Any danger changing feedback line from 16 ohm to 8 ohm tap?

On an original build amp. Just to see if there is a difference in the sound? Any personal experiences from doing this? Thanks!

A generic answer is you get less negative feedback using the 8 ohm tap. This means more gain and wider frequency response at the expense of an increase in distortion, less damping factor, and less stability to oscillation. My experience comes from tube guitar amps so never experimented with Dynaco type amps.

Today most like there Speakers to be in the Feedback loop......so if you not runing 16ohm speakers... I have none.......i run all my tube amps feedback on the  4 or 8ohm taps....i work on amps an people like VTL...only put a so called 5ohm tap on there amps stock outputs .....but on some of there output trans there are 2-4ohm wire inside the amps......
myself an others think it sounds better on the lower taps ....
try it with your speakers....tell us what you think...have fun with tubes......................



Thanks for the site Bob..................

arledgsc wrote:A generic answer is you get less negative feedback using the 8 ohm tap.   This means more gain and wider frequency response at the expense of an increase in distortion, less damping factor, and less stability to oscillation.  My experience comes from tube guitar amps so never experimented with Dynaco type amps.  

WIDER frequency response?? How does that occur?

In an amp using loop negative feedback from the OPT secondary back to the input tube cathode the greater the feedback (overall, across all audio frequencies - not frequency specific) the wider the frequency response will be. This is true as long as the open loop gain is greater than the closed loop gain.

For a nice explanation check out Randall Aiken's site: Aiken's Page On NFB

What a great website of technical information. Thanks for that post.

Hmmmmmmm ... might be fun replacing the 7.5K fixed value with a 10k pot so you can fine tune the feedback to a particular build and speaker ...

Jim McShane wrote: WIDER frequency response?? How does that occur?

My mistake.  Increasing negative feedback tends to flatten and extend frequency response.  Thanks, Scott

Thanks everyone. Great info.

Hi,
   Interesting fact...The original ST-70 Series II produced by Sound Valves used the 8 ohm tap for the negative feed back as opposed to the 16 ohm tap.

At some point (later on) Panor began producing these units & may have retained this same 8 ohm NFB connection. Could there be some benefit?

Kevin@ Dynakit

Could there be some benefit........how will you know less you go?
For me an the people that i know that are into tubes...it all about the sound!
Everone can say what thay well...............But if anyone can move one wire an put the Speakers Drivers in the feedback loop an not hear a diff....why have tubeamp??
I gess your into the look. of tubes..
if thats the case go to ratshak an get a $10. 12V tranfourmer..... lites up some tubes by just runing the heaters.....eveyone well think you have tubeamps eveywhere.....right...
Feedback is one wire an most Dynaco have 3 taps!............gofig
Have fun with tubes........................An get good Sound..Maybe




Thanks for the site Bob...................

ZX...
      I did not appreciate your comments directed to me personally. This Forum is for all members to share information and post questions...I gess you know it all...

Kevin @ Dynakit

Ok... i well keep how you feel in mind.......thanks






Thanks for the site Bob......................

Which transformer tap to use for NFB?  I asked this question to a veteran tube guy once and he stated use the tap that is required for the amount of feedback voltage needed.   But for lowest distortion should you use the same tap as the speakers?   He stated the output transformer windings are tightly coupled so deviations caused by the speaker on say the 8 ohm tap will be reflected as well on the 4 and 16 ohm taps - only at lower and higher voltages.  This NFB voltage will drop slightly if the NFB tap is under load with a speaker but generally not by much.