BIII with Broskie Unbalancer vs. EE Minimax Plus - My experience - Page 5 - diyAudio
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Old 6th March 2013, 07:44 PM   #41
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So, after a few days burn in of the new PSU and the Tantalum resistor, some news: The AN Tantalum has a very beautiful sound signature. I would not call it the most neutral or the transparent reistor in this position, but it adds an unbelievable amount of musicality.

The wirewounds are still more "vibrant". The space is deeper, more air around the instruments...but when you look at your feet: The feet tipping with the music comes with the AN Tantalum. It has a very beautiful tonal richness. It makes as well everything sound "bigger". An effect you need to get used to...

So, I would use the AN Tant for Jazz and the Neoohm for classical music...or other comaprison: the An is the LP12 and the Neoohm a heavy maas turntable. To get me right: The Neoohm is not thin at all. The AN is simply more colorful.
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Old 6th March 2013, 10:14 PM   #42
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pair of both seems like plan.
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Old 7th March 2013, 11:45 PM   #43
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Ooops, had to make a quick order for the Duelund's they where running out at
the sale. Well, that's done anyway
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Old 14th March 2013, 07:49 PM   #44
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OK, some progress report:

I implemented two switches to switch on the fly between 12V and 6 V heater-voltage per tube stage.

So, the tube-rolling was started. this is to be seen as my very first impression, need much more investigation, but I am looking forward if you have similar or different results:

B+ ist 250V. The first stage is with CCS at 6mA. So, I did not change the bias to optimize for each tube, I understand this imperfection of this process, but I rather collect initial impressions than get lost in trying to remember how something was sounding hours or days later. But I would be very interested in your experience how does a 12BH7 changes its sonics quality when not used at 6 mA, but at 12 mA (or 6cg7 etc) etc.

The second stage was originally the ECC99, which sound rather technical and thin. The TAD 12BH7 changed that dramatically to transparent and harmonical at the same time. So, it stayed currently as the cathode follower with 250 Ohm cathode resistor, as well a Neoohm wirewound.

So, given these conditions, istarted to do some tube rolling in the first stage:

- Psvane 12au7 Reference: Warm, good tone, but a little lack of transparency and dynamic.
- JJ 802S: Very fast, very wide soundstage, a little too cool in my view, a little bit technical, but very dynamic, there is a lot of inner structure of how tone is generated. Still one of my reference-tubes here.
- TAD 12BH7: WOW !!! Nearly as transparent as the JJ802S, but warmer and more powerful, adult soundstage. VERY SERIOUS, maybe even better than the JJ802S
- Raytheon 6CG7: Brutal. Even bigger sound and more powerfull than the 12BH7. Like a 12BH7 on steroids. Everything is warm, but less deep space, much bigger instruments than before, in my view unnatural big. You think that your poweramp have now double the power. But you loose the right size of instruments, ervything come more into the front and is less deep.
- Russian 6H23-EV ( my favourite 6922): As well like a 12au7 on steroids...but is it not as neutral as the above. It adds a signature which goes into the direction of a lot off pressure, a bit more noisy, flatter in space, more liek a small brother of the 6CG7, but with a more realistic size of the instruments.

So, I will investigate this further, please let me know what your findings are and if you have similar impressions or hints what to try as well.

ON the resistor front: My initial impressions hold true. Wirewound rules over Tantalum. Next will be the Rhopoint Wirewound against Neohm as I/V. I iwll as well exchange my Kiwame-Anode-Resistors (Carbon-Film) against Wirewounds and see what will happen.

Last edited by Blitz; 14th March 2013 at 07:53 PM.
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Old 16th March 2013, 04:26 PM   #45
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Interesting comments Blitz - I had in fact just this week changed the tubes in my Unbalancer, and now have the input tubes as 6N23P-EV and the output tubes as 6CG7 - your thoughts above are spot on.
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Old 16th March 2013, 06:19 PM   #46
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Has anyone thought what needs to be considered when eunning the unbalancer hotter ? Like with 300v or 350v ? Two lm334 in parallel, ok. Running the input stage with more current and voltage swing. Anything to consider on the outputstage ?
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Old 17th March 2013, 04:46 AM   #47
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Quote:
Originally Posted by malarkey View Post
Yes, for the 6n23p I needed more than the given 10mA. I never tried a rial ccs circuit for biasing, but even though I'm using clean power with salas sshv2, using a battery was still a big improvement. I thought it would be critical to use a battery in a differential amp, but its absolutely not, no hum or anything at all.
Doesn't matter what tube I used, with the battery bias it was always a much cleaner and smoother sound.
How are you all measuring the current?
I've set the LM334 up as per Broskie's instructions:

Note that 10mA, the optimal value for most Unbalancer setups, does not receive a
resistor value, but we can readily see that 6.8 ohms is the correct value. (The LM334
datasheet goes into much more detail, but for tube work, 6.8 ohms is close enough.)
Although 10mA is the LM334's maximum current flow, the device sees less than 10V
with most tubes, such as the 6CG7 and 12AU7, so the device's dissipation is usually
less than 100mW, well below its 400mW limit. Nonetheless, it is a good idea to attach
a small heatsink to the IC, as it better ensures an accurate idle current.


I didn't use a heatsink as there wasn't much heat being generated at all, and I'm using a pair of 6N23P at the input and a pair of 6CG7 at the output. The sound is phenomenal - excellent bass definition. However, from reading through the thread, I'm slightly concerned about the mA currents you are referencing for different tubes - especially given the Broskie's manual notes 6.81R for every tube example he gives....
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Old 17th March 2013, 06:38 AM   #48
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I used the same settings as you did, so 5ma per triode.

Allen Wright wrote once in his preamp cookbook that the 6922 needs at least 10MA per triode before it starts to sing...12bh7 is a 3.5 watt tube vs 6922 1,5 watt...that is why I believe the tubes do not play yet at their sound capabilitieties with 5 mA. 5mA hold the ratio of 24k load impedance at 250 Voot b+ in a nice, stabile relationship for headroom. But when you want to know how the tube can sound, we need to adopt potentially b+, Anodeload and current, that is why I asked if anyone has experience on th changes in sound when doing so....
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Old 17th March 2013, 08:41 AM   #49
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Ok I follow you. I was worried I may have been endangering the tubes and/or the LM334.

Having the 6N23P at the input was a game changer for my system - after trying the all of the other suggested tubes, this one blows them all out of the water (cathode resistor is 300R Caddock MK132).
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Old 17th March 2013, 08:44 AM   #50
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Broskie OTL Variations & Current-Mirror-Based Push-Pull Buffer

Quote:
Next Time
I hope to have more information about my recently restocked PCBs.
This was Nov 13.
Is there anyone that has any knowledge what's happening
with the pcb's (or John for that matter, hope his alrigth) ?
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