Speaking of Gainclones, has anyone ever tried to clone the JOB Circuit?
Here is a link to their website:
http://www.jobsys.com/products.htm
I know that the 47 Labs Gaincard is expensive and has garnered some good reviews so a clone of the same circuit is very interesting. But come on, given the chance to clone the JOB circuit used in the Goldmund Millenium amplifier (and other Goldmund amps), priced at $35,000, one would think that this would be a worthwile effort as well.
link to goldmund products using the JOB circ.
http://www.goldmund.com/old/Millennium/intro.html
http://www.goldmund.com/V4/catalog2/products/ultimate/29.htm
Plus the JOB is just as small as the GainCard, so it doesn't look too tough from a complexity viewpoint. Am I missing something? Does anyone have the circuit? A photo of the insides? Any JOBclones out there?
Here is a link to their website:
http://www.jobsys.com/products.htm
I know that the 47 Labs Gaincard is expensive and has garnered some good reviews so a clone of the same circuit is very interesting. But come on, given the chance to clone the JOB circuit used in the Goldmund Millenium amplifier (and other Goldmund amps), priced at $35,000, one would think that this would be a worthwile effort as well.
link to goldmund products using the JOB circ.
http://www.goldmund.com/old/Millennium/intro.html
http://www.goldmund.com/V4/catalog2/products/ultimate/29.htm
Plus the JOB is just as small as the GainCard, so it doesn't look too tough from a complexity viewpoint. Am I missing something? Does anyone have the circuit? A photo of the insides? Any JOBclones out there?
If you ask me, judging from the picture of the circuit, I would throw out a wild guess of some class-D circuit. This isn't based on any hard facts or data, but simply from looking at the picture of the board.
I see two power chips per channel (don't know what they are, transistors, power op-amps, something else totally different, whatever) very few components, and a central heatsink. Its the central heatsink that has me thinking a class-D. If I recall from, who was it? National or Analog Devices that sells the class-D chipset, that the controller chip could get hot. The biggest argument against this theory is the lack of chokes, but they could easily be on the bottom of the board. (Also the relatively low visible component count, but again, only the top of the board is visible)
Am I completely off my rocker with this thought?
I see two power chips per channel (don't know what they are, transistors, power op-amps, something else totally different, whatever) very few components, and a central heatsink. Its the central heatsink that has me thinking a class-D. If I recall from, who was it? National or Analog Devices that sells the class-D chipset, that the controller chip could get hot. The biggest argument against this theory is the lack of chokes, but they could easily be on the bottom of the board. (Also the relatively low visible component count, but again, only the top of the board is visible)
Am I completely off my rocker with this thought?
i don't think class D for JOB
I'm thinking the JOB amp design just a very simple, highly tweaked/tuned, fairly conventional circuit. They hide it because they don't want you to figure that out.
Bryston power amp designs products are often held up as an example of a fairly conventional circuit that has been tuned and tweaked well (I'm not so sure about "conventional" after looking at the output stage). You can go to the Brsyton web site and see the schematic. However, I have yet to see or hear about any Brsyton clones. And, folks seem to like the products.
Class D? I really doubt it. Did you really want us to tell you if you're off your rocker
So, who has one to cut open, take pictures and report?
mlloyd1
I'm thinking the JOB amp design just a very simple, highly tweaked/tuned, fairly conventional circuit. They hide it because they don't want you to figure that out.
Bryston power amp designs products are often held up as an example of a fairly conventional circuit that has been tuned and tweaked well (I'm not so sure about "conventional" after looking at the output stage). You can go to the Brsyton web site and see the schematic. However, I have yet to see or hear about any Brsyton clones. And, folks seem to like the products.
Class D? I really doubt it. Did you really want us to tell you if you're off your rocker
So, who has one to cut open, take pictures and report?
mlloyd1
Schaef said:
Here is the Circ. Pic
Here is the image. I don't know that I would call it a switching amp, but it does look like there might be some stuff on the back of the board.
Here is the image. I don't know that I would call it a switching amp, but it does look like there might be some stuff on the back of the board.
An externally hosted image should be here but it was not working when we last tested it.
heatsink
What's the big heatsink in the middle of the board for -- regulators? Otherwise it looks like a typical discrete amplifier, probably MOSFET given Goldmund's heritage and the fact that MOSFET amplifiers can be made very simple. I know Redgum's amplifiers, for example, came right out of a circuit book and have only 2 gain stages and minimal feedback (from the horses mouth). They've tweaked and refined it, of course.
What's the big heatsink in the middle of the board for -- regulators? Otherwise it looks like a typical discrete amplifier, probably MOSFET given Goldmund's heritage and the fact that MOSFET amplifiers can be made very simple. I know Redgum's amplifiers, for example, came right out of a circuit book and have only 2 gain stages and minimal feedback (from the horses mouth). They've tweaked and refined it, of course.
Well, as far as I recall, the job circuit has been patented by a group of students, and licensed to Goldmund. From what I've read for yonks, Job seems to be a particular topology, very fast they say . It's always encapsulated in a small metallic case and potted. Seems to me that it has been produced in several versions, one for preamps, and others for amps, that should withstand higher currents/voltages (hence a heatsinked case as shown). Maybe these versions also include VAS ??. From photos I've seen in magazines years ago, the preamp version has a "normal" look (no heatsinks/fins).
But I've never never seen a schematic of it...
The other thing approching (but with other performances/figures) are Marantz's HDAM modules,and scheamtics can be found...
Sorry not to help at all
Edit : ANd it's absolutely not Class D. To be chosen between A/AB/B, but not more
. It's always encapsulated in a small metallic case and potted. Seems to me that it has been produced in several versions, one for preamps, and others for amps, that should withstand higher currents/voltages (hence a heatsinked case as shown). Maybe these versions also include VAS ??. From photos I've seen in magazines years ago, the preamp version has a "normal" look (no heatsinks/fins). But I've never never seen a schematic of it...
The other thing approching (but with other performances/figures) are Marantz's HDAM modules,and scheamtics can be found...Sorry not to help at all
Edit : ANd it's absolutely not Class D. To be chosen between A/AB/B, but not more
JOB Circuit?
Hi , My best guess is that it is a potted module comprised of SMD parts with a yellowish cooler on top driving MOSFETs or bipolar output transistors....
I can no longer stand that hilarious high end talk on Goldmund's and Job's website. Became to sceptical after all those years....
Hi , My best guess is that it is a potted module comprised of SMD parts with a yellowish cooler on top driving MOSFETs or bipolar output transistors....
I can no longer stand that hilarious high end talk on Goldmund's and Job's website. Became to sceptical after all those years....
i had a thought, maybe the amp is based around a simple driver IC like the TDA7250. that would explain the heatsink on the central IC and of coure the small component count
check it out here: http://www.st.com/stonline/bin/hilite.exe?file=/stonline/books/ascii/docs/1472.htm&words=TDA7250
check it out here: http://www.st.com/stonline/bin/hilite.exe?file=/stonline/books/ascii/docs/1472.htm&words=TDA7250
The ferrite bead makes me think its mosfet for sure, and probably class AB. The output devices look like 2SK1058 & its girlfriend whose number i don't remember. If it was class D it would probably be made with ir mosfets. Under the heatsink... I don't expect a discrete input stage and the new drivers are too new, what's under the heatsink? New technology delivering 5 MHz... wow, sure those who have played with the OPA635 will perceive the increase in speed 
...
I bet there is an opamp there, it just fits (i don't see an input stage with 4 input pair transistors + 2 Vas transistors + 4 driver transistors there (Assuming no ccs load of either vas or input stage and no current mirrors for the input stage, that would climb to 16 transistors.)
EDIT: 0.003 % seventh and tenth harmonic?
That's more than 1% THD with (n-1)^2 weighting! Terrible! I don't know how to do worse... well we could have 10% tenth harmonic...
... I bet there is an opamp there, it just fits (i don't see an input stage with 4 input pair transistors + 2 Vas transistors + 4 driver transistors there (Assuming no ccs load of either vas or input stage and no current mirrors for the input stage, that would climb to 16 transistors.)
EDIT: 0.003 % seventh and tenth harmonic?
That's more than 1% THD with (n-1)^2 weighting! Terrible! I don't know how to do worse... well we could have 10% tenth harmonic...
Re: JOB Circuit?
That's just a cover, on top on some TO92 transistors.
The newer Goldmund 390 uses full SMD parts and no longer have this mysterious heatsink.
I was thinking the same, smd module board underleaf yellow heatsink......... until I opened my old SRA and checked closely.Elso Kwak said:Hi , My best guess is that it is a potted module comprised of SMD parts with a yellowish cooler on top driving MOSFETs or bipolar output transistors....
I can no longer stand that hilarious high end talk on Goldmund's and Job's website. Became to sceptical after all those years....
That's just a cover, on top on some TO92 transistors.
The newer Goldmund 390 uses full SMD parts and no longer have this mysterious heatsink.
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