KG amp as a preamp?
Sep 21, 2002 at 4:08 PM Thread Starter Post #1 of 8

Doh

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Hi everybody,
Just a quick question: I am considering buying some board from antness to build my own kevin gilmore amp. I was wondering, has anyone ever tried to use this as a combination preamp/headphone amp with the addition of a few relays and sockets? Would it be appropriate, or might many flavors of badness result? Thanks!

-Doh
 
Sep 22, 2002 at 1:28 PM Post #2 of 8

kevin gilmore

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Works absolutely great as a preamp. Ultra quiet.
Ultra low distortion. Capable of driving any cable in
the universe. If you want to make sure the outputs
are short circuit proof, you can put a 10 ohm resistor
in series with the output connector.
 
Sep 22, 2002 at 9:12 PM Post #3 of 8

antomas

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Dear Doh,

I'll try soon to build a Gilmore dynamic-based head/pre amp as well. My goal is to put two Gilmore amps in a single enclosure with a crossbar switch to be able to select and amplify two independently sources. As far as I've understood the subject, using relays is justified only if you have some complex switching need (like mine: n inputs and two outputs); otherwise you may use a plain dual-pole n-toggle switch, eventually with a shaft extension to keep the switch closer to the RCA connectors. In case, you may find a schematic for a relay-based switch here:

http://headwize.powerpill.org/projec...ammer1_prj.htm

Another relay driver may be found here:

http://homepages.enterprise.net/paul...chtip/art7.htm

I heard that some high-end preamps switch both the input signal and the signal ground, maybe to avoid ground loops (so you would need a 4P-nT switch). Apparently, many others don't.

Ciao,
Massimo
 
Sep 27, 2002 at 5:39 AM Post #4 of 8

Dr_Skoobie

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I'm interested in a combined headamp/pre application for the KG amp as well, but have a few questions:

1. What are the advantages of placing a toggle between RCA (for pre duty) and headphone jack outputs? I assume that simply wiring outputs in parallel might place an odd load on the amp?
2. Are there any switched headphone jacks that could substitute for a toggle (breaking the RCA out signal when headphones are inserted)?
3. Most amplifiers have an input impedance which is many times higher than even high impedance phones (e.g., 50k vs. 300 ohms). The KG amp was designed for lower impedance phones; how is performance affected in a pre application? Does gain need to be adjusted?

thanks!

dr_s
 
Sep 27, 2002 at 4:39 PM Post #5 of 8

Possum

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Dr_Skoobie,

These jacks come to mind: http://www.neutrik.com/content/Produ...?id=204_256671

These types of jacks are used in many commercial headphone amplifiers from HeadRoom, EAR, and others. I myself have used some for my amps. They're availalbe from Mouser and probably other places. Mouser link:

http://www.mouser.com/index.cfm?hand...lst_pcode=5504

What you can do is wire the signals for left and right (and ground if you wish) to the headphone jack at one side - this side also makes a contact with the headphone plug with that's inserted. The other side you can wire to the RCA output, or whatever you have before that. When you insert the headphone plug, the contacts from the input are lifted off of the other side going to the RCAs, breaking the signal's connection to the RCAs.
 
Sep 27, 2002 at 9:55 PM Post #6 of 8

Dr_Skoobie

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Thanks Possum!

I had wondered this myself, but I've never seen one of these jacks in person, and couldn't really tell from the pictures if they had two sets of solder lugs!

It seems like Neutrik NMJ6HF-S fits the bill; stereo, switched, with solder lugs.

So with no headphone plug inserted the signal passes from one set of lugs to the other?

This would be ideal, I'm surprised I haven't seen it discussed before in threads of this type (headphone amps as pre).

thanks!

-dr_s
 
Sep 28, 2002 at 3:09 AM Post #7 of 8

Possum

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Your idea seems like something I might try with the Gilmore amp, since I might also use it as a pre-amp until I get around to building a Nelson Pass Balanced Line Stage pre-amp (after my Leach power amp), but I'd rather just hit a toggle switch rather than remove my headphone plug to switch from headphone amp to pre-amp duty.
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