richie00boy said:
Hi Richie00boy,
I'd like to understand this better. When you remove the balance resistance completely does the signal level rise or fall? I'm struggling to comprehend the mechanism by which the balance resistors function in this schematic: http://www.tcaas.btinternet.co.uk/cyrus1inp.gif
Also I am looking for an easy and perhaps temporary way of increasing input impedance. Could I just use larger resistance values? I suppose no resistance at all is an infinitely large resistance.
As a side issue could these balance resistors be altered to maximise the useful range of the pot. For example late night listening requires low settings on the volume pot where channel matching is not very good. Should I increase the balance resistance or remove altogether?
Cheers.
If you remove the balance pot and do nothing else then the signal level rises as it's no longer passing through the balance chain which has a little attenuation by nature of how it works. Input impedance will rise a little as you remove one leg of the network. Changing the value of balance resistors, i.e. putting in other then 50k (would really be 51k in real world) will have no effect on the volume pot curve or channel matching of it.
Hi,
the signal level will rise when the balance components are removed, but have you tried to calculate the amount it will rise. You will be struggling to measure the change in level and I defy anyone to hear the miniscule change if one tries to return the volume knob back to the same level.
I estimate the level change as follows
Rs=50r <+0.53db
Rs=1k0 <+0.59db
The effect on the bass will also be small, but removing the balance components will extend the frequency response at the bass end by about 0.1 octave.
I would be tempted to reduce R45 slightly. Might be worth trying 3k9 or 3k3, resulting in a tiny reduction of noise and slight extension of extreme treble response.
the signal level will rise when the balance components are removed, but have you tried to calculate the amount it will rise. You will be struggling to measure the change in level and I defy anyone to hear the miniscule change if one tries to return the volume knob back to the same level.
I estimate the level change as follows
Rs=50r <+0.53db
Rs=1k0 <+0.59db
The effect on the bass will also be small, but removing the balance components will extend the frequency response at the bass end by about 0.1 octave.
I would be tempted to reduce R45 slightly. Might be worth trying 3k9 or 3k3, resulting in a tiny reduction of noise and slight extension of extreme treble response.
AndrewT said:
I'll get to work later. ANY increase in bass is badly needed in my system. I'll take what I can get.
Would it then follow that increasing R45 would roll off the treble slightly? This may also be useful in my situation. What kind of values should I try here?AndrewT said:
Sorry for all the questions but I'm really learning stuff here.
Hi,
there are two filters at work in the input section.
A low pass that cuts out the RF and extreme treble.
A high pass that blocks DC and cuts out the extreme bass.
The range for the low pass is usually 0.5uS to 1.5uS. This is determined by the series resistance before that 150pF cap, but it is modified slightly by the following resistances. Let's ignore the following resistances.
Some users report a clearing up of extreme treble when the RC ~=0.5uS or a little less. Some amps don't like very low RF filtering.
It's a compromise. Yours is set at approx 0.8uS, (4k7+Rs)*150pF
if you want to move the other way rather than increasing r45 one could invcrease the 150pF to 220pF or even 330pF but that would sound quite muffled unless you trim R45.
The bass is set by among other things the input filter, the NFB loop filter and the PSU RC filter.
The highest of these should be the input filter. I aim for 80mS to 90mS. Some will accept a lot higher (10 to 20mS).
I do not know the value of the DC blocking caps on your input but the 10k//51k8=8k3 and the 4k7 give an input impedance of about 13k. This is relatively low but can be driven by most sources.
The problem with this low value is obtaining that ellusive 90mS.
The series combination of input cap and source cap interact with Zin to form the single pole filter.
If both DC blocking caps were 1uF (fairly common values) and your Zin=13k the filter (1u+1u=0.5uF *13k) RC=6.5mS (-3db @ 24.5Hz) and would sound VERY bass light. You would need a three to four octave improvement to get the most extended audible bass response. (film sound effects and exceptional speakers would need even more extended bass response).
You would be looking at improving all the aforementioned filters to get significant improvement in bass response because I suspect Cyrus have adjusted all of these to match and work with each other.
Are we talking about a 25year old amp or a 10year old youngster?
there are two filters at work in the input section.
A low pass that cuts out the RF and extreme treble.
A high pass that blocks DC and cuts out the extreme bass.
The range for the low pass is usually 0.5uS to 1.5uS. This is determined by the series resistance before that 150pF cap, but it is modified slightly by the following resistances. Let's ignore the following resistances.
Some users report a clearing up of extreme treble when the RC ~=0.5uS or a little less. Some amps don't like very low RF filtering.
It's a compromise. Yours is set at approx 0.8uS, (4k7+Rs)*150pF
if you want to move the other way rather than increasing r45 one could invcrease the 150pF to 220pF or even 330pF but that would sound quite muffled unless you trim R45.
The bass is set by among other things the input filter, the NFB loop filter and the PSU RC filter.
The highest of these should be the input filter. I aim for 80mS to 90mS. Some will accept a lot higher (10 to 20mS).
I do not know the value of the DC blocking caps on your input but the 10k//51k8=8k3 and the 4k7 give an input impedance of about 13k. This is relatively low but can be driven by most sources.
The problem with this low value is obtaining that ellusive 90mS.
The series combination of input cap and source cap interact with Zin to form the single pole filter.
If both DC blocking caps were 1uF (fairly common values) and your Zin=13k the filter (1u+1u=0.5uF *13k) RC=6.5mS (-3db @ 24.5Hz) and would sound VERY bass light. You would need a three to four octave improvement to get the most extended audible bass response. (film sound effects and exceptional speakers would need even more extended bass response).
You would be looking at improving all the aforementioned filters to get significant improvement in bass response because I suspect Cyrus have adjusted all of these to match and work with each other.
Are we talking about a 25year old amp or a 10year old youngster?
Thanks for the comprehensive response Andrew.
You have confused me just enough to need to study. You have given me a lot to consider. Perfect! I am very grateful.
My own amp is one of the very latest metal ones with the toggle power switch so I reckon about 1990 - 92 making it about 16 years old. Wasn't production halted in '92?
I will check later but last time I looked I found the date markings were very confusing.
I am noticing more and more distortion creeping into my system recently and am hoping that the
In the upcoming recap I am going to replace the feedback cap C43 but would using a slightly lower value be worth the risk here? The series 1K resistor R65 probably affect frequency response too but I'd need to study a bit more myself to understand how exactly.
I'd like to address the abrasively forward nature of my system but don't want to get out of my depth either.
You have confused me just enough to need to study. You have given me a lot to consider. Perfect! I am very grateful.
My own amp is one of the very latest metal ones with the toggle power switch so I reckon about 1990 - 92 making it about 16 years old. Wasn't production halted in '92?
I will check later but last time I looked I found the date markings were very confusing.
I am noticing more and more distortion creeping into my system recently and am hoping that the
In the upcoming recap I am going to replace the feedback cap C43 but would using a slightly lower value be worth the risk here? The series 1K resistor R65 probably affect frequency response too but I'd need to study a bit more myself to understand how exactly.
I'd like to address the abrasively forward nature of my system but don't want to get out of my depth either.
Sorry for the nonsensical post above. My daughter was distracting me. She sees the computer and instantly wants to look at childrens TV websites!!
What I actually meant to say was:
I am noticing more and more distortion creeping into my system recently and am hoping that the recap will remedy the problem.
What I actually meant to say was:
I am noticing more and more distortion creeping into my system recently and am hoping that the recap will remedy the problem.
Hi,
if you intend modifying your Cyrus then research is essential to understanding what options are available to you and what outcome to expect.
Go in blindly, following various often conflicting advice will lead to total confusion and likely to poor sound quality.
if you intend modifying your Cyrus then research is essential to understanding what options are available to you and what outcome to expect.
Go in blindly, following various often conflicting advice will lead to total confusion and likely to poor sound quality.
Sorry about old thread revival...
I bought a Cyrus one a couple weeks ago and did most of the modifications mentioned here:
*New power supply caps (2xRIFA PEH200 10mF)
*New electrolytics alla around (blackgate std, and... don't laugh: jamicons NP caps)
*New pot (alps blue velvet - thanks for the tip Sonusthree!)
*Removed DC blocking cap - replaced with wire (C31/C32). Remenber only to do this if you have no DC going into your Cyrus or you will get DC on your speakers. Measure DC offset at speaker terminals, should be less than 50mV.
*Disconnected phono section (X24/X25)
Sound is actually very good now. Clear (but not bright!), wide soundstage, deep bas. I'm happy.... Almost(audiophile angst never leaves you alone).
Two questions that someone might be able to help me with:
1) I seem to have different biasing of the output transistors Left/Right(measured 12mV for one channel and 5.5mv for the other which equals 55mA and 25mA). So I have double the bias on one channel!!!! Much to my surprise I found a extra resistor soldered piggyback on R85 on the channel with more bias, which makes sense as this was mentioned in some thread as being the place to change bias at (but R81 or R83 was mentioned then but effect is the same)
2) richie00boy: Did you find that disabeling the current limiting function improved the sound in any way? If yes, do you have any advise on how to disable it in a simple way?
No I'm going back to my whisky and Sonic Youth "A thousand leaves".
Glad to have gotten this of my chest... ;-)
Regards
/Niclas
I bought a Cyrus one a couple weeks ago and did most of the modifications mentioned here:
*New power supply caps (2xRIFA PEH200 10mF)
*New electrolytics alla around (blackgate std, and... don't laugh: jamicons NP caps)
*New pot (alps blue velvet - thanks for the tip Sonusthree!)
*Removed DC blocking cap - replaced with wire (C31/C32). Remenber only to do this if you have no DC going into your Cyrus or you will get DC on your speakers. Measure DC offset at speaker terminals, should be less than 50mV.
*Disconnected phono section (X24/X25)
Sound is actually very good now. Clear (but not bright!), wide soundstage, deep bas. I'm happy.... Almost(audiophile angst never leaves you alone).
Two questions that someone might be able to help me with:
1) I seem to have different biasing of the output transistors Left/Right(measured 12mV for one channel and 5.5mv for the other which equals 55mA and 25mA). So I have double the bias on one channel!!!! Much to my surprise I found a extra resistor soldered piggyback on R85 on the channel with more bias, which makes sense as this was mentioned in some thread as being the place to change bias at (but R81 or R83 was mentioned then but effect is the same)
2) richie00boy: Did you find that disabeling the current limiting function improved the sound in any way? If yes, do you have any advise on how to disable it in a simple way?
No I'm going back to my whisky and Sonic Youth "A thousand leaves".
Glad to have gotten this of my chest... ;-)
Regards
/Niclas
Hi,
the extra bias resistor is almost certainly a factory fitted item.
It is possible, but I'm guessing, that this low production company carries out distortion checks on every amp they make and adjusts the bias to minimise to within their specification.
I would be very wary of removing the thyristor latch.
Adjusting to pass slightly more peak current may be a better option.
the extra bias resistor is almost certainly a factory fitted item.
It is possible, but I'm guessing, that this low production company carries out distortion checks on every amp they make and adjusts the bias to minimise to within their specification.
I would be very wary of removing the thyristor latch.
Adjusting to pass slightly more peak current may be a better option.
Thanks AndrewT for the quick reply.
My thoughts exactly. Qustion is if the primary critera is low channel distortion and or channel matching? What I'm fishing for is that perhaps I should increase the bias on the second channel to equal the first or can distortion increase with higher bias in this design?
Regards
/Niclas
My thoughts exactly. Qustion is if the primary critera is low channel distortion and or channel matching? What I'm fishing for is that perhaps I should increase the bias on the second channel to equal the first or can distortion increase with higher bias in this design?
Regards
/Niclas
Hi,
measure and record the bias resistors. That will allow you to return to the factory settings if necessary.
If you have access to distortion measuring hardware or can arrange for the amp to be measured for you then do that as well.
Now try adjusting the bias. Does the amp sound different/worse/better/the same?
Does the amp distortion measure any different? Are the various distortion harmonics maintained in the same proportions with the new bias settings?
Does the amp run at a different temperature? Will this be acceptable for all environmental conditions that your amp will encounter?
I think you have a lot of research to do before you change anything with the bias.
measure and record the bias resistors. That will allow you to return to the factory settings if necessary.
If you have access to distortion measuring hardware or can arrange for the amp to be measured for you then do that as well.
Now try adjusting the bias. Does the amp sound different/worse/better/the same?
Does the amp distortion measure any different? Are the various distortion harmonics maintained in the same proportions with the new bias settings?
Does the amp run at a different temperature? Will this be acceptable for all environmental conditions that your amp will encounter?
I think you have a lot of research to do before you change anything with the bias.
Hi Andew,
What you say makes perfect sense.
Regarding thermal issues, I don't expect it to be a probem.
(Double bias on low channel -> 55mA each channel -> Vrail=60Vp-p -> 3.3W dissepation in idle -> No problem!). Guess I was after whether someone had any general experience of increased bias to admitt more class A opertion in their Cyrus amps. I'll have to try it out myself, or not as I am for the moment happy with the way it sounds.
Regards,
Niclas
What you say makes perfect sense.
Regarding thermal issues, I don't expect it to be a probem.
(Double bias on low channel -> 55mA each channel -> Vrail=60Vp-p -> 3.3W dissepation in idle -> No problem!). Guess I was after whether someone had any general experience of increased bias to admitt more class A opertion in their Cyrus amps. I'll have to try it out myself, or not as I am for the moment happy with the way it sounds.
Regards,
Niclas
6.6W from two channels in that small heatsink with those low power devices is not "no problem".
Hi Andrew,
The way I see it 6.6W isn't going to be a problem. This is based on the current configuration +25% more heat. In its current configuratin the temperature is appoximately 40deg celcius(feels like touching a person with the fever!) while playing music at acceptable levels for the past 3 hours. The +25% increase in idle heat will not cause more than a few degrees higher heatsink temperature I'm certain. Maby I should say that my reference is an Aleph 30 with heatsink temp above 70 deg celcius that's been running for some time now without problems (OK... that's too hot).
Regards,
Niclas
The way I see it 6.6W isn't going to be a problem. This is based on the current configuration +25% more heat. In its current configuratin the temperature is appoximately 40deg celcius(feels like touching a person with the fever!) while playing music at acceptable levels for the past 3 hours. The +25% increase in idle heat will not cause more than a few degrees higher heatsink temperature I'm certain. Maby I should say that my reference is an Aleph 30 with heatsink temp above 70 deg celcius that's been running for some time now without problems (OK... that's too hot).
Regards,
Niclas
Hi.
I would like to replace the pot on my Cyrus One (1988 well treated edition). Could somebody confirm the value of ALPs Blue I need and if poss provide a bit of an idiots guide of which points it should be soldered to and what needs to be shorted to bypass the balance.
Your time is much appreciated.
PS Has anybody changed the op amps and to what effect - see http://www.quadfidelity.co.uk/index2.php?option=com_content&do_pdf=1&id=23
I would like to replace the pot on my Cyrus One (1988 well treated edition). Could somebody confirm the value of ALPs Blue I need and if poss provide a bit of an idiots guide of which points it should be soldered to and what needs to be shorted to bypass the balance.
Your time is much appreciated.
PS Has anybody changed the op amps and to what effect - see http://www.quadfidelity.co.uk/index2.php?option=com_content&do_pdf=1&id=23
Nothing needs to be shorted, you just disconnect the balance part. I can't comment on fitting an Alps blue as I fitted a different pot that was not an easy job.
Hmm that article... Well for a start the original op-amps are not rubbish. Also they are in the phono pre-amp section so if you listen only to other sources it won't make any difference.
Hmm that article... Well for a start the original op-amps are not rubbish. Also they are in the phono pre-amp section so if you listen only to other sources it won't make any difference.
Thanks - I've already been under the hood but I will do so again this weekend and see if I can find out the value for the pot (I have a couple of alps RK27s handy). I'm using a seprate phono preamp so I'll leave the op amps. Again thanks for your time
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