Eico ST-70: I'm getting 'hiss' at idle

[mhardy6647]

If polarity's inverted; just reverse the wiring to the next stage (or hook the speakers up "backwards").

 

[idadude]

You mention crackle sounds. My amp did that too and it went away when I replaced every single capacitor including the cans in mine.

Yes, I am still considering whether to finish the job by replacing the two can caps and the five original smaller ones that are left or just selling it, as is. Though it sounds really good, I don't know if I can live with that hiss. As long as the fix doesn't become too involved I may hold on to it.
Larry

 

[dcgillespie]

Hi Larry -- Converting to a cathode follower input stage for the line amp would in fact cause the phase to change with regards to that of the original ST-70 circuit. As for the 2080, it was implemented in exactly this way, therefore the phase does change 180 degrees in that amplifier. As stated though, if you do install the CF input, simply reverse the leads to both speakers; the phase of the signal to your speakers will then be the same as was presented by the original ST-70 design.

Dave

 

[eduarsan1]

Hi Larry -- Converting to a cathode follower input stage for the line amp would in fact cause the phase to change with regards to that of the original ST-70 circuit. As for the 2080, it was implemented in exactly this way, therefore the phase does change 180 degrees in that amplifier. As stated though, if you do install the CF input, simply reverse the leads to both speakers; the phase of the signal to your speakers will then be the same as was presented by the original ST-70 design.

Dave

Hello Dave

I know that this is a old thread but I like to understand if you have done the cathode follower in a ST70 without "touch" the power stage. There still using the 7247 or there are changed to 12ax7? . CF means cathode follower right?

I have a ST-70 completely NOS and I don't wanna touch the pristine condition that it has, just the necessary to remove the hiss. That is very annoying.
In advance thanks for reading !!

 

[eduarsan1]

Hello Dave

I know that this is a old thread but I like to understand if you have done the cathode follower in a ST70 without "touch" the power stage. There still using the 7247 or there are changed to 12ax7? . CF means cathode follower right?

I have a ST-70 completely NOS and I don't wanna touch the pristine condition that it has, just the necessary to remove the hiss. That is very annoying.
In advance thanks for reading !!

@dcgillespie any thoughts?

Regards

 

[danno2000]

Is the hiss in both channels? If you say go to aux 1, put shorting plus on the input, does the hiss go away. Try to determine if it's internal or external.

 

[idadude]

I did fix the hiss, but ended up selling the amp shortly afterwards. I don't remember what I did or I'd help you out with this. Sorry....

Larry