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Old 22nd February 2005, 01:34 AM   #1
Jean is offline Jean  United States
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Default Fired up DoZ project amplifier

I'll be really honest. I did not expect this little amp to have this much authority . It's driving my 2.5 diy speakers like it's nothing and they drop below 4ohms. It doesn't get as loud as my p3a, but still very very nice little amp.

This is a good suprise.
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Old 22nd February 2005, 03:01 AM   #2
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Putting finishing touches on mine. It sounds suprisingly good...probably the best cap-coupled amp I've ever heard.
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Old 22nd February 2005, 09:25 AM   #3
MikeB is offline MikeB  Germany
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Hmm, it seems not necessary to use the DoZ cap-coupled, at least
i've built mine with symetrical powersupply, not using outputcap.

And i must admit, the DoZ sounds damn good !
And it also handles my 4ohm speakers with ease...

Mike
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Old 22nd February 2005, 10:11 AM   #4
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With the single BJT at the input, DC drift is too high without a servo. I tried split supplies in the early stages and offset was all over the place. Gave up, used a single supply and cap output.
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Old 22nd February 2005, 11:10 AM   #5
MikeB is offline MikeB  Germany
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I have no problems with DC-drift, at startup when cold it's ~50mv,
after heatup it drifts between 20mv and 3mv.
As inputtransistor i use 2n5401, vas/driver is bd139, output is mjl21194.

Mike
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Old 22nd February 2005, 06:44 PM   #6
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I built the DOZ amplifier using MJE3055 TO-220 power transistors,
with a small heatsink and a small pc fan...
It worked perfectly for almost 10 minutes!!



Udi.
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Old 23rd February 2005, 05:57 AM   #7
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Default Mike, can you post the simetrical DOZ schematic for us please

Very interesting, without condenser....very interesting.

Post schematic please.

Carlos
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Old 23rd February 2005, 06:03 AM   #8
Jean is offline Jean  United States
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Default Re: Mike, can you post the simetrical DOZ schematic for us please

Quote:
Originally posted by destroyer X
Very interesting, without condenser....very interesting.

Post schematic please.

Carlos

Carlos, I think it was posted in the Pass forum....there were a couple different versions too
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Old 23rd February 2005, 06:19 AM   #9
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Default Oh!... already concluded! 0 +20 +40 volts is the same as -20 0 +20

But are you using the current that Rodd suggested?

Do you think the input transistor is perfect to that low voltage over it, is it linear using that voltage Mike?

Also your output, is this transistor good to only 20 Volts from colector to emitter, are this unit working in its linear region?

The question is posted my dear friend Mike, because i also like this amplifier, one of the "references" of quality we can have, beeing a real JLH adapted. The standard JLH used some transistor alike 2N3055, and this unit "loves" to work with 2 or 3 ampŤres...and also is very happy when have 20 to 30 volts from colector to emitter, and also feel good when heat is around 30 watts each unit, because of that, that nice transistor unit, was used deeply as series power supply pass transistor.

I have some suspection, herr Bittner, that your amplifier can be even better using 2N3055...... a worst transistor, no doubts!...but match with the design.

Well Mike, i will say that you did not heard JLH yet!.... put the 2N3055 and the correct input....i think it is BC549C (not sure), and select one BD139 with lower gain, to match the old days... something alike 90 of gain.....in the place of 150 you may be using, put the current Rodd suggest and i think you will turn surprised....Yeahh!...i know this is stupid, change modern transistor by 2N3055?....but try it please.

There are some mistery in this universe that we have troubles to understand...this is one of them.

Also...put the damn condenser and non simetrical supply...an see the wonderfull colouration you will have.

I know colouration is not perfect Mike, but, if we go deep into the direction of the perfect sound, instead of searching the good sound.... the conclusion you will find, is that is much better to switch all those things off and change hobbie, and will be frustrated, as perfection do not exist in this universe...we are in an unstable stable world.

regards,

Carlos
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Old 23rd February 2005, 10:17 AM   #10
MikeB is offline MikeB  Germany
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Hi Carlos !

Yes, i think you can make this JLH-type sound even nicer with
these old 2n3055, using outputcouplingcap and so on...

BUT, my problem with the DoZ/JLH is, i can't call this type of
amplifier HIFI... They do sound great, no doubt !
But they are FAR from exact reproduction...
And i really don't like the idea of an amp adding so much to the
music that it sounds totally nice, using the speakers as instrument,
not as reproductiondevice.

I made some tests/experiments, these showed that the DoZ does
not control the speakers, the speakers start to produce their own sound,
giving more volume into the sound, even higher efficiency...
I think this is the reason why these amps sound so powerful.

I would call the DoZ a perfect candidate for "nice sounding" amp !

Mike
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