The simplistic Salas low voltage shunt regulator

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HiFiNutNut

Member
Joined 2004
Salas and friends,

My greeting first as I have not been here for a long time.

Sorry for this out of topic post. Earlier in this thread we discussed the DACT-type attenuator Salas recommended. I bought a couple of them (20k) and found them sound nice. Because dust got in it, it started having some cracking sound when changing volumes. It gets worse now so 20 minutes ago I replaced it with a genuine 50k ALPS pot.

Big shock!!! :mad: The sound was obviously different!!! to the worse.

I could never imagine that an ALPS pot has its own sound and I don't think that a pot needs run-in. :confused: I thought that only capacitors have their own sound.

Regards,
Bill
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
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Hello Bill. Nice to hear from you.The stepped ones have precise matching is one sure thing, when the conductive track ones differ enough between channels. If you could have them non exposed they could be a good deal those cheapos. There must be a way to wrap something around them or find a cap for those so to not gather dust? Don't know, an old film box or something that you could make a cut out for the wires.
 
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HiFiNutNut

Member
Joined 2004
I bathed the DACT Type 21 Stepped Attenuator in methylated spirits and tuned the pot for a dozen times. When dried, I used some RS Component (expensive) contact cleaner to spray it around and used electrical tape to wrap around the opening area. Soldered it back to the preamp. I turned the pot and didn't hear the cracking sound anymore. So the cleaning was successful. And now the good sound is back!:)

I then got an email from the ebay seller that "If there are dust inside or bad contact, I always use "3M Contact Cleaner" to clean it. Not recommended to use spirit or alcohol for electrical contacts. Some buyers said that they use "Hot Shrink Tube" to wrap this Attenuator to avoid dust.". It was too late but never mind.

A big lesson has been learned. Forget about the expensive genuine ALPS pot, despite having measured it and found reasonably tight tolerance between channels. Quite an obvious difference in sound quality. These ebay DACT type 21 pots are highly recommended. Thanks for Salas recommendation.

Regards,
Bill
 
C

canvas

Member
Joined 2003
spicetree.no-ip.com
Salas said:
Surely, coax or twisted is recommended. Shield for sense. But use a faster CCS PMOS. Like IRF9610,9620,9510,9520.
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Hi Salas,
Maybe I didn't say it clearly. I mean one shielded twisted-pair cable will be used for sense+ & force+, and so does sense- & force-. By doing that, the force line will be shielded, too. The reason for this is that I'd like both sense and force line being packed together, having same length and being shielded. Will this have any negative effect?
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
Shielding the sense + line with shield to sense 0 would be preferable since it does the voltage nodes. I don't expect it to give you any real trouble however you prefer it, but a force twisted pair and a coax sense wrapped around, would make one defined terminal as easily. You need no thick gauge. I have even used CAT5 twisted pairs and thin coax. The drop on the force lines will be taken into account is the deal.
 
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