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Old 16th December 2014, 03:37 AM   #1
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Default Cyrus 2 renovation

Hi all, as something to do over christmas rather than just write assignments on vCJD, I'm looking to renovate the input rca's, potentiometer and power amp section of my Cyrus 2. Now I'm a bit unsure about the power amp capacitors though, whats recommended as good quality at the moment? There's so much to choose from, and what i'd really like to do is preserve the original sound and build on it, perhaps slightly more LF and bring out lots of that lovely detail and space cyrus is known for.
Also I understand I should strive for the best possible components in the feedback stage but I'm having trouble identifying exactly which capacitors are in the NFB loop, the service manual mentions C43/44 and that this can be modified to increase bass extension (sounds appealing), but can anyone with some greater knowledge be of assistance?
Thanks!
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Old 17th December 2014, 06:00 PM   #2
AndrewT is offline AndrewT  Scotland
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I don't have my Cyrus 2 to hand (I loaned it out 5 years ago and it has not returned home).
Does that make me "home alone"?
But I seem to recall that the main smoothing caps are close to the main circuits.

This could mean that some of the local decoupling is performed by the mains smoothing.
This puts a very different duty on these compared to normal amplifier layouts.

The slit foil caps may well have a lot to do with the sound.

Someone asked about cloning the PSX (pre r version). There, the same caps are used but are remote. These will have very little to do that can affect the sound, other than the strength of the bass.
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Old 18th December 2014, 07:24 PM   #3
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Haha it possibly does! - Yeah I had a read through the service manual and it does appear the large electrolytic inside the Cyrus do serve as local decoupling - perhaps worth experimenting with bypassing with a small value capacitor (not sure what value would be appropriate)?

It was also me that asked about the PSX cloning, I believe that shouldnt be too difficult but I'm balancing which job to do first amp recap vs power supply build, and from doing some listening I think the amp needs attention first, I was planning on incorporating slit foils into the amp itself and the psx should i build one, sadly i cant fit anything larger than the 10,000f present currently due to space constraints, at the moment i just need to work out what would be a good quality replacement for the caps that exist in the power amp section.
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Old 21st January 2015, 08:15 PM   #4
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I feel I need a little help now.
Ive recapped/ modified the power amp section of my Cyrus 2 in stages,
Ive removed the input and record selector, the balance control and volume pot, i replaced only the volume pot with a TKD pot.
Ive recapped the power amp section with a mixture of nichicon KZ for power polar caps, nichicon muse for the bi-polar, and replaced the rest of what i can with some polyprops from audiocap.co.uk, and used silver wire to route the input signal straight from the RCA's on the back to the input legs of the volume pot, and the signal ground to the same point where the ribbon cable used to ground to.
Following this work there was an hum which magically just disappeared following accidentally brushing a capacitor but while it was there it would become louder when i touched any metalwork on the case. That disappeared so i thought it was settled.
So on with the next stage, i replaces the 1uF and 2.2uF signal path bi-polars with audyn plus caps, and the hum has returned. I tend to use my laptop as my source, and on battery power it hums, however once plugged in that disappears, but system noise from touching the trackpad or the hard disk head moving generates noise i can hear in my speakers. If I leave the laptop unplugged or use my ipod, there is noise present unless I'm touching metal of the source and then touch something else earthed, be it the amp chassis or part of a power connector that's openly earthed. Most unusually the noise reduces/ disappears if i only hold the sides of the 470uF feedback to ground caps, depending on where my fingers are located on the can the noise is attenuated to a varying degree
- Does anyone have and pointers on what i could look at to troubleshoot?

Last edited by James189; 21st January 2015 at 08:31 PM.
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Old 22nd January 2015, 10:08 AM   #5
AndrewT is offline AndrewT  Scotland
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A hum introduced as a result of an electrolytic swap means you have made an assembly mistake.
Find the error and return to original.
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Old 22nd January 2015, 10:54 AM   #6
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Also, the way you have wired direct to the volume pot is potentially not a good idea as it removes the input filtering and exposes the pot to DC should you have a DC coupled source.
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Old 22nd January 2015, 08:25 PM   #7
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To clarify, Richie00boy, what components before the volume pot form the input filtering? ive seen it mentioned several times that the balance selector can be removed with little effect other then on input impedance, there is no other circuitry between there and the input rca's, apart from two resistors hidden under the input selector which ive kept in the signal path, and as far as i was aware the DC blocking was the 2.2uf capacitors on the input to the power amp section unless I'm mistaken? those are still in the signal path - no values have been altered anywhere except for the removal of the balance control.
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Old 22nd January 2015, 09:37 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

A bog standard Cyrus 2 is way too good for a laptop as a source ....

Consider a fairly cheap external USB powered DAC.
e.g : Pro-Ject USB Box S DAC

rgds, sreten.
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Old 23rd January 2015, 01:36 AM   #9
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I have been looking for a better source, for about 100, but I'm torn between a classic dacmagic II, spending a bit more for the azur newer version, or that 4xtda1543 dac everyone raved about a while ago, I'd really like to find a NOS dac but I cant afford something like the rega dac and as far as i can tell most other designs are TDA1543 and probably wont be as detailed as I'd like - any suggestions?
Edit - i'd prefer to use something with a toslink input than usb, ive always had trouble with laptops that werent galvanically isolated.
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Old 23rd January 2015, 08:34 AM   #10
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My mistake on the DC blocking, it's been a while since I worked on one. You will lose a low-pass filter, but there is another one at the amp front end so it's not a disaster. I did actually remove the balance control (actually a twin pot on the ones I worked on) as its pointless IMO.

As for a DAC, don't mess about with NOS rubbish, get yourself an ODAC and a USB isolator from hifimediy.
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