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) 🙂
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) 🙂
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.
adding a thermistor in the ac input circuit to limit the turn on serge.
* 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
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.
Hello Woody and Master Zen.
Thank you very very much for your replies.
I will proceed with my quest. 😎
Thank you very very much for your replies.
I will proceed with my quest. 😎
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! 🙂
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! 🙂
Attachments
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! 🙂
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! 🙂
Attachments
anti-oscillation thingies
you need scope and proper square wave generator to decide are they necessary and of proper value
you need scope and proper square wave generator to decide are they necessary and of proper value
Thank you for the answer.
I guess I'll better do nothing then, as I have no access to either scope or sqare wave generator. 🙁
Hello again.
Caps, trimmers and thermistors have been replaced, amp reassembled and adjusted, and the bias is now more stable. Thank's for the help.
One thing is still puzzling me though: There isn't a shadow of heat-paste to be found anywhere in my amp!
Although the heat-sinks do reach the recommended 40C after an hour, touching the 'transfer-alloy' between the TO3's and the heat-sinks produces a very unpleasant noise (by me) 😱 as it is hot enough to light a cigarette.
Also, using my ears only, I think the musical sweet-spot is hit quite some time before the amp is up to maximum heat-level.
It would make sense to me that both bias and temperature affects the sound quality, so I feel like adding a heat-pad or some paste between the transfer-alloy and the sinks, but is this the right thing to do, or should I leave it as is???
Thank's again!
Caps, trimmers and thermistors have been replaced, amp reassembled and adjusted, and the bias is now more stable. Thank's for the help.
One thing is still puzzling me though: There isn't a shadow of heat-paste to be found anywhere in my amp!
Although the heat-sinks do reach the recommended 40C after an hour, touching the 'transfer-alloy' between the TO3's and the heat-sinks produces a very unpleasant noise (by me) 😱 as it is hot enough to light a cigarette.
Also, using my ears only, I think the musical sweet-spot is hit quite some time before the amp is up to maximum heat-level.
It would make sense to me that both bias and temperature affects the sound quality, so I feel like adding a heat-pad or some paste between the transfer-alloy and the sinks, but is this the right thing to do, or should I leave it as is???
Thank's again!
Hello Master Zen.
Here is a closeup of what it looks like.
As I discovered when it was in pieces, there is no heat-paste anywhere.
None between the TO3's an the transfer-alloy, and none between the transfer-alloy and the heat-sinks.
The transfer-alloy is £$%&¤ hot, while the sinks are comfortable to the touch, so I thought I would put some paste between these, (green arrow).
Attachments
you need cleaning and new thermal goo between all surfaces , so .......... transistors need to go out
work on them one by one , to prevent possible positioning mistakes
work on them one by one , to prevent possible positioning mistakes
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