Cyrus Two would be the best selling and successful British Amp ever made. Definitely, it is the most important product to bring the market standing of Cyrus in its history.
After almost 40 years, it is still a very good amp around. Definitely, very good value for its second hand price.
Cyrus two phone section consists of super matched pair LM394 which is still the best matched pair today.
Here welcomes any idea to maintain and upgrade the Cyrus Two and its Power Supply to improve its performance to race with today's best amp.
For instance,
1. Replace the aged E-cap
2. Replace of coupling cap for better performance
3. Replace low value and better feedback resistor
with higher quality resistor.
4. Replace the important resistors in RIAA section
the best quality type
etc.
However, a lot of component and design is still very good like the Holden & Fisher power transformer is still unmatched quality outperforming a lot transformer in the market today unless you get the transformer used in top FM acoustic amp.
Please feel free to exchange your great idea here
After almost 40 years, it is still a very good amp around. Definitely, very good value for its second hand price.
Cyrus two phone section consists of super matched pair LM394 which is still the best matched pair today.
Here welcomes any idea to maintain and upgrade the Cyrus Two and its Power Supply to improve its performance to race with today's best amp.
For instance,
1. Replace the aged E-cap
2. Replace of coupling cap for better performance
3. Replace low value and better feedback resistor
with higher quality resistor.
4. Replace the important resistors in RIAA section
the best quality type
etc.
However, a lot of component and design is still very good like the Holden & Fisher power transformer is still unmatched quality outperforming a lot transformer in the market today unless you get the transformer used in top FM acoustic amp.
Please feel free to exchange your great idea here
The regulators run hot, so change them, the capacitors, the feedback network (if you want). Another improvement is to match all four diff pair transistors (per channel). They are cfp pairs.
Do not touch the NE5534A op amps! That entire section should be left alone.
-Chris
Do not touch the NE5534A op amps! That entire section should be left alone.
-Chris
Hi Chris,
My Cyrus II has (again) blown output transformers.
I can't find any BUV28 transistors. I read that the BUV48 is a suitable alternative, but it's a T0-247 package in stead of T0-220.
Could you recommend a suitable replacement (still in production) or is it possible to fit the BUV48 in ?
Thanks,
Edwin
My Cyrus II has (again) blown output transformers.
I can't find any BUV28 transistors. I read that the BUV48 is a suitable alternative, but it's a T0-247 package in stead of T0-220.
Could you recommend a suitable replacement (still in production) or is it possible to fit the BUV48 in ?
Thanks,
Edwin
Hi Edwin,
Try the BD911 You could also use the On-Semi MJE15032 (8A) https://www.onsemi.com/pub/Collateral/MJE15032-D.PDF. You don't need 15 A transistors for that power range when you have 4 outputs per channel.
Those transistors you have should not have blown under normal use. I'm worried about the stability of your bias control, or you had a short in the wiring somewhere.
-Chris
Try the BD911 You could also use the On-Semi MJE15032 (8A) https://www.onsemi.com/pub/Collateral/MJE15032-D.PDF. You don't need 15 A transistors for that power range when you have 4 outputs per channel.
Those transistors you have should not have blown under normal use. I'm worried about the stability of your bias control, or you had a short in the wiring somewhere.
-Chris
I second Chris' advice to find the cause of the failure.
Does it look like this?
Cyrus 2
If it were me I would try to replace each TO-220 pair with a single TO-247 (or similar) and each emitter resistor a 0.22 instead of two 0.47. It would require some wiring and maybe new holes in the heat sink.
Does it look like this?
Cyrus 2
If it were me I would try to replace each TO-220 pair with a single TO-247 (or similar) and each emitter resistor a 0.22 instead of two 0.47. It would require some wiring and maybe new holes in the heat sink.
Thank you guys.
The amp is used to drive Electrostatic speakers, filtered by an DSP from 125 Hz up.
This way I tried to avoid any saturation of the transformer of the ES;
Elvee indicated somwhere, that by very assimetrical waves, it still is possible to have the core saturated, with at that moment a very low Z, whch might cause the OP to blow.
I intend to check the bias of course. I suppose the drivers should be checked also.
Is it normal that if the OP transistors of one channel blow, the other blows the fuse to ?
The amp is used to drive Electrostatic speakers, filtered by an DSP from 125 Hz up.
This way I tried to avoid any saturation of the transformer of the ES;
Elvee indicated somwhere, that by very assimetrical waves, it still is possible to have the core saturated, with at that moment a very low Z, whch might cause the OP to blow.
I intend to check the bias of course. I suppose the drivers should be checked also.
Is it normal that if the OP transistors of one channel blow, the other blows the fuse to ?
Update :
I open the case of my Cyrus to check again the output transistors :
one channel is the original PT77, the other is BUV48A. Both are TO-247 transistors.
I noticed that the PCB has prevision for both TO-220 and TO-247 transistors.
After checking the service manual again, I see that for my type (TOG), the format of the transistors is indicated as TOP3, a type I don't know. For the issue 06, the same output transistor PT77 is indicated as TO-220.
So far the good news. Bad news is the price of these transistors : Farnell asks > 14 € per piece.
I open the case of my Cyrus to check again the output transistors :
one channel is the original PT77, the other is BUV48A. Both are TO-247 transistors.
I noticed that the PCB has prevision for both TO-220 and TO-247 transistors.
After checking the service manual again, I see that for my type (TOG), the format of the transistors is indicated as TOP3, a type I don't know. For the issue 06, the same output transistor PT77 is indicated as TO-220.
So far the good news. Bad news is the price of these transistors : Farnell asks > 14 € per piece.
You could use these https://www.eoo-bv.nl/bd-serie/17607-bd250c.html
and make the mod traderbam sugests in #8
Mona
and make the mod traderbam sugests in #8
Mona
Hi Edwin,
If it were my amplifier, I would use MJL2119x series parts. I did do warranty service for Cyrus here in Canada and fixed lots of those amplifiers. But you also need to know why it failed in the first place. You can fix it, but watch the bias currents very carefully for a while before putting it back together.
-Chris
If it were my amplifier, I would use MJL2119x series parts. I did do warranty service for Cyrus here in Canada and fixed lots of those amplifiers. But you also need to know why it failed in the first place. You can fix it, but watch the bias currents very carefully for a while before putting it back together.
-Chris
Thanks Chris,
I came to the same conclusion. But since I'm just a hobby tinkerer, I have no idea what parameters are important to select a substitute (apart from Voltage range and power dissipation). Since these MJL2119x are indicated for audio with even distortion measurements (without feedback, although no level is indicated) and have a larger SOA, I hoped they might be suited.
The Cyrus has driven my ESL's for years, but since they have a very low sensitivity, I regularly push them very (to) hard. Furthermore the sensitivity has a tendency to slowly decrease over time (I have to reapply the conduction coating but haven’t found the time). Furthermore my hearing has deteriorated and I need hearing aeds. Many years ago I had contacted Cyrus service for advise after blowing the fuses, and they advised me to buy a newer version of Cyrus amp because they have protection systems build in. (In the mean time I had a Denon amp for load, with protection system) but it also didn’t survive my speakers.
I’m in the process of developing a special amplifier, based on Elvee’s cyrclophone, but with mosfets. This is a project that’s going on for years (I’m very slow) but the last month’s I’m having a lot of trouble with Ltspice.
So I’m sorry for troubling you guy’s with my problem, but now I now how I can try to revive my Cyrus and restrain myself from pushing it to hard, while I hopefully can build an suitable amp that is capable of surviving the load;
Edwin
I came to the same conclusion. But since I'm just a hobby tinkerer, I have no idea what parameters are important to select a substitute (apart from Voltage range and power dissipation). Since these MJL2119x are indicated for audio with even distortion measurements (without feedback, although no level is indicated) and have a larger SOA, I hoped they might be suited.
The Cyrus has driven my ESL's for years, but since they have a very low sensitivity, I regularly push them very (to) hard. Furthermore the sensitivity has a tendency to slowly decrease over time (I have to reapply the conduction coating but haven’t found the time). Furthermore my hearing has deteriorated and I need hearing aeds. Many years ago I had contacted Cyrus service for advise after blowing the fuses, and they advised me to buy a newer version of Cyrus amp because they have protection systems build in. (In the mean time I had a Denon amp for load, with protection system) but it also didn’t survive my speakers.
I’m in the process of developing a special amplifier, based on Elvee’s cyrclophone, but with mosfets. This is a project that’s going on for years (I’m very slow) but the last month’s I’m having a lot of trouble with Ltspice.
So I’m sorry for troubling you guy’s with my problem, but now I now how I can try to revive my Cyrus and restrain myself from pushing it to hard, while I hopefully can build an suitable amp that is capable of surviving the load;
Edwin
Hi Edwin,
It's a pleasure to help you out. Don't worry because we all want you to succeed.
The output transistors used in that amplifier were basically picked for the highest SOA I think. It is possible that the heat sink needs to be larger, but what is there is substantially better than most other smaller products. In case those MJL transistors are too big, you'll have to move to the MJE product line. Either way, you don't need the +15 amp current. I think it is a heat issue. The problem is that your amplifier will deliver a lot of power. Most won't and can't hurt themselves too badly.
If heat is killing your amplifier, you should be able to feel the heat out the top of your amplifier. Make sure you have about 6" clear airspace above it and a clean, hard surface below. It wouldn't hurt if it were raised another 1/4" or so to get more air underneath it.
-Chris
It's a pleasure to help you out. Don't worry because we all want you to succeed.
The output transistors used in that amplifier were basically picked for the highest SOA I think. It is possible that the heat sink needs to be larger, but what is there is substantially better than most other smaller products. In case those MJL transistors are too big, you'll have to move to the MJE product line. Either way, you don't need the +15 amp current. I think it is a heat issue. The problem is that your amplifier will deliver a lot of power. Most won't and can't hurt themselves too badly.
If heat is killing your amplifier, you should be able to feel the heat out the top of your amplifier. Make sure you have about 6" clear airspace above it and a clean, hard surface below. It wouldn't hurt if it were raised another 1/4" or so to get more air underneath it.
-Chris
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