Transformer based preamp replacement

discussion of magnetic volume control design for both line and speaker levels.

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ospenser
Posts: 4
Joined: Mon Apr 09, 2007 3:49 am

Transformer based preamp replacement

Post by ospenser »

OK,

Got this URL from Russ57 who says that since I'm only using a CD player as input to my amp, might as well go for a transformer based solution - a friends Bottlehead preamp BLEW AWAY my preamp!!! But again, I'm not doing vinyl at this point , an AVC or some such thing will be all that is needed and may sound even BETTER!!

SO - - - I assume I post my system specs and "the boss " here makes a recommendation or two? I'll get back with the numbers but it's the ADCOM 300wpch mosfet amp and a music hall CD player (and mirage om-8 speakers if those numbers are important too - are they?)

Let me know.

Cheers

Mike
dave slagle
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Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
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Post by dave slagle »

sounds like the $200 AVC should be exactly what you need.

What linestage do you use now and what rotation of the volume knob do you use?

dave
ospenser
Posts: 4
Joined: Mon Apr 09, 2007 3:49 am

just to document the process

Post by ospenser »

current linestage is a sound valves vtp101i, (company out of business) - a writeup of it is available here:
http://www.hometheaterhifi.com/volume_3_3/v3n3m.html

and my current listening levels from the CD player (only input used) is about 7:30 to 1pm.

The amp is ADCOM GFA 5802 Mosfet 300 wpch - it has both balanced and unbalanced inputs.

the cd player is Music Hall MMF-CD25 and there is a review here, although the doc on this unit is VERY sketchy even in the user manual.

http://www.hometheaterhifi.com/volume_1 ... -2004.html

I have built a Heathkit DX60B back in the 70s and then a ss preamp and amps that actually worked. (southwest technical products, also out of business SHEESH!!)

and I will make the cabinet myself out of wood (maybe even that fancy Zebra wood !!))

Regards,

Mike
dave slagle
Posts: 2085
Joined: Sat Jan 22, 2005 3:54 am
Location: NYC
Contact:

Re: just to document the process

Post by dave slagle »

ospenser wrote: and my current listening levels from the CD player (only input used) is about 7:30 to 1pm.
good, so it seems you have too much gain and you probably do not need one
The amp is ADCOM GFA 5802 Mosfet 300 wpch - it has both balanced and unbalanced inputs.
do you know if there is a sonic difference between the two inputs?
the cd player is Music Hall MMF-CD25 and there is a review here, although the doc on this unit is VERY sketchy even in the user manual.
since the CD only has SE outputs i'd go for the SE autoformer. I am not a fan of using the magnetic volume controls for SE to balanced conversion.
and I will make the cabinet myself out of wood (maybe even that fancy Zebra wood !!))
sounds good.

dave
ospenser
Posts: 4
Joined: Mon Apr 09, 2007 3:49 am

'the big green light'

Post by ospenser »

well, for now, let's just go with the SE kit.

you have my personal email.
ospenser
Posts: 4
Joined: Mon Apr 09, 2007 3:49 am

i know - it's been a busy year (think TWINS) :oops:

Post by ospenser »

question about the GROUND and the switch supplied with the kit.

you say "When the switch is rotated all the way counterclockwise (off) this is where the ground connection goes, then as you rotate the switch clockwise you simply connect the taps in order (-42, -39 etc.). "


The first of the 24 pins on the supplied rotary switch corresponds to the furthest counterclockwise position of the switch and makes the connection with the common. I take it from the above that the SECOND pin in the row of 24 is connected to the -42 pin on the bobbin, etc.

assume i'm a total newbie although i'm not. i do know how to solder and i have studied the math of AC electronics (think Z) - and built a heath dx-60B and some other stuf . . . . .but i think the last year or so has taken it's toll - and i've been on vacation.


Thanks

Mike
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