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PostPosted: 26 Feb 2012, 12:39 
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Joined: 15 Jan 2012, 12:11
Posts: 5
Ok, I will order JJ tubes.

Thank you for your kind help.

Oguz


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PostPosted: 26 Feb 2012, 16:22 
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Joined: 06 Jun 2008, 18:23
Posts: 5291
Location: Australia
With the Tubecad phono preamp I built I used aged 12AX7 Golden Dragons (gold pin). In my cct. these proved dead quiet.

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Projects:"Illusion" - 6SN7 SRPP preamp in a plastic jiffy box | “Salt Cellar” - Mono 807 triode integrated amp |
"Rosso" - E88CC SRPP preamp | ”Salt Cellar II” - 6EM7 mono wine box triode amp |


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PostPosted: 26 Feb 2012, 17:43 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi Mark, the Golden Dragons are supposed to be good, but I have not tried them yet. The US supplier is a $%$#@! and so on. Maybe they have come to their senses and I'll try again, but with a S/N in the -90s I'm not sure there is anything to be gained. My fridge two rooms away and around a corner makes more noise than the phono preamp. At what would be sonically disastrous levels I have to put my ear to within 2 inches of the speakers to hear any hiss.

Good listening
Bruce

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PostPosted: 26 Feb 2012, 22:52 
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Joined: 06 Jun 2008, 18:23
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Location: Australia
Well my supplier of Golden Dragons doesn't stock them any more. Now they are pushing Gold Lions which appear OK.

I get a very faint hiss from my jFET based BHL phono stage but not from amp or preamp.

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Projects:"Illusion" - 6SN7 SRPP preamp in a plastic jiffy box | “Salt Cellar” - Mono 807 triode integrated amp |
"Rosso" - E88CC SRPP preamp | ”Salt Cellar II” - 6EM7 mono wine box triode amp |


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PostPosted: 04 Mar 2012, 15:18 
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Joined: 01 Feb 2011, 06:57
Posts: 18
Location: Aalborg, Denmark
Just wondering if the resistors in the amplifier section have to be 1W?

Can you go with 0.6W? Would make my life easier since I can fairly easily get the 0.6W, however the 1W I have readily available are quite big.

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Daniel
Luck tends to favor the prepared.


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PostPosted: 04 Mar 2012, 16:05 
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Joined: 02 Mar 2009, 12:41
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Location: Vänersborg, Sweden
The thing with onewatters is the physical dimension. A 0,5 or 0,6W may fix the power, but a high voltage may create an electric field (V/inch) that is strong enoung to successively brake down the resistor. Check the voltage to make sure the resistor will work.

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“If you don't know where you are going, any road will get you there.”
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PostPosted: 04 Mar 2012, 16:50 
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Location: Arizona, USA
Hi, A good point. I like to use resistors rated at least 25% over the maximum expected voltage. Typically 350 V for the preamps and Poddwatt as the max B+ can not get past 250 in the Poddwatt and 280 in the preamps. Even then those voltages are only under no load conditions before the tubes conduct. You can still have some problems though as a batch of 2.7meg 1 watt resistors we got that were rated at 350 had a number of failures when the max B+ was 250.

Good listening
Bruce

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PostPosted: 05 Mar 2012, 13:33 
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Joined: 01 Feb 2011, 06:57
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Location: Aalborg, Denmark
Ok, the resistors I have available should be rated at 350V - so I derive from the above that there is no need for 1W? (don't know the voltage across them, else it is of course easy to calculate.)

Just need to get a hold of the resistors, the last capacitors and make the PCB's - them I'm ready to build :)

I have chosen to do the PCB's myself - just for the fun of it. Perhaps it will be alright :)

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PostPosted: 11 Mar 2012, 00:28 
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Joined: 10 Mar 2012, 23:53
Posts: 2
Location: East Tennessee
I wanted to fab a tube based phono preamp and decided to use the Groovewatt, but added the 3.18us additional time constant. I did a PCB design so adding or removing it is simple. I've been rolling tubes through the input SRPP stage to change the output impedance to the RIAA stack. Still need to listen to it much more, quite pleasant, not harsh at all.
It is part of a Tube/Mosfet preamp-headhone amp. It is a tube input section, baxandall tone section, SRPP buffer to Mosfet follower output to get low output impedance to drive headphones or the next stage. It has 2 power supply PCB's, the largest has the B+ and two 12VDC supplies for the hybrid board; 12 VDC to the output section and another 12VDC to the heaters. The second power PCB is a raised 12VDC for the Groovewatt, using the B+ from the larger PCB. I used a 12AL5 as a slow start pass device for the B+ to both boards.
The PCBs are toner transfer manufacturing method, etched in zip-loc bags to contain the mess.
The pic of stacked amps is a 30 watt/channel compactron amp sitting on top of a headphone preamp.The headphone amp was a stocking stuffer for last Christmas to go with the power amp that was the year before. I'm building another set, but with the Groovewatt phono-preamp and a baxandall tone stack. The amp for this set is started, a Compactron based amp 60watts/channel.


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PostPosted: 11 Mar 2012, 10:39 
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Joined: 14 Feb 2010, 13:13
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Location: Lisbon, Portugal
Good job! :)


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