[BoyElroy]

Holy Cow! Upgraded my power supply, replaced my opa134 servo opamps with opa27's and swapped out my Audio Research LS3BR for the Gilmore unit.

My jaw hit the floor. I was expecting either a loud pop and crackle or decent/acceptable sound. What I got, instead, was a canfull of whup*ss bass and detail and rock-solid imaging. It wasn't even close; it was immediately apparent that the Gilmore was a level of performance above the Audio Research. I kind of scratched my head at this 'cos the ARLS3B was a one-time Stereophile Class A preamp and here was my DIY Gilmore kicking it across the room, smacking it up and down and mopping the floor with the $2499.00 unit. I'm hearing background vocals, echos and instruments that I have never heard before. Pretty spooky.

Maybe its the power supply, or perhaps its the stepped attenuator...I dunno. But I do know one thing, I'm selling my LS3BR. Anyone interested in a very nice looking black facia AR with remote?

Seriously, though, the resolution and bass on the Gilmore has me totally floored. They make my Apogee Stages sing like nothing else I've heard.

I've owned, in no particular order, the following preamps; NAD 1600. BK MC10, McCormack ALD-1 w/ phono and the Audio Research LS3BR. I would say that, if anything, the Gilmore dynamic amp sounds most like the McCormack ALD-1. The airy, transparent soundstage of the Gilmore coupled with my ribbon speakers makes a fantastic, dare I say, sublime, combination.

System:

McCormack DNA1 dlxe
ARLS3BR/Gilmore Preamp
Apogee Stage Speakers w/ stands
Kimber PBJ interconnects
Theta Pearl CD Transport
AA DTI 2.0
AA DDE 3.0


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)

 

[kevin gilmore]

I've been saying for a while that this thing makes a great
headphone amp. But it makes an even better line level
preamp...

I have been building class A preamps since 1974...

 

[Dreamslacker]

Quote:

Originally posted by kevin gilmore I've been saying for a while that this thing makes a great headphone amp. But it makes an even better line level preamp... I have been building class A preamps since 1974...

Hello.. Can I ask you if I could just make a voltage splitter to get the +/- 16v for your servo amp or do I have to use the tranformers and such?

I'm thinking of building the amp but it's difficult to get the right transformers in Singapore. Hell... I don't even know if I can get the dual-fets..

 

[BoyElroy]

Hi Kevin--just wanna say thanks for putting up your work and answering all these questions.

One more question, though; are you ever going to put up a design for a real world solid state "Gimore power amp"? Perhaps a scaled down version of the uber amp you're working on now...

 

[kevin gilmore]

For preamp use a + and - 15 volt fully regulated power supply
of some kind can certainly be used.

As far as the power amp schematics, by the end of december...
scaleable from 200 watts per channel to 800...

Have to publish a +/- 400 volt 200ma supply for the T2 first.

 

[Doh]

This is great news! I can't wait to get started building my own. Thank-you Kevin, for your wonderful design and thank-you BoyElroy for your impressions.

-Doh

 

[aeberbach]

I know I'm not the only one involved in building one of these right now and I was disturbed to find PM's to antness disabled. If you can't PM antness it's because he is hanging out at headwize for a bit - so if you've sent money and want to know where your amps or boards are, try there.

 

[Doh]

I think he posted on headwize a while ago that he would shipping the first set of amps/boards out on Oct 8. If he's already done so, people should start recieving things in the next few days.

-Doh

 

[andrzejpw]

Kevin: wanna trade?

And there's always Christmas. . .

Very nice amp. One day, sometime, I will build it. Let's say my dad is still reeling from me spending over $150 on the meta, in parts.

 

[antomas]

Hi BoyElroy!

Glad to hear you again! I very, very much appreciated your work on pcbs and your reviews! You're the person who made me convinced that "it can be done"! Hope to build a Gilmore Dynamic (with a genuine power supply) as soon as I'll find all the components and a teflon-coated iron....

The idea of transforming the KG amp into a fully-fledged preamp raises (at least to me) many questions like: which kind of switch to use, how important is to position it near to the input jacks, if a 4PnT switch should be used to switch both signal and ground (to avoid ground loops), if DC coupling fits with the other components, how to balance the level among different sources, and so on.

Is there any important "lesson learned" you can teach me about your preamp?

Thanks once again,
Massimo

 

[BoyElroy]

Hi Antomas!

What!!You haven't built the amp yet???!!!

Ah well, it's good to know that you're taking the careful approach...

I have to say that I hooked up my Gilmore as a spur of the moment kind of thing. I'm only now getting around to trying to figure out how to make it into a full fledged preamp so I think you're way of ahead of me there. I'm going away for a week or so and during that time I'll try to figure out what steps I should take.

I made another pcb design (!), this time made to fit on a 6" x 9" board in order to let me fit in really big filter caps and 5uF polypropelene caps as well. I also put on 4" 15 watt heat sinks on the opa548 to better deal with the heat from my dual 30V transformers.

Right now, I'm thinking of just building a new Gilmore and putting it in a 19" case, using ELNA type make-before- break switches and a DACT attenuator. I'm using Kimber cabling now, which I think gives a softer edge than the Canare hook up stuff I was using before.

Other than that, I'd love to hear about your plans because you seem to have a much better idea of where you want to go!

 

[Doh]

Check these links out... I was thinking of trying something similar for a relay-based source selector.

http://www.diyaudio.com/forums/showt...s+input+preamp

http://www.diyaudio.com/forums/showt...s+input+preamp

Doesn't look horribly difficult. Just a 5V power supply, board, a few relays, and a cheap rotary switch to feed power to the relays, no? Each relay switches signal and ground for one channel.

Stick a cheap cap across the relay power pin and you can effectively make the circuit "make before break" if you'd like.

If I could figure out what the heck a "logic chip" was and how I could use a "counter" to switch inputs, I would gladly replace the rotary switch with two momentary pushbuttons of some sort just for the "cool factor" Unfortunately, I think I'm still in the stone age with a bunch of this stuff.

For the volume control, I think I will go with a good old-fashioned stepped attenuator with a nice long extension shaft to keep it close to the inputs. I've seen a few mentions/schematics of a relay-based stepped attenuator driven with a pot and A/D converter, but these seem to be overly-complex and expensive to be worth the effort. Also, all the digital pots seem to either require a large input capacitor (DS1808 and DS1802) to keep them from cutting off the bass or a buffer of some sort, which defeats the purpose of using the KG amp as a preamp.


-Doh

 

[BoyElroy]

Hi Doh--

Thanks for the info and the excellent links. Peter Daniels made that preamp in 2 days!!??? Amazing....

I'm a little confused, though. Why would relays be preferred over using high quality 4 x 6 rotary switches? Could you explain what the advantages of using relays would be? I never even thought of using them but they seem to be the cat's meow.

 

[Doh]

Hehe...you should see the other stuff he's put together, including his own CD transport etc.

It seems that there are advantages and disadvantages to doing it this way.

Advantages:
1) Relay-based switching allow you to use a relatively cheap single pole rotary switch to choose between multiple sources. No signal travels through the rotary switch, so it can conveniently be located on the front panel if one desires without the need for a shaft extension.

2) A DPST or two SPST relays would allow you to switch both signal and ground with relative ease. Signal paths could be kept extremely short, especially if the switching board is attached directly to the rear panel as shown in the links above.

3) Clean wiring. I don't particulary look forward to wiring 4-6 pairs of signal inputs and their grounds to a big rotary switch. The only other alternative is to make a PCB and use a PCB switch.

4) Room to grow. If you ever wanted to get fancy and go with a AVR chip or use logic components to get pushbutton control, relays are the way to go.

Check this out:
http://www.diyaudio.com/forums/showt...=preamp+update

This guy has evidently spent years creating his preamp. I, for one, don't plan on taking that long. Yeesh.

Disadvantages:
1) Expense. Now, we're talking about making PCB's and buying a heck of a lot of relays. Some nice relays may be had surplus for quite cheap prices. Surf the DIYAudio forums for preferred brands. I seem to remember that Coto and Nait (both available from Newark) are good brands. Country of origin (i.e. Japan) may give indication of good quality vs poor (i.e. China). All in all, I think it should come out roughly equal if you compare using a really nice rotary switch with extension and a cheap rotary switch with some nice relays if PCB's are used in both applications. I think I read somewhere that you should stick a diode in to the relay circuit on the power end, but I haven't quite figure that one out yet.

2) Bad effects on signal? This has been a source of debate on the DIYAudio forum. See link below:

http://www.diyaudio.com/forums/showt...ighlight=relay

The question has been raised of whether or not passing your signal (AC) through an active relay and its magnetic field is wise. Possible solutions are the use of a bistable switch or use of normally closed relays (cumbersome and wastes electricity) I don't think this question has ever been answered to my satisfaction.]

3) Relays also seem to "bounce" as they make contact. May lead to a bit of a pop. Mercury wetted relays fix this, but nobody seems to know what the heck these things sound like and they're also very expensive. Like I said before, you can wire up a cheap capactor to the relay and create effective "make before break" switching.

Oh, here's the link to the DIY CD transport...

http://www.diyaudio.com/forums/showt...ighlight=cdpro

Hope this helps.

-Doh

 

[antomas]

Doh,

thanks a lot for the interesting links and for your last post!
I wrote this before seeing your mini-tutorial about input switching, so, as far as the input selector is concerned, better looking at your post.

Chapeau! (I took my hat off)

BoyElroy,

My hesitation in building the Gilmore Dynamic (GD) is a little telenovela...

Just to sum up: I live in Italy and I couldn't find a single source for the GD components;
many components can be purchased only in the USA and shipping costs are $20-$50 per purchase.
Partly because I wasn't so happy to waste such percentage of money in postal expenses,
I started ordering the transistors for 3 amps (2 amps plus some spare parts).
Then I realized that (a) to fully enjoy the Gilmore I should use it as a preamp as well (thanks Dr. Gilmore for the hint!) and (b) that sometimes my wife watches tv (at low volume) on the sofa while I stare at the same tv listening at my headphone (I'm antisocial but she loves me anyway). So I decided to put two GDs in the same enclosure adding a crossbar switch, to be able to independently redirect n sources to the 2 amps (using two selectors and some OR or XOR gates).

Coming to the preamp issues, keep in mind that I never built even one GD, so my ideas are not corroborated by experience... moreover, I'm not anglophone, so my poorly-phrased opinions could sound stronger than they actually are... anyway, this is what I would try to do (sooner or probably later).

Input selector.
Unless you have strange switching needs like me, I don't see the need for using relays and therefore adding so much complexity, making the amp more prone to failures (the Keep-It-Simple principle). I'd prefer using a 4Poles switch to avoid connecting the signal grounds of sources together, even if most ground problems seem to arise from interconnecting complex audio-video systems.
Do we need an esoteric (Elma) switch? There are very low cost silver plated (self-cleaning?) Lorlin switches from UK in the RS catalog that should last longer than my life, so I'd give them a try.
On the other side, adding a relay-based switch could cost less ($50?) than a Elma switch... just a lot of additional work and potential decreased reliability. Using the relays
I would (maybe) take the risk of switching only the signals, connecting together the grounds.

Layout. If you have enough space in your enclosure (look at the KG layout) you don't even need a shaft extension for selector and pot. If you have little space, or like clean layouts, you may use shaft extensions.
Best of all, (look at the Antness amp), put amp and power supply in two separate enclosures: it almost doubles the price of the enclosure, but should remove any hum and give the amp a very hi-end look...
Using shaft extensions, you may probably put the amps under the shafts...

Source levels. To balance the level of different sources you could add a voltage divider, like in this preamplifier:
http://www.tnt-audio.com/clinica/preamble.html
The ideal solution should probably keep the input impedance close to 47k Ohm, that - I think - is the impedance expected by many sources.

DC coupling at the input. What if one of your sources brings DC to the input of the amp? Throw the source away? (nope) Add a capacitor inside the amp (disgusting). Add a relay-based mechanism to add/short a capacitor, depending on source? (complex) Add a small box containing a capacitor to block DC before the amp? (boh)

DC coupling at the output. I think it would be a good idea to study the circuit of the power amp you expect to connect at the output of the GD.
If it starts with a cap, no problem; otherwise, in case of a failure of some component of the GD, (I suspect) you could fry (not your cans but) your $2000 power amplifier and - eventually - your $3000 loudspeakers...
To this purpose, It would be great to implement a (relay-based) "DC watchdog" to disconnect the output of the GD when more than few mv of DC are found. Unfortunately, I'm not able to design that.

Reliability. Just for the peace of my mind, I'd like to put in my preamp a transient suppressor, (MOV), an EMI/RFI filter, two fuses
http://www.pmillett.addr.com/images/ga_powerline.PDF
and a ground breaker
http://sound.westhost.com/earthing.htm
(more examples in headwize.com).

I think that's all for the moment. A apologize with you and with all the readers for my fuzzy opinions. Please consider this just as a contribution to foster further discussion on this topic.

Indeed, the opinion of the Lord of the (low-feedback) rings (i.e. Saint Kevin Gilmore) about the DC coupling aspects would be VERY, VERY, VERY (add 1000 more) appreciated.

Un caro saluto (I don't know how to tell it in english) from
Massimo