Audio research corp D125 Hifi valve amp

[blindboybenton]

Hello to you

Ive got my first Audio research corporation amp D125 Its a valve power amp with mosfet PI.
I believe i have some noisy fets on channel

The amp is a nightmare to work on due to the fact its hard wired with very little slack. I have the parts list and map. But nothing about what the fets are. When i removed one i found the marking been sanded off and painted
Q32-33 and Q7-8

Been in touch with Audio research in USA and they won't tell me what they are I have to buy them from them. Was hoping to avoid that due to time and cost + import duty

Audio research corp D125SchPL.pdf

Does any one had experience and fitted an Off the shelf Fet


BBB

Ps copied the Vt130 map by accident. its there in case any one wants it

[bob p]

What you're describing, with respect to sanding off of the markings and re-covering wiht paint, is not at all uncommon. A great many manufacturers would resort to "house numbering" of the parts, rather than providing the customers with direct access to generic third-party replacements.

This could have been done for any number of reasons. Sometimes manufacturers just want to enhance profit margins by making you buy parts from them at higher prices, but sometimes there's a value-added component to the house numbering paradigm when it comes to high end audio equipment.

A company like Audio Research will test, match and bin their parts from the suppliers. Those that meet spec are inventoried and binned, while those that meet manufacturer's specs but don't meet their more stringent specs will get rejected, discarded or repurposed. This drives up the price of their replacement parts. The upside to this is that when you order a replacement part for a specific model of amp, you're guaranteed to receive a part that has tighter tolerance specs than the manufacturer's part number alone would imply.

As far as repairing the amp goes, there are several ways to approach the problem.

It's entirely possible to look at the circuit, and look over parts tables, to determine a suitable replacement part. I've done it before. It's a PITA. The upside to taking this approach is that it's possible to select modern semis that are on smaller dies and have a better SOA than the vintage semis. Then you get to do your own matching.

Another option is to save yourself the effort by coughing up what it costs to purchase the correct parts from ARC. Yes, the parts are more expensive that way, but time is money and you're guaranteed to get good parts that will function properly in the circuit.

Another option is the hack repair where you just put in something that makes the amp work. I don't like buying audio gear that other people have serviced, because I fear that someone took this short-cut route to repair. I wouldn't recommend this type of repair on a top-tier piece of audio gear.

for a one-off repair it's worth it to me to buy the parts from ARC. that said, i did have to refurbish a dozen of the same model of amp once, and in that scenario it was worth the time to do the engineering and source my own parts.

[blindboybenton]

Hi Thanks for the info. I wanted to avoid that, but the customer has deep pockets and wants to get it sorted, no rush on the time scale either
Have spoken to audio research and getting a price, when you chaps can come back to work after your 4th of july


BBB

[blindboybenton]

Just an update. I ordered 10 fets from audio research 8 x TO220 and 2 x TO92 style, Due to the fact they sand off all the part no's on the fets and don't give info in the schematic of what they are .I was changed $200 and another $51 for duty / customs (Ģ191 ) I think its a rip off for what i got. Its not me that's paying, Oh well never again

Rant over
BBB

[Jazz P Bass]

Hopefully, AR 'matched' the outputs.

If so, piece of mind comes at a price, no?

[bob p]

never again?

working in the service industry requires ignoring your own biases and servicing the needs of the customer.

[blindboybenton]

I just feel that ive paid way over the odds for parts that's all. I expected them to be expensive . Just not that much , excluding the import tax/ duties i had to pay
I know that these are matched but with an amp of this age. are all the other components going to be in their tolerances. who knows..... ive paid for it now
Ive also had to contact AR about missing parts from my order. They have admitted its their fault They have agreed to send more, But know i will have to pay more customs charges
and then get customs here in the uk or AR to refund me.

Have a good day gentlemen
Its lovely and sunny in the uk and hot.. Melting in the workshop and its only 10am

BBB

[Enzo]

You may never know what they select them for. For example certain parts in older Peavey amps are selected for voltage. They tested transistors and ran curves on them, then selected the ones that made it to certain levels for use in certain circuits. If we just bought new industry parts from a supplier, half of them would not survive. Some other situations parts are selected for gain, as in near one extreme of the spectrum as needed.

That doesn't excuse $20 per part, but it hopefully explains potentially why one would stick to factory special parts.

[Enzo]

I have a sign in my shop, I cut it out of a service industry trade magazine. It is a cartoon of a boy scout leading an old lady by the arm across the street, while the lady is frantically pointing the other direction. The text is "Good service is giving the customer what he needs".

[Leo_Gnardo]

That doesn't excuse $20 per part, but it hopefully explains potentially why one would stick to factory special parts.

ARC has always been a "country club" brand. Prices? If you have to ask, you're not rich enough to be qualified to buy their gear.

This all reminds me of the good ol' days when I used to wrench cars for a hobby. You could buy a set of Jaguar ignition points for $90. Carefully remove the stick on label and find "GM/Delco" printed on the box, they would have cost $5. Did Jaguar test them, modify, reject bad ones, give 'em a round trip to England and back, to the point they could justify charging 18X as much? Or just sticker the box and raise the price? Well, (sigh of relief) at least they weren't Lucas points.

ARC were famous for making an order to Richardson when they were making their last runs of GE 6550A tubes. They wanted theirs to all be matched to some ridiculous degree, was it 1% or 1/10%, that detail has drifted outta my brain. Good luck ARCharlie!

Likely your FETs were tested & matched to some highly classified specification, OK that makes sense, but the markup is still ludicrous. If you knew what part they were, you could test them yourself, so they have their rookie tech sand the numbers off to keep it a mystery. All goes to support the idea, if you don't have the money & the patience to deal with us, we're not your brand.

[bob p]

Yes, it's a country club brand, and if you have to ask what parts cost then you're an aspirational buyer. But a bigger part of the problem is that Audio Research isn't an independent company any more. Audio Research used to be owned by the old man in Minnesota who founded it, William Z. Johnson. There used to be a time when ARC prices were not as predatory, and a time when ARC would bend over backwards for their customers. When I bought a used VT-100 a few years ago, I contacted ARC to ask for the schematic. They sent me a very nice spiral bound operator's manual that included the schematic, along with an insulated bias adjustment screwdriver, as a goodwill gesture. I guess they were greasing the skids. lol.

Johnson died in 2011, leaving his heirs with a company that they didn't know what to do with.

The Audio Beat - William Zane Johnson, 1926-2011 - Audio Research founder William Z. Johnson passes away

Like most heirs who don't know how to run their father's business, they sold the company. ARC ended up being bought by Italy's Fine Sounds SpA, who also owns Sonus Faber and McIntosh among others. The result is that as the result of acquisition, the American made, high quality brands like Mac and ARC have transitioned from first quality goods that were expensive because they were manufactured in America, into ridiculously expensive aspirational products where the brand's owner is marketing the brand as if it were designer clothing to be worn on the red carpet. Fine Sounds SpA is marketing the ARC brand with price markups that belong on Versace handbags, not American made audio gear. The snob premium that they've attached to the brand means that today replacing my VT-100 would cost more than 10x what I paid for it when ARC was still an American company.

The nice thing about the ARC products is that they're designed well, built well, and they are durable. They meet their specs with room to spare, and they sound good. In contrast, I think that the builders of Sonus Faber speakers put more development cost into exquisite cabinetry as pieces of fine woodwork than as musical transducers. IMO SF is more about speakers as eye candy than as sound reproducers. In that respect they're like an Italian version of Henredon sideboard.

BBB, I think predatory pricing by Italy's Fine Sounds SpA is the ultimate reason that you're being bent over on price. ARC isn't owned by it's founders any more. It's been sold to an Italian uber-high-end holding company whose intention is to milk every customer for whatever they can, and the era of reasonable price-performance is over. Oppressive import tariffs only exacerbate the problem.

[bob p]

Look at the bright side -- recapping a Krell costs $800, even when you're local.

http://music-electronics-forum.com/t41916/

[J M Fahey]

$25 for a MosFet, delivered from 3000 miles away?

Why do I fail to find that "expensive"?

You neednīt pay those abusive prices, just buy 8 IRF820 and stick them there.

Would also love to know your opinion about Techs who charge U$1 for a 1/4W carbon resistor.

FWIW if I were AR, wouldnīt sell parts to outsiders (non approved Techs) but insist on having the unit Factory or Authorized Tech repaired only.

Nothing personal, just looking at it from the other side of the counter.