Passive Pre-amp

E

earl of sodbury

Guest
Gobind - no camera mate, just imagine a tiny diecast aluminium box the size of a couple of fag packets witha knob at the front and some sockets and switches at the back and you get the picture.

churz, eofs

 
E

earl of sodbury

Guest
Finally found 5 minutes to implement the pseudo-shunt and it's a LOT more civilised: still too toppy for my taste, but bearable, and what's not right is not the fault of the pre
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churz, eofs

 
E

earl of sodbury

Guest
kennyk wrote:

kennyk wrote:
what did you use for resistors?
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edit:

seriously, what type and value?
You know I said I don't do numbers...

It took me this long to figure out that a couple of 150K Dales (old stock) in parallel would be about the right value...

They are, too...
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Will put some modern metal films in one day...

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kennyk

Well-Known Wammer
Wammer
Aug 8, 2005
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HiFi Trade?
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No worries. reason I asked was I've got some Vishay VTA55 59ks I'm not using, which cost me $6 each from partsconnexion. would be happy to let them go for 1 beer
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E

earl of sodbury

Guest
kennyk wrote:

No worries. reason I asked was I've got some Vishay VTA55 59ks I'm not using, which cost me $6 each from partsconnexion. would be happy to let them go for 1 beer
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Just the ticket! I'll see what I can do beerwise
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E

earl of sodbury

Guest
supercapman wrote:

It may be a tad toppy due to the silver cable needing some burn in time, nice work Earl.
Cheers SCM - it may partly be that, but I think it's also down to a combination of factors: the Neats are pretty bright, and MF kit over-emphasises parts of the upper mid to treble: specifically, "ch" and "sh" sounds are lacerating (ditto alto sax), though everything else is sweet as a nut- if I could nail where in the system that arises I'd be a happy man... :Not Sure:

churz, eofs

 
E

earl of sodbury

Guest
supercapman wrote:

Could it be something simple like toeing in your speakers a bit more?
Good point. Actually, reducing toe-in does reduce treble impact, but also has other issues like vaguer imaging and more reflection on the left channel where the speaker is unavoidably close to the wall... I also suspect reflection from the low ceiling may be part of the problem...

 

Puffin

Wammer
Wammer
Oct 2, 2006
508
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58
Surrey
AKA
Rob
Is anyone ableto explain how the "shunt" mod effectively by-passes the pot. What does this mean in practice ? Is it designed to give a purer signal. Is it called "shunt" because it shunts the in and out signals through one side of the pot ?

 

meninblack

Wammer Plus
Wammer Plus
Jul 20, 2005
22,674
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HiFi Trade?
  1. Yes
Puffin wrote:

Is anyone ableto explain how the "shunt" mod effectively by-passes the pot. What does this mean in practice ? Is it designed to give a purer signal. Is it called "shunt" because it shunts the in and out signals through one side of the pot ?
In the "shunt" wiring, a portion of the signal currentis shunted away to earth, the remainder going straight to the power amp.

None of the signal reaching the power amp passes through the pot, eliminating any possibility of the pot affecting the sound.

The pot is acting as a current divider, not a current absorber.

 

Puffin

Wammer
Wammer
Oct 2, 2006
508
36
58
Surrey
AKA
Rob
Thanks for the reply. I asked because I mocked one up at the weekend and it seemed less detailed than when music was played "through the pot". However I suppose resistors take time to bed in or open up. I was only using Maplin metal film 0.6W just to try it out.

 

Puffin

Wammer
Wammer
Oct 2, 2006
508
36
58
Surrey
AKA
Rob
Sorry, I meant to add, does it matterwhat the value of the pot is (20k or 50k) as to what value resistors you use. The pot I used is 20k and I used 47k resistors.

 

Puffin

Wammer
Wammer
Oct 2, 2006
508
36
58
Surrey
AKA
Rob
Sub-alien. Thank you very much for your reply. The link gives me the exact information I was looking for. I was not aware of the WAD forum and I own a WAD Kel 84 !

 

subterranean-alien

Wammer
Wammer
Jul 25, 2005
1,208
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Lancashire, , United
AKA
Stu
Two for the price of one!!

Its actually World Design, unfortunately WAD ceased quite abit back but WD has stepped in and carried on many of WAD's products. Its a great forum (as is this) and vital for us wadders (I have the 300B amp).

 
E

earl of sodbury

Guest
Puffin wrote:

...I own a WAD Kel 84 !
Nice amp - finally heard one at the w/e - probably the single best thing you can spend £300 onin hifi
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