightforward procedure.
There's a bit of noise when you turn it on, whump or thump, but I don't think it's too bad. DC offset was fine. This is only my second amp of this size and it feels like a beast, I'm a little afraid of it!
There's a bit of noise when you turn it on, whump or thump, but I don't think it's too bad. DC offset was fine. This is only my second amp of this size and it feels like a beast, I'm a little afraid of it!
B&K Reference 2220 service manual/schematic
You can measure across the drain resistors too, if you are familiar (more comfortable) with that way. I would just take the 250mA and dive by number of output transistors, most likely 20-25mA per output. As long as the heatsink stays warm not hot, you could go higher too, some feel like 50mA is better sounding - I won’t weigh in on that debate.
You can measure across the drain resistors too, if you are familiar (more comfortable) with that way. I would just take the 250mA and dive by number of output transistors, most likely 20-25mA per output. As long as the heatsink stays warm not hot, you could go higher too, some feel like 50mA is better sounding - I won’t weigh in on that debate.