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Old 22nd October 2007, 10:04 PM   #41
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Hi Salas,

I did trip over your other thread regarding this one and inmediatly called my attention since I started to gear up for yet another tube preamp to replace the 417A that I now use which has two shot fallings, namely hi gain and hi zout used as a CC - plate follower.

Being an addict for simple topologies I had decided to build the 12b4 that has a good reputation from this thread Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid..... but also was thinking on Geeks permutation which shows an even lower zout, not that I need that since Im driving a low capacitance 47k amp input.

Im at the very beginning of this project, have ordered only the tubes so nothing stops me from changing to this very interesting line stage you have concocted.

Had you have a chance to compare the 12B4 to your 6V6? Would love to here some comments to this regard.
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Old 22nd October 2007, 10:34 PM   #42
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Yes, I have tried 12B4 in simple triode once. But I did not choose it as a keeper. Its precise, has impact, but its cold in my opinion. Reminds me of solid state sound somehow. This 6V6 circuit has flow and musicality, along being really big and powerful. If you can accept that it is more easy to pick up vibrations, or that some brands do expand their metals during warm up and you can hear some ding dong sounds for 2-3 minutes, I must say this is the best valve preamp I ever had by a very good margin. If you start from scratch, I highly advise you to build a sub chassis for the 2 6V6s that may be elastically decoupled from the rest of the chassis. This will save 80% of the microphonics. Another good thing with my 6V6 circuit is that it displays very practical gain for modern sources. You get a good rotation range on your volume pot. Driving tube amps or 50k input SS amps is no problem. I have tried many configurations with noval follower output stages that have better Z out on paper, but the 6V6 with 20mA driving an amp, puts you in another league.
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Old 22nd October 2007, 10:58 PM   #43
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And...

If we use a EL84 in Cathode Fallower?

Who many ohms in Zout?

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Old 22nd October 2007, 11:16 PM   #44
Salas is offline Salas  Greece
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If you triode connect an EL84 its rp drops to around 2k. If you wire it as a cathode follower, I would expect it to fall 10 times lower circa 200 Ohm. But why adding a second stage with 100% local feedback? It will steal the natural tone and the immediacy. The 6V6 here has 1.5k Zout and it drives much a bigger sound in the power amps than CF stages I had used before with 3 to 5 times lower Zout.
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Old 22nd October 2007, 11:23 PM   #45
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Its a good idea use local feedback.

I'm thinking to use ECL82 with the Pentode conected in TRIODE MODE, to drive a SENNHEISER HD580.

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Old 22nd October 2007, 11:29 PM   #46
Salas is offline Salas  Greece
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That is a circa 300 Ohm Zload headphone?
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Old 22nd October 2007, 11:33 PM   #47
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Quote:
Originally posted by salas
That is a circa 300 Ohm Zload headphone?
I'm searching a circuit to drive a Sennheiser HD580. 300ohm Zload headphone.
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Old 22nd October 2007, 11:39 PM   #48
Salas is offline Salas  Greece
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Quote:
Originally posted by mod_evil
Its a good idea use local feedback.

I'm thinking to use ECL82 with the Pentode conected in TRIODE MODE, to drive a SENNHEISER HD580.

Best Regards,
Felipe Navarro.

In such a case I would try it. If you go down to 100-200 Ohm with such a cathode follower you may just lose 25-35% of your headphone amp gain when driving the HD 580s. Not too bad when gain is excessive anyway if there is a triode stage before the CF driven by a CD player.
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Old 23rd October 2007, 05:34 PM   #49
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Quote:
Originally posted by salas
I have tried many configurations with noval follower output stages that have better Z out on paper, but the 6V6 with 20mA driving an amp, puts you in another league.

Nice to hear your comments on this one, thanks. Ok, so 1.5 K zout, good to drive a 20K load? Or this would be asking too much like on my 417A? - anyway I think the 417 will be similar to the 12B4 sound wise even though it has a somewhat lower Zout as a CC which is not what Im looking for, I would prefer something like the 6V6 character you described.

Wonder also, if bass gets too rounded, meaning if attack gets somewhat sluggish?
Did you use AC for the heater?

Sorry, to many questions but I has looking to the newer issues from Sovteks or JJ 6V6 seems to have ribbed plates, do you have any experience with those?
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Old 23rd October 2007, 05:46 PM   #50
Salas is offline Salas  Greece
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Quote:
Originally posted by apassgear



Nice to hear your comments on this one, thanks. Ok, so 1.5 K zout, good to drive a 20K load? Or this would be asking too much like on my 417A? - anyway I think the 417 will be similar to the 12B4 sound wise even though it has a somewhat lower Zout as a CC which is not what Im looking for, I would prefer something like the 6V6 character you described.

Wonder also, if bass gets too rounded, meaning if attack gets somewhat sluggish?
Did you use AC for the heater?

Sorry, to many questions but I has looking to the newer issues from Sovteks or JJ 6V6 seems to have ribbed plates, do you have any experience with those?
- 1.5kX10=15k < 20k = OK (Better than ten fold). 22ma of cathode current counts much more in my experience vs lower Zout from a CF working with 5-10mA.

- I was listening to Pictures At An Exhibition (Wiener Phil. / Previn) just before. The double basses and tympani in The Great Gate Of Kiev left me speechless. The attack and body was elastic, majestic and instantaneous.

- LM317T current sourced heaters. One per 6V6, dedicated secondaries, bridges and caps.

- JJ's I had and eye for them, seem rugged. I did not get on a couple yet. Its I am spoiled with excellent NOS I have. I still wanna see how it does for microphony.
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