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6SN7-2A3 SE Amp - James Transformers
6SN7-2A3 SE Amp - James Transformers
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Old 24th March 2010, 04:23 PM   #21
kevinkr is offline kevinkr  United States
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6SN7-2A3 SE Amp - James Transformers
Quote:
Originally Posted by Ty_Bower View Post
Have you ever generated any impedance plots for your speakers? It's fairly common for them to have significant peaks, especially around port resonances and crossover frequencies. I do not recall seeing any feedback in your amplifier design, so high impedance peaks in the load would likely result in measurable changes in the power delivery.

Click the image to open in full size.
http://i69.photobucket.com/albums/i4...usIIleftPR.gif
Impedance minima would also result in measurable changes in power delivery, and my suspicion is that the tweeter impedance is quite low at high frequencies - could well be related to XO design or the driver itself.
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Old 24th March 2010, 04:33 PM   #22
christian.lenci is offline christian.lenci  Italy
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Here is a review of the S2 series (mine is the S3) with an impedance graph.

http://www.audioxpress.com/reviews/media/AX201DA.pdf

I expect the graph to be very similar to mine since there were no major updates (S2 already used Nautilus style tweeters, etc).

If I remember correctly the XO has a 2nd filter for the woofer and a 3rd order filter for the tweeter.

Thank you for your help!
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Old 24th March 2010, 04:35 PM   #23
kevinkr is offline kevinkr  United States
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6SN7-2A3 SE Amp - James Transformers
Default Bingo!

Here is a review of the DM602 S2 by Joseph D'Appolito, shows very clearly what the problem is. Have a look at figure 1 here:

http://www.audioxpress.com/reviews/media/AX201DA.pdf

IMO this speaker is not a very good match to any tube SE amplifier, or indeed any amp that does not use global negative feedback. The average impedance is about 5 ohms so IMHO the 4 ohm tap should be used. The implication here is that the efficiency is lower than stated based on 2.83V into 8 ohms - I think based on the average impedance (excluding peaks) of 5 ohms or so that the efficiency is probably close to 88dB.

This is a good speaker for use with higher powered PP tube amplifiers with feedback or the typical solid state amplifier for which it was clearly designed.

The effects of leakage inductance at high frequencies in your inexpensive OPTs will be worsened by a load that exhibits below expected impedances at HF so it could well be that a better transformer will help a little if these are really poor in this regard. Again I hope you have a 4 ohm tap! A zobel network tuned to the 24 ohm impedance maxima to level out the load impedance might not be such a bad idea either.. (or not..)

Edit: Looks like we both found the review link at about the same time.
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Old 24th March 2010, 04:39 PM   #24
christian.lenci is offline christian.lenci  Italy
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I don't have a 4 ohm tap. These OPTs were custom made, and for the sake of simplicity I asked them to be tailored on my (nominal) 8 ohm speakers.

Last edited by christian.lenci; 24th March 2010 at 04:42 PM.
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Old 24th March 2010, 07:27 PM   #25
boywonder is offline boywonder  United States
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How does one determine the correct C and R values for a zobel, and is the zobel best placed at the amp output or the speaker input?
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Old 11th October 2010, 06:25 AM   #26
mariukasa is offline mariukasa  Lithuania
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Hello christian.lenci I have question for you: do you have enough gain fith 6sn7 driver?
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Old 11th October 2010, 06:28 PM   #27
yagoolar is offline yagoolar  Poland
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Send a message via ICQ to yagoolar 6SN7-2A3 SE Amp - James Transformers
Quote:
Originally Posted by kevinkr View Post

IMO this speaker is not a very good match to any tube SE amplifier, or indeed any amp that does not use global negative feedback. The average impedance is about 5 ohms so IMHO the 4 ohm tap should be used. The implication here is that the efficiency is lower than stated based on 2.83V into 8 ohms - I think based on the average impedance (excluding peaks) of 5 ohms or so that the efficiency is probably close to 88dB.
Guys, what do you say about converting this SE amp into Parallel Feed one? I did it with my ECC82+6C4C SE. Used the same OPT, just added a choke and a cap. The results were satisfactory with my amp.
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Old 11th October 2010, 09:07 PM   #28
mashaffer is offline mashaffer  United States
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Is it possible that connecting the OPT windings the "wrong" way (primary with B+ connection to the plate or wrong end of secondary grounded) could result in different parasitic reactances? Maybe try switching connections around.
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Old 10th September 2019, 08:44 PM   #29
bluebyte60 is offline bluebyte60  United States
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Sorry for resurrect this post. As I am kind of interested in building a 2A3 headphone amp. Yeah, I knew there will be all sort of questions about why use 2A3 as a headphone amp, but let's assume I am a strange person that want to have about 1~2 W output for a headphone amp. Since I am such a newbie, I have several humble questions and hoping can get some help from people with much deeper understanding about how tube work.
1) How much is the gain for this circuit and how to calculate it?
2) How much is the idle current of the 2A3 and plate resistance? Can I use LL2765 as output transformer? It seems by default, LL2765's max idle current is 30ma. The LL2765's primary is about 5K, although it can change when hooking up with different can.
3) This is a bit tricky. If I want to use dc filament supply for 2A3, what kind of change need to be made?

These questions are not easy get solution for me. Really hoping to gain some knowledge about how these question work out. Tks!
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Old 10th September 2019, 11:57 PM   #30
PRR is offline PRR  United States
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Tube maker/seller suggestions are in the datasheet:
http://www.mif.pg.gda.pl/homepages/f.../021/2/2A3.pdf

You don't need 3.5 Watts. You can run a lower current and a higher impedance. The peak grid drive for max output is similar to the "Grid Voltage". For headphones you may not need that much, but it is common sense to have nearly that much (or else you could have picked a less-unsuitable tube).
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