Vintage HiFi Audio Forum
Audio Discussion => DIY => Topic started by: Jim Pittsburgh on August 20, 2014, 02:32:05 PM
-
Just thought I'd share: ordered four OPA 627s and two OPA637s thru eBay / China supplier, after reading such rave reviews about this "upgrade" to the JD9 phono pre-amp on more than one of the boards..... Don't get me wrong, I'm basically very happy with the sound of the Jolida with the current tubes I'm using, but figured "what the heck" after having had such good results with the op amp replacements in the dbx cd player..... Needless to say, this time things didn't go nearly as well lol
Although they were clearly marked as 627s and 637s I'm not at all sure what I actually received. But the resulting change in sound was just terrible.... I tried every possible combination of the existing six matching op amps and the three pair of new ones... with not the slightest improvement in sound.....actually all I got for the effort was varying degrees of muddiness, over emphasis of portions of the audio spectrum and even a bit of distortion.... back to the originals.
Also, a big thing on a number of the boards was to use the high outputs without any gain switch turned on for MM cartridges, and some saying it's the best settings for everything (bypasses a circuit) ... with my ClearAudio MM cartridge the result was that it sounded like the phono pre amp was over driving the inputs at anything beyond background levels.... I even played with a number of other settings on the Jolida and within the receiver to try and make the most of the change...... but again ended up right back where I began....
I know it's a function of different ears, different equipment and maybe for part of these experiments, bogus op amps, but the internet / boards and the sheer number of insistent "best thing since sliced bread" posts, never ceases to amaze me... lol
-
I wouldn't trust parts from China.
-
I guess that's part of the thrill of the chase! At least you were able to tell a difference, for better or in this case for worse. Now you know 1 more thing not to try!
-
I'm not sold on op amp rolling anyway. Some of the specs specific to one amp can be very different on another. I don't know about just throwing anything in.
-
Adam and STAL.... agreed/ understood.... but I found it funny, and frustrating, particularly after all the reading I did.... Most likely it's bogus op amps.... or all those posters on Audiogon, Audiokarma, DIYaudio etc etc have seriously bad hearing .... lol
-
and Anders..... sorry, didn't mean to leave you out.
-
Update
Replaced the 627 with ones that OBG got
Played with every possible combo of the
originals, the new 627s and the 637s. And actually
Came up with an excellent combo that is a real
improvement; viewed from the back left to
right. Originals, 637 and 627... OBG can attest
Sounds pretty sweet !
-
I'm all for op-amp rolling just like tube rolling but you have to be careful.
-
Agreed with Jim, not sure what the magic is but this particular combo worked great on the Jolida JD9. Cannot be placebo effect, we tested the ccmbos back to back and the diff was more than obvious on both preamps.
-
Update
Replaced the 627 with ones that OBG got
Played with every possible combo of the
originals, the new 627s and the 637s. And actually
Came up with an excellent combo that is a real
improvement; viewed from the back left to
right. Originals, 637 and 627... OBG can attest
Sounds pretty sweet !
After many hours of fighting with my JD9 I put 627, 637 and the original 37G's in just like Jim and I like it. I made a chart of the opamps I had on hand, there were 20 possible combinations. My OCD agreed it was a great idea until I tried Jim's setup. No need to go any further, at least for now.
I cured the hiss I was fighting by using an SUT and the MM side of the JD9. No combination I tried on the MC side cured the hiss, there's just way too much gain on that side. If I had two more 627's I'd try them in the middle (gain) position, but that's just based on hours of reading about opamps and a few posts claiming the 637 may be a little hot for that spot.
-
nice glad you found a good combo. I'm still puzzled by the gain noise/ hum . I use the low output side of mine , otherwise too much gain.
-
I've been in industrial electronics distribution for over 30 years as a Field Sales Rep. Trust me, never buy components from Chinese sources! The chances that they are fake, gray market rejects, or relabeled inferior parts is VERY high. Buy real parts from a legitimate franchised supplier like Digikey, Mouser, or Arrow Electronics. You'll pay more but you will have the real deal.
https://www.allaboutcircuits.com/news/how-to-spot-counterfeit-electronic-components/ (https://www.allaboutcircuits.com/news/how-to-spot-counterfeit-electronic-components/)
-
Not that I buy much, but I use Parts Express & Newark (old MCM) & at times Digikey...
Are PE & old MCM still reliable?
Thanks,
George
-
Newark is a reliable source, but they are usually pricey compared to others. Newark is owned by a large European electronics distributor called Farnell. I would say Parts Express is reliable although I'm not sure they are an actual franchised semiconductor distributor. My guess is that they buy their semiconductors from one of the suppliers I previously mentioned. Avnet is also a good legit source I left out.
-
Newark is a reliable source, but they are usually pricey compared to others. Newark is owned by a large European electronics distributor called Farnell. I would say Parts Express is reliable although I'm not sure they are an actual franchised semiconductor distributor. My guess is that they buy their semiconductors from one of the suppliers I previously mentioned. Avnet is also a good legit source I left out.
We need a like button like on FB.
-
Thanks for the info Rgpit. I am guilty for buying op amps from China. With so many options of different chips that “work” I was guessing which ones to get. With state side sellers wanting $30 or more per chip it leaves “rolling” for those with deep pockets. My other mistake was believing what I was reading. I’ve reread a 105 page thread over again and the second read exposes opinion over fact. Too often I think people buy things and try to justify it to the masses on the web. Audiophiles never do that, right??
This article also made me more skeptical of the Chinese parts
https://zeptobars.com/en/read/OPA627-AD744-real-vs-fake-china-ebay
-
The gray market guys will stoop so low it's unbelievable. I had a customer that is large local manufacture of precision instrumentation. They desperately needed parts that unfortunately had a long lead time. Anyhow, they found a 2500pc reel on the gray market. They pulled a few parts off of the reel to validate that they were genuine. The parts were confirmed to be okay and were put on their PC boards with a high speed pick and place machine. Well, the first 100 parts were indeed real after that they were all fake. It cost them a fortune to rework and retest all the assembled boards.
Frequently the Chinese suppliers will take cheap op-amps or other components, sand off the part number and re-mark them with a different and much more expensive part number.
Moral of the story is "buyer beware".
-
The gray market guys will stoop so low it's unbelievable. I had a customer that is large local manufacture of precision instrumentation. They desperately needed parts that unfortunately had a long lead time. Anyhow, they found a 2500pc reel on the gray market. They pulled a few parts off of the reel to validate that they were genuine. The parts were confirmed to be okay and were put on their PC boards with a high speed pick and place machine. Well, the first 100 parts were indeed real after that they were all fake. It cost them a fortune to rework and retest all the assembled boards.
Frequently the Chinese suppliers will take cheap op-amps or other components, sand off the part number and re-mark them with a different and much more expensive part number.
Yea, I have 4 fake OPA627s that I got off Ebay some time back from a Chinese seller. Done with that. Ditto for fancy capacitors from China. If it looks too good to be true, it prob is.
Moral of the story is "buyer beware".