nate867
New Member
Hello,
I have an X202B I've restored and use almost daily. I've done a fair amount of work: all the usual steps, plus replacing worn tube sockets, eliminating the remote control circuitry, etc. Now I want to check/ adjust the high frequency response, since to me the unit sounds a little "edgy." I scoped a 2khz square wave both at the recording output jacks (after V3) and at the speaker output (going into an 8 ohm dummy load.) Attached images show an overshoot that suggests I need to tame the HF a bit.
I've read in the previous thread "Gilding the X-202B" that the relevant caps are C9 + C10, and C19 + C20. I'm thinking I should adjust C9-C10 for a flat response from the recording output jacks, then the 2nd pair measured at a point further down the line. Perhaps at the input to the volume control?
Is there any general advice on tackling this area? Do people just tack additional caps in parallel by trial and error? Would I have to adjust any other components? This is getting deeper into the engineering side of things than I've done before.
I will note that the line stage tubes are Telefunken 12ax7 and Mullard 7247, which test good in my Eico 667 and seem ok. But I suppose I could swap tubes in and out and check the square wave again...
Thanks!
Nate
I have an X202B I've restored and use almost daily. I've done a fair amount of work: all the usual steps, plus replacing worn tube sockets, eliminating the remote control circuitry, etc. Now I want to check/ adjust the high frequency response, since to me the unit sounds a little "edgy." I scoped a 2khz square wave both at the recording output jacks (after V3) and at the speaker output (going into an 8 ohm dummy load.) Attached images show an overshoot that suggests I need to tame the HF a bit.
I've read in the previous thread "Gilding the X-202B" that the relevant caps are C9 + C10, and C19 + C20. I'm thinking I should adjust C9-C10 for a flat response from the recording output jacks, then the 2nd pair measured at a point further down the line. Perhaps at the input to the volume control?
Is there any general advice on tackling this area? Do people just tack additional caps in parallel by trial and error? Would I have to adjust any other components? This is getting deeper into the engineering side of things than I've done before.
I will note that the line stage tubes are Telefunken 12ax7 and Mullard 7247, which test good in my Eico 667 and seem ok. But I suppose I could swap tubes in and out and check the square wave again...
Thanks!
Nate
