rlisin
Quad 4 life
Got my hands on an InKel set of MD2200, PD2100 and EQ 200 (power amp, pre and EQ):
Power and pre were also sold as Sherwood S-6040CP/S-6020CP and as LXI AM 4222/AM4022. I put Sherwood model in the title because I know some ARers have this amp.
The power amp needed adjustments, which I made. At first I missed that 8 ohm load should be connected while adjusting and I couldn't get the right values, but after rechecking the SM I connected an 8 ohm speaker and adjustments went fine. Well, sort of.
I could get the bias to the value range specified in the SM with VR102, but it's not the same on transistor pairs in either channel (off by 2 mV, meaning when I set it to 17 mV for one pair, the other pair in this channel gets 19 mV). Both values are within the range recommended in the SM, so I don't think it's a problem, but if it is, do tell me.
DC offset was more tricky. I could not get it down to near 0 mV using the VR101. According to the SM, values up to 70 mV are fine, but 70 mV seemed scary high to me and I wanted it lower.
But there is a 3rd trimmer on the power board. The SM simply does not mention it and I don't see it on the schematic at all. The reason is, SM is written for the power board part number K40430, and my amp has power board K40430A.
When I moved this trimmer (by mistake), I noticed that it affects DC offset big time, so I set it in the position at which DC offset is 0 mV.
But I hate to not know what exactly I'm doing, so I would like to set it correctly.
So, do you have any idea what the 3rd trimmer does?
It is marked red:
X marks the spot where it should be on the schematic:
I have confirmed that the 3rd trimmer is not unique to InKel-branded amp, some Sherwood S-6040CP and LXI AM 4222 also use power board version K40430A and also have this trimmer. It is not on power board K40430.
Power and pre were also sold as Sherwood S-6040CP/S-6020CP and as LXI AM 4222/AM4022. I put Sherwood model in the title because I know some ARers have this amp.
The power amp needed adjustments, which I made. At first I missed that 8 ohm load should be connected while adjusting and I couldn't get the right values, but after rechecking the SM I connected an 8 ohm speaker and adjustments went fine. Well, sort of.
I could get the bias to the value range specified in the SM with VR102, but it's not the same on transistor pairs in either channel (off by 2 mV, meaning when I set it to 17 mV for one pair, the other pair in this channel gets 19 mV). Both values are within the range recommended in the SM, so I don't think it's a problem, but if it is, do tell me.
DC offset was more tricky. I could not get it down to near 0 mV using the VR101. According to the SM, values up to 70 mV are fine, but 70 mV seemed scary high to me and I wanted it lower.
But there is a 3rd trimmer on the power board. The SM simply does not mention it and I don't see it on the schematic at all. The reason is, SM is written for the power board part number K40430, and my amp has power board K40430A.
When I moved this trimmer (by mistake), I noticed that it affects DC offset big time, so I set it in the position at which DC offset is 0 mV.
But I hate to not know what exactly I'm doing, so I would like to set it correctly.
So, do you have any idea what the 3rd trimmer does?
It is marked red:
X marks the spot where it should be on the schematic:
I have confirmed that the 3rd trimmer is not unique to InKel-branded amp, some Sherwood S-6040CP and LXI AM 4222 also use power board version K40430A and also have this trimmer. It is not on power board K40430.