New (to me) Threshold FET-10 HL (What to refurbish?) - diyAudio
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Old 1st June 2010, 09:54 PM   #1
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Default New (to me) Threshold FET-10 HL (What to refurbish?)

I just picked up a Threshold FET-10 HL for two channel playback, and all I can say is "WOW-What a preamp". This unit has provided a major upgrade for two channel audio playback.

I was using a Krell Showcase for all preamp playback, and while it is a fine preamp/processor, it's not in the same league as the FET-10 for two channel playback. The lite haze one usually hears with most audio playback setups is simplly not there with the FET-10.

For now, using the FET-10 with a newly refurbished Nakamichi PA-5, and the results are stunning with Legacy Signature III's. Can hardly wait to finish getting the two Nakamichi PA-7's refurbished.

Later this year, will be refurbishing the FET-10. The power supply would be a no brainer to refurbish, but how much and what should be refurbished on the main unit itself. Want to make sure to keep (hopefully improve) this level of sonic clairty.

Thanks in advance for any advice.
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Old 1st June 2010, 10:50 PM   #2
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pics , please ;

toss that cover , and shoot .
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Old 1st June 2010, 11:08 PM   #3
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Here is a pic of the speakers from the factory just before shipment:

Will post the inside of the PA-5 refurb and FET-10 soon.
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Old 2nd June 2010, 01:28 AM   #4
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Quote:
Originally Posted by Redwingnine View Post
I just picked up a Threshold FET-10 HL for two channel playback, and all I can say is "WOW-What a preamp". This unit has provided a major upgrade for two channel audio playback.

I was using a Krell Showcase for all preamp playback, and while it is a fine preamp/processor, it's not in the same league as the FET-10 for two channel playback. The lite haze one usually hears with most audio playback setups is simplly not there with the FET-10.

For now, using the FET-10 with a newly refurbished Nakamichi PA-5, and the results are stunning with Legacy Signature III's. Can hardly wait to finish getting the two Nakamichi PA-7's refurbished.

Later this year, will be refurbishing the FET-10. The power supply would be a no brainer to refurbish, but how much and what should be refurbished on the main unit itself. Want to make sure to keep (hopefully improve) this level of sonic clairty.

Thanks in advance for any advice.
I just helped a friend refurb a FET-10. No electrolytic caps in the main unit to worry about. Some larger polyester caps could be upgraded, but I couldn't find any polypro caps that would fit, so I left them alone. I did replace the caps and diodes in the power supply. He is extremely happy and says it is a huge improvement over the Krell preamp he was using. He needs a phono stage, so I told him to wait for the Pearl 2 which I hope will start shipping soon..... (Hint, hint Wayne )
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Old 6th June 2010, 07:51 PM   #5
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Here are a couple of pics: FET-10 and a recently refubished PA-5. The PA-5 had internal wiring replaced, most board caps replaced, and a new rectifier installed, along with the PS Cans bypassed. Made a huge improvement in sound.
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Old 8th June 2010, 08:49 PM   #6
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It's taken about a week, but the PA-5 is just about burned in with the new parts. It's sounds better than new. Changing out the rectifier really helped the sound a lot.
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Old 9th June 2010, 12:53 AM   #7
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Originally Posted by Redwingnine View Post
It's taken about a week, but the PA-5 is just about burned in with the new parts. It's sounds better than new. Changing out the rectifier really helped the sound a lot.
What rectifier did you use?
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Old 9th June 2010, 01:15 AM   #8
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Originally Posted by MashBill View Post
What rectifier did you use?
I got the parts for this from my tech buddy, so not sure of the make/model, but believe it's a HEXFRED type. (You can see it pretty clearly in the pic). I do know that they go for 25.00 a pop, so it's going to cost me 100.00 to install them in the two PA-7's. They made the amp a fair bit quieter, as did replacing the internal wiring.

I'll ask him where he got them, and who made them. I'll post as soon as I find out.
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Old 9th June 2010, 02:46 AM   #9
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Quote:
Originally Posted by Redwingnine View Post
I just picked up a Threshold FET-10 HL for two channel playback, and all I can say is "WOW-What a preamp". This unit has provided a major upgrade for two channel audio playback.

Later this year, will be refurbishing the FET-10. The power supply would be a no brainer to refurbish, but how much and what should be refurbished on the main unit itself.

Thanks in advance for any advice.
Red,
I refurbished an FET-10hl last fall. Here is what I did.

Since it's a 20 year old unit, I was certain that the old electrolytic capacitors needed to be replaced. There are not many electrolytic capacitors in the unit - only 2 for the external power supply (2100uf 35v) and 4 in the on board regulators (4.7uf 50v). I replaced the 2100uf electrolytics with some Panasonic FC 3300uf 35v capacitors and while I was making changes I also upgraded the power supply diodes to some Fairchild stealth soft recovery diodes - model RHRD660. The 4.7uf 50v electrolytic capacitors were replaced with some ASC 4.7uf 50v film caps that I found at a local surplus electronics store.

The output of the preamp is capacitor coupled with some 10uf + 10uf EPCOS film caps. These aren't the best quality caps but as Mashbill pointed out, they are compact. The low profile of the preamp means that there isn't room to fit higher quality 10uf film caps and still fit the top panel. Instead of replacing these caps, I decided to bypass them with some film caps that I had in house. A combination of a 1uf 100v Hovland polypro musicap + 0.1uf 100v Sprague Vitamin Q Paper in Oil gave a very nice improvement in soundstage. I also experimented with the orientation of the EPCOS caps and I think things sound with the EPCOS flipped around 180 degrees - i.e. the input swapped for the output.

Future changes that I'm considering are building a bigger power supply to replace the very small external supply and putting in a stepped attenuator to replace the volume control.

For others interested in experimenting with this preamp, here is a schematic of the gain stage from the 10/hl. I have not included the power supply or regulator schematic.

---Gary

Click the image to open in full size.
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Old 9th June 2010, 08:39 PM   #10
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Thanks, Gary. Most enlightening.


I'll be sure to put your feedback to good use.
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