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In Reply to: RE: The components designations are sanded off and replaced with color codes posted by Wojciech on December 16, 2024 at 12:51:12
are the result of testing each and every device and grouping them by electrical characteristics for matching. Which explains the application specific production SKU.Such is found in Mikey's video of the factory many years ago.
Edits: 12/18/24Follow Ups:
and you have to order the parts from ARC and they are reluctant to give the info on the origins of parts if they have it in the inventory. I serviced tens of ARC boxes. Mostly simple stuff and the company has my respect.
Manley does not erase the parts designations because there are no parts suitable for the erasing in the simple Manley designs.
Cloning a transformer based design is not the same thing as cloning a simple op amp device. Without the original transformers you're never going to get the sound of original. ARC dealer said that he had a chance to hear Chinese cloned ARC amp which looked identical to a last detail. It didn't sound like original
If they did provide you with the part number for the FET and you purchased it from Mouser it is absolutely guaranteed your unit will not operate to factory specifications. They test and scrape 90%+ of the devices. Not because they don't meet the manufacturers specification it is because they don't meet ARC's specifications. They can't return the rejected devices.
Nothing nefarious here. I've been to the factory and watched the process.
This is why a .15 cent FET from Mouser is $15 from ARC. It takes a lot of time to test, reject, select and match the devices. They don't sand off the numbers they color code them and of course that obscures the part number.
If this bothers someone then it is probably best to buy something else.
I only said it was there and they do remove the origin and a part number actually the same way Tom Evans removes the markings on his products because according to him he also matches them in time consuming process. I don't see a difference here implied by Abe and E-Stat. Do you ?? The outcome is the same . You either buy from manufacturer or play a radio.
90% refusal rate is a joke and it is not sustainable in any manufacturing and modern active devices do not have such broad spread of parameters to justify that sort of selection.
They lost some of the database of the devices they used in older lines in power supply regulators. I read now and then of folks (mostly abroad) stuck with those monsters nobody wants to repair due to lack of replacement parts or the price quotes from the local dealers. I do have a fair amount of respect for Audio Research for their (mostly past) construction prowess and parts quality. It was exemplary, but it just didn't sound like it to me. Later gear I worked on (Ref75 SE ) is getting closer to McIntosh in assembly. Much less impressive.
Edits: 12/18/24
ARC removes the part numbers? And you know this how? Have you been to the factory and seen the process?
'90% refusal rate is a joke and it is not sustainable in any manufacturing and modern active devices do not have such broad spread of parameters to justify that sort of selection.'
Again you know this how? You have an understanding of ARC's engineering and tolerance criteria?
Yes you are indeed claiming ARC is behaving in a nefarious way. That they have some agenda to gouge their customers when it comes to replacement parts.
Easy enough to throw out unfounded accusations and make all kinds of assumption with little if any actual knowledge or data. The beauty of the internet I suppose!
I serviced the ARC equipment and couldn't see the numbers behind the color stripes. Either way the effect is the same.
Since you're so deep into subject please provide the types of fets used in Q1, Q2 ,Q3 Q4 positions on posted VT100 so I can exercise my right to repair the equipment I bought and paid for. I will be my own judge if the replacement I use are matched to the needed degree. Also since you're here give me the types of the pass transistors in the regulator circuit which are not subject of matching . I know they are selected because the circuits are marginal and require it in some but not all devices. I used Audio Research as an example of manufacturer who does protect some of the design aspects just like Tom Evans does and not to single it out like you suggest. Please do not tell nonsense of 90% refusal rate on modern production silicon devices from a reputable manufacturer on technical forum.
Edits: 12/18/24
"A friend of mine was swapping tubes in his Audio Research Reference One preamp when he bent and broke one of the leads on an FET that has a heatsink very close to a tube so I contacted Kalvin at Audio Research for a replacement "Green White Brown" FET.
What I received was a Green Green Brown FET in a mailer envelope. They charged $15 for the FET and another $15 to send it in the mailer envelope!
Not to mention the whole parts process took 2 weeks from start to finish and I don't even have the correct "hand painted" part yet.
Needless to say, Audio Research will not be getting any more of our hard earned money for their "hand painted" parts. Or any more components for that matter."
With all due respect for ARC, the paint they use to "code" their components is of such quality that even lacquer thinner will barely break it down. But once it does finally clean away from the semiconductor the reveal is a heavily sanded component that is guaranteed to not expose its identity. The process of disguise must require meticulous sanding and an expert level of artistic painting. A level of personal attention unheard of in other companies products. I've never seen hand sanded and painted components in any Krell or Levinson piece. Slackers.
with blessing of the factory. Like I said ARC are good people and they usually had enough on their plate to worry about repair of a burned screen resistors and blown traces. The newer stuff like ref 75SE isn't built as well as the old boat anchors. It reminds rather the piece of shit Mcintosh tube circuits hidden under the gilded cages and behind blue meters
I return my ARC gear to Minnesota for (rare) service.
Perhaps you're familiar with ARC's history of part identification obfuscation. It's been going on for decades.This is what remains of my D100A with all its "analog module" glory on display.
No discussion of "sonic's" is necessary. This was THEE MOST UNRELIABLE piece of equipment I've ever owned. Main heatsink too small. Main filter caps mounted horizontally by their terminals causing cracked terminal seals that allowed electrolyte to leak out. Frequently blown output transistors requiring a trip back to the factory and many hundreds of $$$ to ship and fix. And then there's those irreplaceable Analog Modules. Must contain Area 51 alien technology to have to pot them to keep earthling eyes away. Actually, pure marketing bullshit. Have never even considered ARC let alone buy the stuff over the past 45yrs. New, used or gift, ARC is not going to be a part of any system I have any involvement with. AFAIC ARC deserves its current "somewhat diminished" status and reputation.
Edits: 12/18/24
...I found part designations on the PCBs and part numbers on the parts for a couple ARC pieces that I repaired myself. The schematics were also good. Perhaps I was lucky in getting the schematics as there was an ARC tech named "Leonard" who just sent them to me upon request.
But in the end, I learned that the ARC sound is not for me. It's like taking the best of SS and the best of tubes and compromising the benefits of each in the mix. Most of their preamps appear to be SS JFET with 6H30 tube buffers on the output.... which only roll-off and veil what the SS side is capable of.
which only roll-off and veil what the SS side is capable of.
I cannot hear what a 0.5 db rolloff at 20 kHz sounds like with mine . More power to you! ;)
Check the low-end of your Audio Precision graph. It shows severe bass roll-off which is audible and not atypical of ARC electronics.
The chart you provided with my annotations
Notes:
dB = 10 * log(P2/P1)
rearranged to solve for P2
P2 = P1 * (10^(dB/10))
My amps have an input impedance of 137k ohms.The cyan plot is for 600 ohms. Even under that ridiculous scenario, your claim about high frequencies is without merit.
Why would anyone attempt to drive such a load with a tube preamp? Or even a 10k load?
Do read the review :
"The SP20's detailed, delicate, extended high frequencies were startlingly impressive with well-recorded orchestral works...
The SP20's bass was beyond reproach...
With the volume control set to its maximum, the frequency response into 100k ohms was perfectly flat within the audioband and superbly well matched between channels."
Edits: 12/24/24
Given the chart YOU provided my assessment and math worked out perfectly for LOW FREQUENCY roll-off. In other words weak bass which is what I experienced in more than one piece of ARC electronics relative to other brands.Hey, I'm not the one who provided the graph that doesn't lie.
Heading out so..... Merry Christmas
Edits: 12/24/24 12/24/24
should you use an amplifier with a 600 ohm input Z. Note there are two separate plots in the graph using different values. Mine is 137,000 ohms!Perhaps you don't understand component matching.
Here's the measured in room response for that system with backplate bass control set flat:
Once in a while, I use the -3db setting to take out the room gain for greater dynamic range when playing stuff like Rite of Spring .
Edits: 12/24/24
....and has nothing to do with component matching, impedance, room acoustics, and all the other distractions you're trying so desperately to inject into the mix. The Device Under Test is what is being discussed. And the DUT shows bass roll-off.The chart and math do not lie. That piece of ARC gear IS rolled-off in the bass region, noticeably so. Period. End of story.
Chart of your ARC preamp......
Rolled-off in the bass region. The chart shows it. The math proves it.
dB = 10 * log(P2/P1)rearranged to solve for P2
P2 = P1 * (10^(dB/10))
Edits: 12/24/24 12/24/24 12/24/24
The graph shows me that the ARC preamp output impedance is probably high and incapable of driving lower impedance loads w/o severe roll-off. The graph shows exactly that. Many other preamps don't suffer in this area. Many are flat from below 10Hz to well beyond 20KHz regardless of what impedance they are driving.
ARC looks rolled off in the bass region of your graph and that is precisely what I've heard in many ARC products. It's their 'house sound': solid-state with a tube output buffer to veil and roll things off.
Some like their 'house sound'. Others don't. Nothing wrong with personal preferences.
The graph shows me that the ARC preamp output impedance is probably high and incapable of driving lower impedance loads w/o severe roll-off.The balanced output Z is 500 ohms. What fool would ever attempt to drive a 600 ohm amp? Contrary to your lack of awareness, matching gear is all about impedance. Hence multiple values tested - 600 and 100k ohms with vastly different results. What amps on the market today use 600 ohms?
ARC looks rolled off in the bass region of your graph
There is no *me* to this. I reference John Atkinson's measurements. Flat to 20 hz is *rolled off* to exactly what? Huh?
First column is 10 hz. Down about a tenth.
Edits: 12/25/24
> > Sanders Sound Systems ESL MkII Monobloc Amplifier < <
1,000Ω input impedance balanced, 100KΩ unbalanced. Amp is supposedly designed specifically for e-stat speakers and their sometimes difficult loads. I have a friend that just bought a pair of these amps. He loves them except . . . He's driving them with an ARC Ref something-or-other preamp in balanced mode . . . and experiences noticeable low-end roll-off. He's in the market for a new and more capable preamp.
because it really does matter. If using balanced, he made a poor choice given the 2:1 ratio. On the other hand, I agree with JA that 274:1 works fine!
The speaker to amplifier relationship is every bit as important. The Sanders hybrid electrostat has a Scream Machine roller coaster impedance curve and has special needs itself. Fortunately, my stats don't exhibit such a ride. Similarly, tube power amps work well driving them with their tame impedance curve. :)
You probably know that 600Ω is a "professional" standard and I'd assume that's one reason Stereophile tests with this loading.* It's unfortunate that a consumer needs to check for this type of compatibility in today's plug-n-play environment. It's not like this is some subtle sonic difference. ARC really should be more up-front regarding the (lack of) compatibility of their products with professional standards. At any rate, no ARC preamps for my friend - one lifetime.
*I've got old VOMs with dB scales where "0dB" is defined as the voltage that produces 1mW into a 600Ω load.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
600 ohms was used in telephone industry. No need for that today.
There have always been compatibility aspects to matching audio gear. I learned that as a teenager. Sorry your friend didn't.
BTW, Sanders doesn't understand cable interaction either. ;)
Posturing, the point remains: there are commercially available amps with very low input impedance, right or wrong. It's interesting to note that ability to drive 600Ω loads would seem irrelevant today esp for home equipment. And yet the ability to do so is claimed as an advantage or feature by some mfgrs. Even some modern (and vintage) "audiophile" grade opamps specify the ability to drive 600Ω loads at low distortion. So maybe 600Ω capability is somehow relevant in modern consumer equipment . . . Shorthand for "Will drive anything likely to be encountered".
.
Have Fun and Enjoy the Music
"Still Working the Problem"
while some inmates draw diagrams, argue and completely miss the point about using (abundantly found) high Z amps with tube preamps - which eliminates frequency based mismatching issues. :)
Edits: 12/26/24
From JA's measurement section:"With the volume control set to its maximum, the frequency response into 100k ohms was perfectly flat within the audioband and superbly well matched between channels (fig.4, blue and red traces). With the high output impedance at low frequencies, it came as no surprise that the output rolled off below 200Hz into 600 ohms (fig.4, cyan, magenta), reaching -3dB at 58Hz. With the volume control set to "73" (green, gray), the line stage's ultrasonic response was more rolled off than with the control set to "103," but the output at 20kHz was still down by only a negligible 0.5dB. "
Details do matter. Can you recognize cyan and magenta? One to which you pointed?
Edits: 12/24/24 12/24/24
View YouTube Video
.
This was THEE MOST UNRELIABLE piece of equipment I've ever owned.
the worst sounding ARC had ever produced as Harry Pearson observed when they first came out. Did you audition before purchase? Bill Johnson said the negative TAS reviews nearly put him out of business. He claims semiconductor provider didn't deliver same quality production devices.
It didn't take long before even better sounding and reliable tube based gear arrived from them.
Have never even considered ARC let alone buy the stuff over the past 45yrs.
In nearly that space of time (44), I've enjoyed a power amp and three preamps, the last of which I continue to happily use. It was the first to *beat* the transparency of a passive. Took me a while to digest and directly experience what Charlie Hansen and John Atkinson had been saying for years. :)
Still isn't. The amp was a poor physical implementation of an unstable design. A design that can't accommodate normal production tolerances of active components isn't ready for prime time. If they still wanted to proceed with this they could have selected parts. Apparently they didn't. Holding component suppliers responsible for their lack of design and manufacturing expertise is just shifting blame. A bad look.
I acquired the amp after listening to it. i liked it. I don't give a shit what Harry Pearson thought of it. He's not me. He doesn't have my system. He doesn't have my room. He doesn't have my ears. Plus he obviously didn't have it long enough to really experience it in all its DC rail fuse blowing glory. No more ARC for me . . . One lifetime.
For any future equipment acquisition. New or used or "gift". Friends have ARC Ref something preamps. Sound decent but unreliable. Most pieces have been back to ARC for repairs at some point. Two of those ARC Refs roll off high end significantly depending on setting of volume control. ARC says "normal". No thank-you! Life is too short to put up with this kind of product (un) reliability and design. Plus, there are plenty of other worthy brands to consider with equal or better sonics. And they don't rely on Russian "super tubes" (6H30).
Edits: 12/19/24
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