Balanced Bridge Gilmore Photos
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BoyElroy

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Happy Holidays, Everybody!

Here are some photos of my work-in-progress BB Gilmore amp. As you can see, I'm using an external PSU that uses two discrete transformer/PSUs feeding 30Vdc each (unregulated) into the Gilmore PSU. I had originally bought the tranny units expecting to simply remove the trannies and feed them directly into the Gilmore PSU, but the units came already mounted with 30,000 mfd each of power filtering, fuses and independent power switches so I just kept the things whole.

I'll be upgrading the PSU soon with toroidal trannies and prob. Schottky rectifiers. It currently uses two standard silicon bridge rectifiers.

As for the amp section, the enclosure you see right now is an old computer case and I've drilled it full of holes trying to see which switch/jack connections work best. I'm also in the process of re-wiring all the internal wires with silver coated solid copper wires and teflon jackets. I had originally used Kimber Cable TC wires for everything, then cat5 and solid magnet wire and now I'll try the silver/copper/teflon combination.

Once I get everything down pat, I'll get a real enclosure and move everything over.

The controls/jacks from left to right are:

1) Passive/active (single ended/balanced) output selector. In passive mode, everything gets bypassed except the 50K DACT stepped attenuator.
2)Headphone/line out selector - left channel
3)1/4" Dual mono left channel headphone jack.
4)1/4" Dual mono right channel headphone jack.
5)Headphone/line out selector - right channel
6)Input selector (single ended only)
7)1/4" Standard headphone (not dual mono) jack
8)Stereo stepped attenuator volume knob.
9)Mini-phone standard headphone jack (not dual mono)








Any other Gilmore pics out there???
 
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kelly

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Damn, that's cool. Why is there only one stepped attenuator? A bit confused about that. Seems like if you'd used two stepped attenuators (one for right, one for left in balanced mode), you could then have two single ended headphone jacks and have the added functionality of letting two people listen at once with their own volume control each.
 
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erix

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Nice farking job, Bob!!

ok,
erix
 
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BoyElroy

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Quote:

Why is there only one stepped attenuator...you could then have two single ended headphone jacks and have the added functionality of letting two people listen at once with their own volume control each.



Hi Kelly--

Boy, talk about increasing costs... One of those DACT's cost me about $129. I don't think I could tell my wife I just spent $300 on a volume control! You're right, though. For the DIY'er who does need two separate outputs, using dual stereo attenuators would be a good thing to have. You could also accommodate balanced inputs as well with that arrangement.


Hi Erix--

Uh...thanks a whole farking lot!
 
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dta116

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Where did you get the transformers?
 
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fyleow

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Hovland Musicaps for PSU circuit? Isn't that a little overkill? Hah I guess overkill is the fun of it all right? But ouch that whole thing must have cost quite a bit of cash.

I cringed when I decided to use an Alps Black Beauty for my Kevin Gilmore amp, I can't imagine adding a stepped attenuator....
 
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BoyElroy

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Hi dta116,

The transformers were part of these Panasonic video camera psu's that I found in a surplus store near Chinatown here in NYC. The psu's were brand new and came in these very nice "Panasonic" logo'd enclosures. The best part was that they cost only about $15 each. I went back a week later to try to pick up some more, but they were all gone.

Hi Fyleow,

The Musicaps were doing duty in my Szekeres which I wasn't using any more so what the heck


Actually, the cost was pretty cheap for the psu and amp. Both transformers came to about $30 and the IEC mains socket, case, power cord and XLR sockets were all used/found/liberated pieces. The only thing that I had to pay for in the psu was the wiring, copper clad board and standard Gilmore components. The 6800 mfd were only $6-7 each.

The stepped attenuator was the only really expensive part. The Stackpole switches only cost $4 each and the wiring originally was cheap also, although that's starting to change


Come to think of it, the Cardas RCA jacks and Neutrik sockets do add up to something like $45-50 so that is a bit high as well.

I'm actually using the BB Gilmore mostly as a line level preamp and it's nice being able to go back and forth between passive and active modes with a turn of the switch.

BTW, how's your BB Gilmore coming along? I was hoping I could compare notes with you soon---
 
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kerelybonto

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Okay, hold up -- does dual mono mean you get one channel in both drivers or that you get the aggregate of both channels in both drivers? I had thought it was the latter, but apparently not ... someone want to explain this to me?

kerely
 
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kelly

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Because there is only one stepped attenuator, I'm quite confused too.
 
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BoyElroy

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Hi Guys,

Well, I guess there are different levels of "dual mono" implementation including and going all the way up to separate psu's and ac cords for left/right mono amps. In the case of the Balanced Bridge Gilmore, I guess I'm referring to the fact that while the input is single-ended, that signal goes to separate left and right channel amps with each amp putting out separate (-) and (+) legs. This is where the dual mono part comes in. In a standard stereo jack, the left and right channels share a common signal ground. In the dual mono output of the BB Gilmore, the left and right channel signals are kept entirely separate and do not share a common signal ground.

Here's a pic. of KG's mod on his Grados to run them in dual mono mode.



Here's a photo of my dual mono modified SR325s


Quote:

Dual mono Grado SR-80s have more and tighter bass when driven with the bridged dynamic amplifier, which can output twice the voltage, twice the current (not at the same time) and double the slew rate, giving better control of the diaphragm and a higher damping factor. --Kevin Gilmore


I hope that at least partly answers your question. Please forgive me if I'm repeating info. that you already know.
 
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kelly

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Thanks for the explanation. This is what I suspected but your post cleared up the confusion. Have you considered taking it further? (Seperate PSUs, etc.?)
 
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BoyElroy

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Hi Kelly,

I have, but the added cost and space requirements are something I have to think about. I'd have to get my hands on four (!) transformers and double everything I have right now. Yikes.

But if I ever come across a super deal on toroidal transformers...
 
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Possum

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You should be able to find 2 toroids that are even overkill for 2 power supplies of a fully dual mono Gilmore amp for maybe $80 or so. Ask for a quote from victoriamagnetics.com (listed in the sticky thread in this forum). I was quoted $38 each for a 25x25V 160VA toroid with $7.28 shipping to New York. Sometimes at diyaudio.com, there are good deals - for example someone was selling 2x24V, 4A toroids for $20 each plus shipping.
 
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fyleow

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Quote:

Originally posted by BoyElroy
Hi dta116,

The transformers were part of these Panasonic video camera psu's that I found in a surplus store near Chinatown here in NYC. The psu's were brand new and came in these very nice "Panasonic" logo'd enclosures. The best part was that they cost only about $15 each. I went back a week later to try to pick up some more, but they were all gone.

Hi Fyleow,

The Musicaps were doing duty in my Szekeres which I wasn't using any more so what the heck


Actually, the cost was pretty cheap for the psu and amp. Both transformers came to about $30 and the IEC mains socket, case, power cord and XLR sockets were all used/found/liberated pieces. The only thing that I had to pay for in the psu was the wiring, copper clad board and standard Gilmore components. The 6800 mfd were only $6-7 each.

The stepped attenuator was the only really expensive part. The Stackpole switches only cost $4 each and the wiring originally was cheap also, although that's starting to change


Come to think of it, the Cardas RCA jacks and Neutrik sockets do add up to something like $45-50 so that is a bit high as well.

I'm actually using the BB Gilmore mostly as a line level preamp and it's nice being able to go back and forth between passive and active modes with a turn of the switch.

BTW, how's your BB Gilmore coming along? I was hoping I could compare notes with you soon---


Err umm were you talking to me about the BB amp? I've been a slacker lately and I haven't started. Actually I wanted to let you take the first leap and tell me how it works out. But with school keeping me busy I haven't found the time to do it yet.
 
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BoyElroy

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Hi Fyleow,

I think it's time you got your priorities straight, young man. Your folks would be very upset to know that you were neglecting your diy'ing while at school. Plug in that soldering iron and get back to work!


Hi Possum,

Thanks for the tip on the toroids. I've heard many good things about Victoria Magnetics and the price seems pretty darn reasonable, too.

BTW, how's Ithaca doing? I lived there 'til I was about 13 yrs. old and I can only guess what the snow conditions are like right now.
 
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