I don't really know much about JRDG but I owned a pair of Boulder 250AE monoblocks a few yeaars back. They were built like a tank and based on the famous Jensen Op Amp. However, they always had a tinge of graniness to them that never went away, weather they were left on all the time or not. They ran very cool so I'm suspecting that they were biased in the class AB range. It seems like the driver stages developed more heat than the output devices did. Overall, my KSA-80B sounded way better as long as it was left on all the time. The old Krells will still give any modern amp a run for the money.
Am getting the parts together to build a pair of Aleph 1.2's. When completed I suspect they will be the best sounding amps I will ever own. My personal feeling is that with the advancements in high power semiconductors these days, the op amp has lost out and is no longer needed in the high end market. Simpler circuits with modern semiconductors are really hard to beat!
Salt Lake City, UT
I agree that with todays semiconductors and designs opamps are no longer needed. They simply don´t sound so good anymore. That´s the reason there are a few good discrete transistor designs replacing opamps the last years.
Well, I'd ahve to see the schematic before I could tell you. These I.C.'s could also be specially selected to achieve the high peformance that JRDG is known for. I for one would not want to build the Boulder 250's that I had, It was based on a discreet Jensen op amp and was quite complex. For the money that Rowland sells his stuff for and to find out that it is I.C. based really makes me wonder about them. Not that I'C's can't sound good. I guess the point is that if they were THAT good more designers would be using them. I can't remember the last time I saw an I.C. in a piece of high end audio gear's signal path. They are usually put to other tasks such as servo feedback, or power supply regulation.
They are some limitations in integrated circuit design, by instance it's impossible to make a high quality resistor, or a very low resistance "wire". Usually, this limitations are surmounted by use of many transistors and sophisticated circuits. But the fact remains that results are not as perfect as desirable.
Better results can be achieved in "hand made" amplifiers because of the large choice of components and design, but the audible difference is only noticeable on very high quality equipements...
I would have to assume then that you've stated the main reason that the Jensen op-amp was done discreetly, out of seperate parts. This would allow for eiminating the problems you mentioned. I think that if the Boulder had a higher bias output stage that it might have not had the graininess it did. Seems like all the remainder of the amp was all class A.
What are you guys talking about? Rowland uses discrete transistors in his designs.And dozens of TO-3 cased output devices.I've personally met and worked with Jeff on one of his amplifiers. "Lack of overall or nested negative feedback eliminates time domain distortion. Each transistor individually tested and matched for optimum operating characteristics. The large number of high-speed bipolar output transistors provides uncompromising reliability and eliminates the need for electronic protection circuitry. A single voltage amplification stage utilizes field effect transistors(operating in transconductance mode), which increases low-level signal recognition. The absence of capacitors, inductors, fuses and protection circuitry throughout the signal path eliminates the adverse effects of these devices. A specially designed toroidal power transformer is supported by the substantial output stage capability. All critical circuitry is encapsulated in a thermally-conductive epoxy to ensure excellent thermal stability, mechanical integrity and to facilitate ease of service."
Encapsulated circuitry?? Thats all I need to know about JRDG. I'd never buy one just knowing that! You'll never know how many pieces of audio gear I have tossed out cause its encapsulated circuitry failed and the company either no longer exists and or they no longer make the encapsulated part. If the circuitry is that sensitive to thermal issues it seems like more thremal functioning design work is needed. A given unit can thermally stabilize on its own if designed to do that. I also know that SOME manufacturers encapsulate circuits because they copy anothers design and don't want anyone to know. My last encounter with encapsulated circuitry was only two weeks ago. It was an older piece of studio gear that had three modules in it. One failed rendering the unit useless and in the trash it went. The chassis went on living though to become an Aleph L.
Salt Lake City, UT
I've run across cases where manufacturers use epoxy blocks to hide the fact that they were using ICs--usually cheap ones, at that (4558s in one case I remember, basically a dual 741). No, I'm not saying that that's the case with Rowland, as I don't know what they use.
I do sympathize with the service issue, though. Several times I've run across otherwise usable gear brought low by mysterious epoxy blocks that no longer functioned.
I guess I'm crazy.I recently repaired a Robertson 4010 by digging out the potting compound, tracing out the circuit, repairing it, and re-potting it.I also repaired the 'black boxes' on a friend's Kawasaki motorcycle.He put the battery in backwards and fried them.Saved my friend $350 for less than $10 worth of parts and two or three hours worth of labor.Maybe this stuff doesn't bother me as much as it bothers the rest of you.
the dc offset can be solved by using ac feedback around each opamp ,or use a servo around each opamp feedback,or trim individual opamp with a vr
you can check national's website there is application note to parallel the active device
"PS: The Synergy preamp also the AD opamps + Jenson trasformer only! LM317,337 for the regulator!"
Which AD opamp; the AD797? I'm curious...
I still wonder why this part never really caught fire in the audio tech world.
And while we're at it, which manufacturer for the 317/337 regulators - Linear Technologies?