I recently did some minor repairs to a fine condition Spectral DMC-12, but have been unable to find a service manual, schematic, or even a user manual.
There are trim pots for gain, and others which are for bias of the output MOSFETs, I assume. There are also dip switches for all of the inputs except the phono section, which appears to have solder pads for loading resistors.
Does anyone have a schematic or manual for the DMC-12, or have knowledge of how to adjust these units?
Thanks!
There are trim pots for gain, and others which are for bias of the output MOSFETs, I assume. There are also dip switches for all of the inputs except the phono section, which appears to have solder pads for loading resistors.
Does anyone have a schematic or manual for the DMC-12, or have knowledge of how to adjust these units?
Thanks!
Hi, I spoke to Spectral yesterday. Even though I was a Spectral dealer in the late 80's / early 90's they will not work on anything older than 2000. When I was a dealer I bought a DMC-6 and DMA-50. I bought my DMC-12 / DMA-90 bout 5 years ago and the phono section was already out. I have to revisit it as the DMC has been sitting in the box for 4 years. My recollection is no output from one phono channel.
Hmm. They are also widely reported to provide absolutely no information on servicing, etc.
If you were interested in trying to diagnose this yourself and had the equipment, you might start by measuring voltages in both channels.
If Spectral didn't give you any leads for a tech, it sounds like you'll have to start calling around.
I've been using mine but decided to make a ventilated top cover because the mosfets generate some heat that I want to get rid of to help stretch out the lifespan of this preamp, since it sounds so good.
If you were interested in trying to diagnose this yourself and had the equipment, you might start by measuring voltages in both channels.
If Spectral didn't give you any leads for a tech, it sounds like you'll have to start calling around.
I've been using mine but decided to make a ventilated top cover because the mosfets generate some heat that I want to get rid of to help stretch out the lifespan of this preamp, since it sounds so good.
You can find the schematics of the DMC-10 at Elektrotanya web site, I hope it helps
https://elektrotanya.com/showresult?what=spectral&kategoria=All&kat2=All
https://elektrotanya.com/showresult?what=spectral&kategoria=All&kat2=All
GKT, does your DMC-12 have the optional phono section?
In the mean time I talked to the service guy at the main Spectral dealer back east and he said when he takes in a Spectral service piece he has to send it to Spectral in California, same place I talked with who wouldn't service mine. He's not allowed to work on them at all. I realized I goofed up when I talked to Spectral and mistakenly said I have a DMC-10 when it is actually a DMC-12. I had a brain fart going back to when I was a dealer and had the DMC-10 in the demo room. I might try calling them again, but am not optimistic about getting through to the tech again. I'm guessing my DMA-90 amp that also needs service is older than my DMC-12. Willy O
GKT,
I don't remember where I got this other photo of a DMC-12, but it has some additional circuitry in between the phono board and the main board. I wonder what that is? I wonder if there was a series 2? I still haven't gotten my DMC12 back out of the box. I also wonder if the coupling caps in the phono circuit (large silver) are paper-in-oil caps. They look like PIO, but maybe they are teflon? I might know more once I get mine back out. I did notice some date codes on components in these pics that are late 1995. Willy O
Attachments
Willy O,
Don't know what those circuit boards are for, but the look like they are perhaps bias circuits for the MOSFETs. Doesn't look at all like stock factory work, and like no other photos I've every seen online. Maybe ask Spectral. Edit... I just found a forum from where that photo came - the new owner had a tech remove it after determining that it was a non-factory modification to the power supply.
Yes, those silver caps look like PIO to me. I left mine in place. If they are anything like the vintage PIOs I have in my parts boxes and in my guitar amps, they are superb, and right on spec.
I've seen photos of DMC-12 units with a black can over the phono sections, but mine doesn't have it and it looks like it never had one.
Greg
Don't know what those circuit boards are for, but the look like they are perhaps bias circuits for the MOSFETs. Doesn't look at all like stock factory work, and like no other photos I've every seen online. Maybe ask Spectral. Edit... I just found a forum from where that photo came - the new owner had a tech remove it after determining that it was a non-factory modification to the power supply.
Yes, those silver caps look like PIO to me. I left mine in place. If they are anything like the vintage PIOs I have in my parts boxes and in my guitar amps, they are superb, and right on spec.
I've seen photos of DMC-12 units with a black can over the phono sections, but mine doesn't have it and it looks like it never had one.
Greg
GKT,
I really need to get my DMC-12 out and try tracing signals through that phono section. I do have a signal generator and an oscilloscope. I'll have to figure out how small of a signal to put into the phono stage. Thanks for figuring out this additional circuitry mystery.
In the late 90's I found an electronics supply store in the LA area, with a 90 year old owner that was still working there since the 60's. He had a surplus of about 10,000 paper in oil capacitors on the shelves that he had acquired from the local aerospace industry over the years. He even had a surplus control panel from one of the Apollo mission capsules there. I examined it and noted which paper in oils went to the moon. They were Gudeman and Vitamin Q Sprague. I relieved him of about 3,000 of these caps and boxes of Allen Bradley Carbon comp resistors for my guitar amp builds. I sold the vast majority of them on ebay years ago, but I still kept the best Vitamin Q's. So I am familiar with PIO's and I have a Sencore LC-102 capacitor analyzer. Willy O
Willy O,
You won't need much signal - 2mV for MM setting and much less for MC setting. It will help you set the gain pots if you do take measurements. My B&K can barely attenuate sufficiently, but my nice Keysight gives me more control. I just bought a reverse RIAA board so I can get meaningful measurements out of my phono sections.
Great story about the stockpile. I grew up in So. Cal., where there were so many aerospace, audio, and other electronics manufacturers, and lots of electronics surplus stores. I was too young to buy much at that time, but your experience reminds me that there must be stockpiles of parts not only in shops, but in the garages of old hobbyists! Wish there was a better clearinghouse for hobbyists to sell/buy out of production parts.
I've got a few hundred PIO caps, and have measured many with my Sencore LC-102 and my other capacitor testors - not one of them has been out of spec. I love using them in my guitar amp builds. On the other hand, I've got thousands of NOS CC resistors, and none of the hundreds I've sample-tested are within spec. I've considered baking the moisture out, but I rarely use CC anymore.
A couple observations on my DMC-12: 1) It sounds wonderful - phono or line section. I have a lot of preamps, and the sound of the Spectral puts it in the top 3, but 2) It runs hot. The mosfets throw off a lot of heat, which is why I made a perforated top cover. I was concerned about picking up RF noise, but that doesn't seem to have happened at all - the perf cover seems to provide the equivalent of a Faraday shield I'm guessing. Only concern now is dust, so I cover it when not in use.
Greg
You won't need much signal - 2mV for MM setting and much less for MC setting. It will help you set the gain pots if you do take measurements. My B&K can barely attenuate sufficiently, but my nice Keysight gives me more control. I just bought a reverse RIAA board so I can get meaningful measurements out of my phono sections.
Great story about the stockpile. I grew up in So. Cal., where there were so many aerospace, audio, and other electronics manufacturers, and lots of electronics surplus stores. I was too young to buy much at that time, but your experience reminds me that there must be stockpiles of parts not only in shops, but in the garages of old hobbyists! Wish there was a better clearinghouse for hobbyists to sell/buy out of production parts.
I've got a few hundred PIO caps, and have measured many with my Sencore LC-102 and my other capacitor testors - not one of them has been out of spec. I love using them in my guitar amp builds. On the other hand, I've got thousands of NOS CC resistors, and none of the hundreds I've sample-tested are within spec. I've considered baking the moisture out, but I rarely use CC anymore.
A couple observations on my DMC-12: 1) It sounds wonderful - phono or line section. I have a lot of preamps, and the sound of the Spectral puts it in the top 3, but 2) It runs hot. The mosfets throw off a lot of heat, which is why I made a perforated top cover. I was concerned about picking up RF noise, but that doesn't seem to have happened at all - the perf cover seems to provide the equivalent of a Faraday shield I'm guessing. Only concern now is dust, so I cover it when not in use.
Greg
Greg,
While in Socal did you ever go to the weekly electronics swap meet at TRW in Redondo Beach? I got a lot of tubes out of there over the years. One other find I had around the same time was walking into a TV repair shop going out of business in Long Beach. He had 20 NOS boxed GZ34 rectifiers branded Valvo, which are of course Mullard/ Phillips GZ34's. 20 bucks each. I should have never sold any of those! And I, too have never found a bad Vitamin Q testing with my LC-102. But, my NOS carbon comp resistors have all been in spec. I have used them in all of my guitar amp builds (about 20 amps, all Vintage Fender Tweeds). And lots of repairs. Of course, the vintage guitar amps had resistor values varying widely anyway, but if they are noisy (as in 100k plate loads) then that is another story.
On another note, the customer I sold the most PIO caps to was Sonny Junior aka Gary Onofrio of harp amp fame. He went on to claim for years that he discovered PIO use in guitar amps and was the only builder "on earth" (direct quote) to use them and claimed to have cornered the world market on them and bought them all up. I had built a couple of prototype amps for him and he didn't even know what a coupling cap was, or anything about paper in oil before I schooled him.
Sounds like we should have an offline discussion about guitar amp building and parts. I'm in Redwing Minnesota. I also have a nice stash of original Mullard / Phillips mustard caps. I'm at odellamps@ gmail.com
Willy O
Hello everybody,
is here someone who knows what kind of capacitor are the 4 big silver cuboids on the dmc12 pcb in the picture above?
I see this type of capacitor in many older Spectral components.
I only know that there are 2 capacitors inside, are they coupled for thermal reasons?
Who ist the manufacturer?
Thank's
Markus
is here someone who knows what kind of capacitor are the 4 big silver cuboids on the dmc12 pcb in the picture above?
I see this type of capacitor in many older Spectral components.
I only know that there are 2 capacitors inside, are they coupled for thermal reasons?
Who ist the manufacturer?
Thank's
Markus