Recapping Individual outs on SP1200 - what caps?
- Thread starter SEED78
- Start date
Help Support GroupDIY Audio Forum:
I wouldn't bet my life that output coupling caps would cause intermittent hissing, but I guess it can't be utterly impossible either.
Internal photos wouldn't hurt, for determining details, though. "What caps" is about as vague a question as they come :
Internal photos wouldn't hurt, for determining details, though. "What caps" is about as vague a question as they come :
The typical symptom for dried up old electrolytic caps is weak LF response.SEED78 said:
JR
analogguru
Well-known member
OMG, another recapping-mania....
Luke 23:34:
Then Jesus said, "Forgive them for they know not what they do!"
Luke 23:34:
Then Jesus said, "Forgive them for they know not what they do!"
analogguru
Well-known member
.....where the (balanced) line-output XLR was connected to the (padded) mic-input XLR with the phantom power switched on ? Yes, I have seen that too.....Khron said:
walter
Well-known member
I don’t even know what a SP1200 is. I searched on-line and found the owner’s manual. The first line of the Table of Contents is “ What is it?” page 1. It is a sampling drum machine, that looks pretty cool. I also found a few discussions on the hiss issue. Since I don’t know what I’m talking about all I can do is Parrot what I found. Including a statement from a service manual, a replacement part, link for replacement part, and a picture. Let me know if it fixes the issue.
service manual:
Problem: Hiss or crackling channel Cause: Bad Sample/Hold Cap Solution: Replace Cap
8 polystyrene S/H caps (originally ASC 4700H) with these LCR Components FSC 160V 4700PF:
https://uk.farnell.com/lcr-components/fsc-160v-4700pf/cap-film-ps-4-7nf-160v-axial/dp/9520147?CMP=ADV-CRUK-LF
service manual:
Problem: Hiss or crackling channel Cause: Bad Sample/Hold Cap Solution: Replace Cap
8 polystyrene S/H caps (originally ASC 4700H) with these LCR Components FSC 160V 4700PF:
https://uk.farnell.com/lcr-components/fsc-160v-4700pf/cap-film-ps-4-7nf-160v-axial/dp/9520147?CMP=ADV-CRUK-LF
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I don't know what it is either but they may be using the sample and hold circuits to multiplex a more continuous audio output signal from very narrow digital samples. Like one relatively expensive DAC generating 8 audio outputs.
Polystyrene is an excellent dielectric for sample and hold circuits because of low dielectric absorption (aka soakage or memory effect). A bad hold cap could introduce noise at the sample/refresh frequency.
If you can't source a polystyrene capacitor a NPO/COG ceramic is probably OK. I doubt it needs to be 160V but that was a typical voltage for polystyrenes.
JR
Polystyrene is an excellent dielectric for sample and hold circuits because of low dielectric absorption (aka soakage or memory effect). A bad hold cap could introduce noise at the sample/refresh frequency.
If you can't source a polystyrene capacitor a NPO/COG ceramic is probably OK. I doubt it needs to be 160V but that was a typical voltage for polystyrenes.
JR
user 37518
Well-known member
JohnRoberts said:
Another good, albeit expensive cap dielectric is polyphenylene sulfide.
If price is no object, teflon is an excellent dielectric for DA. Polystyrene was sweet because it was both cheap and very good, sadly not robust enough to stand up to modern manufacturing processes.user 37518 said:
JR
living sounds
Well-known member
Yes, the polystyrene caps in the SPs are a know problem. You can still buy polystyrene caps, just be careful soldering them, use as little heat as quickly as possible.
For today's too much information, I used thousands of polystyrene caps back in my kit business (Phoenix Systems) days, with ham fisted novice customers, hand soldering these to assemble kits with no significant issues.living sounds said:
Mass production is another story... I had a business partner in the early 80s trash a whole production run of PC boards by trying to spray them dry with a high pressure air hose after water rinsing them (using water soluble flux). He inadvertently blew water inside the polystyrene caps destroying them.
Indeed polystyrene is not very resistant to high temperatures, but it is no coincidence that the lead wires are rather small gauge and not very good thermal conductors. Hand soldering these caps using modest wattage irons is generally not a problem.
Wave soldering or reflow is another issue.
JR
user 37518
Well-known member
living sounds said:
They are only to be found in very limited set of values and high price, they are scheduled for obsolescence if you ask me...
living sounds
Well-known member
user 37518 said:
I can still get them here easily. You need 8 pieces of 4.7N polystyrene caps, that's a very common value.
If you can't, WIMA bills the FKP-2 (polypropylene) as a replacement for polystyrene caps. I'm sure it will work, but it may sound a little different. I compared those two in EQ circuits and found the WIMA to sound "softer", FWIW.
COG/NPO are bound to work as well.
analogguru
Well-known member
I don't know why, but I doubt that they will sound "softer" in a sample & hold circuit...living sounds said:
living sounds
Well-known member
analogguru said:
I might try it in my SP-12 (same circuit) one day. So far the outputs are free of noise (or as free of noise, as a 12-bit sampler can be).
