[drp]

I have a D25 with a periodic distortion issue….. There are certain bass frequencies that cause a static/distortion-type noise, primarily in the right channel. It's only on certain cuts that I can hear it, and usually only if bass (and maybe vocals) is playing. The beginning of Bullet Proof Soul by Sade is a perfect example. It's possible that higher volume tracks in the right channel are drowning out this slight distortion and it's still there, just covered up by other sounds.

The noise sounds most like that of a cracked speaker cone; follows the bass beat, and not very audible. Definitely an electronically induced sound as opposed to motor noise. It's not dependent on high volume like something is being over driven because I can reproduce it at somewhat lower volume levels.

What's weird - In other songs that have equally strong bass, this unit is clean and powerful in all frequencies. Janie Runaway and Negative Girl off Steely Dan's Two against Nature have some serious bass chops that reproduce perfectly (or as closely as possible for a pcdp). All of Johnny Lang, Lie to Me, which has some mean bass, is clean and mean through and through with no hint of static or distortion.

Diags so far - I swapped RCA inputs and it appears in the left channel, so it's definitely in that one channel circuit. HP out and line out give the exact same results, so the problem is upstream of the internal amp (conjecture on my part, of course). Same results using a wall wart or 8-cell ni-cad pack.

I read 555's mention of an electrolytic cap failure that caused one channel to go out in his D555, and that this was a reoccurring issue in this model. Since the D25 is from the same era and practically a little brother, I'm wondering if this might be the case. I've already replaced the two PS caps and the two 100uf caps at the headphone output. Still I'm hoping this is just an issue of chasing down and replacing a discrete component or two.

History - I recently modified this D25 by stacking two DACS, in addition to a few other changes. After stacking the DAC, I believe I might have amplified a glitch that was already present. Prior to the mod, I played a channel integrity test track and could hear very slight static in the right channel during the left channel only test, but nothing visa versa. I was playing through the line out into a Headsave Tempo and using Shure E5s (the stethoscope of portable audio.....). It was not motor noise I was hearing, but more like a slight electronic distortion.

Everything else about the Turbo mod and the overall sound blows me away every time I listen to it. Currently, I'm using HD650 (200+ hrs), ZU Mobius (~100 hours), ZU Pivot (15 hrs) and an XP-7. Again, for most songs, i.e. 98% of the time, this unit in many ways at least matches my Onkyo 717, which has a fairly decent CD section.

I'd appreciate any thoughts from the electronic gurus out there, especially those with a D25 schematic. I can publish small sections of the schematic if this would be helpful.

Thanks,

Dave