Another Recap Thread (Tascam M312b)

[reliableman]

I’ve been doing lots of reading on the subject of recapping in the interest of my Tascam M312B. Coupling my reading with the little bit of knowledge I have of audio electronics plus I’ve been able to practice desoldering and soldering parts onto an old Peavey mixer. It’s making a whole lot of sense to me, for the most part. For those of you, like me, who are scouring the internet for knowledge on these things, here are some of the resources I have found useful on this subject:

https://homerecording.com/bbs/special-forums/diy-mods-homebrew/how-do-you-know-time-recap-266567/

Yamaha M916 Mixer Refurb Questions - schematic included

Eddie Ciletti: From Digital Audio to Vacuum Tubes!

Nick Peck's DIY Audio Gear Information Repository : Soundcraft Ghost Restoration Project

Exploring those websites and being able to read schematics should help most people with any basic question on capacitors. Also, there are members of the Gearslutz, homerecording, and Tape Op forums that you will notice have posted many times on recap threads. Find the people that are giving good advice and search the boards for their posts. There is almost an endless amount of info out there.

However, after lots of research, I still have a few questions regarding my own recap project. So to contribute to the endless amount of knowledge out there....If anybody would be kind enough to take a look at this schematic and lend me some advice, I would be forever grateful. Any advice is welcome regarding upgrading the board in general.

I’ve circled all the electrolytics on the Input PCB. There are a couple of caps that I could use a brief explanation of their purpose (if I am wrong about what I think they are) and value.

C103 and C104 are tied to the mic input on one side and a transistor on the other side. Is their sole purpose to filter out DC before amplification? Am I right to think that this could be “upgraded” to something more like 100uf or 220uf like most other coupling caps?

C107 and C108 I see as decoupling, but why are they 10uf 25v whereas most other decoupling caps in the board are 47uf 25v (mostly straight from PSU, like C101 and C102)? Most decoupling caps I was going to upgrade to 100uf, but I hesitated to do so for this small of a value.

Same question with C127. I see it as decoupling but what is with the 0.47uf 50v rating? I assume it functions in some way with the Overload LED. The way I see it is that this isn’t really in the signal path and doesn’t need to be upgraded. This right?

Thanks for any help, and I apologize for my ignorance.

 

[sweetbeats]

C103 and C104: yes, they are DC blocking. 100uF would be fine here. 10uF seems small to me. Keep them 63V.

Can't help you on your question about C107 and C108, but their purpose in the audio path is different than the purpose of C101 and C102 which are local filter caps.

I believe the purpose of C127 is to prolong the lighting of the OL LED...otherwise it would flicker so quickly on peaks that you might not see it very well. I think C127 helps it to stay on just a little longer so it is more visible when levels are peaking. Leave the value alone unless you don't like the action of the OL LED lighting...decrease value for faster response, larger value for longer release.

 

[reliableman]

Thanks for the reply sweetbeats.

Good info. I've found a lot of your threads to be helpful on this topic.

I figured C107 and C108 have a slightly different function than the local filter caps, but they do appear to be decoupling...just not sure why they are where they are.

James



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[reliableman]

Anybody else?
...
Pleeeease.