Hi.
Read GroupDIY for years--deeply appreciate all the help it and all of its users have been--finally have a project worth contributing. Recently purchased a 70s TEAC M15 24x8, would like to restore and modify it without losing its flavor.
Aside from LED lamps in the VUs, this desk is otherwise bone stock from power supply to channel strip, though it did come with bonus modules from another M15, including 8 input modules modified for 15v center tap phantom with chassis ground.
Though this page catalogued an M15 restoration/modification, I feel as if his goals were far different from mine, seeking to clean up and neutralize the sound as best he could.
Ideally, work to be undertaken includes:
--completely reworking the power supply (using an HDD-15-5AG)
--installing phantom power (using the HB48-0.5 or HC48-1) with individual switches on the strips
--a complete recapping
--installing an LED meter bridge (+ PSU) so as to individually meter channel strips (in complement to the buss/main VUs)
I'm looking at a complete recap and PSU rebuild as this desk will eventually be on 24/7 and put into an at least 8 hour a day production environment.
Jim Williams suggested both of the above PSUs, as well as adding Jensens transformers to clean up the pres and replacing the opamps with something rather more modern and clean. I will likely take his advice on the PSUs and not the rest as, again, the 'compromised' audio quality is part of the charm of this desk. Jim also suggested that converting to balanced, replacing the RCA with TRS connectors, star ground, and most of the mods listed on the website aren't worth the time or expense, and on that I agree.
Caveats: I am good with an iron and can read and understand a schematic and understand some of the theory behind circuit design, but part of the purpose behind purchasing and restoring this desk is to teach me to better understand circuits and their design. This will also be my first time working with AC mains. I also have most of the books suggested at various points on GroupDIY to use as references, aside from the rather more expensive ones. The ease with which this desk can be repaired and modified seemed quite appropriate.
Now, for a few questions/thoughts.
(1) While I can simply purchase the OVP-24 overvoltage module for use with the HDD-15-5AG for the main PSU, no such module exists for the 48v PSUs--what would be the suggested overvoltage circuit for the phantom PSU, if one is even necessary?
(2) Nichicon electrolytics seem to be the only one of the venerable standbys still available as new stock. The PWs seem preferred, and if you believe the dogma they might even fit the desk's existing sonic profile, but the HEs are also an option--happy to acknowledge any 'lytics will likely die of old age before usage fatigue. I would likely uprate the PWs (e.g. 16v->25v or 35v) by choice, while the HEs would require uprating in all cases (e.g. 25v->50v), with a more significant uprating ratio (e.g. 10v->100v) required in some cases. Physically the uprated caps would still fit fine, and I assume even the ESR/leakage/ripple/etc of significantly uprated modern caps would be as good or better than the (all original) Nippon SLs currently installed. Thoughts? Suggestions on other caps most welcome.
(3) Speaking of uprating, there are a couple of caps that could be replaced with higher capacitance to, say, extend/clean up the low-end, but, again, the end game is to keep this desk sounding mostly like it does.
(4) I'm inclined to replace the EQ/pre caps. What manufacturer/line makes the best new stock mica/film? Panasonic? Wima? KEMET? There are a few polystyrene (100pf-470pf) I'd likely leave, but the 15pf micas and the .15uf-.68uf tantalums could probably be upgraded, at very least the tantalums. The EQ/pre caps range from 15pf to .68uf, all (supposedly) 50v, and new stock pickings seem to be slim. Should I bother chasing down NOS polystyrene or other NOS film caps, or just go for whatever new stock mica/polyester/PEN/PET/PPS/PP mouser carries, regardless of voltage?
(5) How necessary is external noise control? The underside is just wood, so the shielding isn't complete, but I figure that isn't that important, nor is running it off an isolation transformer or online UPS or both, given its inherently noisy nature. Still, worth asking.
This amount of restoration and modification may seem like putting lipstick on a pig, but, again, this desk will be as much a learning experience as it will a production tool.
Anyway, this has gotten rather too long, far longer than intended--I do apologize!--so I'll close it out here. Any and all comments most welcome.
I'll leave you with a picture of the desk in her former home, she's currently taken apart in mine!
Read GroupDIY for years--deeply appreciate all the help it and all of its users have been--finally have a project worth contributing. Recently purchased a 70s TEAC M15 24x8, would like to restore and modify it without losing its flavor.
Aside from LED lamps in the VUs, this desk is otherwise bone stock from power supply to channel strip, though it did come with bonus modules from another M15, including 8 input modules modified for 15v center tap phantom with chassis ground.
Though this page catalogued an M15 restoration/modification, I feel as if his goals were far different from mine, seeking to clean up and neutralize the sound as best he could.
Ideally, work to be undertaken includes:
--completely reworking the power supply (using an HDD-15-5AG)
--installing phantom power (using the HB48-0.5 or HC48-1) with individual switches on the strips
--a complete recapping
--installing an LED meter bridge (+ PSU) so as to individually meter channel strips (in complement to the buss/main VUs)
I'm looking at a complete recap and PSU rebuild as this desk will eventually be on 24/7 and put into an at least 8 hour a day production environment.
Jim Williams suggested both of the above PSUs, as well as adding Jensens transformers to clean up the pres and replacing the opamps with something rather more modern and clean. I will likely take his advice on the PSUs and not the rest as, again, the 'compromised' audio quality is part of the charm of this desk. Jim also suggested that converting to balanced, replacing the RCA with TRS connectors, star ground, and most of the mods listed on the website aren't worth the time or expense, and on that I agree.
Caveats: I am good with an iron and can read and understand a schematic and understand some of the theory behind circuit design, but part of the purpose behind purchasing and restoring this desk is to teach me to better understand circuits and their design. This will also be my first time working with AC mains. I also have most of the books suggested at various points on GroupDIY to use as references, aside from the rather more expensive ones. The ease with which this desk can be repaired and modified seemed quite appropriate.
Now, for a few questions/thoughts.
(1) While I can simply purchase the OVP-24 overvoltage module for use with the HDD-15-5AG for the main PSU, no such module exists for the 48v PSUs--what would be the suggested overvoltage circuit for the phantom PSU, if one is even necessary?
(2) Nichicon electrolytics seem to be the only one of the venerable standbys still available as new stock. The PWs seem preferred, and if you believe the dogma they might even fit the desk's existing sonic profile, but the HEs are also an option--happy to acknowledge any 'lytics will likely die of old age before usage fatigue. I would likely uprate the PWs (e.g. 16v->25v or 35v) by choice, while the HEs would require uprating in all cases (e.g. 25v->50v), with a more significant uprating ratio (e.g. 10v->100v) required in some cases. Physically the uprated caps would still fit fine, and I assume even the ESR/leakage/ripple/etc of significantly uprated modern caps would be as good or better than the (all original) Nippon SLs currently installed. Thoughts? Suggestions on other caps most welcome.
(3) Speaking of uprating, there are a couple of caps that could be replaced with higher capacitance to, say, extend/clean up the low-end, but, again, the end game is to keep this desk sounding mostly like it does.
(4) I'm inclined to replace the EQ/pre caps. What manufacturer/line makes the best new stock mica/film? Panasonic? Wima? KEMET? There are a few polystyrene (100pf-470pf) I'd likely leave, but the 15pf micas and the .15uf-.68uf tantalums could probably be upgraded, at very least the tantalums. The EQ/pre caps range from 15pf to .68uf, all (supposedly) 50v, and new stock pickings seem to be slim. Should I bother chasing down NOS polystyrene or other NOS film caps, or just go for whatever new stock mica/polyester/PEN/PET/PPS/PP mouser carries, regardless of voltage?
(5) How necessary is external noise control? The underside is just wood, so the shielding isn't complete, but I figure that isn't that important, nor is running it off an isolation transformer or online UPS or both, given its inherently noisy nature. Still, worth asking.
This amount of restoration and modification may seem like putting lipstick on a pig, but, again, this desk will be as much a learning experience as it will a production tool.
Anyway, this has gotten rather too long, far longer than intended--I do apologize!--so I'll close it out here. Any and all comments most welcome.
I'll leave you with a picture of the desk in her former home, she's currently taken apart in mine!
![Electronics Soldering Iron Kit, [Upgraded] Soldering Iron 110V 90W LCD Digital Portable Soldering Kit 180-480℃(356-896℉), Welding Tool with ON/OFF Switch, Auto-sleep, Thermostatic Design](https://m.media-amazon.com/images/I/41gRDnlyfJS._SL500_.jpg)
