Gilmore, Szekeres and CHA47 Amps -- A Brief Comparison for Fellow Newbies
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BoyElroy

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Hi All,

I just wanted to share some construction notes and subjective sound comparisons with fellow newbies out there re: which amp (s) to build first and/or next. From the outset, I should say that I have never owned or listened at length to a commercial headphone amplifier. However, to give you a perspective on what sort of "sound" I prefer, I will list my current home system; ARC LS3B preamp, McCormack DNA 1 dlxe amplifier, Apogee Stage speakers and a Theta Digital frontend. I like the speed, depth and transparency of the system, but the detail and imaging of a good set of dynamic speakers is lacking. Moreover, I like bass--tight, tuneful bass and the Stages, unfortunately, roll off pretty steeply past 35 Hz or so. I was hoping that a good headphone amp would be able to give me back some of this high end detail as well as tight, punchy low-end bass.

Also, in terms of my electronics/DIY background, I must admit I was a humanities major in school with my only other technical experience consisting of a Radio Shack 100-in-1 construction kit when I was 8 yrs. old.

The headphones that I'm currently listening to are the Sennheiser HD25, Grado 325's and a pair of Ety 4P's with and without a 75 ohm cable.

As a matter of note, I would like to concentrate a bit more on the Gilmore amp for two reasons: it is the one that I most recently finished, and there seems to be relatively little info. posted out there compared to the "47" and Szekeres.

Any comments and input would be welcome!


The Gilmore:

Construction of the Gilmore was actually much easier and straightforward than I expected. I ordered all parts from MCM, Welborne Labs and Digikey and the prices were extremely modest. I actually have enough extra parts lying around to build a second one!


The Gilmore amp site at Headwize (with Kevin Gilmore's high resolution PCB download)


The PCB pattern posted by Mr. Gilmore made things a snap and I was able to etch a dual board without any surprises. The top overlay was helpful, but it would have been much easier if it had contained the resistor values on it as well. As it was, it took a little longer to place the resistor values using the schematic as a key. The one problem I ran into here was orienting the 2sa1015 and 2sc1815 transistors properly. The overlay was a bit off on this and I had to refer to a photo of a finished board to get it right.

Other than this bump, populating the board and soldering the components was easy and the amp came together very quickly.

The most time consuming part of the whole project was hand matching the resistors (I didn't bother matching the transistors--and it works fine). All in all, I had a blast making this and in terms of construction difficulty, it was no more "difficult" than making the JFET-Szekeres, for example.

Power Supply:

The power supply works as advertised--it locks in at +/- 16.40 Vdc and doesn't drift. Very cool to see! I also saved a couple of bucks by using a couple of Radio Shack 25 volt transformers I had lying around and the sound is excellent with them. I suppose I could upgrade to a higher rated toroidal tranny, but the unit sounds fine as is. I broke off one of the power pins on the OPA548 last night by accident so I had to bypass the final regulation stage, but even using only the LM317/337 stage, the amp sounds fine.


Oooppsss...gotta head out right now, but will fill in more details later. Thanks all....
 
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carlo

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Elroy,
wanted to say i'm looking forward to your followup(s), really cool post that many of us not so technically inclined headfiers have been waiting for.

best,
carlo.
 
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BoyElroy

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Well, back again...sorry about that and thanks for the encouragement, Carlo!

The power supply, as I mentioned, works exactly as the schematic shows and I was able to draw up a pcb on a trial version of Protel 99SE in about an hour. I think that I could have squeezed things a little tighter, but I had a 6" X 4.5" board so I gave components plenty of room and drew extremely wide copper traces, bottom side only. I used 4 medium sized electrolytic Panasonic 6800 uF 63 volt rated TSH series caps in place of KG's 4 4700 uF caps. I had a little trouble squeezing in the horizontally mounted 20k pot trimmers to allow access afterwards with a small screwdriver so you should place the pots so the turn-screw faces outward, or something like that....

With regards to the LM317/337's, it is advisable to mount them to a heatsink using proper plastic standoff collars (?) or else they will definitely pass on current to the chassis. How do I know this? Hmmnn.......bzzt..

On the bottom right of the PSU schematic, KG has drawn a lead with one end connected to the - in of the OPA548 and the other end going out to a 10K resistor and then to "+16.4 Vdc". Call me stupid, but it took me a bit to realize that this actually connects back to the +16 Vdc output leg of the positive rail.

It is especially important to keep in mind that on each OPA548, pin #3 and pin #4 should both be connected to the -24Vdc supply rail and pin #5 to the +24Vdc supply rail. I ran wires from just after the last filter capacitors on the negative and positive rails (which should be +24Vdc and -24Vdc at that point) and connected them to the respective pins on the OPA548's. You must do this for each OPA548.

The cost for the power supply was also reasonable; the 6800 uF caps cost about $7 ea. from Digikey, the transformers cost about $10 ea. at Radio Shack (although you might want to invest in a higher quality unit!) and the 20K pots (Digikey # 3009P-203-ND) were $2.72 ea. You may want to get beefier trim pots yourself, but these seem to work okay... The most expensive pieces were the OPA548's (Digikey part # OPA548T) at $10.48 ea. and the Ref02 (Digikey #REF02AP-ND) at $3.56.

In terms of resistors, I ordered a bunch of 1 % metal film Yageo resistors from Digikey as well. They cost something crazy-cheap like .018 cents each so I was able to get 20 in each value and hand match them pretty easily. About 25% of the resistors used were Yageos and the rest were Dale/Vishays from Welborne Labs. They cost a lot more--$.50 each--but their values were noticeably more accurate and they fit like a charm into KG's pcb.

I placed the PSU into a separate 19" chassis with 3 external cable leads (+16.40 Vdc/-16.40 Vdc and ground) to allow me to hook up different amps to the unit and in that respect, I feel that the "ultra-regulation" that KG refers to is really worth it since you will end up with a pretty versatile, high performance power supply that'll last you a lifetime or 'till the warranty runs out...

On the other hand, I've been listening to the Gilmore amp and the Gilmore power supply for a few days now and I can't really tell much difference between the amp running with the final stage of regulation and with it running only with the LM317/337 stage. The amp seems more impervious to power supply changes than the Szekeres, that's for sure.


Updated 9/12/02 !!!!

The Gilmore Power Supply PCB resized for smaller enclosures and surface mount Talema 70075 transformer

Here is a new pcb for the Gilmore Power Supply that measures 8" x 3.8".

The board is designed to accept the PCB mounted Talema 70075 series toroidal transformer or any other 72 mm x 72 mm surface mount transformer with similar pinouts.

Click here for more information on Talema Transformers


You can download the re- laid out Gilmore pcb design here:

The pcbs should be printed out at 8.0" x 3.8" at 300 dpi.

High Resolution Gilmore PSU 8.0" x 3.8 " bottom layer .psd file

Lower resolution Gilmore PSU 8.0" x 3.8" bottom layer .gif file

Composite Master Picture

Drill Drawing 8000 x 3800 mil

Top Overlay with Pads

Top Silkscreen

*note* I tried to get rid of as many extra wires as possible, but if you decide to try this design, you'll need to solder an insulated wire from the pad labeled "+24Vdc out" to the pad labeled "+24Vdc in". Please refer to the above listed "Composite Master" to verify this connection.


Updated 09/14/02

The Gilmore 6.25" x 4.5" Power Supply PCB:


Here is a newer version of the power supply PCB I used in my original amp made from Kevin Gilmore's schematic.

Gilmore Power Supply 6.25" x 4.5" PCB -- High Resolution .psd File -- please download and save with MS Internet Explorer or use "Save Link Target as..." command with Netscape!

Lower resolution Gilmore PSU 6.25" x 4.5"bottom layer .gif file

Gilmore 6.25" x 4.5" Power Supply Composite Master Pic. with notes

Gilmore 6.25" x 4.5" Power Supply Composite Clean with no notes

Gilmore 6.25" x 4.5" Power Supply Top Overlay

Gilmore 6.25" x 4.5" Power Supply PCB Drill Guide




UPDATED 02/26/03


FRED/Schottky Gilmore 6" x 9" High End Power Supply PCB Design :

You can download the FRED/Schottky Gilmore PSU files by clicking on the links below:

FRED Gilmore Bottom .PSD 520K

FRED Gilmore Bottom .GIF 83K

FRED Gilmore Composite w/ Pads 99K

FRED Gilmore Components 30K

FRED Gilmore Master Composite 125K

FRED Gilmore Pads 18K


Here's a picture of an earlier version of the board without on-board rectifiers (they were placed on another board) but it should give you a rough idea of what a finished PSU board looks like.


Please note that the design is made to fit on a 6" x 9" board (I used the Injectorall 1 sided 6x9 copper clad board-Digikey # PC11-ND). There is enough space for up to six 10,000uF capacitors and/or any combination of values that will fit on the board. There is also enough space for large sized polypropelene capacitors both before the OPA548 and after.

The Bottom artwork MUST be printed out at 6" x 9"!!

I left enough space for anyone who wants to use heat sinks with their TO-220 form factor FREDS. Please note that you will need 8 FREDs to complete the 2 full wave bridges.

Also, it is highly recommended that you heat sink the particular FRED diode leg you are soldering due to the possibility of heat damage to the diode.

I also mounted the LM317/337's on "rails" in order to accomodate a variety of different size heat sinks. You can now move the LM317/337's back and forth about 2 to 2.5 inches to mount much larger heat sinks.



*NOTES*

First of all, as all of us budding DIY'ers know, working with mains/ac electricity can kill us/you/me/anyone. It is very dangerous and all necessary precautions should be taken to ensure that you don't hurt yourself or anyone else. If you feel uncomfortable at the thought of working with fairly high voltages, please do not try to build this power supply on your own!

That said, this version of the Gilmore Power Supply PCB features the REF02 and OPA548 voltage regulators. If you look at the schematic, you'll see that you need (1) REF02 and (2) OPA548 chips to complete the PSU properly. In addition, you will also need to get (1) LM317 and (1) LM337 voltage regulators for the intial regulation stage.

I tried to get rid of as many extra wires as possible, but if you decide to try this design, you'll need to solder an insulated wire from the pad labeled "+24Vdc out" to the pad labeled "+24Vdc in". Please refer to the above listed "Composite Master" to verify this connection.

Furthermore, when constructing the amp, please be aware that the LM317 and the LM337 are mounted facing each other. There is some room for a small/medium board-mounted heatsink, but if the temp. gets too hot, you can always run some lead wires from the "Adj", "Vin" and "Vout" solder points on the PCB to chassis mounted heatsinks.

Next, please note that the 2 OPA548s are facing away from each other. Again, there's a lttle room on the board itself to mount the OPA548s and their respective heatsinks, but you may want to consider larger chassis mounted heatsinks for additional temperature control.

You should also note that only the bottom 2 pins on the (2) 20K trim pots are actually connected to anything. The top pin (the one closest to the rotating screw or dial) can either be cut off or used as a mechanical anchor for the trim pot--as long as you make sure it doesn't touch any live circuit paths.

The 5uF capacitors, as shown in KG's schematic, are optional. There is some space on the board to place the 4 capacitors (depending on their size), but, as Kevin says, these caps are not absolutely necessary.

As for the main filter capacitors, I marked them as "6800 uF" caps simply because that's what I used in mine. You can fit smaller radial-type caps or larger ones, too. I tried to leave some extra space for 10,000 uF caps but I don't know for sure if any will actually fit or not. I ended up using (4) 6800uF Panasonic TSH caps and they are actually a bit smaller than the space marked on the board.

As I mentioned earlier, I'm also using two Radio Shack 25 volt/2 amp (?) transformers that cost about $12 each. They actually do a pretty fine job, although they do get kind of hot and I don't know how well they'll survive summer temperatures.

Finally, for all my fellow newbies, please remember to use proper standoffs to lift the board away from any metal surfaces that could short the power supply and surprise the heck out of you.

Good luck and stay safe...



Making the PCB:

In terms of making the PCB's, I'm using a fairly crude, but pretty effective laser printer/transparency/ironing board combination that works okay with minimal investment in materials. First, print out the pcb pattern on a plastic transparency (3M Transparency Film for Laser printers or any similar product).

* The power supply board transparency should be printed out at 6.25" x 4.5" or as close to these dimensions as possible. (actually, 6.250 x 4.503 at 300 dpi)* I sized it to fit on a standard Radio Shack copper board that costs about $3.99 US.

Next, sand and polish the appropriately sized copper board with extra, ultra fine grain sandpaper.

**Wipe the surface of the copper board carefully with a dry cloth before
putting the transparency on top in order to ensure a clean bond between the copper and the ink transfer**

Place the transparency ink side down on top of the copper board.

Next, take a regular household iron and turn it up to max. temp. Wait for the iron to heat up then carefully run it over the plastic sheet for a minute or two until the ink transfers completely/almost completely to the copper.


Please check out Jeff Noxon's site for more detailed information on DIY PCB's


Here's a link to an Excellent Site on How to "Press and Peel" Your Own PCB's.


Here's a link to the Techniks "Blue Transfer Film" Press 'n Peel Site


*TIP*

As you slowly peel of the transfer, you may find that some lines on the transparency may not have transferred completely to the copper board. In this situation, cover the board again with the transparency and using the tip of the iron, re-iron the partially transferred print. Using this method-- slowly peeling, inspecting and then re-ironing with the tip, you should be able to get close to a 100% transfer rate. However, if you take the transfer off completely from the copper board, you will have a difficult time re-registering the transfer exactly. The best technique is to do this slowly--take your time, peel off only a bit at a time and just re-iron the print that didn't transfer properly...

(In any case, its a good idea to cover up any "thin" areas --where you can see some copper showing under the toner ink-- with a black Sharpie. You should, as a precaution, also re-trace any thin lines with a fine tip Sharpie.)

The nice thing is that if you screw up, you can erase the partially transferred ink pattern with some acetone and start over again. Pretty cheap! It is extremely important that you inspect the transfer at this point! If there are any breaks in the pattern or flaws, you can usually touch it up with a fine point Sharpie. If there are unexpected breaks in your transfer, the circuit won't work. You can always try to solder over a broken connection afterwards, but its a pain to do this. Catching mistakes at this point will save you a lot of time.

Once you've inspected the transfer pattern on the copper board, you can then dump it in a bath of Radio Shack ferric chloride "Etching Solution" for a few minutes/hours until all the surrounding copper has dissolved away. Take the board out and rinse it for a couple of minutes under cold running water. Be careful not to drip solution on any metal surfaces!!!!
Next, take some rubbing alcohol (higher alcohol content is better) and rinse off the sharpie ink with a paper towel. You can also buy some stuff called, "resist ink solvent", but rubbing alcohol works fine for me and its much cheaper. Finally, get some medium grain sandpaper and just rub off the layer of toner ink protecting the copper layer underneath. Simple!

(You'll also need a hobby drill like a Dremel or Black and Decker and a mini drill bit to make the holes. You could try to do it manually but the Dremel makes things much faster. You can drill all the holes in about 30 seconds.)


[size=small]Constructing the Amplifier:[/size]

The only problem I had with the amp was that from looking at KG's component placement diagram labeled, "Top White Print" (left), it appears that the top two transistors (circled in the diagram--1815 on the left, 1015 on the right, looking down at the board from above) are facing the wrong way.



That is to say, the flat side of the top right transistor (1015) should be facing the top of the board and the flat side of the top left transistor (1815) should be facing the bottom. The diagram has these two oriented the other way around. Other than that, populating the board should go pretty quickly.

Here is the corrected composite view/stuffing diagram of KG's Gilmore amplifier. Please note that in this picture, the transistors are oriented correctly.



Click here for a higher resolution image of the stuffing diagram

Also, if using KG's PCB design, you can download and then crop the image in Photoshop/Paintshop to get rid of the header containing the words, "Bottom Side Dynamic" and the footer with "3.800 x 3.300..." on it. This lets you resize the image to the specified 3.800" X 3.300" dimensions and print out at that resolution with no problems. You can fit two of the amp circuits side by side on a single large Radio Shack copper clad board.

One final construction note--I know that KG specified 1.6v LEDs from radio shack, but I could only find 1.7v LEDs so I used them and it seems to work okay. The measured dc output voltage is something outrageous like .0012 Vdc to 0.000 so the servo is something swell to have!

Here is some price information for MCM -- 800 543-4330

2SJ109 Toshiba FET $4.15 ea. (2 required)
2SK389 Toshiba FET $3.21 ea. (2 required)
2SA1015 Toshiba Trans. $0.18 ea. (12 required)
2SC1815 Toshiba Trans. $0.12 ea. (12 required)

I am also using the good old OPA134 as my servo opamp, not the OPA227.

For my fellow newbies out there, I want to say that I took a good long time to study the schematic before I understood what was going where, esp. in terms of the servo and where it connects back to the "dc adjust", etc. The great news about the Gilmore amp is that if you use KG's PCB design, you don't have to really worry about that...All you have to do is match the resistors and just solder the components where the diagram says they should go. Its really a great thing for KG to have made this great sounding amp/board and all the other design material available because its basically a cut and paste excercise for us non-techies(if you use his board!). Plus, it gives off a really cool glow--

Anyway, that's it for tonight and my apologies for my long-windedness. I'll actually get down to comparing the sound qualities tomorrow...
 
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BoyElroy

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5/21/02

*Note* It seems that I made a pretty embarrassing error re: the use of the term "CHA 47". The "H" in "CHA" refers to C.E. Hansen, who has been producing professional boards for the Headwize/fi community based on the "47" circuit. The "C" refers to Cmoy and the "A" refers to Apheared who originally designed the amp. (Thanks Thomas
). Since I have never heard or built the Hansen-based version, a better description of the Apheared designed amp described below would be "A47" or just "47". My apologies to all concerned!



"47" Construction Notes:


I've made several of these based on two different PCB designs; the latter one being a more compact version. I guess there are two ways to go about making them. One way would be to try to make the amps as small as possible and prioritize for saving space. Another approach would be to say, "the heck with it, my eyesight's bad enough as it is" and build a medium to largish size amplifier that's a bit easier to put together and troubleshoot. Being pretty clumsy with small things, I ruined a couple of breadboards trying to make an ultra small, point-to-point wired version and instead ended up making a PCB measuring about two 1/2 inches by 4 1/2 inches. While this means that I have to use a larger enclosure than would be ideal for a portable (I've used mostly small sized external modem cases) it also means that that I can use larger components. For instance, I am currently using fairly large 2uF film caps for my input coupling caps and (2) 35v 2200uF caps (with the leads bent over at 90 degrees until the caps are parallel to the PCB) for my power supply. The reason I'm using these components is simply that I found a shop here in NY that sells these guys for $1 each and they sound okay. In fact, when I substituted a pair of 1uF Multicaps and 470uF Panasonic FC electrolytic caps, I really couldn't hear any difference so cheaper seemed better in this case. I even used the blue 1uF radio shack film caps and the amp sounded pretty much the same so the circuit seems pretty insensitive to certain component changes.

Breadboard vs. Printing PCB:

But getting back to the point, the "47" is an extremely easy amp to build and should take no more than a day or two (or three...) to get up and running for most novice level DIY'ers. I guess most people here prefer using a breadboard to solder the individual connections together, and indeed, this may be the better method. But I would also like to urge people to consider making a PCB for the "47" as well. I actually found it easier to make a PCB than to hard-wire all the leads together. Granted, I'm not a very experienced DIY'er, but I tended to get kind of confused trying to connect all the different points together with hookup wire. Making a PCB design and soldering components onto that seemed much more intuitive and reduced my mistakes a great deal. Plus, once you have the basic PCB printed, you can drill the holes and solder the components pretty quickly.



Here is a PCB pattern and top overlay of a basic "47" amplifier with Cmoy's power supply design that I used recently. The bottom PCB pattern should be printed out at 2.5" X 4.5". I also made some small and large .gif/.psd images so pls. download whichever you prefer from the site listed below. Again, if what you're looking for is an ultra-portable amp, pls. don't use this PCB. It is not that small!

Please go here for higher resolution images--

Higher Resolution PCB and Top Overlay Images


The power supply for the unit is taken from Cmoy's design at Headwize, which can be found at this location:
Cmoy Pocket Amplifier Page

Like I mentioned above, a very nice thing about the "47" circuit is that you can use pretty cheap, low end parts and the amp still sounds very nice. My first version consisted almost entirely of Radio Shack parts and it sounded excellent; far superior to my PCDP headphone jack and made my Soundblaster Live output sound more like my home system than I thought possible. I even used a $3 100k Alps pot from Radio Shack instead of the specified 10k pot and while it softened up the sound a bit, it still sounded excellent and that extra softness may actually be preferable for some people. I bought all the switches, hook-up wire and copper boards from Radio Shack as well.

For portable use, I tried using a couple of in-series 9V batteries, but they died in just an hour so I moved up to an external 8 pack of AA batteries that I also bought at Radio Shack. These have lasted me about a week so far and they're still working well.

Another word of advice to a fellow newbie would be, if you haven't soldered IC's before, make sure you get an 8 pin DIP socket for your OPA2132's. Soldering the empty socket first and then placing the IC in the socket is a much safer bet than soldering the IC directly to the board. You can buy a couple of these 8 pin sockets at **Radio Shack** for about $1.

You can start off with a pre-made board or make a breadboard with point to point wiring if you're hesitant, but really, making your own board from Apheared's schematic should be pretty straightforward. Just remember that what appears to be two separate IC's on Apheared's "47" schematic is actually just a schematic symbol for a single "dual" 8 pin OPA2132 chip. Externally, the OPA2132 looks like a typical 8 pin dip opamp(dip means that the opamp has those 1/4 inch metal "pins" sticking out) , but internally, it contains two complete opamp circuits. I hope that makes sense...Go to this website to check on the pinouts for the OPA2132:

OPA2132 Datasheet


There are many PCB design programs out there; freeware/shareware and professional and most are pretty easy to use--ExpressPCB, Orcad,Protel, Eagle, etc. Most have demo versions or student discounts available. You may want to check them out--And remember, you can always draw up a PCB design on a program like Photoshop or Paintshop Pro.

Note*

You can also put an external "dc in" jack into the unit and run it off a generic -/+12Vdc wall wart and the darn thing still sounds swell. Just make sure that the positive and negative contacts of your amp's female "dc in" receptacle match the positive and negative contacts of the wall wart's male plug!

I've also put mini phone jack inputs as well as RCA jacks in my "47"s to give me more flexibility on input choice. I don't have them switched right now, which means that they're both "open", which means that I really don't want to have both connections plugged in and "live" at the same time. I make sure to disconnect one of the inputs before connecting the other. I could add a switch to take care of this problem but...

That's all for me re: this because there are lots and lots of notes that people have written re: the cha47 that you can look up...

For those who haven't found the site for the Apheared 47, here it is:

Apheared's Project Page
 
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BoyElroy

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Szekeres Construction Notes:

The various Szekeres models are in many ways the easiest to work with because the circuits are fairly simple and the parts are robust and large enough to handle comfortably. As far as I can tell, there are these following variations/sub-variations posted on Headwize:

1)The basic Szekeres
2)The AC coupled gain stage Szekeres
3)The DC coupled gain stage Szekeres
4)The direct coupled Szekeres
5)The JFET-Mosfet by Richard Murdey
6)The servo balanced mosfet driver
7)The direct-coupled with gain stage PRR-Szekeres
8)Tomo's constant current source modification

*Actually, variation #8, Tomo's Constant Current Source, can be applied to any of the Szekeres variations.

There are several considerations here for any new DIY'er. Perhaps the first issue is headphone choice. The basic Szekeres, being a current buffer (with no voltage gain), may be a poor match for someone with high impedance headphones like the Senn 600's. They may want to build a version with an opamp gain stage instead, such as the AC coupled or DC coupled Szekeres. On the other hand, someone with low impedance, current hungry headphones like the Grados, may be perfectly happy with the basic Szekeres.

Additionally, if you like the idea of minimizing the use of capacitors, you should look at something like the direct coupled Szekeres. This requires a dual power supply (a -V supply, a + V supply and ground). The other Szekeres models require a single supply (a positive +V supply and ground).

One nice thing about building a Szekeres is that you don't need to build your own power supply; you can buy many low cost, off the shelf linear power supply units that will work fine with the unit as long as it puts out around +12 Vdc to +15 Vdc and has a good degree of power regulation. The direct coupled version, again, needs a dual supply of around +/-6Vdc or so. In all cases, you may want to get a unit that can support at least 1 amp of current as well. Radio Shack sells a regulated linear 13.3 Vdc single supply for $30 or so that works quite well.

One thing about the Szekeres amps that I read before I began building was the sensitivity of the Szekeres to the quality of the power supply. This has proven to be true again and again as I have changed power filter caps, regulator chips and voltage ratings. For whatever reason, the Szekeres circuit is especially sensitive to such changes. Even within the amplifier cirucit itself, you will notice fairly siginificant changes depending on the quality of components you use. Using a Radio Shack 1uF film cap as your input coupling cap will sound harsher and more closed in than using a Hovland Musicap. Likewise, the size and quality of your output caps will also affect your amps freq. response and sound quality.

The most extreme example of this is probably Richard Murdey's JFET Mosfet version where you can tweak many, many components (esp. capacitors) to "tailor" the sound to fit your tastes. You can easily spend days at a time switching components in and out of your amp, all the time thinking to yourself, "Hmmnnnn...did that violin sound just a wee bit more 'airy' with the Nichicons or the Panasonics?"

*ahem* Getting back to the point, I used two really huge heatsinks (each one about 6 inches across, 9 inches long and three inches high) to manage the heat output. I placed a 510 mosfet and an LM317 (for the Constant Current Source modification) on each and watched the temperature rise to about 120 degrees F. This amplifier gets hot hot hot so use big heatsinks! I also used 22 awg stranded hook up wire from Radio Shack to connect the gate/source/drain/in/out/adj points on the board to the pins of the Mosfet and Lm317 mounted on the heatsinks. You don't want to make the wires too long--mine were about four inches in length, color coded to help me keep track of which wire was which.

Finally, I used Protel 99SE to make the PCB's for the various Szekeres models I've built and the process was pretty simple. I laid out the components pretty much according to the schematic and used wide traces to make all the connections.

All in all, the basic Szekeres was my first DIY project and a fairly simple and intuitive amp to build. Most first timers could make one in a day (given that they already have a suitable power supply) and nothing beats that first feeling of jumping up and yelling, "Jumpin' Jehosevuh! The dang thing works!"
 
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Nisbeth

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Jarthel, your amp looks really nice. Where did you get the case?

/Uffe

PS: Any chance of a picture of the amp with the cover off?
 
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BoyElroy

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Hi Jarthel--

That is such a beautiful case and layout job! Mine is stuffed into an old low profile computer case. I haven't found any case manufacturer here in the States that sells something that well finished. Maybe you could start exporting them!
 
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CaptBubba

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There are a lot of custom case manufacturers out there, you just have to look hard.

I am particuarly in love with these, and plan to use one for my next project.

http://www.welbornelabs.com/woodchassis.htm

But the trick is to just keep an eye out for anything that would work as a case. Sometimes when I just wlk through the hardware store I'll see somethign that would work for a case, and often would look pretty good.

I was wondering if you could possibly give us some pictures or an idea of the differences in sound between the amps....
 
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thomas

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Boy elroy: great work... Just to point out, C.E hansen has already made a professional PCB (hence the "H" in CHA), which could save a lot of trouble for designing and building the amp. I've never used one, but they are very popular here.... Personally, i would not design a PCB just for a single amp, the time and cost required, as well as exposing most to all those chemicals etc isn't worth it for me. Soldering on a blank PCB (ie, 1-3 holes per pad) is harder and time consuming than using an etched PCB, but if you factor in the time needed to design/etch the PCB, the blanks are much faster...

anyways, to each his own, but i think i'd be much easier to wire point-point, unless you are doing a whole production run


Jarthel- I'm very impressed with your amp, it's one of the most beutiful DIY amp i've seen... I really like that volume knob and the matching chassis bolts (also from taiwan?)
 
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aos

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jarthel, that's very nice and neat "insider" job!

I can buy those cases here in Vancouver, they're made of aluminum and cost a fortune (depending on size, 100 to 200 dollars Canadian). Same shops sells knobs like that too, they are also not cheap - $15. Since you obviously didn't screw up the construction, I'd say it was worth it, especially for a high-end amp like Gilmore.
 
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jarthel

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It has very hard work drilling all those holes on the chassis. It's 2mm think. :-\ The hardest part is making the rectagular hole for the IEC power connector. Have to draw a rectangle and then drill small holes on the outline. I then use a larger drill bit to increase hole size and use a cutter to get it out. Next comes the file. It's really the hardest job on the chassis.


Thanks for the nice feedback.

Jayel
 
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antomas

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BoyElroy,

Thanks very very much for your posts! I really enjoyed them, especially the ones concerning the Gilmore amp that - now - looks much less difficult to build! (By the way, I'd like to use it both as an headphone amp and to a preamp).

I have a few questions:
- When you ironed the transparencies, did you put anything else between the iron and the transparency (a cotton cloth or other protection)... my wife could get nervous in case of iron damages...
- Which type/value of pot did you use?
- How does it sound, compared to the other amps?

Thanks a lot for your answers!!!!

Jarthel,

It's a beautifully crafted amp! Would it be possible for you to provide details about the company selling the enclosure (web or postal address, price, etc.?). Good enclosures are hard to find in Italy... Thanks very much for your reply!


And finally, best regards and sincere compliments to our host and to all the contributors of this forum!

Massimo
 
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Possum

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antomas,

Jarthel mentioned he purchased the enclosure and knob from www.thlaudio.com in a past thread where he posted the same link to his pictures.
 
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