Thank you everyone! Lynn, you are the man!
don’t tempt me on those new models!
DC Offset Issue in Don Sachs Preamp
I have a nice Don Sachs preamp. It's making an incredibly loud popping sound on power off. Obviously, it's always good to power preamps first then amps and reverse the order for power down. But, I'm still concerned about potential damage to my loudspeakers.
Would this be do to a leaky coupling cap at the output stage? Or not enough uF/capacitance to take out all the DC?
I could email Don but I bought the amp used and I got the sense he may have retired.
Any insight is very welcome. Thank you.
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- 15 posts total
Actually, posting these little "how-tos" on the forum is good for me, since the content can be added to the product manuals. I’m the one that writes them for Spatial. Plenty of experience writing these things ... nine years at Tektronix in Oregon, followed by several years of editing Glass Audio and Vacuum Tube Valley. So it’s just keeping in practice. Many of my designs are "thought experiments" to see if an idea works or not. In audio, you need to physically build something to hear what it actually sounds like. Before it’s built, it’s a sound you hear in your head, but it’s always a surprise to hear it for the first time. That’s been my experience since the Shadow Vector intro at the 1975 Chicago CES to hearing the Raven intro at the Seattle show in 2023. (By the way, I am the owner of a DS preamp. Great design, and yes, I know what's inside.) |
@jbhiller If this problem continues, one of the more common reasons is failure of the bypass capacitor on the power switch. This can result in a loud pop at times, depending on the Voltage of the incoming AC line when you shut it off. So it can seem to come and go. |
Thank you Ralph! The unit had some super microphonic tubes (CV181s) that sounded sublime but were so noisy that after several hours of low volume play, the tubes could pick up nearly any activity in the room and subtlety amplify it, which I've never experienced (outside of guitars, only 10 year of tube experience here). I've got a pair of run-of-the mill reissue Tung Sol and EH in there now and things are quiet. I'll open the unit up shortly to see if there's a bypass cap on the power switch. I could always replace it for like uF/voltage to see if that helps.
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- 15 posts total