Audio Reasearch
Just out of curiosity, has anyone DIYed any audio reasearch equipment?
From my limited knowledge I know that the brand is pretty good.
I was quite surprised to find schematics on the internet so I was wondering if anyone cloned anything, and if anyone did how does it sound compared to other commercial and DIY stuff?
Thanks
Lawrence
Just out of curiosity, has anyone DIYed any audio reasearch equipment?
From my limited knowledge I know that the brand is pretty good.
I was quite surprised to find schematics on the internet so I was wondering if anyone cloned anything, and if anyone did how does it sound compared to other commercial and DIY stuff?
Thanks
Lawrence
Me too. I cloned an SP3 years ago. Worked fine compared side-by-side with the real thing. For power amps, EC8010 is right about the special output transfomers. ARC certainly doesn't need to use off-the-shelf Hammond transformers. They have the volume and resources to design and subcontract whatever they need. Their schematics are good teaching tools. You can watch the progression through the years, especially in power supply regulation techniques.
Years back, the fact that Bill Johnston made circuitry available truly impressed me. It took me three years to locate a pair of output transformers which whilst wound in New Zealand, appeared to take the Williamson ideals to the limit. They have a three inch stack of super-silicon steel, and end-bells caste in aluminium. They are big, big, big, nearly eight inches deep...
I copied the D76 circuit with the tube-realised screen-voltage regulation via op-amp, ECC81, and a KT88. Just loved the comments re why does a power amplifier have three out-put tubes............Will never forget the first "power-on" experiment when the only loudspeaker I could put my hands on was a tiny unit from a mantle-radio,,,couldn't here nothing - no hum whatsoever,,,the wet-finger trick and the poor speaker-cone reversed itself.....Nearly fifteen years later these self-same copies of AR circuitry are my stile to emotional bliss....[just one hiccup when one of the ICs burst)
I copied the SP10 - yes, two chassis and twelve ECC88s..... fabulous. Elsewhere I have commented upon the seemingly-held belief that this circuit is hard on ECC88s. Not true down-here, but I admit to including a mains-filter in the pre-amp. Voltage-readings meet Bill's figures - the thing justs plays - havn't changed a thing - tubes must be six+++ years old.....
I have even played with his [Johnson's) mosfet regulation circuitry using the IPF830...this works too!!!!
(My SP10-copy followed the modification-circuitry where the upper tube in the line-stage was biased from the output cathode)
My personal thoughts are: Triodes, triodes, triodes....with ultra-linear transformers being really naughty for output-stages....I am really-grossed with Quad circuitry where feed-back is provided via the cathode-winding.........Like a baker's daughter, I have dough in both hands..........Have wound some really-nice OPs for 320Bs SE, yet have gone the other-way for PP triodes with cathode-feed-back. Hey!!!!!! Dinner-calll...............
G
I copied the D76 circuit with the tube-realised screen-voltage regulation via op-amp, ECC81, and a KT88. Just loved the comments re why does a power amplifier have three out-put tubes............Will never forget the first "power-on" experiment when the only loudspeaker I could put my hands on was a tiny unit from a mantle-radio,,,couldn't here nothing - no hum whatsoever,,,the wet-finger trick and the poor speaker-cone reversed itself.....Nearly fifteen years later these self-same copies of AR circuitry are my stile to emotional bliss....[just one hiccup when one of the ICs burst)
I copied the SP10 - yes, two chassis and twelve ECC88s..... fabulous. Elsewhere I have commented upon the seemingly-held belief that this circuit is hard on ECC88s. Not true down-here, but I admit to including a mains-filter in the pre-amp. Voltage-readings meet Bill's figures - the thing justs plays - havn't changed a thing - tubes must be six+++ years old.....
I have even played with his [Johnson's) mosfet regulation circuitry using the IPF830...this works too!!!!
(My SP10-copy followed the modification-circuitry where the upper tube in the line-stage was biased from the output cathode)
My personal thoughts are: Triodes, triodes, triodes....with ultra-linear transformers being really naughty for output-stages....I am really-grossed with Quad circuitry where feed-back is provided via the cathode-winding.........Like a baker's daughter, I have dough in both hands..........Have wound some really-nice OPs for 320Bs SE, yet have gone the other-way for PP triodes with cathode-feed-back. Hey!!!!!! Dinner-calll...............
G
I still have the SP3 knockoff I built -- maybe it was 15 years ago -- I also rehabbed a Dynaco ST70 with the AR boards from the article in Audio Amateur -- it really didn't sound that much better than the ST70 (but I was able to sell it for a fortune on EBay.)
At one time you could just call up Audio Research, mail them a couple bucks and voila manual and schematics.
At one time you could just call up Audio Research, mail them a couple bucks and voila manual and schematics.
ARC fan site
Many of you may be aware of this already. But if you’re not, here is a site dedicated to ARC products. In many cases, schematics and internal photographs are offered. This site is even linked from the real Audio Research site.
ARC fan site
Many of you may be aware of this already. But if you’re not, here is a site dedicated to ARC products. In many cases, schematics and internal photographs are offered. This site is even linked from the real Audio Research site.
ARC fan site
Schematic for mod to SP-10?
Graeme, do you have a schematic of this modded version that you can post or link to? I suspect you are referring to an implementation of Johnson's patented circuit which shows up in the MCP-33. All I have on the SP-10 is what is posted in the site mentioned in my previous post. Thanks.
Graeme, do you have a schematic of this modded version that you can post or link to? I suspect you are referring to an implementation of Johnson's patented circuit which shows up in the MCP-33. All I have on the SP-10 is what is posted in the site mentioned in my previous post. Thanks.
Hi Majestic,
The SP10 effort has stood me in good stead since 1990, though I was fortunate years back to score 75 tubes labelled as Amperex.
These have an open-side anode-structure and for me were far more benevolent than both Telefunken and Siemens examples. These proved far too strident. I have not enjoyed a direct comparison ie a direct substitution whilst maintaining the rest og my gear. The biggest step ever taken forwards was buying 15 inch Tannoy Golds a few years back...........
Brian,
My comment upon grid-supply of course relates to the phono-stage - apologies - memory trying to realise activities from 1987 - 1990.
The original phono-stage required three regulators per channel following the pass-tube regulator. One of these provided a 32v feed to the cascode upper-grids. Driving the grids via the cathode-follower tapping dispenses with the regulator circuitry.
The follower-cathode stands at 164v across 25k. Simple to derive a 32v tap - I used paralleled 39k5 resistors from the cathode seriesed with a selected 4k7 resistor to common. (4k787) The tap directly connected to the cascode-grids, but retaining the 1k grid-stoppers......
The only reference I could locate was a single page from an IAR publication. To quote "Bill Johnson has also improved the sound of his other premiere product, the SP10, which has now become a legend among the European and American press, fully justifying the extravagance of IAR's exclusive first review introducing this significant product to the world. The phono front-end of the SP10 has been slightly restructured, with the bias for the 2nd stage cascode now derived from the 3rd stage cathode-follower, instead of from a separate power supply. This furnishes an extra 12db of local feedback, and DC feedback control, to give a self-regulating operating point. This feedback also gives the lower half of the cascode a higher impedance (easier) load, which improves its linearity and also increases its gain (while the gain of the upper-half is lowered). In addition to improved linearity (lower distortion), there's lower perceived noise modulation (which improves transparency and intertransient silence), as well as lower perceived l/f noise (which would also improve transparency and reduce perceived background grunge)."
Seems I moved further away from the original circuitry than I recalled. I used the warm-up delay muting circuitry from the SP9. I also used a four-section volume control with sections at both input and output of the line-stage. It has proved marvellously quiet and without excess gain when driven from a CD source.
Current thoughts are towards a re-build - perhaps using the E81L triode-connected. (Fabulous curves - NOT an EL81 - close-substitute is the 6686)
Graeme
The SP10 effort has stood me in good stead since 1990, though I was fortunate years back to score 75 tubes labelled as Amperex.
These have an open-side anode-structure and for me were far more benevolent than both Telefunken and Siemens examples. These proved far too strident. I have not enjoyed a direct comparison ie a direct substitution whilst maintaining the rest og my gear. The biggest step ever taken forwards was buying 15 inch Tannoy Golds a few years back...........
Brian,
My comment upon grid-supply of course relates to the phono-stage - apologies - memory trying to realise activities from 1987 - 1990.
The original phono-stage required three regulators per channel following the pass-tube regulator. One of these provided a 32v feed to the cascode upper-grids. Driving the grids via the cathode-follower tapping dispenses with the regulator circuitry.
The follower-cathode stands at 164v across 25k. Simple to derive a 32v tap - I used paralleled 39k5 resistors from the cathode seriesed with a selected 4k7 resistor to common. (4k787) The tap directly connected to the cascode-grids, but retaining the 1k grid-stoppers......
The only reference I could locate was a single page from an IAR publication. To quote "Bill Johnson has also improved the sound of his other premiere product, the SP10, which has now become a legend among the European and American press, fully justifying the extravagance of IAR's exclusive first review introducing this significant product to the world. The phono front-end of the SP10 has been slightly restructured, with the bias for the 2nd stage cascode now derived from the 3rd stage cathode-follower, instead of from a separate power supply. This furnishes an extra 12db of local feedback, and DC feedback control, to give a self-regulating operating point. This feedback also gives the lower half of the cascode a higher impedance (easier) load, which improves its linearity and also increases its gain (while the gain of the upper-half is lowered). In addition to improved linearity (lower distortion), there's lower perceived noise modulation (which improves transparency and intertransient silence), as well as lower perceived l/f noise (which would also improve transparency and reduce perceived background grunge)."
Seems I moved further away from the original circuitry than I recalled. I used the warm-up delay muting circuitry from the SP9. I also used a four-section volume control with sections at both input and output of the line-stage. It has proved marvellously quiet and without excess gain when driven from a CD source.
Current thoughts are towards a re-build - perhaps using the E81L triode-connected. (Fabulous curves - NOT an EL81 - close-substitute is the 6686)
Graeme
Graeme,
Thanks, that explains it. Yes this is the circuit that I was thinking of (U.S. Patent 4,647,872), although I didn't realize it had been applied to later versions of the SP-10. Does this change define the MKII version? I would have thought that the additional local feedback would have necessitated changes to the RIAA feedback loop components.
The MCP-33 uses this feedback cascode topology, although the lower tube is in modified grounded-grid configuration with MC cartridge output applied to the cathode.
Thanks, that explains it. Yes this is the circuit that I was thinking of (U.S. Patent 4,647,872), although I didn't realize it had been applied to later versions of the SP-10. Does this change define the MKII version? I would have thought that the additional local feedback would have necessitated changes to the RIAA feedback loop components.
The MCP-33 uses this feedback cascode topology, although the lower tube is in modified grounded-grid configuration with MC cartridge output applied to the cathode.
It really is negative feedback
Feedback from the upper plate to the upper grid (through a non-inverting CF) is truly negative, since the grid and plate are in inverted signal phase relative to one another. That would be true even if this tube were not sitting on a lower tube in cascode. It's similar conceptually to putting a resistor directly from plate to grid, or to the Miller capacitance as a form of high-frequency negative feedback across those two electrodes.
It is useful, especially for more complex feedback loops, to count polarity inversions, starting anywhere in a feedback loop and going around the loop counting signal inversions until you return were you started. If the inversion count is odd (the negatives multiply to a net negative result), the feedback is negative. If it's even (the negatives multiply and cancel the negative sign), the feedback is positive. Polarity from grid to plate is inverting (negative), from grid to cathode positive, and from cathode to plate positive. Ditto for bipolar transistors and FETs.
Feedback from the upper plate to the upper grid (through a non-inverting CF) is truly negative, since the grid and plate are in inverted signal phase relative to one another. That would be true even if this tube were not sitting on a lower tube in cascode. It's similar conceptually to putting a resistor directly from plate to grid, or to the Miller capacitance as a form of high-frequency negative feedback across those two electrodes.
It is useful, especially for more complex feedback loops, to count polarity inversions, starting anywhere in a feedback loop and going around the loop counting signal inversions until you return were you started. If the inversion count is odd (the negatives multiply to a net negative result), the feedback is negative. If it's even (the negatives multiply and cancel the negative sign), the feedback is positive. Polarity from grid to plate is inverting (negative), from grid to cathode positive, and from cathode to plate positive. Ditto for bipolar transistors and FETs.
As far as i remember the quality of the 32v had profound effect upon the sound. Eventually i moved to a separate source and even tried batteries. Also replaced the opamp 'regulators' as they really didn't sound that great. Not to mention that eventually went for single triodes rather than paralleled 
And never used the fets - don't know if that had a real effect upon tube life.
So i guess my SP10 was a rather loose clone ...
And never used the fets - don't know if that had a real effect upon tube life.So i guess my SP10 was a rather loose clone ...
These FETs are protective at start-up, but I'm a bit concerned about their residual non-linear capacitance. Granted, the FET is bootstrapped across the grid-cathode pins of the CF and there's a fixed 620pF cap in parallel too, but still...
Also, the 32V upper grid bias value sets a pretty low plate voltage on the lower tube. I would feel more comfortable with a little more breathing room down there. Regarding the quality of that supply, it makes sense that the PS would affect the sound at these low signal levels. Since current draw by the grids is neligible, why not put a large resistor (say 100K) in series with the 32V supply, with a nice polypropylene shunt cap to ground just before the grid stoppers? This RC filter would clobber any noise in the audio band. Start-up sequencing might be a problem then; I don't know. Or, you could implement the feedback trick described above.
Also, the 32V upper grid bias value sets a pretty low plate voltage on the lower tube. I would feel more comfortable with a little more breathing room down there. Regarding the quality of that supply, it makes sense that the PS would affect the sound at these low signal levels. Since current draw by the grids is neligible, why not put a large resistor (say 100K) in series with the 32V supply, with a nice polypropylene shunt cap to ground just before the grid stoppers? This RC filter would clobber any noise in the audio band. Start-up sequencing might be a problem then; I don't know. Or, you could implement the feedback trick described above.
Audio Research clones
The resources at Manfred Persson's site are impressive - it really is a labour of love!
Of all the ARC preamps on the arcdb site, the documentation on the SP-11 is the most useful to the cloner. Not only are the DC voltages at all critical nodes marked in, but the schematic is very clearly legible (unlike the one for the SP-10, for instance).
A while back I seriously considered making an SP-11 for myself, but I don't think I will ever get around to it - I will probably tackle one of Allen Wright's preamps instead. I did, however, put together a set of notes on the SP-11's circuits which are on my website (here) and which may be of interest. I also have tentative PCB foils for both the preamp circuits and the PSU. These are functionally the same as the ARC originals, but not identical (and not completely checked).
I haven't ruled out a clone of the Classic 30 in the not-too-distant future, though...
Alex
The resources at Manfred Persson's site are impressive - it really is a labour of love!
Of all the ARC preamps on the arcdb site, the documentation on the SP-11 is the most useful to the cloner. Not only are the DC voltages at all critical nodes marked in, but the schematic is very clearly legible (unlike the one for the SP-10, for instance).
A while back I seriously considered making an SP-11 for myself, but I don't think I will ever get around to it - I will probably tackle one of Allen Wright's preamps instead. I did, however, put together a set of notes on the SP-11's circuits which are on my website (here) and which may be of interest. I also have tentative PCB foils for both the preamp circuits and the PSU. These are functionally the same as the ARC originals, but not identical (and not completely checked).
I haven't ruled out a clone of the Classic 30 in the not-too-distant future, though...
Alex
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