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Old 4th January 2006, 05:46 AM   #1
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Default JE LAB's 2001 2A3 & Preamp???

I recently completed the JE Labs 2001 2A3 amp (mono blocks) and I am quite happy with the results and performance.
Though not overly loud through my early 1990's Missions 762 (made in the UK) the frequency response is quite surprising.

My question is....
How much sonic improvement would there be if I were to use a dedicated tube pre-amp (6SN7 or 12AU7's)

If so, what would be the best circuit mod for the front end of the amp?
Obviously I can ditch the 100K pot (the passive volume control) but should it be replaced with?

Thanks

Mike
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Old 4th January 2006, 07:18 AM   #2
arnoldc is offline arnoldc  Philippines
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hi, although i have the SRPP version (no volume pot), i liked it with a borrowed passive (DACT 10K).

i have built a Foreplay and used it for two years with my 2A3. it was ok and i never wanted more gain driving my vintage Altec+Oxford Horn+Fostex tweets. now, i'm using it with another preamp that gives more balls and top end extension (coloration? ) if you can call that a sonic improvement.

what i have tried also are the Berman 76 (or the JE Labs adaptation), a 6SN7 preamp (slow for me), zen buffer (no gain, don't like too).

you need to find that "synergy" so borrowing some preamps from friends will let find the "flavor" that you will like, then you make one.

hope this helps.
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Old 4th January 2006, 02:38 PM   #3
kmtang is offline kmtang  Canada
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You may try to replace the 6SL7 driver stage with the 6SN7. The schematic is same as the JE Lab 300B. It should have better sonic performance. I am experiencing with different driver config for their different sound characteristics. It's fun.

Surely, adding a tube line amp could have some improvements as well.


Johnny
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Old 4th January 2006, 11:58 PM   #4
AJT is offline AJT  Philippines
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Quote:
Originally posted by kmtang
You may try to replace the 6SL7 driver stage with the 6SN7. The schematic is same as the JE Lab 300B. It should have better sonic performance. I am experiencing with different driver config for their different sound characteristics. It's fun.

Surely, adding a tube line amp could have some improvements as well.


Johnny
6SL7 has a mu of 70, while 6sn7 has a mu of 20, so gain will be much lower if you use 6sn7, but if you can live with lower gain, then you can try it.

imho, you will need a line amp if you use 6sn7.
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Old 6th January 2006, 01:15 PM   #5
pieroh is offline pieroh  Germany
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Default Re: JE LAB's 2001 2A3 & Preamp???

Quote:
Originally posted by wwflyball
I recently completed the JE Labs 2001 2A3 amp (mono blocks) and I am quite happy with the results and performance.
Though not overly loud through my early 1990's Missions 762 (made in the UK) the frequency response is quite surprising.

My question is....
How much sonic improvement would there be if I were to use a dedicated tube pre-amp (6SN7 or 12AU7's)

If so, what would be the best circuit mod for the front end of the amp?
Obviously I can ditch the 100K pot (the passive volume control) but should it be replaced with?

Thanks

Mike
Hello Mike,
this what I use, but with differnt parts values:

http://www.diyparadise.com/etude.html

This valve was used in TV sets as deflection tube (in the US and maybe Canada) has low gain and sounds suprisingly good.

I have chosen a resitor of 6,8K/5W as anode load and a 1k as cathode resistor. I did not bypass the cathode resitor because I wanted some local feedback. Voltage from the psu is 260V.

Peter
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Old 2nd March 2006, 04:27 AM   #6
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Well, I finally got around in making a preamp.

I built "Frank's 6SN7 cap coupled preamp"

Which 6SN7 preamp should I build?

Did it make my system sound better?
Not really, just different.

At low volume it sounds quite good.
When you turn up the volume a little the highs get a little harsh/bright and the lows get muddy.
The sound stage gets VERY wide, almost sounds like someone added reverb to the mix.
Applying a more volume results in heavy distortion!

I honestly don't think this preamp added any sonic improvement to my amp.

I believe that the preamp is overdriving the 6SL7 input/driver tube of my 2A3 Amp.
I guess I should try reducing the gain on the preamp. Any suggestions on what would be the best way?

Thanks

Mike
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Old 2nd March 2006, 04:55 AM   #7
kmtang is offline kmtang  Canada
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Hi,

You need to know that SE 2A3 only gives you 3.5W. When you overdrive it, surely it will have lots of distortion.

If you want louder sound, you may have to consider getting a pair of more efficient speakers.


Johnny
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Old 2nd March 2006, 05:00 AM   #8
arnoldc is offline arnoldc  Philippines
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Hi, I haven't liked a 6SN7, yet. Heard various preamp using that tube, but just can't get my fancy. Must be the tube itself. I mostly feel they're overly colored, flabby bottom end, slow, but yes big sounding.

I built the 12B4 preamp, and I can tell you I like the synergy with my JE Labs 2A3! Next to my 407A pre, the 12B4 is it!

ps.

I used to drive an Infinity Kappa 200 (89dB) bookshelf with my JE Labs 2A3. Lived with that for a while, but when I got the Altecs, there's just no turning back (and the amps I build are decreasing in power). So, I'd look at the speakers too as mentioned in the post above.

I also babysitted a Mission B(ronze) bookshelf before (I think B4) and the Kappa can be driven a lot easier by my 2A3 compared to that Mission even if the Mission specs higher sensitivity.
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Old 2nd March 2006, 05:11 AM   #9
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I understand what you are saying but loudness is not the issue here.

Before I built the preamp the amp was loud enough and sounded good with only a small amount of distortion when maxed. Now, I can only turn it up 1/2 as much before is starts doing funky things.

I'm not searching for louder, just better sonic qualities.

Mike
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Old 2nd March 2006, 05:29 AM   #10
arnoldc is offline arnoldc  Philippines
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Hi, if you already like it without a pre-amp, what "improvement" are you looking for?

I like my 2A3 with a simple DACT (borrowed) and sounds loud with my speakers. But DIY'ing is fun so I built several pre-amps too, including a Foreplay. I can't afford a DACT and most preamps I built costs much less than a DACT, but in the end I'd still go back to a DACT. I also drive a 5 meter interconnect and for that purpose I use a preamp now. If you have access to a 12B4 tube, I would say it's worth a try!
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