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Old 23rd March 2015, 12:00 AM   #1
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Default Threshold S/150

Hello there...

An old dream of mine to own a piece of Pass, has just come true in the shape of a wonderful Threshold S/150.
I absolutely love the sound, and couldn't be more happy with my choice.
However... being an old lady, she has a few issues that needs addressing.

I have tried to find and read everything possible, but before taking her apart and putting any of it to the test, I would like to be absolutely and totally sure, so I don't harm this fine piece of art in any way!

First up... the bias drifts (around 30-40mv) slowly up and down, typically a couple of times every hour, in both channels.
From what I've been able to find, changing the 470uF lytic and the 150nF tantalum caps on the circuit bords should solve this issue, but is there anything else regarding this issue I should check/change while I'm at it?

It has been recommended to change the tantalum to a poly, but what about the lytic? Does it have to be audio-grade, or just whatever is on the shelves?

Next... I have ordered a fresh pair of (33.000uF) caps for the power-supply. Is it necessary (or a good idea) to change the rectifier because of this upgrade, or will the original one be strong enough to deal with the xtra surge?

The previous owner have placed a couple of 6.8uF film-caps parallel with the powerlytics. Would it be a good idea to change the size on these as well, or perhaps to just get rid of them? There seems to be a lot of religion involved when the talk is about placing film caps across the power-supply caps!?

And finally... I have read that placing a 100nF cap on each of the rectifier-diodes, will reduce transformer-hum. Can this be done without compromising the sound in any way??

Actually... I think that was it... for now.

I hope you can find the time to help this old fart getting a bit closer to heaven, and my amp a bit closer to its original glory!

Thank you very much!

...'squeeeeeq'... (the sound of my body bowing in deep respect of your knowledge)
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Old 23rd March 2015, 04:47 PM   #2
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If those 33,000uF caps are a lot larger than was originally there you might want think about
adding a thermistor in the ac input circuit to limit the turn on serge.
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Old 23rd March 2015, 05:23 PM   #3
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Quote:
Originally Posted by baeijsman View Post
Hello there...

An old dream of mine to own a piece of Pass, has just come true in the shape of a wonderful Threshold S/150.
I absolutely love the sound, and couldn't be more happy with my choice.
However... being an old lady, she has a few issues that needs addressing.

I have tried to find and read everything possible, but before taking her apart and putting any of it to the test, I would like to be absolutely and totally sure, so I don't harm this fine piece of art in any way!

*First up... the bias drifts (around 30-40mv) slowly up and down, typically a couple of times every hour, in both channels.
From what I've been able to find, changing the 470uF lytic and the 150nF tantalum caps on the circuit bords should solve this issue, but is there anything else regarding this issue I should check/change while I'm at it?

**It has been recommended to change the tantalum to a poly, but what about the lytic? Does it have to be audio-grade, or just whatever is on the shelves?

***Next... I have ordered a fresh pair of (33.000uF) caps for the power-supply. Is it necessary (or a good idea) to change the rectifier because of this upgrade, or will the original one be strong enough to deal with the xtra surge?

****The previous owner have placed a couple of 6.8uF film-caps parallel with the powerlytics. Would it be a good idea to change the size on these as well, or perhaps to just get rid of them? There seems to be a lot of religion involved when the talk is about placing film caps across the power-supply caps!?

*****And finally... I have read that placing a 100nF cap on each of the rectifier-diodes, will reduce transformer-hum. Can this be done without compromising the sound in any way??

Actually... I think that was it... for now.

I hope you can find the time to help this old fart getting a bit closer to heaven, and my amp a bit closer to its original glory!

Thank you very much!

...'squeeeeeq'... (the sound of my body bowing in deep respect of your knowledge)


* replace all lytics and Tantalums

**regular industrial types are way to go ..... and some of them are simply missing audiophool label , just because techies are ignorant (Panasonic , Elna, Rifa , Matshusita etc)

*** good 35A bricks are cheap

**** let your own ears decide

***** same as above , however if it's not for hum , but for decreasing rectification spikes
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Old 23rd March 2015, 05:36 PM   #4
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Those 100nf caps you talked about across the rectifier diodes are you talking about in the power supply ? If so they are refered to as snubber caps. They help damp any high frequency spikes that power supply diodes usualy make when the switch off. We have lots of post about that here but I will leave that search up to you.
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Old 23rd March 2015, 06:49 PM   #5
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Hello Woody and Master Zen.

Thank you very very much for your replies.
I will proceed with my quest.
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Old 29th March 2015, 01:41 PM   #6
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Hello again.

Can anyone tell me the size (type) of thermistor on the circuit board!?
There is no print on the actual component in my amp, and the resolution of the available schematic is pretty low...
I'm guessing it's a 1K NTC, but I would really like to be sure!

Thank's!
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File Type: gif s150-300-500.gif (61.7 KB, 142 views)
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Old 29th March 2015, 01:46 PM   #7
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1K from schm
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Old 29th March 2015, 01:57 PM   #8
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Quote:
Originally Posted by Zen Mod View Post
1K from schm
Thank you!
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Old 12th April 2015, 04:24 PM   #9
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Hello.

Refresh in progress, so my amp is now in pieces.
Because of the handcrafted nature of these babies, I guess a certain amount of individuality is to be expected, but looking closely brought up a new question:
Compared to the schematics, my amp has a couple of more caps on the circuit-boards.
I've added these to the schematic, marked with a couple of arrows.
The green one is 20pF, and is mounted on both channels.
The red one is 75pF, and is only mounted on one!
Could this be an error made by the soldering-dude back in the day?
I feel like just adding the one cap missing, but should I... or is there a deeper meaning behind this strange asymmetry?
I have absolutely no clue to what they do, and if this is normal on all S/150's!?
I hope someone can enlighten me!

Thank ya'll!
Attached Images
File Type: gif s150-edit-2.gif (64.5 KB, 103 views)
File Type: jpg ch.JPG (199.7 KB, 101 views)
File Type: jpg other_ch.JPG (196.4 KB, 97 views)
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Old 12th April 2015, 05:35 PM   #10
Zen Mod is offline Zen Mod  Serbia
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anti-oscillation thingies

you need scope and proper square wave generator to decide are they necessary and of proper value
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