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 Post subject: Single stage preamps.
PostPosted: 11 Aug 2008, 19:47 
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Location: Australia
I have build a number of two stage preamps in SS and valve but was thinking lately of building a single stage SS preamp. The last SS pre. used Jupiter beeswax and paper caps. I would use once again around the Burr-Brown OPA2134.

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After seeing the single stage valve pre. it has given me some more ideas.To get extra speed through the preamp stage having a single stage battery powered unit with big input/output caps maybe the way to go. You only need a little gain (e.g. 3 to 6db) but the buffer effect and volume attenuation are mandatory. OP amps make it so easy but I think the science will be in the PS and the coupling caps.

Evidently in the audiophile world the drive is for the preamp to decide the audio signature of the system and the power amp to convey that to the speakers un-coloured. That makes playing with exotic caps a must to get the sound right closest to the source where you can have the greatest effect.

Comments welcome. Any good OP amp single stage preamp schematics?

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
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PostPosted: 11 Aug 2008, 22:26 
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bsgd wrote:
I used chloroform to glue the parts. They came already cut to the right size so I didnt have to use any of my cutting skills!

My goodness Bernardo, that is very dangerous stuff! :hot: You don't want to be breathing that in!

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PostPosted: 12 Aug 2008, 06:57 
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Well, I had to go bid on some wooden tea boxes :)
Chloroform is fine in ventilated area. We used to use it in 10th grade biology to knock out frogs.

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PostPosted: 12 Aug 2008, 12:09 
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Wooden boxes can look nice. Mark has used them a few times now. You can consider using aluminum tape on the inside of the box for shielding.

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PostPosted: 12 Aug 2008, 12:53 
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bsgd wrote:
I used chloroform to glue the parts. They came already cut to the right size so I didnt have to use any of my cutting skills!

gio wrote:
My goodness Bernardo, that is very dangerous stuff! :hot: You don't want to be breathing that in!

Hi Gio! Dont worry, I did it in an open place, didnt breath it.
You just remebered me of those Blendtec videos: "Dont breath this"! :mrgreen:

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PostPosted: 12 Aug 2008, 12:55 
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Gio wrote:
Wooden boxes can look nice. Mark has used them a few times now. You can consider using aluminum tape on the inside of the box for shielding.

Yes, they really can look nice.
I would certainly consider using that tape if we had those around here. I have a hard time even finding resistors here! No, I'm not joking.

I also hear of a metalic, conductive paint. But never seen it around....

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PostPosted: 12 Aug 2008, 17:54 
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I suppose plain old Aluminum Foil and some contact cement could do the trick, or no? I do have some copper tape.... the type they use for stained glass. So, do I need to cover the sides completely or just every other 1/2"? What do you guys think?
Ri

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PostPosted: 12 Aug 2008, 19:08 
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Copper tape. That is interesting.

It would be best if you cover it all. What I am not sure of is if the foil should be grounded?

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PostPosted: 12 Aug 2008, 19:29 
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I suppose one could add a ground plane by just adding in a small piece of copper plate, but the foil would not need grounding simply to act as a shield. Copper screen also works for shields. It can be done for way less money than a lot of folks end up spending on aluminum plates to cordon off the transformers etc. from the rest of the circuit. I guess AL plate is not that expensive, but copper screen is just so easy to mold around your trafo.
Ri

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 Post subject: Don't be foiled
PostPosted: 12 Aug 2008, 19:30 
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RiGuy wrote:
I suppose plain old Aluminum Foil and some contact cement could do the trick, or no? I do have some copper tape.... the type they use for stained glass. So, do I need to cover the sides completely or just every other 1/2"? What do you guys think?

I use the sticky al tape (we call it flashing because it is used externally on houses to seal and water proof where lead may have been used at one time) for both sound dampening, because it has a thick tar like very, very sticky glue and shielding. The foil is quite thick. It comes on a roll and is easy to used. I would recommend using it to line all non-metal cases. Especially preamps, headphone and phono amps.

Look around at the local supermarket for small timber boxes. They often have tea bags in them or even jewelery boxes. Cedar is hard to get now so most boxes are a composite material, like MDF.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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