Dieselpunk Preamp of Doom and the Beast with Two Backs

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Mike H
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#286 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Mike H »

Thermionic Idler wrote: Mon Nov 11, 2019 12:39 pm Thanks Mike - might be worth a try. This bit is on the PCB so adding it could be a touch fiddly.
I'd just bung it across on the track side. :D
 
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#287 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by jack »

What frequency is the oscillation at?

If we're over a few 100 kHz, then just using a suitable ferrite bead close to the first grid may well be enough. Won't effect AF at all but will kill most RF.

I use these: https://uk.farnell.com/wurth-elektronik ... dp/1635667

Never notice any audible difference from the insertion, but they kill RF. I've given some to other group members who have used them with success.
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#288 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Nick »

What frequency is the oscillation at?
Already asked that question.
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#289 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Ant »

116.2khz calculated, says it in a post on the last page
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#290 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Mike H »

Forgot about ferrite beads. Good thought.
 
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#291 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

Mike H wrote: Mon Nov 11, 2019 2:03 pm
Thermionic Idler wrote: Mon Nov 11, 2019 12:39 pm Thanks Mike - might be worth a try. This bit is on the PCB so adding it could be a touch fiddly.
I'd just bung it across on the track side. :D
Sadly it's a double sided PCB with insulated tracks... :(
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#292 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Nick »

Thermionic Idler wrote: Tue Nov 12, 2019 2:32 pm
Mike H wrote: Mon Nov 11, 2019 2:03 pm
Thermionic Idler wrote: Mon Nov 11, 2019 12:39 pm Thanks Mike - might be worth a try. This bit is on the PCB so adding it could be a touch fiddly.
I'd just bung it across on the track side. :D
Sadly it's a double sided PCB with insulated tracks... :(
I think Mike means the side without components. You can scrape the resist of the tracks if there isn't a convenient soldered point.

is there any frequency compensation in the feedback loop?
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#293 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

Nick wrote: Tue Nov 12, 2019 2:39 pm
Thermionic Idler wrote: Tue Nov 12, 2019 2:32 pm
Mike H wrote: Mon Nov 11, 2019 2:03 pm

I'd just bung it across on the track side. :D
Sadly it's a double sided PCB with insulated tracks... :(
I think Mike means the side without components. You can scrape the resist of the tracks if there isn't a convenient soldered point.

is there any frequency compensation in the feedback loop?
Good point Nick.

I believe there is but I'm not sure I understand the circuit well enough to be sure. I'm sending you a PM.
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#294 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Mike H »

LOL .. :lol:

Obviously it seems er, obvious, only to me :D

What I meant was:

Presumably there is a solder pad for V1A anode. Also presumably, there is a solder pad for C10 positive end wire. Solder the small cap between those two. If too far apart, add on a bit of wire. Seemples. :thumbleft:
 
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#295 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by jack »

Ant wrote: Tue Nov 12, 2019 1:38 pm 116.2khz calculated, says it in a post on the last page
Thanks - missed that - bit late to this party...

Quite possible that there's something far higher going on and that 'scope can't see it. I'd definitely try the ferrite beads.
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#296 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Mike H »

What is the bandwidth of the oscilloscope?
 
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#297 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by jack »

Mike H wrote: Tue Nov 12, 2019 3:55 pm What is the bandwidth of the oscilloscope?
My point entirely...
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#298 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Thermionic Idler »

jack wrote: Tue Nov 12, 2019 3:59 pm
Mike H wrote: Tue Nov 12, 2019 3:55 pm What is the bandwidth of the oscilloscope?
My point entirely...
It's a second-hand Tektronix 466 which apparently goes up to 100 MHz, or at least it did when it was new. I might need to get better probe connectors for it though, the one it came with disintegrated a few years ago and I bought rather cheap replacements...
Deck: Garrard 301 - Audio Origami PU7 - NW Analogue DH3S
Phono: Pete Millett LR, Lundahl SUT, AMB σ22 PSU
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#299 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by Mike H »

OK fairy nuff!

Any higher RF stuff should be noticeable then.
 
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#300 Re: Dieselpunk Preamp of Doom and the Beast with Two Backs

Post by jack »

Mike H wrote: Tue Nov 12, 2019 7:32 pm OK fairy nuff!

Any higher RF stuff should be noticeable then.
Maybe. Maybe not!

I would try the beads for sure.
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