thermionic
Well-known member
- Joined
- Jun 3, 2004
- Messages
- 1,671
Hi,
Over the 20-odd years I’ve been DIY-ing, I’ve built many amps / preamps / EQs / PSUs etc. However, the one thing I’ve never tackled is synths…
I have some decent test gear + tools, including a digital Weller iron + De-non desoldering station (ideal for DIL ICs and caps).
A couple of years back, I picked up a Prophet 5 rev 2 at a bargain price. I was told it didn’t work, and I ushered it away before the owner could change his mind. The synth has been living in storage ever since and I haven’t attempted to turn it on. This may sound cautious (it is), but my moral is that it should be easy to replace the obvious perishables, i.e. electrolytic caps, look for any visual damage, and then try and turn it on via variac… I think this makes sense as the PSU in the P5 is notorious for problems (some people cite its inadequacy as being part of the early P5’s sound), and if it hasn’t been on for years, turning it on with caps that pass DC could do a lot of damage.
Anyway, according to my synth geek friends, this guy knows his stuff, and he’s published an article here on his website: http://www.oldcrows.net/~oldcrow/synth/tips.txt
Now, I know that replacing all the electro caps will appear conservative to some of you – you might argue to replace them only if you can tell they’re gone, but if you read the link, he recommends going way further than just replacing the wet caps…
Adding additional PSU bypass caps to ICs… A good move IMHO, if they’re not there in the first place (I’ve seen what op-amps do without bypassing, it surprises me that the synths lack them…)
Replacing all 4000-series ICs on the spot… The reasoning makes sense, so maybe I’m missing a point here, but if an IC has worked ok for 30-odd years, isn’t there an argument to let sleeping dogs lie?
Swapping out all tants for electrolytic caps Tants do get leaky after a few years use and can fail in a multitude of ways (I’ve seen burning ones fly across the room…), but surely, if the original OEM specified tants when they could’ve fitted electrolytics, couldn’t one argue the tants are there for a reason? My impression was that tants were developed to get a lot of capacity into places where electrolytics wouldn’t fit, so I can’t see an issue, aside from authenticity.
I don’t want to appear to be doubting the engineer who wrote the link – I’m sure he knows much more than I do about synths, but replace every 4000-series IC? Am I naïve here, or is this uber-conservative?
Thanks in advance for your thoughts,
Justin
edit - I hope this is in the right forum... If the moderator wants to move the thread, I won't be offended - I do think some of the questions relate to 'design', so I posted here.
Over the 20-odd years I’ve been DIY-ing, I’ve built many amps / preamps / EQs / PSUs etc. However, the one thing I’ve never tackled is synths…
I have some decent test gear + tools, including a digital Weller iron + De-non desoldering station (ideal for DIL ICs and caps).
A couple of years back, I picked up a Prophet 5 rev 2 at a bargain price. I was told it didn’t work, and I ushered it away before the owner could change his mind. The synth has been living in storage ever since and I haven’t attempted to turn it on. This may sound cautious (it is), but my moral is that it should be easy to replace the obvious perishables, i.e. electrolytic caps, look for any visual damage, and then try and turn it on via variac… I think this makes sense as the PSU in the P5 is notorious for problems (some people cite its inadequacy as being part of the early P5’s sound), and if it hasn’t been on for years, turning it on with caps that pass DC could do a lot of damage.
Anyway, according to my synth geek friends, this guy knows his stuff, and he’s published an article here on his website: http://www.oldcrows.net/~oldcrow/synth/tips.txt
Now, I know that replacing all the electro caps will appear conservative to some of you – you might argue to replace them only if you can tell they’re gone, but if you read the link, he recommends going way further than just replacing the wet caps…
Adding additional PSU bypass caps to ICs… A good move IMHO, if they’re not there in the first place (I’ve seen what op-amps do without bypassing, it surprises me that the synths lack them…)
Replacing all 4000-series ICs on the spot… The reasoning makes sense, so maybe I’m missing a point here, but if an IC has worked ok for 30-odd years, isn’t there an argument to let sleeping dogs lie?
Swapping out all tants for electrolytic caps Tants do get leaky after a few years use and can fail in a multitude of ways (I’ve seen burning ones fly across the room…), but surely, if the original OEM specified tants when they could’ve fitted electrolytics, couldn’t one argue the tants are there for a reason? My impression was that tants were developed to get a lot of capacity into places where electrolytics wouldn’t fit, so I can’t see an issue, aside from authenticity.
I don’t want to appear to be doubting the engineer who wrote the link – I’m sure he knows much more than I do about synths, but replace every 4000-series IC? Am I naïve here, or is this uber-conservative?
Thanks in advance for your thoughts,
Justin
edit - I hope this is in the right forum... If the moderator wants to move the thread, I won't be offended - I do think some of the questions relate to 'design', so I posted here.