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PostPosted: 15 May 2009, 03:26 
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Location: Duesseldorf, Germany
And again Hi!

I think i got the same idea like Rogers to build the amp.

IMHO Rogers Hybrid is an very fine amp. Regards Rogers :up:
And even thought if there is anything to do it better. Very hard ...

There might be some thing that are worth to give it a try. I wanted to suggest some changes as summary from the things i saw at the thread.
( please apologize my bad english. I'm still have something to learn and for me it's really not easy to find the right words ;-))

The 24V mod is surely an very good one.
Aslo from me - Good work john :up:

John, IMHO i see some things (not really problems) that are not to prevent to do.

First i thought about the MosFet stage, that should work better with an bias circuit as seen at Rogers and Greg Szekeres amp.
That might be the best way to get an superb output. There should be an solution to build it with less parts...?!

Then i thought about the ECC82/12AU7. The tube is not an "High end" solution to drive amps that are powered by low voltages. As described in some books the ECC82 provides an very low amplifying/gain at low voltages. It's normally used as phase inverter or oscillator (u=17). An good alternative tube is the ECC81/12AT7 (Audio pre tube ued with El84)) (u=60) that is worth to try. Or the russian 6N23P that works with another system (gates) also is a good one for low voltages - even the PC88 (Used in audio pres). The ECC81 also has an 12,6/6,3V heater. I didn't look for the others what voltages they use for heating.

Rogers - what do you think about? (Rogers or Roger.. still don't know :? )

The circuit from the 24V Mod where the heater is used as resistor or the circuit with the bulb... Worth a try but IMHO i think a NoGo!
Rogers should see the same ?!? It seems that there are too many problems given by this ones...
Better use the common Anode-follower (Cathode-basic) circuit with well dimensions and fixed BIAS (if possible) or the heater resisted version decoupled from the MosFet.

Now - that are only some of my thoughts... I keep searching for somewhat else...

Greets and 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: 15 May 2009, 08:57 
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Hi Tom

I wish i could write a lot like you, but i'm a man of few words. :mrgreen:

It's great to see your opinion Tom, just what i was looking for. Rogers Gomez has already made a good sounding hybrid, no doubt ( thanx again to Mr. Gomez :up: ). When i began to change/modify the construction, i was hunting for even better sound ...if possible, but the criteria was still a low budget of money and few parts.

I guess the spatial problem maybe could be the placement of the 1 uF condensator. Look at the placement of the condensator at the Starving Student http://www.pmillett.com/starving.htm, it's placed between the tube and the Mos-Fet. At the Gomez construction it's placed before the tube. It's just a guess ...but i will try to move it and then get back with info, if it helps to get the spatial sound dissapearing. :ugeek:

I had tried different tubes, but until now the 6J5GT sounds best, in my ears. If the 12J5GT is easy to get here in DK, i might try that. The heater is 12,6 V for this tube and amp. factor is "20". ( Beacuse i want the 25 V version for my high imp. Sennheiser HD 650 ). http://www.mif.pg.gda.pl/homepages/frank/sheets/127/1/12J5GT.pdf. :lightbuilb:

About LM regulators, they are fine for making a stabilizing supply, but i don't think they are doing anything for "the good sound" in the curcuit ( come on someone, tell me if i'm wrong ). 8-)


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PostPosted: 15 May 2009, 12:33 
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Hi Kramme - nice to hear from you :D.

Write like me... omg - don't try ;-) Its only because i can't do it better. English is not my native language - as yours...
For me it is an really hard thing to write all this stuff but i'm learning to be better.
DK is easier to reach with an bicycle than denver... just kidding...

OK - i studied the Millets amp and tryied to follow the hole circuit by reversing before i posted the previous. The Cap you meant is (IMHO) placed there to avoid DC at the modulation signal (audio signal) - so not to alternate the MosFet BIAS. This all looks like an common cathode-basic circuit.

The idea with the diodes (i didn't think to take an LM or CCS at the MosFet drain) was to set it up with rectifier diodes like 1N4004 ones or maybe there could work zeners to drop the voltage at the needed points. I'm just thinking about it and when i got more time - to figure out "howto". It is still the drain to heaters connection that makes me sorrows. Millet uses an 48VDC plate voltage. The voltage is a lot higher than the heater voltage so that there is an high potential to the heaters self. IMHO - The overlay should be slightly minimal. When i saw the circuit i first thought that there can only be overlay or alternating heater resistance. OK - slightly minimal in compare with the plate VDC.
At 24VDC the potential to the heaters is lowered that ther really may be influences. Millet decouples the DC from audio out AGAIN at the speaker. There is no DC at the speaker and the only way to the modulated DC from drain is to the heaters that causes the overlay rising up. Thats is the thing like i see it (me personal). Maybe others have an other view to this. I didn't test it.

Soz - i didn't take a look to the 6J5GT yet. Like Arny said - i'll be back ;-). The really interresting point is current drawn and the "rise".
Soz again - i don't know the english word for "Steilheit"...

Let's find the way :-)

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: 16 May 2009, 04:24 
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And again,

Hi all!

Ok - got an idea that's maybe not sooo bad.

Added Zeners and a cap. I have no idea if that works fine. For "testing" only.
Attachment:
np-100mods rev..PNG

Short description:
Zener to filaments to fix them at 12 - 13VDC drawn by the drain.
Zener from VDC to keep the fet gates open, that the filament is powered. (kind of "bias")
Cap to keep away the added zeners DC in both directions (zd current to plate and from audio to gate).

Costs: not a thing and only 3 parts more...

Any comments, hints and corrections are very welcome!!!
As i said: This is only an idea!!!

Greets and cheers,
Tom.

ps: 6J5GT :up:


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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: 17 May 2009, 11:43 
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Hi John, Hi Rogers, Hi all!

Once again i had the time to look at Millets "Starving Student".

Really - before i did again i had an wrong view to the whole things because the schematic pointed me to wrong thoughts.
Now i think that Millets 20 years of experience never can't be wrong. So i asked me why to change or try anything else???
That's "High End" with a few parts.

Even like Rogers amp that is (once again) a really fine work too.

Does it make a sense to try anithing else?? IMHO i think no.

Regards and 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: 15 Jun 2009, 16:18 
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Hi

For a long time, i owe you guys to show my "Gomez-headfi-amp" :headphones: ...as i call it. 8-)

http://johnkramme.dk/hifi/gomezamp/

The box seen on the pictures with switchmode psu, has supplied some fiber-equipment ( i got four of them, two white and two black, when they was throwed away at work ). I took the fiberpart out and mounted a veroboard instead, with the Gomez-hybrid. The switchmode psu gives 17 VDC output, when i use the 12 V+ and the 5 V- and it's totally free of hum. It measures 12,7 VDC when it's running, it's nearly perfect for this construction. :up:

NOTE: The "slot-in" veroboard, is easy to take out for service or modifications, when or if it's needed. :lightbuilb:

There is no potentiometer mounted, because the signal from both SONY cd-player and pc is variabel outputs.

I'm also going to make a simular white one, for pc use. :wizard:

Regards from Kramme :mrgreen:


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PostPosted: 15 Jun 2009, 18:20 
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Hey John,

congrats to this fine build ;-) The idea with the "slot in board" is crazy good! (You should offer it to B&O...)
Did you apply changes to Rogers' circuit?

One further thing:
I'm thinking about using an similar circuit for an Power amp. Something like the tubes for the pre and some IRFs for the power stages.

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: 15 Jun 2009, 22:16 
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Joined: 28 May 2008, 21:53
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Location: Winnipeg, CANADA
Very nice work John. What brand of 12AU7 are you using?
Cheers,
Gio

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PostPosted: 16 Jun 2009, 09:50 
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gmilitano wrote:
Very nice work John. What brand of 12AU7 are you using?
Thanx Gio :up:

It's a no name tube. Only description is ECC82/12AU7A ( I bought them from L.A Audio, when they were established in Denmark for a long time ago ).
tombethe wrote:
congrats to this fine build ;-) The idea with the "slot in board" is crazy good! (You should offer it to B&O...)
Did you apply changes to Rogers' circuit?

One further thing:
I'm thinking about using an similar circuit for an Power amp. Something like the tubes for the pre and some IRFs for the power stages.
Thanx Tom :up:

Naahh, I guess B&O would laugh their behind off, if they saw it. :D

Changes = Yes, 180 Ohm resistors instead of 100, 330 Ohm instead of 220 and 470 uF capacitors instead of 1000 and it still gives an okay sound. It's usable with both my low imp. Philips SHP8900 and high imp. Sennheiser HD 650. The reason for not using the 100 Ohm resistors, is because the voltage drop from the switch mode supply, will lower to 11,2 VDC. With 180 Ohms it's stable at 12,7 VDC. :headphones:

About a power hybrid amp = me to :P
The last months i've tried the 6J5GT triode, together with the BUK453 mos-fet as a SE power amp, with a 36 VDC supply, but the sound isn't good :bawling: ....but i won't give up. :twisted:
Let's try something out Tom, i'm glad you want to do the same ....any ideas ? :wizard:
( when ready, we should make a new thread )

I guess some theoretical spying on Passdiy.com, would be learning and giving for me. 8-)

Regards form Kramme :mrgreen:


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PostPosted: 16 Jun 2009, 23:06 
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Location: Denver, Colorado
Hi all,
John, that is one nice amp. I like what you Tom and all have done to make the project grow. Keep up the good work!

Rogers


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