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PostPosted: 20 Jun 2009, 17:38 
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Joined: 08 May 2009, 08:20
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Location: Duesseldorf, Germany
Hi all, at first - i still have to learn some more grammar :? Who cares?!? Here's the point:

After the Szekeres Buffer is more and more going to be my favourite headamp, i did some (little) changes to make it more like the "angels sing". The first built sounded a bit flat in the deeper frequencies and the mids imho could have more room. The heights - very clear - as expected. So i did some changes to get a wider mid range and more bass. Today i got the chance to compare an other headamp (my friends one) with my beloved Szekeres. (BTW - he even brought me some ordered components). After this we did some fine tuning with this new components.
So - here it is:
Attachment:
Szekeres rev2..JPG

Now - this is really yummy yummy :mrgreen:
The bass is a lot deeper and more direct, not so sponge alike than before.
The mids now became much more clear and have a wider range / area. Even the heights are more going to be clear as crystal.

For this, the PSU is also changed a bit. Before the changes i used an PS built from Rod Elliots capacitance multiplier. The PS now has an double / splitted output to feed each channel seperatly. The basic layout from the PS is here:
Attachment:
Szekeres PS rev2..JPG

Splitting of the PS provides an wider area / range and higher separated channels (more stereo). The PS is to adjust at the 2,5K pot. It must be set to an output of 15Volts DC at the "Plus" line. Please keep an attention on the Base / Emitter voltage. The TIP142 can hanlde up to 5 Volts. This depends on the Transistor you might use. An TIP3055 or the IRF types are also suitable.
(Adjusting the PS is still needed with them!). An B/C - G/S protection Zener is fine to keep the values at the right point. (please - look on the datasheets). The diodes D1 / D2 are 1N914 - their values wasn't added on the schematic...

At all, the Szekeres now imho is a dream. Listening with it really is a pleasure ;-) Maybe there is still something to change?! Maybe Later...

Any questions or comments are very welcome!

Cheers,
Tom.


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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 22 Jun 2009, 10:36 
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Joined: 03 Aug 2008, 20:22
Posts: 386
Location: Denver, Colorado
Hi Tom,
I have not added zobels to my amps, I have to try that. I also like to use a variable resistor/ pot in place of R2 to vary the bias on the mosfet.

Just a question about the schematic, the ground point at the bottom of D1 is connected?
Attachment:
Szekeres rev2a.PNG

Do you have any pics?

Good job!

Rogers


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PostPosted: 22 Jun 2009, 12:50 
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Location: Winnipeg, CANADA
The laptop power supply I was using for my IRF610 buffer died and all the replacements I have kicking around are noisy and inject hum. So I am going to try a 7815 so I can use it with a unregulated laptop power supply of which I have plenty.

I'll second Rogers on the the use of a trim pot for R2. It will allow you to accurately spit the supply across the mosfet.

Also, what advantages are there to using D1 and D2?

Cheers, Gio

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PostPosted: 22 Jun 2009, 15:54 
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Location: Duesseldorf, Germany
Hi Rogers, Hi Gio,

yep, the gnd (below D1) from the circuit is connected to the PSU gnd (common ground). Definately.

But - the ground is actually not connected to earth. I use ground to earth with wooden chassis / enclosures. That helps to prevent blowing all the stuff while some ***** happens. With metal chassis the earth is directly connected to the chassis - decoupled from ground! Take "gnd to earth" as an option.

Your pot instead of using an fixed R2 to set the quiescence current is imho an very good idea!!! I think have to replace it too ;-) Please keep in mind that an higher quiescence-current also dissipates more and the coolers must be larger. To the two diodes (D1 - D2) - I didn't think about that as i had built the first Szekeres using the original Greg Szekeres schematic. It looks like a kind of Bias reversing protection?!? I have no other idea now but that seems to be accurate.

Now - as the szekeres still isn't ready ;-) and there are two more projects waiting to be done... There are some pictures from the older - not new soldered version:
Attachment:
szek_1_channel.JPG
Attachment:
szek_board_r2.JPG

On this pictures the Caps C1 and C8 are not replaced with the Audyn ones yet. C1 is an Wima MKP4 and the C8 is an ERO - Roederstein MKP (Orange cap). The Zobel already was installed. The PS for the 2nd channel was an external connected. That's the only difference to the older pictures. Don't think about the wiring...

I'll post the new version if it's wanted on the community. Imho still its "b" state. I'll try the pot too first...

Cheers,
Tom.


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Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 22 Jun 2009, 19:42 
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Hi Tom, that is a nice clean build that most would not consider a beta. ;)

What type of diodes did you use for D1 and D2?

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PostPosted: 23 Jun 2009, 10:21 
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Hi Gio ;-)

The Diodes are 1N914. Imho that's not a really nice and clean built. I think i'll rework it later. I'm sure now that i don't add a pot for the quiescence current. The changes that i will do further are to integrate the new PS and do some new and clean wiring with shielded material and putting some other insulated spacers under the coolers. As the boards are all modular and seperated, that shouldn't be a problem to do it in a few hours... To do any more changes doesn't make a sense (imho). After this - it's ready :-)

Cheers,
Tom.

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 20 Aug 2009, 16:43 
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Joined: 15 Aug 2009, 18:11
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Hi Tom,
Looked at you mini clone amp...pretty cool. Questions:
Why or why not use a selector switch when using dual inputs like to switch between headphones and speakers?
Also, your case is painted and your heat sinks are on the outside of the painted case without direct IC contact. I would think this is not the best scenario but maybe it means the case is a good enough heat sink by itself. Your thoughts? Also please look at my post regarding my recent ebay purchase.
Best Regards,
Mark


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PostPosted: 21 Aug 2009, 01:58 
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Joined: 14 Oct 2008, 17:35
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Location: Dartmouth, Nova Scotia
That project cirtianly looks allot nicer than what was supposed to be "miniature". :) It uses the IRF510 hybrid design using the IRF640, LM317 for bias and a clear top 12AU7 RCA in a really small hammond case, REALLY SMALL!!!!

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PostPosted: 22 Aug 2009, 04:05 
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Hi Mark,

sorry for the late response. I didn't recognize the thread was going further...
Quote:
Why or why not use a selector switch when using dual inputs like to switch between headphones and speakers?

I think the question is for the TDA :? The Szekeres has no speaker output.... OK - i didn't build the stuff with multiple inputs and selectors because mostly i only use 1 source. I've no need for multiple inputs... Surely it can be done ;-) Also a treble and bass adjustement could be added... The LM3886GC also doesn't have selectors or controls... Just clean in- and output.
Quote:
Also, your case is painted and your heat sinks are on the outside of the painted case without direct IC contact. I would think this is not the best scenario but maybe it means the case is a good enough heat sink by itself.
It's a powder coated hammond case. The TDA package is directly mounted to the coolers! The enclosure has 2 drilled holes that are cutted out to fit the size of the package (TO-220). The package is mounted isolated to the coolers by using the TO-220 mounting kits. I.e. like this one: http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&WT.z_homepage_link=hp_go_button&KeyWords=HS417-ND&x=18&y=18

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Cheers,
Tom.

Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 28 Aug 2009, 20:45 
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Joined: 06 Jun 2008, 20:12
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Location: Houston, TX
Just found the thread. Great build! I am into it and nicely documented to!
My suggestions to improve sound would be to get rid of any terminal blocks in the signal and output. Solder right in. The other would be to use LDRs for a pot. Yeah yeah I sell them and this isnt a plug for buying them from me, I just think its flat out the best sounding pot this side of heaven, so since the pot is such an important part of the sound, thats my other suggestion.
EDIT: Oh, another suggestion... use super thin wire for input signal. I was reading a book by Allen Wright and his suggestion is 40AWG for signal and 30AWG for speakers and I thought that was all crazy talk til I tried it. The interconnects are awesome with the super thin wire.
I like it. Nice job.
Ri

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