Pre Amp - Modifications

[Suraj143]

1. Can I use the below pre amp with a 12V single power supply?

2. How can I couple the below loudness circuit to above? Is it power amp volume or loudness volume?I see 4 pins in the volume..!!

 

[Nigel Goodwin]

1. Can I use the below pre amp with a 12V single power supply?

Yes, as long as you create a split supply from the 12V source - there are details in the sticky at the top of this forum.

2. How can I couple the below loudness circuit to above? Is it power amp volume or loudness volume?I see 4 pins in the volume..!!

Between the output of the preamp and the power amp - can you source the extremely rare special volume control with the loudness tap on it?.

The control is overall volume - the point of the 'loudness' setting is simply to increase the bass and treble at low levels - quality amps don't have such settings.

 

[Suraj143]

I'm unclear on this.

*If I make the loudness circuit do I need additional "loudness control Pot"?
*Or can I directly connect to power amps volume?
*In the above schematic I see 4 connections ...!!!

 

[ronsimpson]

2. How can I couple the below loudness circuit to above? Is it power amp volume or loudness volume?I see 4 pins in the volume..!!

It is a little hard to see in the picture but there is a 4th leg on this pot. I do not know where you can get them now days.

 

[Nigel Goodwin]

As I said, you need a special 4 pin pot - this becomes the volume control, and you can remove the original one.

Why do you want a loudness control?.

 

[Suraj143]

Thanks everybody now I understood.It needs a special volume control.But l see some modern DIY pre amp boards has loudness switch but it has normal 3 pin volume controllers.

 

[Nigel Goodwin]

Thanks everybody now I understood.It needs a special volume control.But l see some modern DIY pre amp boards has loudness switch but it has normal 3 pin volume controllers.

Probably not as effective, the whole point is it only operates over part of the controls range - post a link to one.

For service purposes, it's normal to replace with a standard control, and throw the loudness parts away.

 

[dr pepper]

Connect a 2 x 1k resistors in series, one end to V+ and the other end to V-, then connect a 100uf capacitor from the center of these 2 resistors to V- and also to the + input of the Tl084 on the right, and instead of connecting the 10k resistor to ground thats on the left hand Tl084 + input connect it also to the junction of the 1k resistors.
Both op amp non inverting inputs will then have a 1/2 supply reference, and Lm358 might be a better op amp too.

If you already have the loudness pot you might just be able to connect it before this circuit, the 10k to ground on the first op amp might need replacing depending on the value of said pot.

 

[audioguru]

The amount of "loudness" boost needed depends on the sensitivity of the speakers and the amount of power produced by the amplifier. It will almost always have the wrong amount, don't use it.
Why are you using a ordinary TL082 opamps that might be noisy instead of using audio TL072 opamps that are selected and guaranteed to have low noise?

 

[Nigel Goodwin]

The amount of "loudness" boost needed depends on the sensitivity of the speakers and the amount of power produced by the amplifier. It will almost always have the wrong amount, don't use it.
Why are you using a ordinary TL082 opamps that might be noisy instead of using audio TL072 opamps that are selected and guaranteed to have low noise?

I don't see as it matters in that circuit, it's only a unity gain buffer, followed by a baxendall tone control, so all at lone levels and no noise issue (741's would be fine )

 

[audioguru]

All half-decent audio products use low noise audio opamps. I have never seen a TL082 or a lousy old 741 opamp in anything.
I have used and designed audio products that used tens of thousands of TL07x opamps and none ever failed.

 

[Nigel Goodwin]

All half-decent audio products use low noise audio opamps. I have never seen a TL082 or a lousy old 741 opamp in anything.
I have used and designed audio products that used tens of thousands of TL07x opamps and none ever failed.

So?, no doubt a TL082 is just as reliable as a TL072?, and in this case the TL072 has zero advantages over the TL082. Incidentally, I'm currently using TL072's in a high gain preamp, it was what I tested first (using a socket), and I was going to try various low gain types, but the 72 was perfectly fine so I never bothered.

 

[ronsimpson]

Can I use the below pre amp with a 12V single power supply?

Here is a try to use a single supply. Note the input has a return of ground. The output is ac coupled and has the same return. The "1/2" point must have a large cap to the same return "ground". The 1/2 point does not need to be accurate.

 

[dr pepper]

Just what I was describing, with the important addition of the o/p cap, I forgot about that.

 

[Nigel Goodwin]

Just what I was describing, with the important addition of the o/p cap, I forgot about that.

And as I mentioned the sticky about in post #2, at the top of this very forum.

 

[Suraj143]

Ok thanks everybody.Thanks Ron for the adjustments.

I want more bass on low volume thats why I need a loudness switch.Now from your comments I think I'm unable to add one

 

[Nigel Goodwin]

Ok thanks everybody.Thanks Ron for the adjustments.

I want more bass on low volume thats why I need a loudness switch.Now from your comments I think I'm unable to add one

Turn the bass and treble up at low volume, job done.

As I, and others, have said - good quality equipment doesn't have a loudness control (and often not even tone controls).

 

[crutschow]

It is a little hard to see in the picture but there is a 4th leg on this pot. I do not know where you can get them now days.

What about one of these?

 

[crutschow]

good quality equipment doesn't have a loudness control

The quality of the system is not the main factor in whether you have (or use) a loudness control.
The loudness control is to compensate for the ear frequency response versus sound intensity, not to correct for equipment deficiencies.
If you look at the updated Fletcher-Munson loudness curves below, you see that the ear is relatively more sensitive to bass frequencies at a high volume as compared to a low.
To compensate for this, the loudness control adds bass as you lower the volume, so that the bass sounds relatively the same compared to the higher frequencies.
In other words it tries to make the lower volume curves have a shape similar to the high volume curves.

I had an old Eico amp that had both a loudness control and a volume control.
You calibrated it in your system by adjusting the volume to the highest level you listen to with the loudness turned to the maximum (where the loudness control response was basically flat).
Then you used the loudness control to adjust the volume.
That would seem to be the proper way to use a loudness control, if you have one.

 

[Nigel Goodwin]

The quality of the system is not the main factor in whether you have (or use) a loudness control.

It certainly is as regards 'have', as good quality equipment doesn't provide it.

The loudness control is to compensate for the ear frequency response versus sound intensity, not to correct for equipment deficiencies.

I know exactly what it's for, but better quality gear doesn't use it.