universal chip pre-amp project

[mjf]

hello.
yes, 2,3v /10 ohm =230ma..............that is heavy!
without a load the power dissipation of the z-diode is around 12v x 0,23a = 2,7w!
make the res bigger.............22ohm or better try 33 or 47ohm.
greetings............

[tent]

Originally Posted by mjf

hello.
yes, 2,3v /10 ohm =230ma..............that is heavy!
without a load the power dissipation of the z-diode is around 12v x 0,23a = 2,7w!
make the res bigger.............22ohm or better try 33 or 47ohm.
greetings............

Hi Mif!
great suggestion, I substituted the two resistors with two 47ohm (2w) ones and now I can read 12.3V after the zeners! and it seems also a lot less hot!! ok after some 10 minutes it still gets somehow hot (resistor + last cap) maybe I still have some 75ma that I should dissipate at the res.. should I increse the res even some more?

thanks!
tent:wq
PS: digi01 -> the preamp sounds charming.. now working at the volume pot (actually some resistor based attenuator and fighting with the gain of my tamp which is too hig.. 33.. ) and also the cabling I currently have is to undergoing some rework since I get some buzz in the background.. probably going too near to the toroid..

[cancerkazoo]

Is there any reason there should be a lot of hiss? With my laptop connected directly to my Sure TA2024 amp there is very little hiss, with the preamp connected there is a lot.

[digi01]

to cancerkazoo,
i think there are two reason caused the hiss.one is components itself,the other is the source.
look at your attached photo,i think you have not set up a volume pot for the preamp.the preamp gain setting is 10,it means 0.1V noise floor will get 1V noise output.you can disconnect the laptop watch if the hiss is gone.
i am always believe the laptop is not a good source for hi-fi.i think you'd better use a external sound card.and you'd better add dummy load(47ohm to 300ohm)for the card without line output.

Zang

[tent]

what would be a good gain setting with this preamp? You say preamp has gain 10, I have a LM3668 with gain 33.. would it be ok, just design correctly my attenuator with resistances? or probably better change amp gain?

tent:wq

[AndrewT]

Originally Posted by tent

what would be a good gain setting with this preamp? You say preamp has gain 10, I have a LM3668 with gain 33.. would it be ok, just design correctly my attenuator with resistances? or probably better change amp gain?

tent:wq

Hi,
what is either side of the pre-amp?The signal level and the power amplifier and the speakers as well as the pre-amp each affect the final SPL at the ears.
One must consider the system as a whole.

[cancerkazoo]

Originally Posted by digi01

to cancerkazoo,
i think there are two reason caused the hiss.one is components itself,the other is the source.
look at your attached photo,i think you have not set up a volume pot for the preamp.the preamp gain setting is 10,it means 0.1V noise floor will get 1V noise output.you can disconnect the laptop watch if the hiss is gone.
i am always believe the laptop is not a good source for hi-fi.i think you'd better use a external sound card.and you'd better add dummy load(47ohm to 300ohm)for the card without line output.

Zang

That would make sense, I was under the impression that this was a unity gain preamp. ( I thought I read that somewhere)

Is there a way to make this unity, or less? as my TV output is higher than what I want for my amp.

EDIT: I did find that my mains wiring is wrong in my living room (ground loop) because of the preamp, so I run it on an extention cord from the kitchen until I can correct it. But, now when I unplug the input (from laptop) I get noise, any idea what could be causing it now? The kitchen plug has 0v from neutral to ground and 120v from hot to ground, so it is wired correctly.

[tent]

Originally Posted by AndrewT

Hi,
what is either side of the pre-amp?The signal level and the power amplifier and the speakers as well as the pre-amp each affect the final SPL at the ears.
One must consider the system as a whole.

Hi Andrew,
I didn't understand this so well.. what do you mean? I'm going to use different surces to be attached to the preamp (cd player, sat receiver, evne an ipod, etc..), then after this preamp stage with gain 10 it will enter my LM3886 stereo gainclone which currently has gain 33.. (860ohm res to ground and 22kohm as feedback) and finally all goes to my ciare speakers, 8ohm, fullrange, 96 efficency.

tent:wq

PS: cancerkazoo is now your buzz away? no hum any more (I mean by powering from the kitchen)?

[AndrewT]

Hi,
your chipamp can output a maximum ~22Vac to your speakers giving ~108dB SPL at maximum signal.
The maximum input signal to reach transient peak is 22/33 =660mVac.
Using a 10times gain pre-amp. the maximum signal required to give maximum output ~66mV.
Most, if not all modern, sources give way over this output voltage, some could be as high as 2500mVac.

Using excessive gain that has to be attenuated to a useable value has consequences that impacts on the overall performance of the system without any compensating gains in performance.
You probably don't need any pre-amp gain and I suspect all your sources need only an attenuator to drive your system into clipping.
You will need further attenuation just to make the system enjoyable for the majority of your normal listening time.

[tent]

Originally Posted by AndrewT

Hi,
your chipamp can output a maximum ~22Vac to your speakers giving ~108dB SPL at maximum signal.
The maximum input signal to reach transient peak is 22/33 =660mVac.
Using a 10times gain pre-amp. the maximum signal required to give maximum output ~66mV.
Most, if not all modern, sources give way over this output voltage, some could be as high as 2500mVac.

Using excessive gain that has to be attenuated to a useable value has consequences that impacts on the overall performance of the system without any compensating gains in performance.
You probably don't need any pre-amp gain and I suspect all your sources need only an attenuator to drive your system into clipping.
You will need further attenuation just to make the system enjoyable for the majority of your normal listening time.

Well I perfectly agree, I definitely will need to attenuate my surces: if I'd connect my CD source directly to my LM3886-based power amp I'd sureli fire off my windows!!
So I was wanting to build a pre-amp to a) select sources via switch pot, b) attenuate volume via attenuation pot and c) I tought that using this also LM based pre-amp would improove sound.
At the end you probably would like to suggest me to use some less gain pre-amp? or maybe to rething the current gain of my power amp maybe? or just bypass pre-amp?

Thanks in advance,
tent:wq