Kevin Gilmore amps
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kelly

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Has anyone (other than Kevin Gilmore) built any of the Kevin Gilmore designed amplifiers posted to HeadWize?

Has anyone even gotten to hear one?

His dynamic solid state and tubed Stax amps are of particular interest to me. Of course, if I end up taking one on as my first project, it may be quite the undertaking.
 
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ppl

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I Built Kevins Class A amp some time ago i was so impressed that someone besides me thought that a true Complimentry symmectrical Topology from input to throught the Output stages was the best Topologyy available. Another feature that I like is parralell output Devices. I know long time Followers of this fourm Know i like to Parralell Buffers, Well I also like to parralell Transistors, can't imagine using just one pair of output transistors. By paralelling several High Speed Transistors you get the Current and Power ability of larger but slower devices with the added benifit of High speed and gain. I at first used Kevin's power supply but later changed to My Dual tracking Discreet component supply using LED's as Voltage references to obtain no Thermal Drift. this sounded slightly better to me than Kevins supply. I also did some slight circuit changes that i felt this circuit needed and was easy to rework Kevins PC Board Artwork to acomidate. The major change was to use a Cascode second stage's for improved speed and higher open-loop bandwidth. This amp sounds wounderfull It is Dynamic! lots of guts and Clear, No audible distortions and this is importent since my ears pick up nonlinear Distortions that seem to escape the attention of most people. I am sure others hear have also built Kevins amp do a search.
 
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jarthel

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I have built Kevin's Pure Class A amp and I love it. I've built only 2 amps, this one and the cmoy. Kevin's amp is much better.

If you decided to build one, I suggest you print the project page in headwize as you need to look at it frequently during construction phase. Also, post your questions in Headwize as I'm very sure that Kevin checks Headwize every morning as far as I know. So if you want a reply to a problem quickly, post a question early morning and expect some reply before lunch. This is what I do.

I think there are more messages about Kevin's amp in headwize that here.

If you need some help, email me. I checked it frequently. I can pass on some knowledge I learned from Kevin and other sources (other headwizers and websites) when I built the amp.

Jayel
 
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jarthel

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Quote:

Originally posted by ppl
I also did some slight circuit changes that i felt this circuit needed and was easy to rework Kevins PC Board Artwork to acomidate. The major change was to use a Cascode second stage's for improved speed and higher open-loop bandwidth.


Can you send me the modified schematics PPL? if not available, maybe you can describe it to me.

Thanks


Jayel
 
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kevin gilmore

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Its always morning somewhere in the world
 
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jarthel

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I meant morning in Illinois.


But I'm right that early morning is the best time to get a reply from you as I've experienced it.


Jayel
 
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aos

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I've also built Kevin's amp over a year ago, I believe I had the honors of being first (at least on Headwize). Even had to design my own PCB as there wasn't one at that time. The amp sounds great, it's easy to build and is even relatively cheap. In comparison to amp on my portable DAC - or META42 which is essentialy the same - I really couldn't decide which one is better. They sound different, but of same caliber. I always have disadvantage of having to use interconnects with it (PDAC doesn't need any) but in general I found Kevin's amp very smooth sounding, possibly at the expense of some detail - probably due to the fact that my construction of inputs/crossfeed uses tons of wire, and having to use interconnect. For someone wanting a good solid state discrete amp, this one and possibly Kumisa 3 are best bets, at least as far as Headwize library is concerned.

Oh - and where's my 500+ status
?
 
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kelly

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Thanks for all the replies.

PPL, how do you feel the performance of your Gilmore amp compares with other amps? Any specific qualities you find better/worse?

Knowing virtually nothing about electronics, the Gilmore amps have been my favorite designs to look at and scratch my head at in HeadWize's library. They're just really interesting but someone like me isn't going to be able to tell whether his theories pay off without hearing it. My biggest concern was that he liked Grados and built the amp with Grados in mind. I have a tendency to rather dislike Grados.

aos
I'll have to look at the Kumisa 3, I don't remember looking at that design.
 
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aos

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Kumisa 3 is the next step after Kumisa 2 which is posted in the library, and is on author's website. Special think about it is that it is a zero global feedback apmplifier, and the bipolar transistors it specifies use of happen to be very linear.
 
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jarthel

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Quote:

Originally posted by kelly
My biggest concern was that he liked Grados and built the amp with Grados in mind. I have a tendency to rather dislike Grados.



I don't have any Grados but have AKG K401 and Philips HP890. It sounds very nice using the Gilmore amp.

Jayel
 
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kevin gilmore

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kelly i sent you email. If you don't get it PM me.

I designed the amp for low impedance headphones.
Like the grado's. For me the grado's are terribly uncomfortable,
but i happen to have 2 pair laying around.

Works great with any headphone, and plenty of headroom
even with 300 ohm headphones to get your ears to bleed.

And just in case that is not enough you can go to the fully
balanced output version.

I'm still a stax man. Likely always will be. Going to have to
buy a pair of the new sealed ones...

Some people don't want to build a headphone amp with
12 tubes 40 fets and 7 power supplies.
 
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ppl

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I don't use Grado's anymore mine bit the Dust and since those were my second pair that bit it i decided not to renew my Grado's I am quite Happy with the Sony MDR-V6 and MDR-7506. if i get another pair of open cans i think ill try some from sen.

Kevins Amp sounds great with the V6's and thay did Drive Grado's quite well. Kevins amp puts out lots of output Curent and both Grado and Sony cans like that alot. In Basic, Kevins amp is Dynamic Clear and has great sound stage I cant complain and i am Critical. I have in the Past recomended Kevins amp to alot of Head-Fi'ers and that Recomendation still stands
 
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transducer

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PPL,

I am about to build the Gilmore amp, also for a pair of Sony MDR-7506 cans. Can you give me details of your circuit changes, maybe a revised schematic or board layout?

Have you heard anything better with the Sonys? They are higher impedence cans than the Grado's that Kevin designed the amp for, still enough drive?

Thanks,
Ron
 
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ppl

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transducer> The Main Improvement in my Mods to Kevins amp was in the High frequencies. bells cam across more Potent and with a nice decay. in stock form the Bells were slightly soft and the Decay disipeared more quickly like Missing the last bit of sound prior to compleatly quiet. Air was also improved. Prior to my building this Amp i ran the Idea Of casscoding across kevin and he thought that cascoding the second stage was a good idea but Casscoding the Output stage was silly. I still may try cascoding the output stage at a later date, Because i am a cascode fanatic. I did not do notation on what i did To the Amp as far as values i just did it and so i will have to Look at the board again and note what parts i used. basicaly the 2SA1015 and 2SC1815 after the input dif's was what was done. and i think i also added a resistor from the Collector of the input stage current source for the pos dif amp to the Col of the Neg diff amp. this technique is one i got from Argon Amps. apparently it improves the slew rate by allowing one diff pair to borow curent from the other diffamp pair depending upon the signal's pol. I used MPS-8099 & MPS-8599 rather than the 2SA1015 & 2SC1815 since i have alot of the motorolla transsistors and only a feew of the 2S types and I think Kevin sed that the MPS's were fine. at least thay work good in mine.

I built the Old krisma II havent tried the III yet.on a pref board since the output stage was interesting. This amp had ringing on 10KHz. sq wave. so i also did some changes to the way the AD-844 was used. I used the comp pin to drive the output stage rather than the nominal opamp's Output pin. This is also what i do with AD-744 opamps. This allowed me to control the Open-loop gain with just one resistor and thus i was able to get rid of the ringing.

Kevins Amp IMHO is better in sound quality but has that No neg feedback sound that alot of folks like. I do at times but i think Feedback improves the bass on most amps but reduces the involvement in the mids and highs if too mutch feedback is used, so a delicate balancing act is required when adjusting the Feedback factor ( Open loop vs Closed loop gain) on any amp. since kevins Amp is overall feedback free the feedback factor is not an issue. kevins amp works nice with tthe MDR-V6 and MDR-7506. I can connect both at once and not notice any quality change when pluging in the second pair. Alot of Amps will lose eather dynamics or detail when driving two pairs of the above sony's. these cans are sensitive to the driving Amp alot more that most would think Highly reactive and the high "Q' of the Driver requires an output Impedance near Zero ohms and plenty of output Curent to drive the Huge amout of capacitence. Kevins Amp dose very well at this. I did not like the sound of kevins Power supply made the sonys somewhat fat in the bass and this is not a good thing with these cans. Kevins Supply was OK in the Mids and High's presenting a fast quality but the Bass turned me Off so a Good regulated supply with Big Caps work nice.

I hope this helps and ill look at the board and note the changes and post them in a few days. Heck I might try cascoding the output stage just for The Hell of itt and see what happens, Ya never know Could be a Dud or the Next sonic revalation.
 
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andrzejpw

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Kevin's Dynamic amp and the Kumisa III have always been a source of interest for me. Sort of a "i'll do it one day" project. Something scares me about the kumisa though. There's absolutely NOTHING written about it, beyond headwize's library. I mean, do people just not want to build it? Is it because its VERY complicated?
 
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