Amp Hospital: Cyrus One

[istari_knight]

I recently purchased a Cyrus One amplifier partly out of curiosity & partly because I felt sorry for it.

It was in a sorry state as you can see with nextel paint flaking off all over the place, all of the controls only worked in certain positions, 50hz hum over the speaker outputs & the phono stage sounded like aliens were trying to make contact !

http://i26.photobucket.com/albums/c129/istari_knight9/DSC01079.jpg

I disassembled it & found a very nice Holden&Fisher transformer, LM317 regulators, Alps controls, soft recovery diodes & slit foil psu caps all with a very high quality circuit board & layout... I like !

http://i26.photobucket.com/albums/c129/istari_knight9/DSC01080.jpg

Started work on it today, now I dont normally bother with fancy capacitors but decided to give this one "the works" so replaced all of the electrolytics with Nichicon Muse (pretty colours!) The power supply caps got changed for Kendeil 10000uf/50v (originals were 7000uf/40v) both bypassed with MKP films... Also replaced the power amplifiers input caps with MKP films. I've just finished cleaning the volume control/input selectors with Servisol which seems to have helped them.

http://i26.photobucket.com/albums/c129/istari_knight9/DSC01083.jpg

Currently giving it a little test run & it sounds very promising indeed ! Just waiting for some more capacitors to arrive + DIP8 sockets for the opamps :eyebrows:

I'll be stripping & respraying the cast aluminium casework at the weekend.... Keep you posted :cool:

[Reid Malenfant]

:lol: I had a Cyrus amp here a while ago for some reason or other, it went back working at any rate :)

Consider yourself lucky that your amp has a real heatsink :eyebrows: The Cyrus that I was working on only had a shallow U shaped 4mm thick alloy heatsink - a bloody joke :eek:

Think of the outer two fins & flat bottom of yours that the transistors are attached to... It wasn't even black anodised :doh:

[istari_knight]

:lol: I had a Cyrus amp here a while ago for some reason or other, it went back working at any rate :)

Consider yourself lucky that your amp has a real heatsink :eyebrows: The Cyrus that I was working on only had a shallow U shaped 4mm thick alloy heatsink - a bloody joke :eek:

Think of the outer two fins & flat bottom of yours that the transistors are attached to... It wasn't even black anodised :doh:

Ah yes, the MK1 ! AKA V6. Mines the V7... They removed the headphone socket, cast a heatsink into the bottom panel & fitted a rocker power switch otherwise the same though.

[DSJR]

The main cause of hum on output used to be the supply caps in the phono stage failing (yours had the later ones fitted thoughm the failing ones were the encapsulated Roe's originally fitted). The basic circuit is almost bomb-proof I reckon and is basically a power amp with a volume control on the front. If you have means of measuring, make sure there's no ringing at higher power levels, as it's slight (almost) oscillation that could make the sound "exciting" back then....

[istari_knight]

The main cause of hum on output used to be the supply caps in the phono stage failing (yours had the later ones fitted though the failing ones were the encapsulated Roe's originally fitted). The basic circuit is almost bomb-proof I reckon and is basically a power amp with a volume control on the front. If you have means of measuring, make sure there's no ringing at higher power levels, as it's slight (almost) oscillation that could make the sound "exciting" back then....

Your quite right Dave, the phono fault was caused by the 470uf caps in the power supply. I measured them after desoldering & they read 29uf for about 1 second before shorting, Amazing the thing kept working at all !

I dont have a scope but IME if oscillation is occurring certain parts will get hot. Its now been running 4 hours & everythings cold :)

[Reid Malenfant]

I dont have a scope but IME if oscillation is occurring certain parts will get hot. Its now been running 4 hours & everythings cold :)
Nice to know the heatsink works in that one :rfl:

You are pretty much on the money, ultrasonics will heat things pretty quickly ;)



Enjoy :)

[istari_knight]

The V7 Cyrus One & Cyrus Two both share the same casework so the heatsink is rated for 50wpc outputs. This being the One outputs 25wpc so it runs stone cold.

I've seen pictures of the earlier example & the heatsink is woefully inadequate.

[DSJR]

Apologies. When I said "oscillation," I meant slight oscillations on transients, which is something done back then to get an impressive sound and an easy quick dem. Arcams and Marantz's did this as a matter of course at certain times and on certain models to keep their 5 star ratings. You don't always notice this as an issue until you hear a bigger and better amp that doesn't do it...

Anyway, glad you're getting good sounds from the Cyrus One. These later ones did feel quite solid and phono supply caps apart, they were very reliable. Once upon a time, an owner's girlfriend accidentally turned the record and play switches to the same source with the volume turned up. The squeal took out the tweeters very quickly, but the amp continued like this (inaudibly) for a good while. the board and most components were well cooked, but the amp was repairable, and I don't think a new board was fitted either :)

All I'd ask is to use efficient speakers with it and don't push it flat out, since it isn't a soft-clipper :)

[alan47]

A great amp,for the money,i used a V7 for a few years on my PC system with a v-dac into an old pair of alesis 4 ohm studio monitors.Sometimes sounded better than my main system,ie late at night with a large glass of malt :cool:
Just sold it for more than i paid for it,:( because my Mrs seemed to think that my computer room was her dinning room,and why can,t i just use a laptop like everybody else :eyebrows:)It never got hot and put up with everything i did to it...
Look forward to seeing the photo's of the finished restoration.

[istari_knight]

Apologies. When I said "oscillation," I meant slight oscillations on transients, which is something done back then to get an impressive sound and an easy quick dem. Arcams and Marantz's did this as a matter of course at certain times and on certain models to keep their 5 star ratings. You don't always notice this as an issue until you hear a bigger and better amp that doesn't do it...

Anyway, glad you're getting good sounds from the Cyrus One. These later ones did feel quite solid and phono supply caps apart, they were very reliable. Once upon a time, an owner's girlfriend accidentally turned the record and play switches to the same source with the volume turned up. The squeal took out the tweeters very quickly, but the amp continued like this (inaudibly) for a good while. the board and most components were well cooked, but the amp was repairable, and I don't think a new board was fitted either :)

All I'd ask is to use efficient speakers with it and don't push it flat out, since it isn't a soft-clipper :)

Its currently driving a pair of Mordaunt-Short Classic 20 standmounts I got for 99p ! apparently they were £400 new & their quality would support this.

I normally listen at around 75db according to my meter which into 90dbw speakers = what ? 1/2watt output or something silly! I dont think I use more than 5watts ever to be honest so no chance of me getting ringing on transients... Not that I've noticed anyway. I did push it harder than I ever normally would earlier and there was a detectable change in character as you describe I can imagine complimenting alot of 70's speakers.

If used at a low level with 90db+ speakers theres little need for anything more it would seem.

[Rare Bird]

Why throw the Slit Foil idea out the window! Why didnt you fit new Slit Foils?

[istari_knight]

Why throw the Slit Foil idea out the window! Why didnt you fit new Slit Foils?

2 reasons, firstly because they are £16 each & the amps only worth £75 on a good day. Secondly slit foils have lower impedance & better HF performance than regular caps, both of these "features" can be replicated by simply bypassing the regualr caps with films as I have done.

[Rare Bird]

:lol:

[istari_knight]

:lol:

You disagree ?

[Reid Malenfant]

I disagree, kind of ;) Slit foils are a way of making a capacitor behave like a load of smaller electrolytics, they'll have a much lower ESR.

While you will get the benefit of lower ESR at a higher frequency with the bypassing, you won't get the same at a low frequency as you'll be using some kind of standard electrolytic :)


So, kind of :eyebrows:

[istari_knight]

I disagree, kind of ;) Slit foils are a way of making a capacitor behave like a load of smaller electrolytics, they'll have a much lower ESR.

While you will get the benefit of lower ESR at a higher frequency with the bypassing, you won't get the same at a low frequency as you'll be using some kind of standard electrolytic :)


So, kind of :eyebrows:

Well you learn something everyday ! Thank you for taking the time to explain :)

Do you think the 22 year old original slit foils had lower ESR than the new bypassed replacements ?

My cap meter only measures capacitance not ESR which is a PITA.

[Reid Malenfant]

Ah, good point :eyebrows: Your more modern replacement capacitors are likely to be in better condition ESR wise due to age...

If I wasn't going to replace them with slit foils, I'd use something like Panasonic FC series instead, they are very low ESR for the money :)

[istari_knight]

Good choice - I used those on a faulty plasma tv power supply last week with good results... well, it fixed it lol.

Dont know if you will be able to view it but: http://www.kendeil.com/pdf/K05_type.pdf Part number : K05050103_PM0E040

Would actually be handy to get your opinion on them as I always use them when replacing large filter caps in amps - If they're shite I wont bother anymore :lol:

[Reid Malenfant]

I don't need to hit the link :eyebrows: They are very high quality capacitors & I wouldn't hesitate to use them, same as BHC ;)

[istari_knight]

I don't need to hit the link :eyebrows: They are very high quality capacitors & I wouldn't hesitate to use them, same as BHC ;)

Thats exactly what I wanted to hear :D

For those that are interested I bought some chemical etcher & black spray paint today ready for the weekend. I did look into getting some nextel from Germany but it was a complete PITA so decided against it. I see Nextel is now used in interior design to make textured walls etc... different! thats for sure :scratch:

[Yomanze]

Thats exactly what I wanted to hear :D

For those that are interested I bought some chemical etcher & black spray paint today ready for the weekend. I did look into getting some nextel from Germany but it was a complete PITA so decided against it. I see Nextel is now used in interior design to make textured walls etc... different! thats for sure :scratch:

Interesting, I have a Systemdek III turntable painted in Nextel, which over the years has become sticky! I wonder if a simple spray job will be OK over the Nextel? Let me know how it turns out!

As for the PS caps you can't go wrong with Kendeils.

[Rare Bird]

I bought a metal body Cyrus 1 a bit back which was in a right state, i stripped it & took it to be proffesionally re-sprayed in a very fine satin black splatter finish, looked brilliant.

[istari_knight]

Getting there....

I Haven't taken loads of pics as I've been concentrating too much !

So far:

Brushed on paint stripper, left for 15 mins, scraped off the Nextel, rinsed in warm soapy water, wet & dry, etch primer, dust coat.... now its another round with wet & dry.

It was quite shocking what poor quality the casting are - Lots of imperfections & I wonder if they used Nextel deliberately to hide how shite the castings were ? It seems like a good choice if you need to 'lose' lots of dips/bumps :eyebrows:

Anyway, this ones smooth as a babies bum now.

http://i26.photobucket.com/albums/c129/istari_knight9/DSC01092.jpg
After the dustcoat, ready for another sanding.... Next update tomorrow I expect.

[istari_knight]

Finally managed the topcoat today but the capacitors I ordered still havent turned up so I cant reassemble yet :rolleyes:

Hopefully update tomorrow :)

[istari_knight]

:steam:

Well that didn't go very well... Must have buggered up somewhere as the topcoat shriveled now have to re-strip the whole thing & start again :doh:

On the plus side all of the wima caps I ordered finally arrived, they had to send them twice due to some thieving post office worker :punch: I replaced all of the 1uf electrolytics with wima mkp & it seems to have made a large change in the sound signature of this little cyrus, its a lot smoother with less grain but the top end is quite revealing now... not sure my metal dome tweeters are a match made in heaven !

[Rare Bird]

:steam:

Well that didn't go very well... Must have buggered up somewhere as the topcoat shriveled now have to re-strip the whole thing & start again :doh:



:rfl:

Take it & have it done professional like it will be worth while. :)

[istari_knight]

Wheres the fun in that ?

[istari_knight]

Finally got round to sorting this out today...

http://i26.photobucket.com/albums/c129/istari_knight9/DSC01146.jpg
http://i26.photobucket.com/albums/c129/istari_knight9/DSC01150.jpg

Flash shows up every little thing :( it actually looks nice in the flesh.

Internals are pukka, externals are errrr better than they were :lol: Had I taken rare birds advice it would undoubtedly look far better but I've never painted anything other than a bike frame 15 years ago so I wanted to give it a go & I think it turned out okay considering.

Overall a good mini project & its always nice to save something from a skip!

[synsei]

Nice job James it looks great. How does it sound?

[istari_knight]

Nice job James it looks great. How does it sound?

Cheers :)

It doesn't sound bad considering how little it cost (total after refurb is £42)

I would say the biggest improvement is in the phono stage which is very good after a recap & little tweaking (the low cut filter is passive so the input cap dictates the cut off frequency) doubling the size of these really opened up the bass - Quite anemic before.

Originally it sounded very analytical, actually reminded me of an old denon PMA... In a bad way! it still has a slight metallic edge but the bass region has really filled out which helps it overall - I think the stock input caps are too small which goes a long way to explain the "signature sound" of the Cyrus One - gutless bass & zingy treble.

In the past couple of weeks I've also repaired a Myst TMA3 & Linn Classik. Spent a few hours comparing them all today, the Myst blows everything else away...far superior. The Cyrus is a significant step above the Linn which was a surprise! Apples and oranges I know, would have expected some competition but it was obvious within seconds of switching the Linns are comparatively poor.

[synsei]

I've a confession to make, I have a soft spot for the TMA3. I love the simplicity of its design and yet it still manages to look very classy. The circuit boards are exquisite and look as if they are a doddle to work on and the amps sound very nice indeed although I found bass lacked a little weight for my liking. Mind you, the example I heard was driving a pair of Kan's so that might have had something to do with it :)

[Marco]

Jeez, mate, 4.20am... Has she kicked you out of bed? :eek: ;)

Marco.

[synsei]

No :lol: Had a bad back night, it happens from time to time :(

[Marco]

Regular horizontal jogging will sort that out! ;)

Marco.

[Rare Bird]

I've a confession to make, I have a soft spot for the TMA3. I love the simplicity of its design and yet it still manages to look very classy. The circuit boards are exquisite and look as if they are a doddle to work on and the amps sound very nice indeed although I found bass lacked a little weight for my liking. Mind you, the example I heard was driving a pair of Kan's so that might have had something to do with it :)

I used to own a Blue/Silver 'TMA3', very neat laid out inside..

[istari_knight]

http://i26.photobucket.com/albums/c129/istari_knight9/myst_internal.jpg

:eyebrows:

[DSJR]

Was recommended in 'Choice too and when I heard it, it sounded lovely and far more delicate than the Nait and equivalent pre-powers. Sadly, the Naim-Guru of our sales director argued the Salisbury case too far and we never took them on. Built like that, it should have been more successful - another brand all but stamped on by the Linn/Naim alliance-dealers back then. Of course, Mission and the then related Cyrus offered annual skiing holidays to senior managers of dealerships if they sold enough so we had them instead and this man often phoned me with pep talks on how good Mission and Cyrus were :(

[Rare Bird]

I particulally remember the Phonostage section sounded very good.

[istari_knight]

Was recommended in 'Choice too and when I heard it, it sounded lovely and far more delicate than the Nait and equivalent pre-powers. Sadly, the Naim-Guru of our sales director argued the Salisbury case too far and we never took them on. Built like that, it should have been more successful - another brand all but stamped on by the Linn/Naim alliance-dealers back then. Of course, Mission and the then related Cyrus offered annual skiing holidays to senior managers of dealerships if they sold enough so we had them instead and this man often phoned me with pep talks on how good Mission and Cyrus were :(

The more I learn about the hifi industry the more I :lol:

Goes a long way to explain how some crap products gain reputations as 'giant killers' while well made, honest designs flounder. how sad.

[Freddypipsqueek]

istari.

I am a new forum member so my apologies for making a request via my first post. I am also a bit of a newbie with the DIY electronics side though I have recently rebuilt quite a bit of my Chiarra headphone amp.

I have a couple of Cyrus 1s. I bought the first in 1989 and it still works with the addition of an alps pot (big difference) and new phono plugs. The second one I bought as spare but found it worked after I fixed the mains switch and did the same with the volume pot and plugs.

I was wondering if you could provide a list of the capacitors you changed and with what new values. I would like to replicate what you have done.

I do not use the phono stage on mine but this because I bought an external stage a couple of years ago.

Many thanks for your time

[istari_knight]

Hi Adrian, I have sent you a PM listing all of the capacitors I changed & where I purchased them from.

Cheers.

[Jasnochytron]

Hi, sorry to revive such an old thread.

I don't suppose that either of you still have the list of caps replaced?

Many thanks

Petr

[hifihouse]

Hi Adrian, I have sent you a PM listing all of the capacitors I changed & where I purchased them from.

Cheers.

Hi James, I also own the Cyrus 1 v6. It is still working. Should I have it recapped?

[M6NTL]

Been working at an Electronics manufacturing and repair place this week in Beeston, Notts.
Among other things, they are building Cyrus 1 Amps there!!! https://uploads.tapatalk-cdn.com/20190425/4b1618146ed641988643977aee845729.jpghttps://uploads.tapatalk-cdn.com/20190425/3acf6ca0b03e929f257d002a0204e7c4.jpg

Sent from my G8441 using Tapatalk

[hifinutt]

wow thats interesting