I think I have found the condition that causes the pop at turn on.
I noticed that the first time (after 24 hours powered down), the amp is powered on, there is barely a sound out of it. But if it is turned off and turned back on a few minutes later, there's a good sized pop (3 volts positive peak spike).
I initially had looked at the rise time of the rails and found them matched pretty well, but I didn't consider that one rail had a 30V head start. What is happening is the negative rail discharges down to .6V in about 15 seconds, while the other rail remains in the 30-40V range for an extended period of time. Something is draining the rails asymmetrically.
To attempt to narrow it down, I pulled the fuses for first the right, then the left channel, but the problem remained. It's didn't clear until I pulled the rail fuses for BOTH channels at the same time. It appears that both channels have perhaps a leaky transistor on the negative rail. At this point, all of the capacitors in the amp have been refreshed with new product.
What I'm curious to know is whether there is a known issue with the negative rail transistors becoming leaky. I would imagine the cost of obtaining a matched set would be substantial.
Others have told me that a workaround is to install bleeder resistors to discharge the capacitors. Indeed, discharging the positive supply with a 400 ohm 10W resistor seems to get the job done.
I noticed that the first time (after 24 hours powered down), the amp is powered on, there is barely a sound out of it. But if it is turned off and turned back on a few minutes later, there's a good sized pop (3 volts positive peak spike).
I initially had looked at the rise time of the rails and found them matched pretty well, but I didn't consider that one rail had a 30V head start. What is happening is the negative rail discharges down to .6V in about 15 seconds, while the other rail remains in the 30-40V range for an extended period of time. Something is draining the rails asymmetrically.
To attempt to narrow it down, I pulled the fuses for first the right, then the left channel, but the problem remained. It's didn't clear until I pulled the rail fuses for BOTH channels at the same time. It appears that both channels have perhaps a leaky transistor on the negative rail. At this point, all of the capacitors in the amp have been refreshed with new product.
What I'm curious to know is whether there is a known issue with the negative rail transistors becoming leaky. I would imagine the cost of obtaining a matched set would be substantial.
Others have told me that a workaround is to install bleeder resistors to discharge the capacitors. Indeed, discharging the positive supply with a 400 ohm 10W resistor seems to get the job done.
Maybe one of the members have create this schematics in the meantime. Also the driver stage schematic for the power meter I miss.
Thank you for upload.
Here's a link to the FET 10e phono schematic http://www.diyaudio.com/forums/pass-labs/193194-restoring-threshold-fet-10e-few-questions.html#post2649216
---Gary
Until now I haven't heard about Threshold phono stages. I know only complete pre-amplfiers with integrated phono RIAA stages.
At that time, as the X-ONO/Aleph-ONO was released in the market,
Threshold had already a new owner.
Or am I wrong?
If you look at the 1st post in this thread from someone you know (hint - it's you), you'll see a list of Threshold equipment released over the years. Under the heading "Stereo Line + RIAA Preamplifier", you list the following items:
FET-10Pc Stereo Phone Gain Stage (1986-89)
FET-10Pe Stereo Phone Gain Stage (1990-98)
These are both stand alone phono stages that matched with the FET 10hl and the FET 10he respectively. The schematic shown a few posts earlier is for the FET-10Pe.
---Gary
Yes - the gain module is almost the same as the line stage. If you look at the schematic for the gain module, you will see that there are a few capacitors changed when the gain module is used for the phono stage. They share a common design for the PCB and the phono stage version just adds the extra parts. The parts are labeled on the schematic with an asterisk.
---Gary
Re: The S-300 turn on thump. Mine did that when it was brand new and the entire time I owned it. It's nothing to worry about and it completely normal for this amp. I had mine driving Martin Logan Sequel's at the time. I sort of wish I still had the amp today.... Perhaps it's time to build a clone of the S-300!
Mark
Mark
What about this S/400??? I did not see nothing about it at Threshold.
KRAFTWERK Threshold S400 » Verstärker, Equalizer, Receiver aus Bochum Oberdahlhausen
KRAFTWERK Threshold S400 » Verstärker, Equalizer, Receiver aus Bochum Oberdahlhausen
Threshold active impedance matching module, Model "M1"
This seems to be a MC head amp similar to Hiraga's Prepre and to Mark Levinson's JC-1DC - go to
Threshold ƒwƒbƒhƒAƒ“ƒvm1‚ÌŽd—l ƒXƒŒƒbƒVƒ‡ƒ‹ƒh
http://auctions.c.yimg.jp/images.au.../sellhry-img599x398-1445002910kytsqe24613.jpg
RARE Threshold M1 Moving Coil Pre Preamp Only for NS10 Great Nelson Pass Design | eBay
Unfortunately this model is only for use with this preamplifier:
http://www.audiocostruzioni.com/r_s/pre/thteshold-ns10/ns-10.htm
Both devices I haven't mentioned here.
From there I can download the schematics ?
Thank you for advices.
The thread
http://www.diyaudio.com/forums/pass-labs/26003-threshold-ns-10-m1-info-wanted.html
don't provide the wanted informations.
This seems to be a MC head amp similar to Hiraga's Prepre and to Mark Levinson's JC-1DC - go to
Threshold ƒwƒbƒhƒAƒ“ƒvm1‚ÌŽd—l ƒXƒŒƒbƒVƒ‡ƒ‹ƒh
http://auctions.c.yimg.jp/images.au.../sellhry-img599x398-1445002910kytsqe24613.jpg
RARE Threshold M1 Moving Coil Pre Preamp Only for NS10 Great Nelson Pass Design | eBay
Unfortunately this model is only for use with this preamplifier:
http://www.audiocostruzioni.com/r_s/pre/thteshold-ns10/ns-10.htm
Both devices I haven't mentioned here.
From there I can download the schematics ?
Thank you for advices.
The thread
http://www.diyaudio.com/forums/pass-labs/26003-threshold-ns-10-m1-info-wanted.html
don't provide the wanted informations.
Last edited:
There was a separate PSU for the M1 as well, named the M7. The NS10, I believe, runs from one +24V rail. I think +24V is just fed over to the M1 via the XLR. Find a good PSU and an XLR and you are up and running.
More info might reside here.
/RK
