Multi earphone amp system-help - Page 4 - Electronic Circuits Projects Diagrams Free

giusepped · 31st May 2007, 01:43 AM

Ok, maybe the words are misleading.
I have ONE microphone, which is powered. It comes with battery inside a small box. SO I think it is powered. In this case I don't nedd R1, do I? Becasue, R1 serves to power the mic. The OPAMP should separate the two input of the preamps. In this way their reciprocal input impedence should not be affected.
Suppose now that the mic is not powered: I have to power it, haven'I? In this case, I use R1, and again the OPAMP separate the two preamps.
Don't you agree?

audioguru · 31st May 2007, 02:04 AM

The purpose of R1 is to power the mic. So if your mic has a battery then tou don't use R1.

The mic preanp I showed has an input impedance of 50k ohms. You could connect up to 10 of them to your mic and they won't affect it. So the extra opamp is not needed.

giusepped · 31st May 2007, 08:45 AM

OK , but I don't know which is the input impedance of the other preamp(remember that it is a closed box to me)
G

audioguru · 31st May 2007, 01:50 PM

Quote:

Originally Posted by giusepped

OK , but I don't know which is the input impedance of the other preamp(remember that it is a closed box to me)
G

If it works then its input impedance doesn't matter. If its input impedance is too low like the preamp you posted then the mic signal is attenuated. Simply turn up the gain of your preamp to compensate.

giusepped · 10th June 2007, 03:42 PM

I implemented the audioguru's preamp, and an amp with tda052 from philips.
The mic is an electrect, I think. It is 2 terminal mic which need a power source.
Now the problem is that the system is to powerful! I can hear sounds very far from the mic...and also I can easily pick up the sound emitted inside the earphone capsules, located more far than 50cm, generating a larsen effect.
Actually, I did not inserted the potentiometer inside the preamp, so the gain is fixed. I just used a signal reduction at the ingress of the tda.
Any suggestion?
G

audioguru · 10th June 2007, 04:09 PM

Quote:

Originally Posted by giusepped

I implemented the audioguru's preamp, and an amp with tda052 from philips.

Now the problem is that the system is to powerful! I can hear sounds very far from the mic.

Actually, I did not inserted the potentiometer inside the preamp, so the gain is fixed. I just used a signal reduction at the ingress of the tda.
Any suggestion?

The pot in the preamp circuit adjusts its amount of gain. The TDA7052 amplifier also has gain. Your signal reduction ingress circuit should be a volume control that will adjust the volume from zero.

The preamp gain is set by the value of its pot like this:

giusepped · 11th June 2007, 11:01 AM

Than kou for your time, audioguru.
I will insert the pot.
However, there is a way to know which the peak-to-peak output of a typical electret mic?
More, may I ask you which eda do you use to draw schematic and to do simulations?
Regards

audioguru · 11th June 2007, 12:57 PM

The output of a mic depends on how far away from your mouth it is and how loud you speak or sing. A low load impedance reduces its level. It is typically about 14mV p-p.

I use Microsoft Paint program to make schematics. Straight lines are made with the Shift key down and most things are copied and pasted from other schematics or datasheets.

I use SwCAD III from Analog Devices simulation program that is excellent and is free.

TheVictim · 11th June 2007, 05:10 PM

I'm a throwback, I use DPaint IV on an Amiga 1200. Schematic symbols are copied as "brushes" and stamped onto the pic, then connected with straight lines. I have text on some of the more common values already.

**Nigel Goodwin** · 11th June 2007, 09:54 PM

Quote:

Originally Posted by TheVictim

I'm a throwback, I use DPaint IV on an Amiga 1200. Schematic symbols are copied as "brushes" and stamped onto the pic, then connected with straight lines. I have text on some of the more common values already.

Amiga 1200! - modern machine!

I loved DPaint!.

TheVictim · 12th June 2007, 12:37 AM

I have Dpaint V on a 800mhz Amithlon box, but for some reason I find IV much more useful.

Hero999 · 17th June 2007, 02:31 PM

Is that the DOS version or are you using an emulator?

TheVictim · 18th June 2007, 06:24 AM

Amithlon is an emulator/licensed OS & ROM package for 68K based Amiga OS's. It includes Workbench 4.0, but you can run newer or older versions on it as well. It supports Cybergraphix, but not AGA, so 1200/4000 specific apps won't work in AGA modes. That is why I'm using DPaint IV on the 1200 and Dpaint V on the Amithlon box.

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31st May 2007, 01:43 AM	(permalink)
giusepped	Ok, maybe the words are misleading. I have ONE microphone, which is powered. It comes with battery inside a small box. SO I think it is powered. In this case I don't nedd R1, do I? Becasue, R1 serves to power the mic. The OPAMP should separate the two input of the preamps. In this way their reciprocal input impedence should not be affected. Suppose now that the mic is not powered: I have to power it, haven'I? In this case, I use R1, and again the OPAMP separate the two preamps. Don't you agree?

31st May 2007, 02:04 AM	(permalink)
audioguru	The purpose of R1 is to power the mic. So if your mic has a battery then tou don't use R1. The mic preanp I showed has an input impedance of 50k ohms. You could connect up to 10 of them to your mic and they won't affect it. So the extra opamp is not needed. __________________ Uncle $crooge

31st May 2007, 08:45 AM	(permalink)
giusepped	OK , but I don't know which is the input impedance of the other preamp(remember that it is a closed box to me) G

10th June 2007, 03:42 PM	(permalink)
giusepped	I implemented the audioguru's preamp, and an amp with tda052 from philips. The mic is an electrect, I think. It is 2 terminal mic which need a power source. Now the problem is that the system is to powerful! I can hear sounds very far from the mic...and also I can easily pick up the sound emitted inside the earphone capsules, located more far than 50cm, generating a larsen effect. Actually, I did not inserted the potentiometer inside the preamp, so the gain is fixed. I just used a signal reduction at the ingress of the tda. Any suggestion? G

11th June 2007, 11:01 AM	(permalink)
giusepped	again gain Than kou for your time, audioguru. I will insert the pot. However, there is a way to know which the peak-to-peak output of a typical electret mic? More, may I ask you which eda do you use to draw schematic and to do simulations? Regards

11th June 2007, 12:57 PM	(permalink)
audioguru	The output of a mic depends on how far away from your mouth it is and how loud you speak or sing. A low load impedance reduces its level. It is typically about 14mV p-p. I use Microsoft Paint program to make schematics. Straight lines are made with the Shift key down and most things are copied and pasted from other schematics or datasheets. I use SwCAD III from Analog Devices simulation program that is excellent and is free. __________________ Uncle $crooge

11th June 2007, 05:10 PM	(permalink)
TheVictim	I'm a throwback, I use DPaint IV on an Amiga 1200. Schematic symbols are copied as "brushes" and stamped onto the pic, then connected with straight lines. I have text on some of the more common values already.

12th June 2007, 12:37 AM	(permalink)
TheVictim	I have Dpaint V on a 800mhz Amithlon box, but for some reason I find IV much more useful.

17th June 2007, 02:31 PM	(permalink)
Hero999	Is that the DOS version or are you using an emulator? __________________ I also post at the following sites: http://www.stop-microsoft.org http://www.heated-debates.com Screen name: Aloone_Jonez And http://www.silicontronics.com, same screen name as here.

18th June 2007, 06:24 AM	(permalink)
TheVictim	Amithlon is an emulator/licensed OS & ROM package for 68K based Amiga OS's. It includes Workbench 4.0, but you can run newer or older versions on it as well. It supports Cybergraphix, but not AGA, so 1200/4000 specific apps won't work in AGA modes. That is why I'm using DPaint IV on the 1200 and Dpaint V on the Amithlon box.