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
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
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.
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.
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
Surely, adding a tube line amp could have some improvements as well.
Johnny
wwflyball said:
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
Well, I finally got around in making a preamp.
I built "Frank's 6SN7 cap coupled preamp"
http://www.diyaudio.com/forums/showthread.php?s=&threadid=71813&highlight=
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
I built "Frank's 6SN7 cap coupled preamp"
http://www.diyaudio.com/forums/showthread.php?s=&threadid=71813&highlight=
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
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.
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.
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
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
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!
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!
hi peter, this preamp is still going through various modifications. currently using 5Y3 rectification, and 40V heaters and is very silent. i used the load lines to figure out the operating points and TubeCAD software to help validate it, and then tuned by ear 
. i don't use a cathode follower and i'm not bothered by the ~4K output impedance as i like it that way. the final version will be regulated (MOSFET) B+. when it's done, i'd be glad to post it.
i saw the PCB of Gary sometime ago that has a 2C51?? label on it? i know the 2C51 is the 6.3V version (or similar) to it.
i have tried the WE396A on this preamp with a change to 6.3V heaters, and all i can say is- it rocks! however, i do find the RCA 407A to be a little bit better (subjective) to the WE407A.
. i don't use a cathode follower and i'm not bothered by the ~4K output impedance as i like it that way. the final version will be regulated (MOSFET) B+. when it's done, i'd be glad to post it.i saw the PCB of Gary sometime ago that has a 2C51?? label on it? i know the 2C51 is the 6.3V version (or similar) to it.
i have tried the WE396A on this preamp with a change to 6.3V heaters, and all i can say is- it rocks! however, i do find the RCA 407A to be a little bit better (subjective) to the WE407A.
arnoldc said:hi peter, this preamp is still going through various modifications. currently using 5Y3 rectification, and 40V heaters and is very silent. i used the load lines to figure out the operating points and TubeCAD software to help validate it, and then tuned by ear
i saw the PCB of Gary sometime ago that has a 2C51?? label on it? i know the 2C51 is the 6.3V version (or similar) to it.
i have tried the WE396A on this preamp with a change to 6.3V heaters, and all i can say is- it rocks! however, i do find the RCA 407A to be a little bit better (subjective) to the WE407A.
Hi,
many thanks for your quick reply.
Did you choose the values from the WE407 spec-sheet for the bias? I think there is a quiescent current of around 8mA per section with a Va of 160V and a 270 Ohm resistor.
I want to use one tube for both channels, there is a shield between the sections. The amplification factor is rather high, or do you use global feedback?
Peter
hi peter, we are off topic here and i suppose the mods will move us somewhere else as appropriate.
anyway, i started high, but i ended up quite low (tuned by ears )
here is the op point-
my friend told me that the Rp is 5,500 so i used a 24K riken for the plate load and ended up with around 3mA, -2.2V bias with 820R bypassed Rk. voltage on the plate is 115V, measured. TubeCAD says around 4K Zout.
ps.
yes, gain is rather high at 27dB (TubeCAD) and i did not use feedback.
anyway, i started high, but i ended up quite low (tuned by ears
)here is the op point-
my friend told me that the Rp is 5,500 so i used a 24K riken for the plate load and ended up with around 3mA, -2.2V bias with 820R bypassed Rk. voltage on the plate is 115V, measured. TubeCAD says around 4K Zout.
ps.
yes, gain is rather high at 27dB (TubeCAD) and i did not use feedback.
Attachments
Hello again,
Well, back to the original topic: 6SN7 pre into JE labs 2A3 2001.
Tonight I stripped out "Frank's 6SN7" pre and built VTV 6SN7 circuit.
http://www.geocities.com/northbirdten/line_stage.htm
I used 250K pot's and my own PSU design.
Haven't done too much serious listening yet but so far this pre is a way better match for my amps.
With my speakers the highs are almost right, the mids are perfect and the staging appears wider than without a preamp.
I could use a little more bottom end though.
I also still feel there is still a bit to much gain so I'll have to tone that down a bit, any suggestions?
I'm getting near to what I think sounds good to me.
Thanks again for all your advice.
Mike
Well, back to the original topic: 6SN7 pre into JE labs 2A3 2001.
Tonight I stripped out "Frank's 6SN7" pre and built VTV 6SN7 circuit.
http://www.geocities.com/northbirdten/line_stage.htm
I used 250K pot's and my own PSU design.
Haven't done too much serious listening yet but so far this pre is a way better match for my amps.
With my speakers the highs are almost right, the mids are perfect and the staging appears wider than without a preamp.
I could use a little more bottom end though.
I also still feel there is still a bit to much gain so I'll have to tone that down a bit, any suggestions?
I'm getting near to what I think sounds good to me.
Thanks again for all your advice.
Mike
So far in my preamp (line stage) I've tried numerous 9 pins, of which the best was E80CC, then the rimlock ECC40 which was better than the E80CC with a particularly lovely high end. Then 6SN7 and 6J5GT, which were very clear and clean but a little thin. Then 2C22 which were more immediate (bit like a DHT) and detailed than the 6SN7s - an obvious improvement.
Then one day I tried the 1626 - now, I really love this tube. It had by far the best bass and a real 'boogie factor' - sounded great on rock and jazz.
I substituted the 26 DHT and the two sounds couldn't be more different - where the 1626 was robust, the 26 was delicate, where the 1626 had the bass, the 26 had the air and highs. I decided to go with the 26 but still regret the 1626. For classical music I'd go with the 26, but if I just listened to rock and jazz I might prefer the 1626. I found both to be better than the 6SN7, and the 6SN7 (or preferably something like the 6P5GT) better than the 9 pins.
26 could be substituted with a 12a for instance, haven't tried that but others report good results and less hum problems. I found 26 with DC heaters OK in a 89db setup - no real need for batteries.
I have a 12b4 line stage on the launch pad - just need to add the coupling caps and volume control. Should be interesting.
Then one day I tried the 1626 - now, I really love this tube. It had by far the best bass and a real 'boogie factor' - sounded great on rock and jazz.
I substituted the 26 DHT and the two sounds couldn't be more different - where the 1626 was robust, the 26 was delicate, where the 1626 had the bass, the 26 had the air and highs. I decided to go with the 26 but still regret the 1626. For classical music I'd go with the 26, but if I just listened to rock and jazz I might prefer the 1626. I found both to be better than the 6SN7, and the 6SN7 (or preferably something like the 6P5GT) better than the 9 pins.
26 could be substituted with a 12a for instance, haven't tried that but others report good results and less hum problems. I found 26 with DC heaters OK in a 89db setup - no real need for batteries.
I have a 12b4 line stage on the launch pad - just need to add the coupling caps and volume control. Should be interesting.
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