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AUDIO FORUMS >> D.I.Y. >> New Idea for 'Voltage Box' project
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Message started by 4krow on 12/30/17 at 19:14:57

Title: New Idea for 'Voltage Box' project
Post by 4krow on 12/30/17 at 19:14:57

Do I place it on the mantel for all to see, or go another direction and re-purpose it? This box is of museum quality and craftsmanship, yet I felt that it deserved another life of new purpose. What I have decided is to take out the large internal resistors, and then step by step, install a line level BSC circuit, plus a battery powered pre-amp. Both of these circuits are designed by the BottleHead Company, and will work together. I am using upgraded parts, and the search continues for just the right thing in the right place at this point.
Here are a couple of shots of the hand wound, wire resistors used in the original design.

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/01/18 at 22:12:44

As usual, I will post these photos one at a time. First, to show the original box that I purchased.


Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/01/18 at 22:14:56

Next the re-drilling of holes to accommodate tubes, switches, and other controls on the top and front.

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/01/18 at 22:27:10

And a brief explanation of the purposes of the circuits/project. The controls that you see on the topside are 3 volume controls for volume. they are wired both in ladder and series connection to provide 36 steps of attenuation IIRC. The center control is the coarse volume adjustment with 6db steps for both channels. Each flanking control adjusts the L or right channel in 2db steps. This also works as a balance control to a degree. You will notice two tube sockets recessed into the top panel. A 7 pin 3S4 tube from the 50's is used for preamplification. They are directly heated triodes that perform admirably. There is only 6-7db of amplification available, which leads me to the next circuit. This circuit is called a line level BSC (Baffle Step Correction). Normally this is done in the speaker design phase, but in the case of single driver speakers, it can become useful for an adjustment of both bass and treble. A concept that Yamaha used in their earlier amplifiers at one time. The midrange is reduced a bit, allowing the bass and treble to sound louder by comparison. Of course, the volume must also be adjusted for any increase of all of the audio signal. The BSC circuit has a 4db insertion loss, and the pre-amp cuit has only a 6-7db gain, so the outcome is about the same as a buffer amp. I wouldn't say that this has limited value, or is only useful in certain systems. It probably is a try before you buy idea. And lastly, the pre-amp is likely to be battery powered. I may turn to conventional power supply. We'll see as things develop.

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/03/18 at 02:34:07

Next step is making brass volume control knobs. This is a work in progress, so don't wince too much.

Title: Re: New Idea for 'Voltage Box' project
Post by Lonely Raven on 01/04/18 at 20:35:49


I'm feeling like a slacker - I've got projects stacked on top of projects, and yours are progressing well. Nice Work!




Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/05/18 at 04:05:49

LR,

 Thanks, but don't worry... I got a few projects in the background that are stuck for whatever reason. And then this one. Yes, it is progressing, but I can't believe just how slow I am at some parts of it. Even further, when I complete a certain part, I look at it and it is NOT perfect. Do I start that part over? I don't think so. Not after epoxy has set. Somewhat like concrete. When it dries, that's what you got.

Title: Re: New Idea for 'Voltage Box' project
Post by Lonely Raven on 01/05/18 at 17:52:46


I know that feeling well...and I expect perfection of myself in everything.

Needless to say, I'm disappointed in my lack of perfection. LOL


Title: Re: New Idea for 'Voltage Box' project
Post by Lon on 01/05/18 at 18:13:51

I used to be that way. I had a grandfather that I was very much alike. I saw the need for control and perfection turn him into one of the unhappiest persons I knew. I decided in my early adulthood I would fight back that part of me and I succeeded quite admirably I feel I don't obsess over perfection, and I consider myself happier for it.

Temper that if you can is my humbly offered advice. . . . Happy new year.

Title: Re: New Idea for 'Voltage Box' project
Post by Lonely Raven on 01/08/18 at 18:58:21



Quote:
Temper that if you can is my humbly offered advice. . . . Happy new year.


That's good advice my friend. :)

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/08/18 at 20:34:19

I have almost painted myself into a corner by using a different value attenuator than the pre-amp calls for. 100k is the desired value, yet I mistakenly installed a 20k attenuator. The rub is that to change out the many resistors to make it the correct value is problematic. Anyway, what determines the correct value in the first place, and what effect will it have on the performance of the pre-amp?.... Anyone?

Title: Re: New Idea for 'Voltage Box' project
Post by Lonely Raven on 01/11/18 at 17:59:25


If I remember correctly, it will change the width of the usable window of attenuation. At one end you have full off, at the other you have full on - you're only getting 20% of the sweep between those two points.

But then we don't hear linearly but... logarithmically is it? So that 20% might be even less sweep (subjectively).

Of course, I could completely be talking out my arse - I was good at math, but never learned how to properly apply it to circuits - I was too busy chasing girls and being a rebel in school. (shrug)  I really need to take the time to (re) learn basic electronics.

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/11/18 at 23:33:29

LR,

 That is a good point. I remember now dealing with much the same thing when I worked on the headphone amp. Also, Doc at Bottle Head mentioned that it has to do with the source being able to drive the Attenuator in the first place. Details details. At the moment, I am waiting on more parts, so it leaves me with some other details to work on. Simple in design, yet more than that in practice.

Title: Re: New Idea for 'Voltage Box' project
Post by Crazy Bill the Eel Killer on 01/16/18 at 01:57:49

Nice work 4krow, I'll be following this. I like your thought process.
Who wound your resistors ? I'm thinking of this for my ultimate Zen project in the works. I'll be having Dave Slagle wind them if I go in this direction.

Cheers,                CrazyBill

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/16/18 at 04:02:34

We will never know who wound those resistors Bill. May he rest in peace. I am making progress on this project and will post new photos soon. Parts can be challenging to find. It took a bit just to find square wire, which you will see in the next set of photos.

Title: Re: New Idea for 'Voltage Box' project
Post by 4krow on 01/17/18 at 02:36:09

A bit of an update on the build. I have made a brass 'stand/mount' for the two ceramic solder lugs, and then proceeded to install ground wires to the ground bus that I placed on the Bakelite panel. The fine/coarse attenuator used here provides 66 steps by means of a ladder and series resistor arrangement designed by John Broskie. Very useful. It is going slow, but fortunately, this is not as complicated as it could be. I just want to get it right as possible.

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