Input stage Coupling capacitors block DC offset voltages that may come from the signal source, to keep DC off the input tube's grid.
Low pass filter caps (series R, and cap to ground) that reduce the slew rate and bandwidth of the amplifier input, so that a square wave is less likely to show "ringing" and "overshoot" at the amplifier output, are a completely different thing.
Do not confuse the two. They are not the same.
If you modify either of these, understand which characteristic you are modifying.
Low pass filter caps (series R, and cap to ground) that reduce the slew rate and bandwidth of the amplifier input, so that a square wave is less likely to show "ringing" and "overshoot" at the amplifier output, are a completely different thing.
Do not confuse the two. They are not the same.
If you modify either of these, understand which characteristic you are modifying.
Bill's stated reason for the input filtering (which was not used in their amplifiers before the D76A), was that
an amplifier should not be forced to do what it cannot do. I would say that, judging by the considerable
improvement in sound just by the removal of the input coupling capacitor, the amplifier indeed can do it.
an amplifier should not be forced to do what it cannot do. I would say that, judging by the considerable
improvement in sound just by the removal of the input coupling capacitor, the amplifier indeed can do it.
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An outboard phono preamp that does not have the modified subsonic filter (modified from the original RIAA spec), and a record with a record warp, is not going to sound very good.
Overload.
The coupling cap might lessen that problem too.
For today's modern signal sources, that sometimes have ultrasonic spurs, and switching transients, no matter how small . . .
A low pass filter might be a good thing.
Hi Fi and Stereo playback systems, are just that, a system.
Positive Synergy
Negative Synergy
Pick one
Overload.
The coupling cap might lessen that problem too.
For today's modern signal sources, that sometimes have ultrasonic spurs, and switching transients, no matter how small . . .
A low pass filter might be a good thing.
Hi Fi and Stereo playback systems, are just that, a system.
Positive Synergy
Negative Synergy
Pick one
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Hi
Here is the scans of the danish magazine High Fidelity 1977.
Fun fact: the unit pictured on the cover is the unit I own.
Erik
Here is the scans of the danish magazine High Fidelity 1977.
Fun fact: the unit pictured on the cover is the unit I own.
Erik
Reply to the last three posts
Hello there,
First of all thanks for the prompt response regarding the article Erik🙂
Input filter:
Totally agree low- and high- pass are two different things.
As the grids of the input tubes refer to ground (and hence the DC blocking input capacitor literally only blocks DC, it has nothing to do with input stage biasing), I have in mind to to have two sets of input terminals - one AC-coupled and one DC-coupled (my source does not generate DC) and there is enough iron in the output transformers (just finished measuring them) that they will not have an issue with core saturation at low frequencies (AND the circuit is LF stable).
I will do this mainly because the input coupling capacitor is the main source of not constant group delay at low frequencies.
Regarding the input bandwidth limitation, I tend to find that this is most often included just to give a visually "nice" behavior of square waves on an oscilloscope. From most of my experience, I prefer the sound where the input is less bandwidth limited and hence has a little more leading edge to square waves. Matti Ottala in the 70's argued a lot for bandwidth limiting the input of the amplifier (while leaving the amplifier itself more wideband - in that way hindering slew induced distortion). Personally I do not find these theories to align well with listening experiences; I prefer to have a total wider bandwidth. The closed loop behavior of the D150 is by itself completely stable and, for this reason, I intend to open up the bandwidth of the input so that it is more aligned with that of the dominant pole determined by the overall global feedback loop.
In general I literally do not intend to modify the amplifier very much - BUT specifically the input bandwidth limitation does capture my attention when considering both the design of the total amplifier (combined with my experience with input bandwidth limitation in amplifiers in general - and the audible effects of these).
I appreciate much all the feedback, thanks & BR
It will still be some time (regretfully) before I have enough material of interest to share some of my progress. I do work in quite a thorough manner - and so eventually I will be able to provide both simulations, calculations and measurements of things like what we have discussed here.
Morten
Hello there,
First of all thanks for the prompt response regarding the article Erik🙂
Input filter:
Totally agree low- and high- pass are two different things.
As the grids of the input tubes refer to ground (and hence the DC blocking input capacitor literally only blocks DC, it has nothing to do with input stage biasing), I have in mind to to have two sets of input terminals - one AC-coupled and one DC-coupled (my source does not generate DC) and there is enough iron in the output transformers (just finished measuring them) that they will not have an issue with core saturation at low frequencies (AND the circuit is LF stable).
I will do this mainly because the input coupling capacitor is the main source of not constant group delay at low frequencies.
Regarding the input bandwidth limitation, I tend to find that this is most often included just to give a visually "nice" behavior of square waves on an oscilloscope. From most of my experience, I prefer the sound where the input is less bandwidth limited and hence has a little more leading edge to square waves. Matti Ottala in the 70's argued a lot for bandwidth limiting the input of the amplifier (while leaving the amplifier itself more wideband - in that way hindering slew induced distortion). Personally I do not find these theories to align well with listening experiences; I prefer to have a total wider bandwidth. The closed loop behavior of the D150 is by itself completely stable and, for this reason, I intend to open up the bandwidth of the input so that it is more aligned with that of the dominant pole determined by the overall global feedback loop.
In general I literally do not intend to modify the amplifier very much - BUT specifically the input bandwidth limitation does capture my attention when considering both the design of the total amplifier (combined with my experience with input bandwidth limitation in amplifiers in general - and the audible effects of these).
I appreciate much all the feedback, thanks & BR
It will still be some time (regretfully) before I have enough material of interest to share some of my progress. I do work in quite a thorough manner - and so eventually I will be able to provide both simulations, calculations and measurements of things like what we have discussed here.
Morten
to Erik
Hi Erik,
Amazing - so you are lucky to have had it from new!
I was wondering, I seem to recall that there was an Erik Larsen at high fidelity towards the final years?
/Morten
Hi Erik,
Amazing - so you are lucky to have had it from new!
I was wondering, I seem to recall that there was an Erik Larsen at high fidelity towards the final years?
/Morten
Hi Morten,
I didn't have the amplifier from new, but I can tell from the unique crinkle finish on the output transformers that the one tested is mine.
I am not connected to "High Fidelity" in any way.
Best regards
Erik
I didn't have the amplifier from new, but I can tell from the unique crinkle finish on the output transformers that the one tested is mine.
I am not connected to "High Fidelity" in any way.
Best regards
Erik
I heard a friend’s D150 several times in the mid-1970s powering his Fulton E-Modular speakers. I recall being very impressed with the sound quality especially the inner detail and dynamics. That said, when I look at the schematic and then look at the photo showing the interior layout, I realize the D150 is not the amp for me. That amp is a beast! More complicated in design and construction for me to be able to maintain on my own. Nevertheless, for someone who has the skills and patience to maintain it, I am sure the D150 will provide much musical pleasure.
Reply to the last two posts
Erik: OK, thanks for the info
Salectric: Frankly speaking, it is not pleasurable to work with because it is build like a tank and things are not easily accessable - I like the amp, but find it extremely cumbersome to handle 🙂
Erik: OK, thanks for the info
Salectric: Frankly speaking, it is not pleasurable to work with because it is build like a tank and things are not easily accessable - I like the amp, but find it extremely cumbersome to handle 🙂
Dave Gillespie did a great writeup on a D115 over at AudioKarma. It's a must read for anyone working on one of these great amps. Search the tube forum for
Parts and Pieces: A True ARC Mystery
BillWojo
Parts and Pieces: A True ARC Mystery
BillWojo
To BillWojo
Hello Bill,
Thanks for pointing me there - just looked swiftly around in the thread; am it seems indeed a more than worthwhile read, appreciated.
A ltlle "touched" by this, I am tempted to express a humble attempt to hint at the "more than what you see on the surface" description of what I am going through respectfully renovation exactly D-150:
I am an electronics engineer at the university level, professionally worked in the audio industry for many years (now I am in the communications industry), loong time audiophile (in the service of being a music lover). Lucky to have personal friends in the high end whom develop Internationally acclaimed tube equipment. As such, the subject of tube amplifiers is daily on my mind and dialog with people whom takes a professional living from it.
The slowly "crawling in" under the skin of the designer of this amp through initially only the schematics and parts list makes it almost like knowing the designer personally - no wonder Audio Research become what it is (or was?); it is so well deserved.
The subleties and insight (and innovation) going into this amp evidently shows how Bill was an extraordinary mind - there is an in-depth understanding of so many fundamental, but well hidden aspects of amplifier design that you simple have to acknowledge the mastery (trying not to become boring with too many details, some of his patents are indicating just parts of this insight) - internal impedance levels, drive levels, balance/"harmony" to the circuits, the guts to go your own way not fearing inorthodox (but beautiful solutions) addressing even very subtle aspects in a new and fundsmentally better manner is plain out impressive...
There has been several great designers over the years, but he really stands out with this and the cousins of this period of A&R amplifiers.
Regretfully, now becoming a bit cynical, to design an amplifier that merely produces sound is not difficult. Or hearing difference between capacitors is not diffcult. So the entry barrier to calling yourself an amplifier is very low indeed - and personally I see too many products promissing to be designed by someone closer to god than others and delivering nirvana...
This kind of inferior products are to my mind just spam and regretfully our industry is more or less overloadet with unjustifyable products which literally does more harm than good to a lot of people and to the joy of music. Disrespectful, but probably not with bad intentions, just lack of insight and respect!
A design like the Audio Research amps of this period has not come easily; they have been brought to life by an effort and insight that above mentioned "designers" not even comprehend.
Enough said - sorry for the angry attack on the mediocry that has become the norm - and that people buy into because words are free...
Hello Bill,
Thanks for pointing me there - just looked swiftly around in the thread; am it seems indeed a more than worthwhile read, appreciated.
A ltlle "touched" by this, I am tempted to express a humble attempt to hint at the "more than what you see on the surface" description of what I am going through respectfully renovation exactly D-150:
I am an electronics engineer at the university level, professionally worked in the audio industry for many years (now I am in the communications industry), loong time audiophile (in the service of being a music lover). Lucky to have personal friends in the high end whom develop Internationally acclaimed tube equipment. As such, the subject of tube amplifiers is daily on my mind and dialog with people whom takes a professional living from it.
The slowly "crawling in" under the skin of the designer of this amp through initially only the schematics and parts list makes it almost like knowing the designer personally - no wonder Audio Research become what it is (or was?); it is so well deserved.
The subleties and insight (and innovation) going into this amp evidently shows how Bill was an extraordinary mind - there is an in-depth understanding of so many fundamental, but well hidden aspects of amplifier design that you simple have to acknowledge the mastery (trying not to become boring with too many details, some of his patents are indicating just parts of this insight) - internal impedance levels, drive levels, balance/"harmony" to the circuits, the guts to go your own way not fearing inorthodox (but beautiful solutions) addressing even very subtle aspects in a new and fundsmentally better manner is plain out impressive...
There has been several great designers over the years, but he really stands out with this and the cousins of this period of A&R amplifiers.
Regretfully, now becoming a bit cynical, to design an amplifier that merely produces sound is not difficult. Or hearing difference between capacitors is not diffcult. So the entry barrier to calling yourself an amplifier is very low indeed - and personally I see too many products promissing to be designed by someone closer to god than others and delivering nirvana...
This kind of inferior products are to my mind just spam and regretfully our industry is more or less overloadet with unjustifyable products which literally does more harm than good to a lot of people and to the joy of music. Disrespectful, but probably not with bad intentions, just lack of insight and respect!
A design like the Audio Research amps of this period has not come easily; they have been brought to life by an effort and insight that above mentioned "designers" not even comprehend.
Enough said - sorry for the angry attack on the mediocry that has become the norm - and that people buy into because words are free...
I'm not an EE but I agree with what you said. Surprisingly Dave G found a few things that needed attention in the design, things that keep the amp from having distress and going into meltdown or burn up mode. I would read the entire thread, some of his mods may be useful to you. I have found that Dave is also easy to communicate with by PM's as well if you have any questions. He is a treasure on the tube forum on AK.
Keep us posted on your D150, I love all things ARC, using a SP8MKII in my system right now and have a VT100MKII sitting here that I need to retube and setup.
BillWojo
Keep us posted on your D150, I love all things ARC, using a SP8MKII in my system right now and have a VT100MKII sitting here that I need to retube and setup.
BillWojo
MortenD150
Your reply got me interested in taking a closer look at the ARC designs from the 70s through 90s. I am not an EE, but I have learned a few things along the way. To my untrained eyes, it looks like Bill changed his design philosophy in the late 90s. The Reference 3 preamp may not be everyone's cup of tea. But it was clearly a game changing design. Many reviewers and customers said that it set a new standard in sonic performance. In a lot of ways the Ref 3 is just a Ref2 mkII with the whole JFET front end ripped out. I see the same thing in the amps as well. Lower overall parts count that lead to simpler circuits. I always wondered what led him in that direction.
Your reply got me interested in taking a closer look at the ARC designs from the 70s through 90s. I am not an EE, but I have learned a few things along the way. To my untrained eyes, it looks like Bill changed his design philosophy in the late 90s. The Reference 3 preamp may not be everyone's cup of tea. But it was clearly a game changing design. Many reviewers and customers said that it set a new standard in sonic performance. In a lot of ways the Ref 3 is just a Ref2 mkII with the whole JFET front end ripped out. I see the same thing in the amps as well. Lower overall parts count that lead to simpler circuits. I always wondered what led him in that direction.
Hei Morten,
Rune fra Norge her.
Har også en AR D-150 som jeg tenkte "restaurere"
Den fungere som den skal, men vil gjerne gjøre de oppgraderinger som er mulig.
Du er muligens ferdig med prosjektet?
Vil gjenre høre hva du har utført av arbeid på den.
Mvh. Rune
Rune fra Norge her.
Har også en AR D-150 som jeg tenkte "restaurere"
Den fungere som den skal, men vil gjerne gjøre de oppgraderinger som er mulig.
Du er muligens ferdig med prosjektet?
Vil gjenre høre hva du har utført av arbeid på den.
Mvh. Rune
English please. It's in the Rules
https://www.diyaudio.com/community/help/terms/
Hi Morten,
Rune from Norway here.
Also have an AR D-150 that I thought I would "restore"
It works as it should, but would like to make the upgrades that are possible.
You may have finished the project?
Would love to hear what work you have done on it.
Etc. Rune
https://www.diyaudio.com/community/help/terms/
Hi Morten,
Rune from Norway here.
Also have an AR D-150 that I thought I would "restore"
It works as it should, but would like to make the upgrades that are possible.
You may have finished the project?
Would love to hear what work you have done on it.
Etc. Rune