BrianGT's Gainclone hisses. what to do?

[fallow]

Hi,

I just finished my first gainclone, and found out that it hisses. hiss can be heard putting my ear right next to speaker, my test speakers are not very sensitive.

What can I do to reduse this hiss, can transforers cause this hiss?
could regulation off power supply help?

I measured the dc offset and it was quite small around 30mV.

I drive cainglone through pre amplifier, which is my own making, and it's output noise level is around 5 uV, couls this be the source of hiss?

what output level is enough to generate noise from speaker? off cource this depends on sensityvity of speaker, but let's say sensitivity is 89db/W.

[peranders]

The amp _has_ noise and you will hear it if you have your ears very close to the speakers.

If the gain is 30 the noise would be 2-8 uV times 30 = 240 uV worst case. If you don't have optimized the feedback resistor values the noise can get higher.

[fallow]

Ok,
thanks for replying.

Noticed that the source of main noise was my preamplifier.

if shorted the input of gainclone the noise was almoust diminished. but when driving through preamplifier the noise was increased to level which is irritating, now have to do something to get rid of that noise.

Or can the noise become from impedance mismatch?.

[peranders]

If you have an opamp based preamp it's rather easy the enhance the noise performance. Even the old good buddy NE5534 will make things quiet. Check for an opamp with less noise than 10-15 nV/Hz

[Peter Daniel]

Since you are using preamp, you might reduce the gain of your GC amp. You can do that by replacing feedback resistor with 20k value and using 1k insted of 680R for gain setting resistor. You might also add 22k input resistor (insted of 220R). This will reduce the hiss in your speakers.

[djQUAN]

also, use good quality metal film resistors in all audio circuits.

[janneman]

Originally posted by Peter Daniel
Since you are using preamp, you might reduce the gain of your GC amp. You can do that by replacing feedback resistor with 20k value and using 1k insted of 680R for gain setting resistor. You might also add 22k input resistor (insted of 220R). This will reduce the hiss in your speakers.

Peter,

Is this a series or a parallel resistor? Generally, increasing the resistor INCREASES the noise. The (thermal) noise is determined by the equivalent input resistance, seen from the input towards the source, with the source replaced by a short. In other words, the equivalent resistance becomes the series resistance in parallel with the resistor to ground, if this last one is directly on the input. If it is on the sources side, it is effectively shorted by the source (low) output impedance.

Jan Didden