Cyrus 2 Resistors

[Geoff]

Originally posted by optimiser
Is there a way of getting more bass out of the Cyrus, or do the later versions with metal case have more bass? or should I think about getting a PSX like I had before. I sold my PSX a few years ago.

The circuit for v7 (metal case) is basically the same as that for v6 (plastic case) so there is unlikely to be any significant audible difference between the two.

The changes made between the two versions were the addition of a protection sub-circuit at the output and the use of single, higher power rated, transistors in the output stage rather than parallel pairs.

As indicated earlier in this thread, when I carried out a side-by-side comparision between a Cyrus 1 and a Cyrus 2+PSX my preference was for the greater delicacy of the standard Cyrus 1. However, if your speakers need more current in order for them to perform to your satisfaction then adding a PSX (or a DIY clone, it is a simple circuit) may help.

Before adding a PSX, I would be inclined to replace the two non-polarised 470uF capacitors in the feedback path (C41 and C42) and the two 2u2 capacitors at the input (C33 and C34) as these can deteriorate with age and adversely affect the bass response. The 2u2 capacitors could usefully be changed from non-polarised electrolytics to a similar value film type.

[vinotinto]

thanks a lot for the information that helped me to fix a cyrus 1 and a new cyrus 2.I think a BD249c would make a good job as well.The only problem that still makes me doubt is an older cyrus 2 with 8 PT7-4 each channel.In each channel 3 of the PT7 got the additional Information"644n"and one"638n".In each channel it is the second(from the left)they are in the same place and original.Does anyone know if it is different to the others or can I substitude this "638n"as well with a TIP41c?It seems to be a PNP as well...but I am not shure-the two are broken...thanks..

[vinotinto]

a few years ago I compared the cyrus 2 with PSX with other classics(audiolabor,Thorens,big Yamahas...)resulting that the bass of the mission in the aspect of clarity,dryness was a class of its own-unbeateble!If you think that your mission needs more bass it seems to me that possibly there is a problem,perhaps a capacitor fails.I agree that the substitution of some capacitors in any case is a good thing.As mentioned c33 and c34 are very important-there you should put in the best you can get( I use Mundorf silver/oil,but the "normal"MKPs from Mundorf,the white ones are very good and not that expensive).The WIMAs(green)normally last the whole life and do not need to be changed.The others(2,2 and 1,0uF)should be replaced after all these years and as well the four 100uF nearby the main transistors(you can try 220uF as well.Some older versions got 220,some got 50uF).In any case with these new capacitors you will note a difference,more clarity and freshness in sound.A good improvement is changing the NE5532 to an OPA627 from BurrBrown,but expensive.I think the PSX do not give more bass.The PSX makes the sound more equilibrated and less nervious-more relaxed.I would never sell my PSX.Its a good improvement for almost every amplifier(working with40 Volt).Now it works with a Mclaren A150-fantastic!It hurts to say that-but better than the cyrus.Try to get another PSX!Its worth

[stoolpigeon]

I also have a damaged plastic cased Cyrus 2 with the fuses blowing on power up but I wanted to ask about the transistor which you can see in the 3rd photo of post #1.

There is 1 transistor Q33 straddling mounting positions for 2 transistors and I wanted to know if this was standard.

My pcb has this arrangement for the 4 driver transistors and in fact I was just about to pull them out thinking it was a dodgy repair.

I notice that Geoff's schematic shows only 1 transistor but it's for the Cyrus 1.

Any ideas? Thanks SP

[Geoff]

Originally posted by stoolpigeon
I also have a damaged plastic cased Cyrus 2 with the fuses blowing on power up but I wanted to ask about the transistor which you can see in the 3rd photo of post #1.

There is 1 transistor Q33 straddling mounting positions for 2 transistors and I wanted to know if this was standard.

My pcb has this arrangement for the 4 driver transistors and in fact I was just about to pull them out thinking it was a dodgy repair.

The standard arrangement uses 2SC1775 for Q27/Q28 followed by MJE243 for Q33/Q34 (2SA872 for Q29/Q30 and MJE253 for Q37/Q38).

From the photo to which you refer, it would seem that Q27(pre-driver) and Q33 (driver) have been replaced with a single transistor and you say that your pcb is similar. Presumably all the pre-driver/driver pairs have been modified in the same manner.

There would appear to be two possibilities here, either both amps have been 'bodged' by the same repair shop or amateur or Cyrus made the change during certain production runs, possibly due to a problem sourcing one or more of the standard transistors.

I would expect the single transistor replacement to be a Darlington and it would be interesting if you could check the number printed on this transistor.

I notice that Geoff's schematic shows only 1 transistor but it's for the Cyrus 1.

As I indicated earlier in this thread, the later (metal-cased) v7 used a single output transistor in both the One and the Two but the earlier (plastic-cased) v6 used a single output transistor in the One and a parallel pair in the Two.

[stoolpigeon]

Thanks Geoff,

I checked the transistors and they are as you listed.

It looks as though my version of the pcb and that shown in the 3rd photo of post #1 have markings and holes for another transistor.

Referring to the photo the nearer transistor is labelled Q33 and the one just behind is Q31 (and Q27 is behind Q31). The transistor fitted is a 243 with 1 leg in the Q33 position and 2 legs in the Q31 position.

I checked the spare solder pads for Q31 and Q33 and it looks like they have not been soldered so this could be a factory mod. I can't be certain because whoever tried to repair it has got solder everywhere.

By the way is the Cyrus 2 schematic same as the 1 except for the extra outputs?

Thanks, SP

[Geoff]

Originally posted by stoolpigeon
Thanks Geoff,

I checked the transistors and they are as you listed.

It looks as though my version of the pcb and that shown in the 3rd photo of post #1 have markings and holes for another transistor.

Referring to the photo the nearer transistor is labelled Q33 and the one just behind is Q31 (and Q27 is behind Q31). The transistor fitted is a 243 with 1 leg in the Q33 position and 2 legs in the Q31 position.

I checked the spare solder pads for Q31 and Q33 and it looks like they have not been soldered so this could be a factory mod. I can't be certain because whoever tried to repair it has got solder everywhere.

Hi SP

I have just dug out an earlier Cyrus 1 from the back of a cupboard and lifted the lid. The board arrangement around Q33 is the same as you describe, with the MJE243 being spread across Q31 and Q33.

It would appear that very early Cyrus's had an extra transistor in each output half and that, after making some circuit changes, Cyrus used up the old pcbs by inserting the MJE243/253 in this fashion prior to having some new boards made.

The pcb marking on my earlier Cyrus 1 (Serial No 112877) is 'CEN C 85 45' and that on the later one (Serial No 119805) is 'CEN C 86 34'. I suspect that the 85 and 86 refer to the year in which the pcb layout was finalised but I cannot be certain.

Both these amps have been owned from new, one by myself and the other by my brother so I can confirm that the MJE arrangement of being spread across two positions on the pcb (Q31 and Q33) is how the board originally left the factory.

By the way is the Cyrus 2 schematic same as the 1 except for the extra outputs?

Virtually yes. The only other difference of which I am aware, in the power amp section, is the addition of a 3k6 resistor in parallel with the 1k resistor in the feedback network to increase the closed-loop gain of the Cyrus 2. Of course there are further differences in the phono stage and the power supply, though for the latter it is mainly a case of the transformer rating and secondary voltage.

I will attach a copy of the v6 Cyrus 2 schematic to another post when I have retreived it from my old pc.

Geoff

[Geoff]

Originally posted by Geoff
I will attach a copy of the v6 Cyrus 2 schematic to another post when I have retreived it from my old pc.

Done.

I have had to reduce the size of the image to comply with the forum limits and this has lowered the quality. If you would like a full size original send me an email.

[optimiser]

[QUOTE]Originally posted by Geoff
[B]

The circuit for v7 (metal case) is basically the same as that for v6 (plastic case) so there is unlikely to be any significant audible difference between the two.

The changes made between the two versions were the addition of a protection sub-circuit at the output and the use of single, higher power rated, transistors in the output stage rather than parallel pairs.

Hi Geoff,

Since replacing the output transisistors in my early plasic case Cyrus 2 Two, and running it in for several hours, the bass has improved, and now I am quite impressed once again with what this amp is capable of.

I have since purchased an issue 07 Cyrus Two, and the difference between them is extremely marginal. I think the later Cyrus Two has more attack in it's sound, but really there is probably a hairs difference between them.

The issue 07 Cyrus Two has a problem with a noisy input selector switch, which I have sprayed with contact cleaner, but it will need replacing in time.

Is there a recommended replacement part for the input selector switch, and where is best place to purchase and part number?

[Sonusthree]

Originally posted by optimiser

The issue 07 Cyrus Two has a problem with a noisy input selector switch, which I have sprayed with contact cleaner, but it will need replacing in time.

Is there a recommended replacement part for the input selector switch, and where is best place to purchase and part number?

Hi, I would guess that only Cyrus would have these. Cyrus offer a refurbishment service which, to my mind, implies that they have switches.

Alternatively (if you don't need to record through the amp), you could swap the record output and input selector switches around. They are identical parts but the output selector is usually far less worn. Give it a quick squirt of switch cleaner to shift the old dust and Bobs your mother's brother.

Regards,
Martin.