New (to me) Threshold FET-10 HL (What to refurbish?)

[Eric Juaneda]

Hi GaryB,

I built a new external power supply for my FET 10hl... I upgraded the transformer to a 28VA transformer...

This new power supply integrates very interesting solutions for audio rendering: using inductor before capacitors, putting Earth at silent point ground...
I'm sure that it sounds good.

Don't you try to use bigger transformer? (160VA for example?). Comparison might be easy now.
I wrote few line about this: power supply

 

[GaryB]

This new power supply integrates very interesting solutions for audio . . .

Don't you try to use bigger transformer? (160VA for example?).

Eric,
Thanks for the comments. I had seen your web page before but I had not visited it in a long time. I enjoyed it quite a bit.

The reason that I use a choke input supply is that with the right choice of components and matching them to the current draw of the preamp, one can achieve your goal of having the transformer supply constant signal to the capacitors. With the values I use, the charging current flows constantly through the inductor and is a nice sinusoidal waveform. The ripple on the output is also small - about 7mv, so the supply is quiet. A rough guideline is that if L (H) > Vout / Isupply (ma) then you will achieve constant current operation through the choke. So for a 0.32H choke and an output voltage of 25.5v one wants Isupply to be greater than 80ma. A detailed simulation shows that the real minimum current is 71-72ma, but this is a nice simple formula to remember. That is the reason for the 1000 ohm resistors in the schematic. The FET 10/hl draws around 55ma so there needs to be some extra current consumed to achieve constant current operation. The resistors add another 25ma current draw and insure constant current operation.

The impedance of the choke limits the current so a larger transformer won't provide any higher charging current. Thus I am not sure there will as much benefit from a larger transformer in a choke input supply as one sees with a capacitor input supply. But I have been surprised in the past, so I agree that it is a worthwhile experiment.

Best regards,
---Gary

 

[Eric Juaneda]

Hello GaryB,

...The impedance of the choke limits the current so a larger transformer won't provide any higher charging current. Thus I am not sure there will as much benefit from a larger transformer in a choke input supply as one sees with a capacitor input supply. But I have been surprised in the past, so I agree that it is a worthwhile experiment.

Right.
I use 8H or 10H inductor in my model 4 preamplifier and Jundac One DAC. I was surprised that changing 80VA transformer to 200VA increase audio rendering too
Very surprising !

http://tech.juaneda.com/gallery/jundac-03.jpg
Jundac One DAC

 

[Redwingnine]

Sorry it took so long, but here is a picture of the custom power supply for the FET-10.

It's overkill to the max, but really opens up the soundstage.

 

[jacco vermeulen]

Looks pretty neat too.

 

[GaryB]

new power supply

I've built yet another power supply for my Threshold FET 10/hl. I've incorporated suggested from Zenmod and Eric Juaneda by moving the position of the inductor for the negative supply and also increasing the size of the power transformer from 28VA to 160VA. I used a transformer that I got from ApexJr. Attached is a copy of the new schematic. In addition to what I've drawn, there is also a snubber across the transformer secondary (324ohm + 22nf) and bypass caps across the 10kuf electrolytics (10uF 63v (type K73-16) and 1uF 200v (type K40Y-9) and 0.1uf 630v (type K42Y-2)).

As Eric suggested, the bigger transformer is a worthwhile improvement giving better soundstage and a more natural and musical bass line.
Definitely worthwhile - if you're going to the trouble to build a new supply then go for a big transformer.
---Gary

 

[GaryB]

photos of new supply

Here are a few pictures of the new supply.

1) The 3 supplies stacked; the latest one is on the bottom of the stack, the original is on top, and my previous supply in the middle.

2) A view inside the power supply.

3) The back of the supply. The switch is for AC polarity.

---Gary

 

[Zen Mod]

 

[Redwingnine]

Nice job, Gary.

It is remarkable how much of an improvement is rendered from a beefier power supply for the FET-10.

 

[margannai]

I've built yet another power supply for my Threshold FET 10/hl. I've incorporated suggested from Zenmod and Eric Juaneda by moving the position of the inductor for the negative supply and also increasing the size of the power transformer from 28VA to 160VA. I used a transformer that I got from ApexJr. Attached is a copy of the new schematic. In addition to what I've drawn, there is also a snubber across the transformer secondary (324ohm + 22nf) and bypass caps across the 10kuf electrolytics (10uF 63v (type K73-16) and 1uF 200v (type K40Y-9) and 0.1uf 630v (type K42Y-2)).

As Eric suggested, the bigger transformer is a worthwhile improvement giving better soundstage and a more natural and musical bass line.
Definitely worthwhile - if you're going to the trouble to build a new supply then go for a big transformer.
---Gary

Hello. Excuse me, but I follow your discussion. My friend wants me to build a clone of fet10. I wanted to know, value of supply voltage is 12V 0-12V? Components such as FET input type you use? Thanks. Regards

 

[Apesbrain]

Hi, I'm coming late to this thread but I do have the appropriate pages from the FET/9e operator's manual. The switch operation is NOT the same as the FET/10.

 

[a.wayne]

^^^^ Thanks ...............

 

[clintalloy]

I've built yet another power supply for my Threshold FET 10/hl. I've incorporated suggested from Zenmod and Eric Juaneda by moving the position of the inductor for the negative supply and also increasing the size of the power transformer from 28VA to 160VA. I used a transformer that I got from ApexJr. Attached is a copy of the new schematic. In addition to what I've drawn, there is also a snubber across the transformer secondary (324ohm + 22nf) and bypass caps across the 10kuf electrolytics (10uF 63v (type K73-16) and 1uF 200v (type K40Y-9) and 0.1uf 630v (type K42Y-2)).

As Eric suggested, the bigger transformer is a worthwhile improvement giving better soundstage and a more natural and musical bass line.
Definitely worthwhile - if you're going to the trouble to build a new supply then go for a big transformer.
---Gary

Gary B, would this PS work on a Threshold 9/e? Or would I need to change anything? I am a bit of a noob

thanks

 

[nguy14]

Hi I am new to the forum and am trying to update the power supply and preamp cap replacement when I noticed 3-4 of the small silver painted transistors? are cracked. Anyone know if the exact replacements are still available?

Any recommendations on what is best to use for the 1uf 63v and 10uf uf along with the 4 4.7uf capacitors in terms of brand and sound quality? Any other caps that needs replacing?

I do have the Fet ten/hl with the green ERO MKT1813 cap.

 

[nguy14]

I found what I need after looking that the thread...

 

[GaryB]

Gary B, would this PS work on a Threshold 9/e? Or would I need to change anything? I am a bit of a noob

thanks

Sorry for not noticing this message earlier.

You should be able to use the same power supply for the 9/e preamp. It use an on board regulator, so any voltage in the range of +-24v will be fine. The connectors on a 10/hl power supply and a 10/e or 9/e supply are different, so it's hard to swap the stock power supplies from one version to another. But that isn't a problem if you're building your own power supply.

---Gary

 

[tfender]

Sorry for not noticing this message earlier.

You should be able to use the same power supply for the 9/e preamp. It use an on board regulator, so any voltage in the range of +-24v will be fine. The connectors on a 10/hl power supply and a 10/e or 9/e supply are different, so it's hard to swap the stock power supplies from one version to another. But that isn't a problem if you're building your own power supply.

---Gary

Hi Gary

I need to Threshold FET -10hl Power supply SCHEMATICS , My power supply 15-0-15 AC.

Thanks
tfender

 

[GaryB]

The original power supply is very basic. It uses a small transformer (6VA), standard diodes, and modest capacity electrolytic capacitors. If you're building your own power supply from scratch then you want to improve each part. Use an 18v/18v transformer but increase the capacity to >200V. Use better quality diodes. And increase the electrolytic capacitors to >10Kuf. Other things that I would do include adding snubbers to the transformer to kill off any remnants of the diode reverse recovery and adding some film capacitor bypasses to the big electrolytic.
Or if you want to try something different, take a look at the power supply that I built in post 66 http://www.diyaudio.com/forums/pass-labs/167856-new-me-threshold-fet-10-hl-what-refurbish-7.html#post2442801
But the biggest benefit comes from using a bigger power transformer.
---Gary

 

[treuben]

fet nine, nine/e, tenHL, ten HLe differences?

I have posted in a few threads in the past asking about the differences between the line stages of these designs. I wonder if anyone here (since there seem to be some quite familiar with the circuits here) would be able to enlighten me as to the differences? I know the 10 HL/e were servo, balanced. The nine/e didn't seem balanced output though from pictures. Is the old nine and 10HL the same line stage? (wondercap coupled?)

Kind regards, from Australia.

"I love what you've done with the place, but this place is a prison, essentially, as much as you all like to deny it. I've seen insects with kneepads and you live approximately three quarters of a mile away from the sun." - Dylan Moran, On Australia

 

[treuben]

I did succeed in finding a schematic for a fet nine. The plain old non-e version. It looks very similar to the fet 10HL (non-e) though it uses only one 2N5566 in the input versus the 2 paralleled in the fet 10HL. I've heard it said that the psu's are the same between the two. Also, there seems to be a slightly different arrangement for the resistors and caps in the feedback loop with the nine having an extra set in series vs the ten. Would the paralleled 2N5566 in the 10HL be for lower noise or something else? It seems odd to my limited knowledge to need that in a line stage. Perhaps someone here will know more!

All the best!