Requiring a quality buffer and volume control between a CD player and power amplifier, and having a small amount of otherwise waste space when panellising my current run of PCBs,
I decided to do a small board for a volume control and OPA2134 dual FET cascode chip to run from an external +/- DC supply of up to +/- 25V with onboard zener reduction and secondary filtering. Once again fully ground planed top layer with through hole plate and teflon solder mask/component overlay.
Unpretentious but fully functional.
Cheers,
Greg
I decided to do a small board for a volume control and OPA2134 dual FET cascode chip to run from an external +/- DC supply of up to +/- 25V with onboard zener reduction and secondary filtering. Once again fully ground planed top layer with through hole plate and teflon solder mask/component overlay.
Unpretentious but fully functional.
Cheers,
Greg
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Well Chicco,
I, and others, have a primary or maybe single source, say a CD or DVD player that they wish, as I do, to keep a simple signal path. The CD won't like loading lower than about 10K and the power amplifiers don't want more than 100R source impedances or their HF rolloff comes early. The output of the CD player is too high to run directly and very few have a volume control built in (or remote) so this simple cct provides a 10K or 25K (pot value) load to the CD player while buffering it and providing a 47R output Z to drive the power amps. It's stereo and only puts one op amp in the signal path so is minimalist. The PS can even be configured to split a DC walwart supply.
There's not too much a unity gain OPA puts in the way of the music.
You have a passive alternative?
Cheers,
Greg
I, and others, have a primary or maybe single source, say a CD or DVD player that they wish, as I do, to keep a simple signal path. The CD won't like loading lower than about 10K and the power amplifiers don't want more than 100R source impedances or their HF rolloff comes early. The output of the CD player is too high to run directly and very few have a volume control built in (or remote) so this simple cct provides a 10K or 25K (pot value) load to the CD player while buffering it and providing a 47R output Z to drive the power amps. It's stereo and only puts one op amp in the signal path so is minimalist. The PS can even be configured to split a DC walwart supply.
There's not too much a unity gain OPA puts in the way of the music.
You have a passive alternative?
Cheers,
Greg
Hi Chico,
i appreciate your material, but none seems to fit with the need.
Conside a CD player
Z out 100R ; Vout max 2V ; load needs >10K
Power amp input
Z in > 10K ; Vin max (say) 2V ; source Z needed << 1K to not upset input HF filter.
So your passive divider could be 9K series 1K ( 10% of the way on a 10K pot) and I would halve the HF response and get 10% of the voltage signal so max 1/100 of the power.
Turn it up, I can't hear it! But you can't, as loading will get worse and HF will get worse. Your zip article refers to both having equal output and drive needs but that's not reality. It means they both clip at the same level.
You just can't load the CD with 10K min and provide the power amp with volume control ( to more than 10%) with < 1K source Z.
That's the nub of the need.
Hi Stocker,
Would you rather I didn't post simple little solutions to a need - such as this. I wasn't gushing about it just showing how it can be implemented/solved. The circuit is so simple I didn't think there'd be any point. I'll do the schema...
Cheers,
greg
i appreciate your material, but none seems to fit with the need.
Conside a CD player
Z out 100R ; Vout max 2V ; load needs >10K
Power amp input
Z in > 10K ; Vin max (say) 2V ; source Z needed << 1K to not upset input HF filter.
So your passive divider could be 9K series 1K ( 10% of the way on a 10K pot) and I would halve the HF response and get 10% of the voltage signal so max 1/100 of the power.
Turn it up, I can't hear it! But you can't, as loading will get worse and HF will get worse. Your zip article refers to both having equal output and drive needs but that's not reality. It means they both clip at the same level.
You just can't load the CD with 10K min and provide the power amp with volume control ( to more than 10%) with < 1K source Z.
That's the nub of the need.
Hi Stocker,
Would you rather I didn't post simple little solutions to a need - such as this. I wasn't gushing about it just showing how it can be implemented/solved. The circuit is so simple I didn't think there'd be any point. I'll do the schema...
Cheers,
greg
amplifierguru said:
Something that is obvious by describing it to you or me, is completely incomprehensible to a novice who thinks your solution is the best thing since sliced bread but can't afford one. You have a camera to take a photo for the product shot. Even if you sketch the schematic by hand, it's another 10 seconds to shoot it and post it. Is it asking too much for schematics to be posted on a DIY board?
Grrr!!!
Gosh people. Lighten TFU!
Greg chips in by showing US (which might include you!) a DYI project that he did with scraps.
He illustrates to us how to get more efficiency out of our PCB's footprint by utilizing the scrap margins that typically go to waste. That seems practical to me.
Then, when asked by those who missed the point, he takes his time and extends much effort, and patience explaining why it is needed, how it works, and how it fills a specific need. His theory and math is sound whether it is perceived that way or not.
I don't see anywhere where he has announced a price for this "It's New!!! It's You!!! It's fiftybux!!!" gizmobob. (not his words)
In spite of Greg's good intentions, there are always some dimwitts who feel that they must insert their god-like opinions, at the expense of everyone else. Where can I obtain such audacious g'nads?
Suggestion... If your passions and devine perceptions lead you to follow a passive path, that's fine. But why come here and shyte all over someone who obviously has the education, the ability, the experience, and the desire to help other's who wish to follow a different path?
Ever wonder why it's always the same ba$tards who chase off the professionals? It is the attitude and arrogance of morons that ruin the atmosphere here. I admire zeal, when it is tempered with humility instead of arogance. Given the choice, I'd trade the bad apples for good apples anyday!
I am grateful for Greg's patience... because he is one of the best contributers on DYI. Not that I agree with everything he says or does, but out of respect because he has earned it. Respect is earned... it is never given freely. AND... once it is earned... it is deserved!
I'll bet that Greg gave this audience too much credit when he reasoned that a schematic should not be necessary for something so elementary. He probably felt that a schematic would be an insult to everyone's intelligence. Judging from hindsight, I'd say that forgiveness for such an error is manditory in this case. Let this be a lesson to us all.
Don't make me come over there!
- head_spaz
</soapbox>
... soapbox terminated successfully...
C:\>
</rant><enter>
</RANT><RETURN>
<END RANT !!!>
<Calm T F Down><enter>
<^F6>
<Ctrl-Alt-Del>
- Hire the teenager --- while he still knows everything -
________________
Jesus loves you, but I have reservations.
Gosh people. Lighten TFU!
Greg chips in by showing US (which might include you!) a DYI project that he did with scraps.
He illustrates to us how to get more efficiency out of our PCB's footprint by utilizing the scrap margins that typically go to waste. That seems practical to me.
Then, when asked by those who missed the point, he takes his time and extends much effort, and patience explaining why it is needed, how it works, and how it fills a specific need. His theory and math is sound whether it is perceived that way or not.
I don't see anywhere where he has announced a price for this "It's New!!! It's You!!! It's fiftybux!!!" gizmobob. (not his words)
In spite of Greg's good intentions, there are always some dimwitts who feel that they must insert their god-like opinions, at the expense of everyone else. Where can I obtain such audacious g'nads?
Suggestion... If your passions and devine perceptions lead you to follow a passive path, that's fine. But why come here and shyte all over someone who obviously has the education, the ability, the experience, and the desire to help other's who wish to follow a different path?
Ever wonder why it's always the same ba$tards who chase off the professionals? It is the attitude and arrogance of morons that ruin the atmosphere here. I admire zeal, when it is tempered with humility instead of arogance. Given the choice, I'd trade the bad apples for good apples anyday!
I am grateful for Greg's patience... because he is one of the best contributers on DYI. Not that I agree with everything he says or does, but out of respect because he has earned it. Respect is earned... it is never given freely. AND... once it is earned... it is deserved!
I'll bet that Greg gave this audience too much credit when he reasoned that a schematic should not be necessary for something so elementary. He probably felt that a schematic would be an insult to everyone's intelligence. Judging from hindsight, I'd say that forgiveness for such an error is manditory in this case. Let this be a lesson to us all.
Don't make me come over there!
- head_spaz
</soapbox>
... soapbox terminated successfully...
C:\>
</rant><enter>
</RANT><RETURN>
<END RANT !!!>
<Calm T F Down><enter>
<^F6>
<Ctrl-Alt-Del>
- Hire the teenager --- while he still knows everything -
________________
Jesus loves you, but I have reservations.
Hi to all,
I much appreciate Greg’s work and I highly rate him as one of the best experts here, so when he comes here with “solution”, I pointed different one. Is it a sin if we think different?
If we start active/passive preamp debate I think we will be divided on two equal groups.
Spaz, are you a professional lawyer, or you like to be one? No need for that kind of language, cool down a bit!
I think Greg is capable to defend himself if he feel need for that.
Greg, keep up the good work
Chicco
I much appreciate Greg’s work and I highly rate him as one of the best experts here, so when he comes here with “solution”, I pointed different one. Is it a sin if we think different?
If we start active/passive preamp debate I think we will be divided on two equal groups.
Spaz, are you a professional lawyer, or you like to be one? No need for that kind of language, cool down a bit!
I think Greg is capable to defend himself if he feel need for that.
Greg, keep up the good work
Chicco
Although there are some parameters that are different,
when using only passive components before a power amplifier
compared to buffering with op-amp or transistors,
both methods have proven to work good.
This is, if source have reasonable good drive capacity
and the amplifier input does not represent a too difficult load.
If you have very special requirements regarding cut off frequencies
then use a buffer.
Otherwise you can often do without
with no noticable effect on performance.
There is some logic in,
that a component that is not there
can not harm and add distortion.
On the other hand, we can not take way all components.
At least not in every situation.
In the end it is up to each and everyone's judgement
when is a call for an input buffer.
when using only passive components before a power amplifier
compared to buffering with op-amp or transistors,
both methods have proven to work good.
This is, if source have reasonable good drive capacity
and the amplifier input does not represent a too difficult load.
If you have very special requirements regarding cut off frequencies
then use a buffer.
Otherwise you can often do without
with no noticable effect on performance.
There is some logic in,
that a component that is not there
can not harm and add distortion.
On the other hand, we can not take way all components.
At least not in every situation.
In the end it is up to each and everyone's judgement
when is a call for an input buffer.
Hi lineup,
I think you've hit the point on the head. Whether an input buffer is needed depends a great deal on the input of the amp. Both Nakamichi and Marantz were able to improve the sound of amplifiers using bipolar differential pairs by using input buffers. Nakamichi called it "HTA", Marantz did the same thing in the late sixties with the 500. There are probably others.
If a manufacturer can get away with something, there is an economic force at work to try to do so. You can't assume that the bulk of equipment out there is designed correctly. Many of us know as a fact that it isn't. Not for performance anyway.
I guess I'm saying that Greg's suggestion is perfectly valid. To test, build a circuit [properly] and test it. This will be true for that particular situation and person.
-Chris
I think you've hit the point on the head. Whether an input buffer is needed depends a great deal on the input of the amp. Both Nakamichi and Marantz were able to improve the sound of amplifiers using bipolar differential pairs by using input buffers. Nakamichi called it "HTA", Marantz did the same thing in the late sixties with the 500. There are probably others.
If a manufacturer can get away with something, there is an economic force at work to try to do so. You can't assume that the bulk of equipment out there is designed correctly. Many of us know as a fact that it isn't. Not for performance anyway.
I guess I'm saying that Greg's suggestion is perfectly valid. To test, build a circuit [properly] and test it. This will be true for that particular situation and person.
-Chris
amplifierguru said:
It does, Greg, it does.
Anyway, the OPA2134 will not sound at it's best with that PSU bypass layout.
Move the cap for the positive voltage to pin 8 (direct between pin 8 and ground, no long / inductive tracks, please).
The 'idea' is fine, and you could even have made provision for feedback resistors, if gain is needed.
I don't understand your worries about HF preformance though, as you have a 1k series resistor on the input of your power amp, with 1nF to ground (~159Khz lowpass).
That 1k resistor will add to the series output impedance of a volume pot, and you were worried about the pot.
The pot will not drive very well the 10k input impedance of your amp, if that's what you mean.
Small battery powered preamp.
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