DIY option for spectral amps?

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#41
bear said:
This is somewhat of a cross-post, since rwwear started a thread with the same preamp questions here: http://www.diyaudio.com/forums/solid-state/273391-spectral-dmc-10-repair-help.html#post4302968


suggest this is likely contrary to the "rules" here... since you've been here since 2005, that ought to make sense??

I just happened to recognize the thread topic and clicked on it, was surprised as a result.
Click to expand...

Sorry if there was a conflict. I didn't mean for it to happen. I thought my original post was lost because I couldn't find it here. So I started another thread not knowing the original did get posted. Sorry for the confusion but I do appreciate the help received by you.

Robt.
 
#42
1audio said:
That's the component placement drawing, not the schematic. There is a simplified schematic in the early version of the manual.

The caps are all in power supply locations. The caps were the largest low esr caps available in the late 1970's. This would be a good choice: EEU-FM1H181L Panasonic Electronic Components | P12396-ND | DigiKey Do confirm the fit and the lead spacing. Its similar to what I have used in previous upgrades. The big cap bank is really hard to remove so don't unless you see evidence that you need to.

Most electrolytic caps have paper inside saturated with the dielectric fluid in my experience.

The DMA 50 is very similar in circuitry. What do you need to know about it?

I do not have the schematics but I can replicate them from memory if really necessary.
Click to expand...

Would these be better since they have a longer life?
EEU-FR1H181LB Panasonic Electronic Components | P15373CT-ND | DigiKey
 
#43
Dear Demian,
would you kindly advise me on the dmc-5 preamp? I bought one recently on ebay as a non-working unit. When I checked it, it is oscillating crazy at 21.1KHz square wave 35 volts peak-to-peak. I believe this oscillation occurs in right channel line stages.
I would like to know any schematic on the line stage portion will be great for trouble-shooting. Any advice or comment will be greatly appreciated. Best,
 
#44
I don't have a schematic but could recreate the basic circuit. Major oscillation at such a low frequency is quite unusual. First check the basics like the power supplies. Should be +/- 24V on each channel. Then look for issues in the feedback circuit like an open connection.

The sketch below is the basic form used in all the Spectral preamps and amps. I believe a variation is still used. Enhancements and details will be different from unit to unit. You can usually look at the circuit and see it follows the schematic.
 

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