Does anyone have any ideas into a DIY option for cables/zobel to use with spectral equipment. I'm looking more for network recommendations than cable. I've purchased some older gear (DMC-10 and DMA-50), and don't feel like dropping the silly cash required for the MIT cables. Of course their marketing has scared me just enough that I would rather not have the amp oscillate into oblivion either 😀
I don't think they are known for oscillation... but read this:
http://uk.geocities.com/cyrilb2@btinternet.com/cable_3.html
will probably give you peace of mind...
_-_-bear
http://uk.geocities.com/cyrilb2@btinternet.com/cable_3.html
will probably give you peace of mind...
_-_-bear
Thanks for the link! I'll read up and see what he has to say. It's just a bit irksome that they are "insistent" on using MIT cables with their equipment. Especially on older products, the last thing you want to do is cause some harm. Other than that, I think they are some of the best sounding amps out there and I need a "non diy" system as well so the tunes are always flowing 😉
I doubt that you have to use MIT...
Many people have Spectral and use other cables.
Regardless the article solves the underlying problem - if there is one.
DIY amps, fwiw, can be just as reliable as a Spectral - depends on the amp and the user no matter what design it is.
Fwiw the designer of the Spectral amps participates here...
_-_-bear
Many people have Spectral and use other cables.
Regardless the article solves the underlying problem - if there is one.
DIY amps, fwiw, can be just as reliable as a Spectral - depends on the amp and the user no matter what design it is.
Fwiw the designer of the Spectral amps participates here...
_-_-bear
Yeah, I read that paper...very interesting! I had no idea that reflections based on quarter wave theory were to blame. It also made me wonder what is going on with the higher end MIT boxes that tout having 28 poles. It seems as if there wouldn't be much (if any) of a benefit over a standard network like the author describes in the paper.
I didn't understand any of the modeling specifics he was talking about, but surprisingly got the rest of it. I now have 100% confidence in using some standard cables with the addition of a C/R network at the speaker end of things.
Of course it also now makes sense that Spectral amps could be more prone to serious issues (if RF reflections were taking place) since the amps operate so linearly into the Mhz range.
I cracked open the DMA-50 last night because I thought spectral didn't utilize any type of network on their outputs (and relied solely on the MIT cables). Much to my surprise there was a network across the outputs. That is good to know as it seems from the paper that having one inside the amp and one at the speaker terminals was more efficient than just having the network at the speaker terminals.
As for DIY solid state...i'm completely ignorant. I built one of the xen variations, but as a rule, solid state eludes me. I'm just a good craftsman, not an engineer 😀 Most of my DIY amp building has been tube amps as they are simpler as a rule and I "get" them. I'm not against building another solid state amp, but again...the point behind buying this gear was to have a "tweak free" setup so I always have something running.
Finally, I didn't realize that the designer of the Spectral gear was active here. Is it Keith Johnson you're referring to? I'm not super familiar with their design team, but had read that he was on board.
Thanks again for the link!
**digression**
One thing that also draws me to Spectral products (other than sounding amazing) is the firm grounding in science as opposed to voodoo. I got sucked into the whole realm of psycho-acoustics, and it took me years to drag myself out. From now on, I'd like to concentrate more on the measurable than the hyperbole. Audio engineering (as any engineering) is an art for sure. But it's the creative thought of the design itself that I feel lends toward better designs, better sound, etc. Not which brand of capacitor you are using (not counting measurable properties of said capacitor).
I didn't understand any of the modeling specifics he was talking about, but surprisingly got the rest of it. I now have 100% confidence in using some standard cables with the addition of a C/R network at the speaker end of things.
Of course it also now makes sense that Spectral amps could be more prone to serious issues (if RF reflections were taking place) since the amps operate so linearly into the Mhz range.
I cracked open the DMA-50 last night because I thought spectral didn't utilize any type of network on their outputs (and relied solely on the MIT cables). Much to my surprise there was a network across the outputs. That is good to know as it seems from the paper that having one inside the amp and one at the speaker terminals was more efficient than just having the network at the speaker terminals.
As for DIY solid state...i'm completely ignorant. I built one of the xen variations, but as a rule, solid state eludes me. I'm just a good craftsman, not an engineer 😀 Most of my DIY amp building has been tube amps as they are simpler as a rule and I "get" them. I'm not against building another solid state amp, but again...the point behind buying this gear was to have a "tweak free" setup so I always have something running.
Finally, I didn't realize that the designer of the Spectral gear was active here. Is it Keith Johnson you're referring to? I'm not super familiar with their design team, but had read that he was on board.
Thanks again for the link!
**digression**
One thing that also draws me to Spectral products (other than sounding amazing) is the firm grounding in science as opposed to voodoo. I got sucked into the whole realm of psycho-acoustics, and it took me years to drag myself out. From now on, I'd like to concentrate more on the measurable than the hyperbole. Audio engineering (as any engineering) is an art for sure. But it's the creative thought of the design itself that I feel lends toward better designs, better sound, etc. Not which brand of capacitor you are using (not counting measurable properties of said capacitor).
Spectral Cables
I acquired as set of old MIT cables and opened up the transmission boxes because something was rattling around in there. The network had come off and was flying around.
It was an RC to ground (zobel) but I forget the values. I may have pictures somewhere if it will help. I recall it was one of those old transparent caps. Anyway, sorry I cannot help more.
I acquired as set of old MIT cables and opened up the transmission boxes because something was rattling around in there. The network had come off and was flying around.
It was an RC to ground (zobel) but I forget the values. I may have pictures somewhere if it will help. I recall it was one of those old transparent caps. Anyway, sorry I cannot help more.
Thanks a lot for the offer, but it's not necessary at this point. The paper bear posted a link to put my mind at ease on that front. And spectral actually has specific cables that MIT manufactures for them, so I bet the networks are different inside.
I've seen photos online somewhere of the inside of an MIT cable. Were those your pictures?
I've seen photos online somewhere of the inside of an MIT cable. Were those your pictures?
enochRoot said:
No problem. I did see these pics recently and wondered if I had posted or not. So the answer is "I forget!"
Hi Enochroot,
No Kieth Johnson afaik is not here...
I think that because of the wider bandwidth of the Spectral the signals that might bother most amplifiers will not, but signal of higher frequency might... guessing here.
lgreen, post 'em up here, would like to see the innards...
_-_-bear
No Kieth Johnson afaik is not here...
I think that because of the wider bandwidth of the Spectral the signals that might bother most amplifiers will not, but signal of higher frequency might... guessing here.
lgreen, post 'em up here, would like to see the innards...
_-_-bear
wow. those aren't cheap, and yet they have cheap metal film resistors, and what looks like regular solid core hookup wire with cheap switches. so much for exotic cable being under under the thick core and huge boxes.
I designed the DMC-10 and the DMA-50. Keith took over after I left. The core principles have not changed.
The really wide bandwidth makes them more sensitive to the capacitive loading. If you add a resistor or RC in parallel with the load it will be stable. A pure capacitance between .05 uF and about 2 uF will make them oscillate (and many other amps) A 5W 100 Ohm resistor will work wonders for the stability and the sound. The article will help explain why.
The really wide bandwidth makes them more sensitive to the capacitive loading. If you add a resistor or RC in parallel with the load it will be stable. A pure capacitance between .05 uF and about 2 uF will make them oscillate (and many other amps) A 5W 100 Ohm resistor will work wonders for the stability and the sound. The article will help explain why.
enochRoot said:
Yes. High-end stuff is often disappointing under the lid. Still, don't forget these components terminate the cable at RF and are not in series with the signal.
Thanks for the reply Demian. And thanks for the wonderful designs! I did read the article and it was very helpful in understanding what exactly is going on (if a bit surprising).
Would you mind emailing me off-forum as I have another question or two for you? it would probably be best not to post the questions here.
Actually, I do have one other question for you that would be fine to post. If a DMA-50 was damaged do to a runaway oscillation, the amp would cease to work, correct? IE: is there any way an amp can be damaged without knowing it? Would the sound just be degraded? I was under the impression that an amp is either working, or ruined because you blew an output device.
Would you mind emailing me off-forum as I have another question or two for you? it would probably be best not to post the questions here.
Actually, I do have one other question for you that would be fine to post. If a DMA-50 was damaged do to a runaway oscillation, the amp would cease to work, correct? IE: is there any way an amp can be damaged without knowing it? Would the sound just be degraded? I was under the impression that an amp is either working, or ruined because you blew an output device.
1audio said:
In my experience those amps are pretty durable. The output transistors (Hitachi's) are nearly bulletproof. If it is oscillating the output network would heat up and the heatsinks will get hot but no other bad side effects. It was designed to deliver full power to 500 KHz. If the components were unable to handle that then we would have lots of smoke in testing.
The problems with that amp are: first, thermal cycling will cause the connections between the outputs and the circuit board to get flakey. They may need to be resoldered. Secondthe bias may have drifted. Its open loop so it should be checked. I don't remember the settings.
FET failures are easy to spot, the gate current goes up. If there is a measurable voltage across the gate resistor the device is blown. However if its working and doen't have offset it should be fine. The heatsinks will run warm.
The preamp is even simpler. The output protection circuit is its problem. Just remove the LM339 and it will sound better. As usual thats a fix for the earlier preamp that was not necessary for this generation.
The problems with that amp are: first, thermal cycling will cause the connections between the outputs and the circuit board to get flakey. They may need to be resoldered. Secondthe bias may have drifted. Its open loop so it should be checked. I don't remember the settings.
FET failures are easy to spot, the gate current goes up. If there is a measurable voltage across the gate resistor the device is blown. However if its working and doen't have offset it should be fine. The heatsinks will run warm.
The preamp is even simpler. The output protection circuit is its problem. Just remove the LM339 and it will sound better. As usual thats a fix for the earlier preamp that was not necessary for this generation.
enochRoot said:
If I see the schematic diagram of this Spectral devices, I can about simulation find out exactly boucherot- (zobel) network values for recommendation. Do you have schematic diagrams of this spectral devices?
I have now quickly only found this one in the web:
http://stefano.marchiori.eu/download/Spectral-DMC10-Manuale.pdf
http://www.smugmug.com/popular/Electronics/1/50655530_o97n9#50655530_o97n9
Since the circuit looks simple, you could even draw a circuit diagram (schematic) and sending to me as pdf attachement.
Demian: Thanks for the info! I just checked the DC offset (I figured it was a good starting point) and it came out to 13mV left and 72mV right. I assume i'm going to need to adjust the right channel? If you don't remember the correct bias, is there any way for me to measure the L channel and shoot for that bias since the offset is so low? Which trim pots are used for this?
tiefbassuebertr: Thanks for the offer! No idea on the schematic. I'll see if I can track it down somewhere.
tiefbassuebertr: Thanks for the offer! No idea on the schematic. I'll see if I can track it down somewhere.
Ok, I just measured the voltage across the FET resistors (both gate and source since I wasn't 100% sure which was which), and had readings of about 112mV on each of one (the one I believe to be gate). On the other resistors for what I'm assuming is the source, one was around 185mV and the other was around 212mV. Are these values acceptable and "almost zero", or are we looking for a 0V reading?
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