BIII with Broskie Unbalancer vs. EE Minimax Plus - My experience - Page 6 - diyAudio
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Old 17th March 2013, 07:55 PM   #51
Rolle is offline Rolle  Denmark
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Hi are you guys running the 6n23p on 250v B+ ?

I tried 5814a RCA from 1966 as input tube, but the JJ ecc802s was better. I have ordered TAD 12bh7 and EH 6072a based on your comments.

I changed the output coupling cap from RTI film to jantzen superior z cap. That really took away the artificialness in human voices - now they sound much more lifelike and natural. Tried also some Russian k75-10 - more warm sound but definitely not neutral. Also swapped in some K73-16 that I had good experience with earlier - but they were dull sounding - so they were removed quickly again.

Blitz - really appreciating that you share your experience with different resistors, caps and tubes in the unbalancer :-)

Best regard
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Old 17th March 2013, 08:49 PM   #52
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Hi,
When the unbalancer is used with an es9018 DAC what's the output voltage, is it close to 2Vrms ?
I suppose it depends on which tubes(mu) are used.
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Last edited by danny_66; 17th March 2013 at 08:52 PM.
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Old 18th March 2013, 01:01 AM   #53
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Yes, I used 250 v as well for the 6922.

You can tune it like you like, reg. 2v. The 6922 has double the amplification than the rest of the bunch, but if you like the 6922 soundwise best: Great, you can lower the i/v resistor to half of its value and drive the dac more in current mode which sounds better. I am using 20 ohm in double mono setup of the dac for 12au7. With the 6922 in double mono 10 ohm would be fine. to get to 2v i guestimate.
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Old 18th March 2013, 06:19 AM   #54
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K73-16 are strange – in solid state gear they sound phenomenal, but with tube gear they seem to suck the life out of the sound!

Re the B+, note that the Broskie circuit halves the b+ for the input tubes. Hence on mine, I get 140v on the 6N23P (input tube), but 240v on the 6CG7 (output tube) – this is measured on the square solder pad of each tube, with reference to the GND terminal in the middle of the board (sorry, don’t know the specific terminology here).
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Old 18th March 2013, 07:40 AM   #55
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Well, it does not Half b+...b+ is 250v. you are measure below the Anode resistor. the anode load resistor of 24k produces at 5ma a voltage drop of 120v. Over this anode load resistor the voltage swing is defined of the Anode of the tube... So, with a current source at the cathode, the tube sees the remaining 130v*0,005mA=0,65Watt, which is pretty save for the 6922. you could run the 6922 with double the current which Allen Wright adivised.
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Old 18th March 2013, 09:39 AM   #56
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OK thanks, lots of options to play with:
so with a high mu tube for the first stage I can use a low i/v resistor.
Now I only need the find a high mu tube that sounds good
Or I use a lower mu tube that sounds good with a higher i/v resistor.
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Old 18th March 2013, 10:13 AM   #57
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Yes, I did not tried this part yet...changing from 12au7 and 22 ohm to 6922 and 10 ohm - both with Neoohm Resistors...need to order the neoohms in 10 ohm first. You could go even further with an 12ax7 and 4 Ohm I guess...at a diffferent current of 1 mA though, so no plug and play.

Last edited by Blitz; 18th March 2013 at 10:40 AM.
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Old 18th March 2013, 10:46 AM   #58
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...Too much fun and stuff to play with...I have on my list as well:

Good Design Bad Design and DIY: Juli 2010

(build your own I/V-Resistor with Manganin-Wire, which is 86% Copper and should sound best...)

One El34 just died in my Amp and I need to fix this first as it seems it destroyed a reistor somewhere if I interpret the smell right...so slowed down again...
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Old 18th March 2013, 10:55 AM   #59
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Quote:
Originally Posted by Blitz View Post
You could go even further with an 12ax7 and 4 Ohm I guess...at a diffferent current of 1 mA though, so no plug and play.
Broskie gives an example of an IV stage using the 12AX7 w/Unbalancer here:

The Unbalancer

I think all you'd really need to change is the 6.81 resistor for the LM334 (not sure what value you would need). You could even try a 5751, which should sound fantastic.

Interestingly, the 6072/12AY7 is quite similar to the 12AX7 as per the datasheet, so perhaps you could use the 12AX7/5751/6072 to cycle through a few tests on the gain required.

That said, I changed input tubes from the 6072 to the 6CG7 then to the 6N23P (using the heater jumpers and 0.1uF capacitors to ground the tubes that have screens) without needing to change any part of the circuit. As I said in an earlier post, thank god for Broskie!

Last edited by lordearl; 18th March 2013 at 11:00 AM.
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Old 18th March 2013, 05:19 PM   #60
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Quote:
need to order the neoohms in 10 ohm first
Try the Rhopoint squaristor or econistor, from what i've read they are even better as i/v resistor.

Quote:
thank god for Broskie
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