cyrus 1 capacitors & rebuild

[nerd]

Dear All

Firstly thanks for all your contributions to a great website. I’m the new boy. My plan is to service and upgrade a pair of Cyrus 1s for vertical bi-amping. I have managed to source most of the information I need, however I am having trouble obtaining information regarding which capacitors to replace, and more importantly, with what.

I intend to replace all the caps but what I need to know is where to spend the money, at £ 25 a pop for good ones it could get a bit expensive, especially with two amps.


Vinotinto has given some good advice here http://www.diyaudio.com/forums/showt...23#post1355323 so I will probably use Black Gates for the 4 near the output transistors. And am happy to use say some Mundorf m-cap Zn for the power amp input caps (C31&31). I have sourced some Mundorf 470uf from here http://www.hifisound.de/oxid/oxid.ph...07b98.58220416 to replace C43&44 but I’m not sure these are any good they seem a bit cheap
@ £ 2.70. Any better suggestions, or are they ok?

In summary If anyone can give me some advice on which caps to change for expensive ones and which to replace with normal ones and were to get them (Cricklewood sell “audio grade” for about 40p/ unit) it would be greatly appreciated.

Sorry if this has already been done, it’s a massive forum I could have well missed something.

[Sonusthree]

Hi Nerd,

I've completely recapped a cyrus 2 and PSX. Be wary of the limited case size when choosing input caps. You can probably see from my picture that the leads touch the top of the case ....

I'm quite busy tonight at least so PM me if you'd like more info.

[nerd]

Hi Martin

I was hoping you would post somthing, I have a picture of your amp on my wall! not really. It looks good though.

Unfortunatly I can't PM you untill I have done a few posts, that's the way it is for new boys.

Any help you can give me would be greatly appreciated.

I will post my planned specification later today.

Thanks for the reply.

Phil

[nerd]

THE PLAN

Replace the output transistors with buv 48s
Set molex in pcb so R 81,83&85 can be changed / trimmed easily
Replace all caps and upgrade where needed
Remove op-amps and replace with 8 pin dil sockets
Attach heat sinks to voltage regulators.
Replace power supply capacitors with 22,000uf ( with the aid of an angle grinder you can get them in!)
Attach socket for external power supply
Remove and replace ribbon cable.
Maybe some bling, gold bananas.

[Sonusthree]

Hi Phil,

There are some great experts on the Cyrus stuff around here ... I'm not one of them ...... but I have three of them and have always wanted one since they first came out and I was too young and broke to buy one! (Not the experts. I mean the amps.)

There are loads of threads about the early Cyrus amps. Definitely read through as many as you can. Stuff about the Cyrus one and two usually gets lumped in together with the occasional thead about the PSX supply for the Two.

Anyway, I recapped my Cyrus two a while ago now and changed the volume pot. I use my Cyrus two with the seperate PSX power supply and that's why you'll see the original power caps in my photo. They're not in use anyway so I didn't change them.

In my opinion, probably most of the caps are very important. The input caps have a signal passing directly through them so I wanted quality there .... I used Sonicaps BUT really they are way toooooo big for the job. Check dimensions before purchase!. The original electrolytics are very small and fit in a tight space. I do sometimes wonder why they chose electrolytics in this location ...... perhaps it wasn't just a cost issue?

Feedback caps, these are also in the signal path so I went for Black gates here. I don't have any conclusive proof that they are better than any other brand ..... I just didn't want that nagging feeling that my amp could have sounded better!

Power caps: Now, The originals are usually, but not always, split foil types which are very expensive but lots of people think that they are special. The capacitance counts here too. It's entirely reasonable to increase the capacitance a little here. The 'One' can sound a little anaemic compared to the 'Two'. The 'Two' is more powerful anyway but has a bigger transformer and more capacitance. I use my 'two' with a PSX. I recapped my PSX from 60,000uF split foil to 80,000uF Mundorf caps.

I mention this because my Two has awesome bass but sounds a little slow in the mid and treble. I didn't notice until I tried the unmodified Cyrus 'One'. My Cyrus 'One' has noticably less bass control .... and well .... less bass in general but it follows EVERY nook and cranny in the music at the speed of light!

My point being that more capacitance might give you a bit more bass but I'm not exactly sure if this extra capacitance would slow down the upper frequencies. Also, maybe not using 'slit-foil' caps is the cause. I'm not trying to confuse you, honestly, I just don't understand why the 'One' sounds better than my 'upgraded' 'Two'.

You can see in the pic that I used some Elna Silmics by the output transistors. They don't fit either! The legs are longer than ideal and are twisted over to avoid other components.

Chris (Anatech) has mentioned elsewhere that he has seen a few cases where the caps in the phono section have dried out and caused the phono section to oscillate. So, even if you don't use a record deck, still change the caps there or disconnect the section entirely by removing the voltage regulators or wire links or etc etc.

I removed the ribbon cable and replaced with silver and teflon wire underneath. The original ribbon wire has push-fit connections at one end which can't be a great idea after all of these years.

In my opinion the solder traces are very delicate so go carefully with your iron!

The pic shows an Alps 'Blue Velvet' pot that I fitted with some pin bending and improvisation.

These days I have bypassed all of the switches and use an external stepped attenuator.

I'm currently passively Bi-amping:
A Cyrus one for the tweeter and Cyrus Two/PSX for the mid and bass duty.

I hope that helps in some way!

Edit: I posted this before reading your plans. Wow .... that's pretty much a rebuild your planning!

[AndrewT]

Originally posted by Sonusthree
.....because my Two has awesome bass but sounds a little slow in the mid and treble. I didn't notice until I tried the unmodified Cyrus 'One'. My Cyrus 'One' has noticeably less bass control .... and well .... less bass in general but it follows EVERY nook and cranny in the music at the speed of light!

My point being that more capacitance might give you a bit more bass but I'm not exactly sure if this extra capacitance would slow down the upper frequencies. Also, maybe not using 'slit-foil' caps is the cause. I'm not trying to confuse you, honestly, I just don't understand why the 'One' sounds better than my 'upgraded' 'Two'.
.........................................

I'm currently passively Bi-amping:
A Cyrus one for the tweeter and Cyrus Two/PSX for the mid and bass duty.

optimising the amps for their duty should give some benefit.
The treble amp could use fairly small polypropylene capacitors and still pass all the frequencies necessary for good treble performance. I wonder if a 10uF polyester cap in the NFB leg would get sufficient bandwidth for the treble?

[nerd]

Gentleman

Thank you so much for your input. I have ordered a load of bits and then I am off on hols for a few weeks. I think when I get back I will create a new thread showing my efforts at a cyrus re-build.

Martin thank you for such a comprehensive reply, I am using Panasonic FM and FCs for all the small caps. Some big fat Mundorfs for the inputs and some black gates for the NFB.

Andrew, I note your comment regarding the caps on the NFB. Interesting as the final plan is to quad amp my four way speakers. I have a slight dilemma regarding buying some additional Black Gates for future use (limited stocks), if possibly changing the value of the caps here will make the amps more suited to high frequencies.