| globalweb |
Here’s a question for you knowledgeable people out there. Why do you need a preamplifier?
Searching the web I found these answers.
- If you have more then one source it’s easier then disconnecting the devices.
- If you have a turntable you need to amplify the signal before the power amplifier.
- If you don’t have a volume control on the CD/DVD player you need a volume control on the preamplifier.
- Anything else?
So if you use only a CD player. Can you connect it directly to the power amplifier? What could possibly go wrong? |
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| darkfenriz |
| I don't need a pre for the same reasons. |
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| nikwal |
| Volume control is nice.. everything else is just bloat ;-P |
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| Gordy |
If you use predominantly only one source, and that source has a good quality variable level output (i.e. a volume control that you believe to be of good quality), and there are no impedance mis-match problems between source and target amplifier, then you may not need a pre-amplifier.
However a pre-amplifier is a good solution for bringing together (any of) the following functionality:
Source selection
Record outputs (buffered ideally)
Volume control
Balance control
Home theatre by-pass (to use your 2 channel kit as part of a home-theatre system without swapping connections)
Tone controls (if it takes your fancy)
Filters
Mute
Unbalanced to balanced conversion
Balanced to unbalanced conversion
Impedance conversion (high in / low out) |
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| globalweb |
Hi Gordy
Thanks for answering. When you say “there are no impedance mis-match problems between source and target amplifier”. What do you mean?
I’m just a beginner so that’s why I’m asking. |
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| lumanauw |
Depends on the quality of the preamp.
If the preamp's input is more sensitive than power amp's input, then there will be better music (via preamp connection) compared if the source connected directly to the power amp.
"Impedance Bridging", Darkfenriz? :D |
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| mtlin12 |
I need a good preamp or a buffer which can provide large current
to drive the signal cables' capacitive reactance.
Passive preamps seldom do this well. |
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| dshortt9 |
If one is not careful about the source impedance, amp input impedance, and cable capacitance there can be a rolloff in the high frequencies. Here is a calculator:
http://www.dact.com/html/ac_calculator.html
I use a passive and prefer it. |
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| globalweb |
dshortt9
In practical terms. What does it mean? Will it brake any parts? Will it degrade the sound? Is it possible in the technical specs to see if there’s going to be any problem?
I’m sorry for being so inquisitive but I’m worried I going to brake something. |
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| Gordy |
1.
The output impedance of your preamp and the input impedance of your power amp form a 'potential divider'. The power amp 'sees' the signal at the junction of the potential divider.
To make sure that the maximum level of signal is available the output impedance of the preamp should be very small compared to the input impedance of the power amp. A good solution is input impedance of power amp = output impedance of preamp x 100.
This is not always possible. When the two impedances are closer in value the signal level 'seen' by the power amp will be lower. This is not ideal, however it may not be a big problem. It is very unlikely to break anything.
(At the very worst case it will cause high current to be drawn from the preamp, which may be excessive and cause the preamp protection circuits to work. However this is very rare).
2.
The output impedance of the preamp works with the capacitance of the interconnect cable to form a (low pass) filter which can cut some high frequency information. It depends on the values of both the output impedance and capacitance. Keeping the output impedance of the preamp low can help prevent this.
Most solid state equipment (CD players for example) have fixed output impedances in the range 50 - 1000 Ohms.
Passive preamps (such as potentiometers) have impedances of typically 10k to 20k Ohms. These vary according to volume setting. The simplicity of the potentiometer is then often negated by the poor interaction of the impedance and the capacitance of the cable, which is often audible as a loss of high frequency information. So if you use a passive preamp, keep your cables very short. |
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| janneman |
| quote: | Originally posted by lumanauw
[snip]
If the preamp's input is more sensitive than power amp's input, then there will be better music (via preamp connection) compared if the source connected directly to the power amp.
[snip] |
David,
That's not true. If the preamp's input sensitivity is higher, your sound LEVEL will be higher, unless you turn down the volume. There is no reason why there would be any diference in sound quality from the difference in sensitivity. It just means that the power amp will reach its max output level with lower source level, so you need to turn down the volume more.
Jan Didden |
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| lumanauw |
Hi, Janneman,
Yes, you are right. I use wrong words (again). I don't mean sensitivity in term of gain, but "sensitive" in terms of higher input impedance. I'm thinking of signal voltage transfer. A better signal voltage transfer is possible if the (lower) source impedance is headed with a (higher) input impedance. This is possible if we insert a preamp. If the CD player has a certain output impedance (say 100ohm), the power amp has input impedance of 47kohm, then if we put, say Jfet preamp with input impedance of 1Mohm and output impedance of 47ohm, then (if the preamp itself is good), we can get better sound from the whole system. Am I right with this thinking of "sensitive"? |
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| Sonusthree |
| quote: | Originally posted by globalweb
So if you use only a CD player. Can you connect it directly to the power amplifier? What could possibly go wrong? |
Beware that some CD players have software controlled volume levels that reset to MAXIMUM when switched on. :bigeyes:
That's a great way to start your day!!! :bomb: |
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| janneman |
| quote: | Originally posted by lumanauw
Hi, Janneman,
Yes, you are right. I use wrong words (again). I don't mean sensitivity in term of gain, but "sensitive" in terms of higher input impedance. I'm thinking of signal voltage transfer. A better signal voltage transfer is possible if the (lower) source impedance is headed with a (higher) input impedance. This is possible if we insert a preamp. If the CD player has a certain output impedance (say 100ohm), the power amp has input impedance of 47kohm, then if we put, say Jfet preamp with input impedance of 1Mohm and output impedance of 47ohm, then (if the preamp itself is good), we can get better sound from the whole system. Am I right with this thinking of "sensitive"? |
Yes, I see what you mean, and I agree with that part. But I don't see how this leads to better sound. The difference between 47k load or 1M load (100 ohms source) is just a fraction of a dB loudness, undetectable unless you use precision test equipment. So, I don't see any need for a preamp here.
It is another case with a tube source with several k Zout, and a ss amp with low (5-10k) Zin, because the tube source may well increase its distortion if it has to drive the ss amp, as tube stuff is known to have often weak drive capability.
Jan Didden |
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| lumanauw |
Hi, Janneman,
| quote: | | But I don't see how this leads to better sound. |
Now I'm confused myself :D. You are right, where the "better sound" is coming from, if we only look at the input-output impedance? If we thinking of "black box", there is no such thing as preamp (as black box) that will deliver 100% of what it's receiving. 99% signal delivery will still have 1% corrupted.
So, what is the need of preamp? |
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| Sonusthree |
I'm currently passive Bi-amping. Each amp is an integrated with it's own 10K volume pot. I'm planning to build an external passive pre to control both and bypass the amps volume pots. So .......
Are there any extra considerations when using a passive pre to feed two power amps in parallel? The gain of both amps will be equal.
Many thanks,
Martin. |
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| globalweb |
| Today I connected the CD player to my power amp. Directly the where a loud buzzing sound. Any ideas why? |
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| AndrewT |
| quote: | Originally posted by Sonusthree
I'm currently passive Bi-amping. Each amp is an integrated with it's own 10K volume pot. I'm planning to build an external passive pre to control both and bypass the amps volume pots. So .......
Are there any extra considerations when using a passive pre to feed two power amps in parallel? The gain of both amps will be equal.
Many thanks,
Martin. |
hi,
a few issues, but easily handled.
the effective load impedance seen by the pre-amp is Zin//Zin.
The effective cable capacitance seen by the pre-amp is Ccable+Ccable.
The input offset current of each power amp can interact if BOTH are devoid of DC blocking input caps.
Since one amp is handling low frequency, the input conditions can be optimised for that end of the frequency range. The amp handling the upper end of the frequency spectrum can have it's input conditions optimised for the higher frequencies. |
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| Sonusthree |
Andrew, as always, thanks.
You have just given me another reason to reduce the input cap on the tweeter amp. I guess I will need to be conservative to minimise phase problems. I've ordered a stepped attenuator from Hong Kong so it'll be a while before I see the results.
| quote: | Originally posted by globalweb
Today I connected the CD player to my power amp. Directly the where a loud buzzing sound. Any ideas why? |
How is your player setup? Does it have a volume control? Did it buzz while playing music?
It sounds a little like the volume was not lowered and the power amp was amplifying the noise from the player????
Tell us more. |
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| Cloth Ears |
Volume control. The ones available on source items (CD/SACD/DVD players are the only sources that have them, I think) just don't cut it. Then again, some pre-amps volume controls don't cut it either.
Switching is useful, as my partner likes listening to the radio and does not like crawling around behind power amplifiers (although I like the idea, :devilr: now that it comes up).
Oh, and loudness and tone controls - where would we be without them? Oh dear, it's time for the white coat with the long sleeves again - they're coming to take me away, ha ha! |
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| globalweb |
Sonusthree
The volume was set om min. No music. |
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| Gordy |
| With respect, and not meaning to sound offensive, but did you have the cables connected to the Audio outputs left and right connectors (often white and red), or to some other connectors? |
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| Sonusthree |
| quote: | Originally posted by globalweb
Sonusthree
The volume was set om min. No music. |
What kind of volume control is it? Is it part of the CD player and is it software or hardware controlled? Give us some more information. We don't know your system!
| quote: | Originally posted by Gordy
With respect, and not meaning to sound offensive, but did you have the cables connected to the Audio outputs left and right connectors (often white and red), or to some other connectors? |
.... or some kind of grounding issue.
Tell us more Globalweb. :) |
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| globalweb |
I forgot.
Gordy
Yes I connected it correctly. Red to red, white to white. |
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| unclejed613 |
actually, if the preamp is well designed, that figure should be that the signal is corrupted .01% or less (this is called distortion). other than the fact that you can add tone controls, etc... to a preamp, the two main reasons for having a preamp are 1> signal switching and routing, and 2> volume control.
reason 1 exists because people like to be able to re-record music, listen to various audio sources, and don't like replacing worn-out cables every month or so.
reason 2 exists, because people like to sometimes listen to their music loud, and sometimes not so loud. there are vast differences in the signal levels of different sources, and even between various recordings on the same source. there are also amps made with no volume controls. there are also vast differences in people's tastes of how loud they want to listen.
tone controls and other signal processing are a convenience that people happen to like. and a preamp is a convenient central location to put these functions into. at one time, music recording and playback offered no control whatsoever over source and playback levels. edison's phonograph offered only one recording level and only one playback level. whatever was present in the studio is what went onto the cylinder, and whatever was on the cylinder was what was played back. the technology for recording, then mixing and re-recording a master, did not exist. |
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| Sonusthree |
| quote: | Originally posted by globalweb
I forgot.
Gordy
Yes I connected it correctly. Red to red, white to white. |
Have you tried using different interconnects?
Is the buzzing sound a low 50/60Hz? Does the buzzing sound change when you touch the metal of the CD or amp? This would indicate a grounding issue.
Does it sound OK with a preamp between CD and amplifier?
What happens to the buzz when you turn up the volume?
What happens when you play music?
Sorry for all the questions! :D |
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| IrishboyM4 |
| If you have a MP3 player you can easily drive an amplifier directly from the player. That is the way i drive my amp, and when i want to connect the computer I just swap it. |
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| globalweb |
Sonusthree
So far I haven’t tried different connects. I’ll do it as soon as I can
The buzzing sound is much higher than 50 – 60 Hz about 1000 Hz or so.
There is no change when I touch the metal.
It sounds ok when there is a preamp.
The buzzing doesn’t change when I change the volume.
I can play music but the buzzing is still there.
Also I tried something interesting. I put the probes of my multimeters between the connection of CD-output/power amp input and ground. There where definitely a change in the buzzing. It didn’t stop but the sound changed.
Any ideas?
IrishboyM4
MP3? Perhaps in the future. No plans so far. |
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| Sonusthree |
| quote: | Originally posted by globalweb
Sonusthree
The buzzing sound is much higher than 50 – 60 Hz about 1000 Hz or so.
There is no change when I touch the metal.
It sounds ok when there is a preamp.
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Wow! 1000Hz?
I wonder if it's some kind of oscillation? :scratch: |
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| globalweb |
Here’s some FAQ taken from the CDP homepage:
“Can it be run without a pre-amp?
Yes. It has a volume control on the remote, and a very high quality analogue section (that is a big part of what you are paying for) with low output impedance, so even running 25 ft cables is no problem. Click here for info. The volume control is defeatable by pushing a button.”
And
“The Ah! Njoe Tjoeb 4000 has a volume control which is digital. Nice convenience if you have no pre-amp, or your pre-amp has no remote. Some notes on operation
• The volume control can be defeated by holding down the edit button for two seconds on the front of the machine.
• The volume performed in the digital arena, so the control should be as high as possible for the best sound during typical listening. At lower level you may lose some resolution...though people don't seem to notice as it is low for background listening.
• If you have an amp that needs little voltage, you can adjust the maximum voltage of the Njoe Tjoeb. It is set at the factory at 2.5v, but can be adjusted up to 5v, or down to 1.25v or .7v to fit a variety of systems. To change the voltage requires soldering and is quite easy. We can do it for you too now or later no charge for labor to the original owner.
• The control will lower the volume, but not all the way. It does not turn down to a whisper. With that, we have customers using the Tjoeb with no preamp and sing its praises. It may still be good to have a preamp if you need big volume swings on the fly.
The output section is robust, and has a low output impedance. So you have the option of using no pre-amp if that is your preference, or if you are in-between or waiting for your next pre-amp.”
Maybe it gives the answer. |
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| globalweb |
| Finally I've got a tone generator. The sound is at 250 Hz not 1000 Hz. |
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| Sonusthree |
| quote: | Originally posted by globalweb
Anyone? |
I'm afraid I'm lost!! The frequency that you mention doesn't make any sense to me. I would have assumed some kind of ground loop and it is still a very slight (???) possibilty that the 250Hz buzz is a harmonic of the mains frequency? Are you sure that there is no lower frequency content ,50/100Hz, in the 'buzz'.
Have you tried plugging the CD into a different mains circuit than the amp? This can help sometimes.
Come on folks, someone must have some better ideas. :scratch: |
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| SY |
| Stick a scope on the power supply rails. |
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| sandyK |
Yesterday I heard the best sound that I have ever heard, when a friend brought over his Oppo DV981HD universal player.(this player has improved , both in Audio, and even video via HDMI (!) since the switch mode bridge diodes were replaced by BYV26C
diodes, a parallel 100nF 630V fitted across the main PSU electro, and some sound deadening material fitted)
We fed the Oppo into a highly modified Musical Fidelity X-DAC V3, and then directly into my Class A 15W Ch. amplifier. The Oppo has the ability to control volume in the digital domain via SPDIF.
After this revelation, I have ordered an Oppo player.There doesn't appear to be too many other DVD players with SACD and DVD-A capability with this option.I will soon be adding an extra relay switched input to the Class A amplifier and using my very high quality Class A preamplifier for sources like DVB audio etc.
It appears that even the best preamplifiers, whether active or passive, degrade to some extent the ultimate audio quality.Why put 2 lots of electronics in tandem, UNLESS you need all the other facilities as mentioned in a previous reply ?
SandyK |
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| Gordy |
globalweb, I think you may have to try substitution to trace your problems. Try and borrow another amplifier, substitute it into your system, and using the same CD player, see if the problem is still there.
If the problem is still there then the problem is inside the CD player.
You say the problem is 250Hz? How strange. I am guessing, but the power supply may be the best place to start looking. As SY said, you are likely to need a 'scope. |
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| globalweb |
Thank you all for your interest.
About the frequency. All I have is a PC tone generator. And its speaker can’t produce any lower tone then about 105 Hz. So maybe I have frequency’s of 100 and 50 but I can not tell. Sorry.
Trying different mains I will definitely do. I just need to buy longer power cords. Hopefully this weekend.
Sticking a scope on the power supply rails.
I’m a bit of a dummy when it comes to electronics so if anyone could give me some guidelines would be much appreciated.
Exactly where do I measure? What should I look for? After the power supply capacitor?
Substitution solution, will absolutely do. As soon as I can get hold of another CD player.
Anybody have any ideas why the buzz changed when I put the probes between earth and output? |
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| preiter |
On the original question of why do you need a pre-amplifier.
I think some of the confusion on this topic may revolve around the fact that discussions of specific pre-amplifiers tend to revolve around the gain stage.
Reading these discussions, one can easily come to the conclusion that the whole reason to have a pre-amp is just for the gain stage. |
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| FastEddy |
sandyK: " ... the best sound that I have ever heard, when a friend brought over his Oppo DV981HD universal player. ..."
Besides volume control via the remote, it also has several EQ options ... in case you don't have a sub woofer, try the "Live" setting ... This player also has a "secret" code that will allow playing of all Zone1 and PAL Zone2 DVDs ... plus as you now know, DVD-audio or SACD discs = much more "universal" than most = :D
" ... the switch mode bridge diodes were replaced by BYV26C diodes, a parallel 100nF 630V fitted across the main PSU electro, and some sound deadening material fitted) ..."
Is this some sort of Mod to the Oppo player or to a pre-amp ?? If to the Oppo, please start another topic, say over in "Digital" or somewhere besides this thread = Thanks ... :smash:
FYI: I play my Oppo '981 through a BottleHead tube pre-amp then through a DIY MOSFET amp through two mains only = ordinary old fashioned stereo ... :) |
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| sandyK |
FastEddy
I was trying to fit in with the INITIAL general thrust of this topic.The mods were briefy mentioned to illustrate only that the audible results in this test may not have been quite so dramatic with a standard Oppo Player. In another small Forum that I am a member of, those small mods are generally known. I expect to take delivery of the Oppo later today.Obviously, for use in this manner ,you would not need a preamplifier, if your primary uses were watching DVD movies and listening to CDs. Many people (not me) would'nt bother with their audio setup to watch TV.
SandyK |
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| FastEddy |
" ... In another small Forum that I am a member of, those small mods are generally known. ..."
?? Another Forum?? Like who? AudioAsylum.com ? Other? = me too, & several others, but not regularily.
" ... expect to take delivery of the Oppo later ..."
Super. If you decide to make some mods, lert us know [on another topic / arena of your choice]. (All I did was add some plastic caps to snubb down the +/-9 VDC power at the DAC analog board connector.)
I have the tube pre-amp in the daisy chain string to have a quiet source switcher (FM tuner, Oppo DVD player and of course my iTunes / Mac Internet radio feed) and an impedence matcher ... and to take the edge off and mellow out any clipped signals ... :smash: |
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| sandyK |
Fast Eddy
The small forum is "Rock Grotto Audio Forum"
Since a few days ago you have to register to view. It is mainly devoted to Headphones and their amplifiers, DACs , Valve gear in general , and general chit chat/discussions.If you need further information email me.
SandyK
alexkethel@optusnet.com.au |
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| FastEddy |
" ... amplifiers, DACs , Valve gear ..." = My meat ... :D
(As I write: Listening to Apple MacBook <<>> Radio Skipper (iTunes internet radio feed @ 128k) <<>> 2 channel, 24 bit/96K Echo Digital AudioFire4 DAC <<>> ForePlay III tube pre-amp <<>> DIY 150 Watt X 2 MOSFET amp <<>> Maggie MMG planar speakers ... :spin: ) |
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| sandyK |
Seems like the small >400 member Rock Grotto forum should be of interest to you. It may be small, but it has members globally, although some of the equipment mentioned is from British
"boutique" manufacturers. You will even see a thread by me on Extreme Modifications to the Musical Fidelity X-DAC V3.
It is a very informal group and very helpful.
However, for the sheer breadth of information, as well as some very clued up people.(some major designers and gurus too)
This forum is undoubtedly the premier forum. I prefer Class A solid state,preamp and power amplifiers, and enjoy trying the latest devices (LM4562 etc-overhyped? I am "burning in" a couple of LM4562 at present) and new circuit techniques.Most of my gear, however, doesn't stay stock standard very long, though.
SandyK |
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| FastEddy |
http://www.national.com/pf/LM/LM4562.html =
* Ultra high quality audio amplification
• High fidelity preamplifiers
• High fidelity multimedia
• State of the art phono pre amps
• High performance professional audio
• High fidelity equalization and crossover networks
• High performance line drivers
• High performance line receivers
• High fidelity active filters ...
...
THD+N (AV = 1, VOUT = 3VRMS, fIN = 1kHz)
?RL = 2k? 0.00003% (typ)
?RL = 600? 0.00003% (typ)
? ?Input Noise Density 2.7nV/ ? ^Hz (typ) === :cool:
One could imbed this chip in a small switching box (for selecting sources) and have a tidy little stereo pre-amp, two for 4 channels, three for db 5.1 surround ... |
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| Daveis |
| What's the opamp eval board for? |
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| sandyK |
I am presently trialling the LM4562 in a preamplifier designed by Silicon Chip magazine, and which used OPA2134s.Initially, I was impressed by the big soundstage and the wealth of detail, but hoping that the "brashness" would improve as the chips burned in. A friend and I, both felt that in this particular application, the LM4562 didn't handle complex stuff as well as the OPA2134.
Overall, my existing Class A home brewed preamp is noticeably better. I offered my friend a couple of LM4562 to try in his preamp, but he declined the offer ! My preamp is still switched on,
and I will leave it on for another couple of days.
Thanks for the info.
SandyK |
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| sandyK |
It is to allow designers/manufacturers to properly evaluate the chip in the manufacturer's recommended layout, so that they can decide if they want to buy zillions of them from N.S. for use in their new products.
SandyK |
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| Daveis |
| quote: | Originally posted by sandyK
It is to allow designers/manufacturers to properly evaluate the chip in the manufacturer's recommended layout, so that they can decide if they want to buy zillions of them from N.S. for use in their new products.
SandyK |
Ok, what I'm wondering is if the opamp eval board has inputs and outputs for use as a line level preamp? |
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| sandyK |
There doesn't appear to be any further info on their website. You would have to ask N.S. that one, unless of course, some forum member has tried the eval board ?
SandyK |
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| FastEddy |
The Evaluation board probably does not have the connectors, but would offer the evaluator these specs, at least:
"¥ Easily drives 600½ loads
¥ Optimized for superior audio signal fidelity
¥ Output short circuit protection
¥ PSRR and CMRR exceed 120dB (typ) ... "
... and use this partial circuit plus provisions for adding PS filtration / connections: http://www.national.com/images/pf/LM4562/201572k5.pdf |
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| neazoi |
Hi I have a basic question about the attenuator and I would need only some techical advice on this please.
I have found a wonderful rotary military switch from a local military surplus for only $15. The switch is porcelain with golden contacts and plastic domes to prevent the dust going on the contacts. More superior in my oppinion to the classic high quality golden pins pcb chip resistors pontentiometers and far more supperior to the $20 plastic ladder attenuators sold on ebay.
I am thinking of making a very high quality attenuator using caddock resistors with it.
Note that I am going to use it with a PSE 2A3 tube amplifier.
My first question is:
The switch is 26 positions but because of the flange configuration I can use only 13 positions. What a nomimal maximum value in KOhms will be suitable for my passive preamplifier?
This 13 position switch will be suitable for the preamplifier or the steps will be so far appart? (i.e. big difference from the lower music level to the next higher)
My second question is:
I have seen almost all good quality passive preamps on the web using stepped ladder attenuator with this signal divider (or composer) approach where the output signal is composed of a portion of the input signal + the rest from the GND (earth). In a simple not ladder pontentiometer this is, connecting the input signal in the left pin of the pontentiometer, the output in the middle pin and the GND in the right pin.
Now, why this is done? Why can't I just ignore the GND and connect the pontentiometer as a reostat, like a single variable resistor between the signal input and the output? Or can I?
And my third question continues the previous one:
If I do have to use this GND approach can I just use the pontentiometer as a reostat (variable resistor) and having the GND resistor to be the one that is used in the grid of the tube in the next stage? Note this grid resistor is connected from the input signal of the amplifier to the GND and there is no capacitor in the imput of the amplifier.
Thank you very much! |
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| AndrewT |
| quote: | Originally posted by neazoi
My first question is:
The switch is 26 positions but because of the flange configuration I can use only 13 positions. What a nomimal maximum value in KOhms will be suitable for my passive preamplifier?
This 13 position switch will be suitable for the preamplifier or the steps will be so far appart? (i.e. big difference from the lower music level to the next higher)
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if you can arrange for the zero attenuation of the switched volume control to match your maximum output you will ever listen to (by adjusting the gains of both the pre-amp and power amp), then you can sometimes find that -20db to -30db covers a range of volume that you are happy with.
If each step is 2db then you can get 0db to -24db using your 13 steps.
Why can't you get to the other 13 steps? |
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| neazoi |
Thank you,
I cannot because the flange of the switch has holes that correspond to every two switch positions. i.e. each "klick" corresponds to two positions of the switch.
There is also another thing, using caddock resistors a 26 position will greatly double the cost to high levels for my budget..
How about these PRECISION MULTITURN pontentiometers? Why couls not I use them? are they noisy compared to a stepped ladder? Very inductive, or what? |
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