Cyrus PSX dead - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th January 2007, 09:24 AM   #1
diyAudio Member
 
Join Date: Dec 2006
Default Cyrus PSX dead

Hi,

Yesterday the loudspeaker wires on my Cyrus II & PSX combo
made a shortcircuit and now it is quiet....... . I checked the transistors of the amp, looked OK, put in the fuses and it worked.
Check the PSX, dead, does anybody knows the schematic ?
I only see 2 transistors/regulators and some diodes.

gerald.
  Reply With Quote
Old 16th January 2007, 02:29 PM   #2
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Default Re: Cyrus PSX dead

Quote:
Originally posted by gfredriks

Check the PSX, dead, does anybody knows the schematic ?
Gerald

The circuit of the PSX is basically the same as that of the power supply section of the Cyrus 1 (and 2). The schematic is on my website:

http://www.tcaas.btinternet.co.uk/cyrus1ps.gif

The main differences for the PSX are as follows:

The transformer is 27.9V-0-27.9V 240VA.
C65 and C66 are two 15000uF 50V slit foil capacitors in parallel.
D13, D14, D15 & D16 are two PFR852 diodes in parallel.
R113 & R114 are two 3k9 resistors in parallel.
F1 & F2 have a higher current rating.

It sounds as if you may have been lucky and that the fuses in the PSX blew before the output transistors. My experiences with the Cyrus 1 have been that the output transistors protect the rail fuses rather than the other way round.

Geoff
  Reply With Quote
Old 16th January 2007, 05:08 PM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
I have not opened the PSX for the Cyrus11 but I think it only has the top half inside i.e, no regulated part.
But there are 5pins on the plug so there is something else coming out of there, but what does it supply?

The Cyrus output has some current limiting.
I guess the current limit triggered, protecting the output transistors. Then the PSX fuses overheated and opened.

I think the PSX fuses are F3.15A . Do not fit standard or T fuses.

Geoff,
when you said parallel, did you mean in series?
__________________
regards Andrew T.
  Reply With Quote
Old 16th January 2007, 05:42 PM   #4
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Quote:
Originally posted by AndrewT
Hi,
I have not opened the PSX for the Cyrus11 but I think it only has the top half inside i.e, no regulated part.
But there are 5pins on the plug so there is something else coming out of there, but what does it supply?
The PSX has both the high current supply (for 'upgrading' the Cyrus 2) and the regulated output as it was also sold as an 'upgrade' for the Cyrus CD player.


Quote:
I think the PSX fuses are F3.15A . Do not fit standard or T fuses.
The Cyrus 1 has F3.15A rail fuses and the Cyrus 2 has F4.0A so I would expect the PSX to have fuses of at least 4A and possibly higher. Unfortunately I didn't make a note of the fuse rating when I tool the lid off a friend's PSX a few years ago.


Quote:
[Geoff,
when you said parallel, did you mean in series?
No, I meant parallel for the reservoir capacitors, for the rectifier diodes and for the capacitor discharge resistors.
  Reply With Quote
Old 17th January 2007, 01:22 AM   #5
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Guys,
Actually, these questions are easily answered as soon as Gerald pops the cover and has a look. I've not looked inside one of these for a few years. They almost never give trouble.

The newer PSX-R is really cool. It detects the unit and adjusts it's output voltage to suit. Neat eh?

-Chris
  Reply With Quote
Old 17th January 2007, 02:06 AM   #6
diyAudio Member
 
Sonusthree's Avatar
 
Join Date: Dec 2005
Location: Sussex, UK
Default Re: Re: Cyrus PSX dead

Quote:
Originally posted by Geoff

The transformer is 27.9V-0-27.9V 240VA.

Geoff
It's late here, but I'm pretty sure that the PSX transformer is 400VA or more.

Perhaps the Cyrus Two already has 240VA compared to the smaller Cyrus 1?

Martin.
(..........who loves to be right on small techical issues like this because I don't understand the more complex ones.)
  Reply With Quote
Old 17th January 2007, 07:48 AM   #7
diyAudio Member
 
Join Date: Dec 2006
Hi,


Thanks for the schematics, I thought it would be more complex
because of those voltage regulators, but this an independent circuit,
just for the CD output (+/- 18V).
Yes, you're right only one fuse was blown (T 5A),
after measuring the diodes and replacing the fuse,
it works again. This is really a huge transformer,
taking almost 30% of the contents of the PSX and
twice as big as the one in Cyrus2-amp.

But now that it works again, I have another challenge:
I own a Cyrus 1 and a Cyrus 2 amp, because I have a small room,
I do not need the higher power of C2 and I am happy with
the C1 performance. What I would like to try is Cyrus 1 + PSX.
As an experiment I can solder the supply wires between
the two, I can also try to find the original plug and solder that one in.

PSX delivers 38V, Cyrus 1 has a 30V railvoltage.
Since I cannot lower the PSX voltage,
I have to work with 38V and must adjust the idle current.
Although I know electronics, I'm more digital based
so I wonder if you guys know which resistor(s) to in/de-crease.


gerald.
  Reply With Quote
Old 17th January 2007, 09:56 AM   #8
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Hi,
you can probably build a clone of the PSX for less than what extra value PSX adds to the Cyrus 2 on the secondhand market.
Have a look at Ebay and see what price you can get for a 2 or a 2+psx.

The PSU, as you have seen, is just a transformer + rectifier + smoothing.
The caps in tha PSX are now very old and may not be performing at their best. They were of a make and type specifically selected to sound good.
You need to clone or replace with something equally good.

I have seen a report suggesting that the Cyrus 1 is suitable for conversion to 1+psx.
You have both, so it is easy for you to compare the device types and the mechanical layout. It should be easy to add a 5pin xlr socket in the same location and wire it in appropriately. If the PSX voltage is just a bit too high for the Cyrus1, then your clone can use a slightly lower voltage transformer i.e. 25Vac rather than 28Vac, but keep in mind these early Cyrus designs were specified for 8ohm use not 4ohm. By the way a modern 25Vac transformer that is rated for 230Vac mains is equivalent to 26Vac when running on 240Vac in the UK.
Low load impedance is more likely to kill the amp than running slightly higher voltage.
I would check into that T5A fuse. Can you find confirmation that T (anti-surge=time delay) is the appropriate type? Can you find confirmation that 5A is the appropriate value?
I have found that F5A supports peak output currents of up to 10A (when fitted to the supply rails after the main smoothing). That implies 80Vpk into 8r=400W into 8r. That is too high for a Cyrus1 or 2. Try F4A (<=250W into 8r) and see if you get any nuisance tripping. F3.15A gives <=150W into 8r)
__________________
regards Andrew T.
  Reply With Quote
Old 17th January 2007, 11:30 AM   #9
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Quote:
Originally posted by gfredriks

PSX delivers 38V, Cyrus 1 has a 30V railvoltage.
Since I cannot lower the PSX voltage,
I have to work with 38V and must adjust the idle current.
Although I know electronics, I'm more digital based
so I wonder if you guys know which resistor(s) to in/de-crease.

Probably a ridiculous suggestion, but why don't you have a try at regulating those 38v onto 30?

High current regulators like Kit Ryan's or Boak's could be applied on the Cyrus.


Carlos
  Reply With Quote
Old 17th January 2007, 12:02 PM   #10
Geoff is offline Geoff  United Kingdom
diyAudio Member
 
Join Date: Apr 2001
Location: UK
Quote:
Originally posted by gfredriks
Hi,

But now that it works again, I have another challenge:
I own a Cyrus 1 and a Cyrus 2 amp, because I have a small room,
I do not need the higher power of C2 and I am happy with
the C1 performance. What I would like to try is Cyrus 1 + PSX.
As an experiment I can solder the supply wires between
the two, I can also try to find the original plug and solder that one in.

PSX delivers 38V, Cyrus 1 has a 30V railvoltage.
Since I cannot lower the PSX voltage,
I have to work with 38V and must adjust the idle current.
Although I know electronics, I'm more digital based
so I wonder if you guys know which resistor(s) to in/de-crease.
IMO, there is little point in trying to connect the PSX to your Cyrus 1 because due to the higher supply rail voltage you would need to change the output transistors to ones similar to those used in the Cyrus 2 otherwise you run the risk of exceeding the transistors SOA (the PT7, alias BUV28, is only rated at 65W for case temperatures between 25 and 60degC).

If you change the output transistors you will effectively have a Cyrus 2 because the only difference between the 1 and the 2, apart from an improved phono stage and a beefier power supply, it the use of different output transistors (or paralleled PT7s in the earlier plastic cased Cyrus 2).

As Andrew has said, if you want to improve the power supply for the Cyrus 1 you would probably be better building one from scratch, using a higher VA rated toroid and larger reservoir capacitors but keeping a similar supply rail voltage to that of the standard Cyrus 1. This would better suit modern speakers that tend to have a lower minimum impedance.

Alternatively, as Carlos has indicated, you could use the PSX but lower the rail voltage using a regulator circuit, though this solution would lower the efficiency (more heat dissipated) and would require some additional heatsinks.

For what it's worth, in a side-by-side comparision of the Cyrus 1 and a Cyrus 2 + PSX in a small room and at moderate volume I much preferred the standard Cyrus 1. It had more delicacy, detail and finesse on my taste in music (acoustic jazz and baroque classical). In a larger room or at higher listening levels or with very low efficiency speakers, where a higher power output is required, the situation might be different.

For the later v07 (metal cased) versions of the Cyrus, the quiescent current for the output stage is set by the values of R81/R83 in one channel and R82/R84 in the other (see schematic linked below). The earlier versions had a preset (RV2/RV3) for adjusting Iq.

http://www.tcaas.btinternet.co.uk/cyrus1pwr.gif
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cyrus One hacknet Solid State 31 29th June 2012 04:50 PM
cyrus 2 atomised Solid State 350 19th December 2011 11:42 AM
WTB Cyrus 1 or Cyrus 2 amplifier monstertrucker Swap Meet 0 20th November 2008 02:04 AM
cyrus 2 dead c32 &amp; 31 wrong way help paul_peraic Solid State 0 29th May 2008 04:26 PM


New To Site? Need Help?

All times are GMT. The time now is 05:40 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2