My ACF pre.

What people are working on at the moment
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pre65
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#61

Post by pre65 »

IDM wrote: Did you use cathode bypass?

Cheers
Ian
No. It could be an option for future testing.:)

I suppose that anyone who only has one amp can tailor the pre to suit.

But as I have several amps of different input sensitivity my pre needs to be more versatile.
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David
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#62

Post by David »

I'm interested you found it lacking in scale..........for me its strengths are vocal articulation and dynamics and scale. The dynamics on a dynamic track are staggering. All compared to a modded Pre 3 /modded CF, not the best Phil can muster! But also using the Mundorfs as input caps which I think contribute quite a lot. In a way, it combines the best of CF and Pre3 for me, all coming from an inky black background.
David
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#63

Post by Mike H »

simon wrote:Mike,

I'm on my phone so it's not easy to post links but if you google "tubecad Aikido cathode follower" I'm sure you'll get a number of helpful pages.
Thanks Simon found it. :thumbleft:

@ Phil s'OK it's on there.

This is like my Nelson Pass style jFET buffer, but with better speaker leads it sounds 'muffled' though so I stopped using it.
 
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pre65
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#64

Post by pre65 »

David wrote:I But also using the Mundorfs as input caps which I think contribute quite a lot.
David
What Mundorf was it you used ?

Perhaps I should treat 26 pre to a supercalifragilisticexpealidocious input cap ?
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#65

Post by David »

Mundorf Silver Oils. Expensive but none better IMHO

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pre65
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#66

Post by pre65 »

David wrote:Mundorf Silver Oils. Expensive but none better IMHO

David
What size ? (in uf)
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pre65
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#67

Post by pre65 »

I tried ACF with 811a late morning, and it sounded very good. Mind you 811a is quite sensitive so not much travel on the volume pot needed.

But, this has thrown up a hum problem. :(

With volume pot (Tocos) full off no hum. With volume pot just off minimum a bit of hum, which gets louder up to half way then diminishes up to full volume.

A grounding problem I assume ?

And because it was such a nice day (and wet/cooler from tomorrow onwards) I went out on the Triumph this afternoon. Bugger the hi-fi. :lol: :lol:
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#68

Post by IslandPink »

I'm going to butt in and say I've never found the Mundorf silver-oils all that convincing. They are still after all a metallised cap and lack body and tone in the bass and mids to my ears , vs. all the true film/foil caps. The treble detail and refinement is however excellent .

I would encourage anyone who hasn't tried, to buy at least one pair of the Mundorf 'ZN' which are the updated version of the old Audyn KP-SN . The newer, lead-free tinfoil ZN's are quite a lot better than the KP-SN, match or nearly match the Silver/Oils in the treble but are superior lower down .
They are also a lot cheaper than the Silver/Oils .

I did some reviews of them on a thread on DIY Audio a while back, listing what others I had tried :
http://www.diyaudio.com/forums/tubes-va ... ors-8.html
and here :
http://www.diyaudio.com/forums/tubes-va ... ors-7.html

Right, I'll get off my soap-box now and do something more useful !
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#69

Post by Ali Tait »

Agreed about the silver/oils Mark, I tried them a good while ago and found the same as you, though I also got a slight sting in the treble.
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#70

Post by David »

I havn't tried those Mundorfs but jan did and he was not that convinced. I will look at your thread tho.

Phillip, I used 0.1ufs. But as you are doing a scratch build and seemingly have a few txs around, why don't you try the Aikido with the centre tap tx circuit which means you can normally run into valve amps with no input or output caps. The signal out is effectively at the mid point i.e 0v. The circuit is up on his site. I didn't go for that version as it was not up there for a no gain or CF version.
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#71

Post by simon »

I tend to agree with Mark and Ali about the Mundorf silver oils, a bit too "smooth" for me, smooth in a kind of unexciting way. They might work well in the right situation though. I intend to give them another go in the GM70 amp when I eventually get around to it.
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#72

Post by pre65 »

As it's supposed to be wet tomorrow I have put ACF on the operating table and scheduled a Friday AM session.

I might have identified the source of hum (I hope) so that can be dealt with and I've found two 0.1uf (100nf) Clarity caps for the input. Got to be worth a try.

Another question David, what size output cap did you use ?
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#73

Post by pre65 »

Also, I think I've cocked up with the positioning of R1 & R4.

I assume they are grid stoppers ?

If so they should be on the valve base, not on the tag board.

DOH. :oops: :oops:
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#74

Post by David »

Phillip, I stuck with the 3.7uf polyprops supplied for output caps as I had nothing better to hand.

What about my suggestion of trying the centre tapped tx capacitorless version?

I would be interested to hear how that one sounds!
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#75

Post by pre65 »

David wrote: What about my suggestion of trying the centre tapped tx capacitorless version?

I would be interested to hear how that one sounds!
David
I thought you said it was not for the ACF, only the version with gain ?

My output cap is 1uf, I'll see what I've got that's a bit larger. I have got some Russian 4uf brown cans (PIO I think) if necessary.
The only thing necessary for the triumph of evil is for good men to do nothing.

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