EL84 SE question

[hkoetz]

I have built an EF86 + EL84 SE amplifier according the attached diagram. It works fine, except for the volume control. I operates very abruptly. Over a very small turning range (in the beginning) it gives a huge increase in volume. Then for the rest of the range the position hardly has any effect, although a have used a logarithmic one.

Any suggestions?

 

[Fuling]

Well, the problem must be the volume pot, right?
Try a different one.

 

[Geek]

Sounds like you have used a linear potentiometer where a logarithmic should be.

Look for a pot with [value]/A on it. Those with [value]/B on them are linear.

 

[hkoetz]

EL84 SE problem

It is a logarithmic one.

 

[moamps]

..... Over a very small turning range (in the beginning) it gives a huge increase in volume. ...

Hi,
Your OPT's wireing isn't correct, IMHO.

Regards,
Milan

 

[rdf]

Do you know what the circuit gain is? A Mullard 3-3 is based around those two tubes and, though admittedly a completely different circuit, still has a 100 mv full power sensitivity wrapped with plenty of feedback. I recall it was designed to be fed directly with crystal pickups.

 

[hkoetz]

Do you know what the circuit gain is? A Mullard 3-3 is based around those two tubes and, though admittedly a completely different circuit, still has a 100 mv full power sensitivity wrapped with plenty of feedback. I recall it was designed to be fed directly with crystal pickups.

The gain of the EF 86 circuit is about 25 - 30. The EL84 needs about 4.5 V RMS for 5 - 6 Watts, but my EL84 circuit use some local feedback (see writings of Claus Byrith). Without feedback my amp needs 4.5 / 30 is appr. 150 mV for full power, but this will be more with the feedback..

My CD/DVD player puts out app. 200 mW RMS, so this signal level is not too high. This is supprted by the fact the with the volume pot wide open the distortion is still fairly low.