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Old 7th September 2013, 03:13 AM   #21
jdkJake is offline jdkJake  United States
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Quote:
Originally Posted by brunk View Post
Thanks for the link, I'll keep it for reference just in case mine come out to be fakes even though the seller said they are originals.
No doubt he stated they were originals...

Of course some folks on the Internet tend to stretch the truth a wee bit. So, trust, but verify.

Or drop spencer a line....
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Old 7th September 2013, 03:30 AM   #22
brunk is offline brunk  United States
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I went ahead and changed from 4x 33000uf to 8x 15000uf because the PDF someone linked appears out of date compared to the current schematic in the store.
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Old 7th September 2013, 04:02 AM   #23
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Quote:
Originally Posted by brunk View Post
Thanks for the link, I'll keep it for reference just in case mine come out to be fakes even though the seller said they are originals.
Would recommend Spencer as your primary and the one you got from ebay...is your back-up....

Its very frustrating you got all your parts and you found out you have the fake JFETs....

Though frustration is part of DIY....Looking 3 to 4 weeks downtime if you dont act early

Save all your energy on your first time power-on, smokes and all time favorite HUM..
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Old 7th September 2013, 04:48 AM   #24
brunk is offline brunk  United States
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Originally Posted by abadsantos 7 View Post
Would recommend Spencer as your primary and the one you got from ebay...is your back-up....

Its very frustrating you got all your parts and you found out you have the fake JFETs....

Though frustration is part of DIY....Looking 3 to 4 weeks downtime if you dont act early

Save all your energy on your first time power-on, smokes and all time favorite HUM..
How can I test them if they are fake or not? i have a semiconductor tester on my DMM, it has like 4 holes with npn/pnp would that do?
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Old 7th September 2013, 05:22 AM   #25
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Quote:
Originally Posted by brunk View Post
How can I test them if they are fake or not? i have a semiconductor tester on my DMM, it has like 4 holes with npn/pnp would that do?
Hi Brunk,

You can check this out Mystery 'sj74'? jfets and still have many others Quick search here in
DIYaudio pointing how to test your JFETs if fake or not.

At the end of the day...they will point you out to Spencer...

Based on my experience, fake JFETs still, will make your amplifier work. But you will run into several issues such,
high DC offset upon cold start, unstable bias, misleading measurements and many other issues.

One good example:F5 Turbo Builders Thread Check #1143 but the problem description starts at #1122
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Old 7th September 2013, 06:44 AM   #26
Hikari1 is offline Hikari1  United States
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Brunk:

The PDF build guide uses v.1 of the diyaudio PSU board. You have v.2. It's a little different layout and may have different cap spacing. The v.2 board is a Universal board not specifically designed for the F5 and this is where a lot of your problems are coming from.

You want 8 caps. 15,000uf minimum each. 35V preferred (vs 25V). The THSA's are OK. I'd spent a few extra bucks and get 22,000 uf caps or maybe even bigger caps if they will fit the board. More capacitance is a good thing in the PSU. I am using 6 x 33,000. Dollars spent here is good. Don't go crazy though.

Remember, you are just trying to match the pass PSU schematic. The diyaudio PSU board is a universal board designed for a lot of different applications. Just match the Pass schematic using the boards. Which means (and iam generalizing here)...Transformer >rectifiers > First set of caps with bleeder resistors (3 watt 4.7K ish), second set of caps > 4 x .47ohm 3 watt resistors > third set of caps > 4th set of caps bypassed with poly caps (4.7uf or so). Trust the Pass schematic and it will guide you.

Once you figure out how it works you could just wire it yourself without a board. It's not hard. Then you can use better caps with screw terminals (i.e. computer grade) Here's what I did and how everyone helped me along the way:

Jim's Audio F5 power supply board

Regrading the Jfets...without a curve tracer you probably wont be able if tell if they are genuine or not. They may work. Best case scenario is they work and the amp runs fine but does not sound as good as an amp with genuine jfets. Worse case is your amp catches fire. If you can I'd order jfets from Spencer. His parts have been curve traced and are genuine. It is pretty well known that the 174 jfet is highly counterfeited and pretty much no one on this forum has ever received a genuine 174 through ebay. It's worth the money to get fets from Spencer or some other reputable source here. It will not cost a lot in the grand scheme of things and it will put your mind at ease. Would you build a nice tube amp and then use $3 cheap chinese tubes in it? Same thing.

You are getting there. Learning all this stuff is more important than the end product which is the amp. I am no expert but building this amp really was a lesson in diy audio for me that has been the building blocks of everything I've done after. It'll be hard, frustrating and confusing but you will get it.
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Old 7th September 2013, 09:37 AM   #27
brunk is offline brunk  United States
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OK looking at that schematic now makes complete sense. I had seen it before, but got lost in the parts finding frenzy lol. I have everything i need and a bit extra I'm sure, but that never hurts lol. I did get 8x 35v rated caps, 15000uf 30mm diameter. Does it hurt if i put bleeder resistors on all the caps or does it not matter?
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Old 7th September 2013, 03:03 PM   #28
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Originally Posted by brunk View Post
Yes I will definitely test them beforehand. I didn't see anything in the seller's feedback about fake parts so I'm having my fingers crossed.

Would you be able to provide some answers to my questions? It would be much appreciated
Unless you get them from spencer, H_a, or other known good suppliers, it is about 99.999 percent sure they are fake. Off of ebay, its probably closer to 100%. These fets are not being manufactured anymore by Toshiba, and are heavily faked. Finger crossing wont help. Measure, throw away, contact spencer...

Russellc
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Old 7th September 2013, 03:12 PM   #29
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Another nubie mistake is buying non approved Pass diy stuff (boards, kits, etc. not electronic parts like you bought) off ebay, like JIMs an so forth....some folks here will tell you to "go ask jim" with your questions. This sort of business is a slap in the face to everything Mr Pass has done for us.... just saying. Stealing, plain and simple.

Russellc
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Last edited by Russellc; 7th September 2013 at 03:23 PM.
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Old 7th September 2013, 03:23 PM   #30
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Quote:
Originally Posted by brunk View Post
Yes I will definitely test them beforehand. I didn't see anything in the seller's feedback about fake parts so I'm having my fingers crossed.

Would you be able to provide some answers to my questions? It would be much appreciated
Unless you get them from spencer, H_a, or other known good suppliers, it is about 99.999 percent sure they are fake. Off of ebay, its probably closer to 100%. These fets are not being manufactured anymore by Toshiba, and is heavily faked. Finger crossing wont help. Measure, throw away, contact spencer...

Russellc
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