parasound hca-1000a input stage transistors

vze1lryy

Member
2016-05-19 4:41 pm
Hi,

I have an HCA-1000a that is a "passion project" of mine that I've been keeping alive piece by piece for the past 11 years. I recently had a bridge short and after replacing, seems to have issues with the cascoded differential gain stage on input.

Finding 2SC2240, 2SK170, 2SJ74, and 2SA970 seem to be limited to eBay, which is where in my other field of work, I am used to being sold fake/broken/junk. :)

I have been doing my due diligence on the forum on suitable replacements for each of these. I've found some suggestions for 2SK370/2SJ108 which I can't seem to find anywhere but eBay(which scares me).

I can see that they are tightly matched and want to tread carefully here. I replaced the output stage about seven years ago and was able to find new, not fake transistors and matched them and it has worked beautifully since! I truly do not want to dump such an amazing amplifier, nor subject it to eBay parts if not 100% necessary.

Thank you!
 

vze1lryy

Member
2016-05-19 4:41 pm
Thank you very much for the replies. I wound up finding a set on eBay - a little pricy, but they actually worked. Toshiba 2SJ74 Two Matched Pairs 2 Pairs to 0 03mA 4MV in Temp Control Lab | eBay

I did something pretty dumb here, I went through all this troubleshooting before I tried tying grounds from left to right. The completely destroyed sounding right channel sounds fine if I run a jumper between left channel ground and right channel ground. Which obviously isn't a real fix. Time to keep hunting. It is odd since it failed in the middle of playback, not from a drop, a move, or a loud musical passage that it has failed in this way. I've never experienced this before.

That's what keeps this fun!

Thanks again!