Hi Matthieu
The noise is only aparent if I left the CDP running in stop mode (not playing), and than turn thevolume full up.
It is a slight vrzzzz.... looks like some hiss plus some 50Hz component.
It is not possible to hear when playing a disc.
As I removed the mutting circuit, I will build one with reles and I will be able to live with this for sure...
Sometimes mods do not workout as expected but after all the mods I have done following this thread, the sound is unbelieavable good now. (Fast bass.... detail.... pace.... stereo image..... but it can be better still)
I am afraid to break anything everytime I do a new mod but the outcome is very rewarding.
If you read this thread from the begginning, you will know what are the best mods and in what order they should be done. (These guy´s know what they are talking about... believe me)
I am just learning about the discrete output before I attempt anything.
PS - I did not hear anything different from China... what is the matter ?
Regards
Ricardo
The noise is only aparent if I left the CDP running in stop mode (not playing), and than turn thevolume full up.
It is a slight vrzzzz.... looks like some hiss plus some 50Hz component.
It is not possible to hear when playing a disc.
As I removed the mutting circuit, I will build one with reles and I will be able to live with this for sure...
Sometimes mods do not workout as expected but after all the mods I have done following this thread, the sound is unbelieavable good now. (Fast bass.... detail.... pace.... stereo image..... but it can be better still)
I am afraid to break anything everytime I do a new mod but the outcome is very rewarding.
If you read this thread from the begginning, you will know what are the best mods and in what order they should be done. (These guy´s know what they are talking about... believe me)
I am just learning about the discrete output before I attempt anything.
PS - I did not hear anything different from China... what is the matter ?
Regards
Ricardo
Thank you Ray6h5c said:Yep, the current is modulated by the audio-signal that is fed to the two transistors and 'transformed' into a voltage swing by the 4k7 collector resistors.
The bias of the output transistor is set by the 1k8 resistor and the voltage at it's base. So it also depends on the voltage-drop across the 4k7 resistor. And yes, it is highly affected by the supply voltage. That's the drawback of this circuit....
But it keeps everything nice and simple, without coupling caps.
Gain: see previous post.
I must use a +-15v PSU because that is what I have invested in.... Should any modifications be done to ensure stability ?
Regards
Ricardo
Malefoda said:
Not me, I'm now happy with my player, every aspect is finally excellent. It only took some expensive caps, a discrete output stage, many power supplies & additional transformers, 2 clocks, 6 super regs and some other tweeks!!
Like you I'm using speakers that are letting the rest down in some ways. I need to find a way of getting good bass from this tiny room
Simon
6h5c said:
The bias of the output transistor is set by the 1k8 resistor and the voltage at it's base. So it also depends on the voltage-drop across the 4k7 resistor. And yes, it is highly affected by the supply voltage
But it keeps everything nice and simple, without coupling caps.
Hi RaySimontY said:
Nope, it just works fine (better than fine
Does this mean the bias current is independent of the voltage input as long as it stays simetrical (+-12v or +-15v) ?
Thank you for the feedback Simon.
Regards
Ricardo
RCruz said:Thank you Ray
I must use a +-15v PSU because that is what I have invested in.... Should any modifications be done to ensure stability ?
Does this mean the bias current is independent of the voltage input as long as it stays simetrical (+-12v or +-15v) ?
Thank you for the feedback Simon.
Regards
Ricardo
Hi Ricardo,
No, this current is NOT independent of supply voltage. The fact that they are equal doesn't help one bit (sorry Brent
). The circuit doesn't use GND as a reference (remember, it's a differential amp!), so the circuit doesn't 'know' whether it's running on a single 24V or +/-12V or +14V/-10V. The exact voltage is not important, it will be fine anywhere between +/-12...15V (even +12/-15V will do fine), it's more important that the supply is STABLE and NOISE-FREE. The rejection-ratio of this circuit is poor, so any noise on the supply-lines will be present almost completely on the output.A higher supply voltage will cause the current through the output transistor to be higher, in this case over 13mA. To correct this back to about 10mA, the 1k8 resistor has to be raised to 2k4. Nothing bad will happen if you don't, by the way
. Make sure you use a 1W resistor then, because dissipation is going up exponential. The input stage uses the current source, so that will stay the same.Regards,
Ray
Hi Ray6h5c said:
Hi Ricardo,
No, this current is NOT independent of supply voltage. The fact that they are equal doesn't help one bit (sorry Brent
A higher supply voltage will cause the current through the output transistor to be higher, in this case over 13mA. To correct this back to about 10mA, the 1k8 resistor has to be raised to 2k4. Nothing bad will happen if you don't, by the way
I am finally understanding the schematic... if I raise R7 and R8, will I be reducing the gain ?
Regards
Ricardo
Hi SimonSimontY said:
I was wondering if I could atenuate the signal in the CDP because I am afraid to dismantle the 101 pre.... very old thing... might brake something...
Now a merely academic question:
So you mean that the level is fine tuned?
If lowering the discrete gain might compromise sound quality... What about raising the gain... would that give me some benefit ? (Of course I would need to build another pre....)
Another question rose right now:
Comparing Brents discrete layout with Ray´s, I see that Brent used The following values in the filter (C3 680p) (R3 2.2k) and lowered the gain using R7=R8=820ohm.
What was your choice of values Simon ?
Regards
Ricardo
The level is close to the standard 2V RMS. I can only assume this is standard because it's "good" in some way. I don't think it's pushing my understanding of cables too far to suggest that a weaker output will rely more on the interconnect feeding the next audio stage. Might it also pick up more RFI and hum, I wonder?
I honestly don't think reducing the gain slightly will hurt too much, as long as the circuit remains stable. Increasing the gain will make it sound worse. The poorer sound caused by excessive gain is well-documented on this site. I know from my last preamp that turning the gain up made the sound harder, harsher and brighter. This is why I've happily moved over to a simple buffer (also called unity gain or a gain of 1), and it sounds peachy, no complaints! The only problem I could face is if I needed to use the system for a party, where I could easily run out of gain to reach maximum level from the speakers, if using a weak source. Plug the 2v p-p cd player straight into a power amp and you'll see it's loud, but less than 2v and I'm not sure you would necessarily reach full output, particularly if playing a quiet CD that doesn't get near 0dBFS (as with some older 1980s CDs).
So I do think (in a round about way) there are reasons to leave that CD player and consider using a bigger value volume pot (I assume you need more low range control) or to upgrade to a logarithmic or audio taper pot (if you're stuck with a linear) or reduce the gain in the preamp.
You could also try attenuating the signal with an L-pad resistor network, which is harmless, but I'd rather not throw away the signal, if I can reduce the gain elsewhere.
Simon
I honestly don't think reducing the gain slightly will hurt too much, as long as the circuit remains stable. Increasing the gain will make it sound worse. The poorer sound caused by excessive gain is well-documented on this site. I know from my last preamp that turning the gain up made the sound harder, harsher and brighter. This is why I've happily moved over to a simple buffer (also called unity gain or a gain of 1), and it sounds peachy, no complaints! The only problem I could face is if I needed to use the system for a party, where I could easily run out of gain to reach maximum level from the speakers, if using a weak source. Plug the 2v p-p cd player straight into a power amp and you'll see it's loud, but less than 2v and I'm not sure you would necessarily reach full output, particularly if playing a quiet CD that doesn't get near 0dBFS (as with some older 1980s CDs).
So I do think (in a round about way) there are reasons to leave that CD player and consider using a bigger value volume pot (I assume you need more low range control) or to upgrade to a logarithmic or audio taper pot (if you're stuck with a linear) or reduce the gain in the preamp.
You could also try attenuating the signal with an L-pad resistor network, which is harmless, but I'd rather not throw away the signal, if I can reduce the gain elsewhere.
Simon
Thomo said:
Sorry, this is stupid advice of me, with some CDs and power amps you could cause damage doing that. Please don't *actually* do it.
With a voltage gain of, say, 40 you'd be asking for peaks of about 80V, and that would be interesting. PA speakers could take it, but some would be blown, and the amp would go into mega-clipping unless it's a high power design.
The point is not all sources, preamps and power amps are designed to work together, they just work well enough.
Simon
Hi LeeThomo said:
These are very good news. When did you send them ?
SimonSimontY said:
I would really like to know if your filter is like my future one... Much better when I start posting results and everybody uses the same setup.
Thomo said:
Of course I understood the point... I would never connect the CD direct to the power amp without a pot in between.
Ricardo