Allen Bassman Mod first impressions

Discussion in 'Amps and Cabs' started by fr8_trane, Oct 17, 2005.


  1. fr8_trane

    fr8_trane Member

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    I just got my David Allen modded SF head back last Friday. I sent it out the previous Friday so the turnaround time is amazing. It cost me $330 for the basic mod, mid boost on the normal channel, new filter caps, 2 TAD 6l6’s, a 12at7, and shipping. He also did a few extra things to clean up the amp free of charge. The work looks first rate and is done with total respect for the vintage aspect of the amp (he left all the blue mallory caps intact and all mods are reversible).

    OK… so what you really want to know is “how does it sound”?. Keeping in mind that I'm in the honeymoon phase and I haven't gigged it yet I would conservatively say that the Bass channel is...FANTASTIC! With the volume on 7 the thing growls like an old Marshall. In fact David told me that his circuit actually has MORE gain than an original plexi. It easily cops AC/DC gain and tones from humbuckers and a boost or OD pedal can put it into EVH land. I’d love to a/b this amp with the Fender Tweed Bassman or Marshall JTM-45 reissues. I have a feeling that it would easily hold its own. Both settings (tweed/plexi) are useful with the Tweed setting having a fuller bass and slightly more gain and the plexi having a more punchy, focused midrange tone. I like the tweed sound at lower volumes and the plexi setting when the amp is cranked (although the extra bass in tweed mode never really gets flabby like a fender can). The normal channel is a clone of the stock AA864 BF bassman normal channel. Its got the classic punchy attack, scooped midrange and chimey treble that we all know and love. The only thing I don’t like about it is that it seems VERY bass heavy (I have the bass on 1). I may modify the tone stack on this channel to reduce the low-end and have been in contact with David about this. The mid boost is a great feature that replaces the absolutely useless (IMO) bright switch. It increases the gain slightly, thickens the tone and cuts treble. All of this works wonders with the bridge pickup on my Tele and Strat although it can sound a bit dull on other pickup positions. All-in-all the amp now has a new lease on life. It sounds great, is way more versatile, and will now last another 30 years with only basic maintenance.:dude
     
  2. UconnJack

    UconnJack Member

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    Nice report! I have the same amp and am digging it. I can run my bass way up on both channels though. I'm running thru an avatar 2x12 (Governor & Wizard - 8 ohm). With an A/B switch, this amp covers alot of ground. I haven't been able to crank the Bass channel past 5 or so, it's way loud. Thinking about an attenuator.

    I will add that it really fits-in, in a band situation. I've been using it in a 2-guitar jam band, with my strat. Can get realy greasy!
    Cool amp for sure.
     
  3. fr8_trane

    fr8_trane Member

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    Oh its LOUD for sure. But I had to see what it could do cranked. I have an attenuator and honestly I don't see getting the bass channel past 5 for bar gigs even with the mini-mass. The cranked tones unfortunately are probably only for the studio, bigger stages or outdoor gigs. Are your cabs closed back? I am running thru a Marshall 4x10 and the bass on the normal channel is seems excessive. On the bass channel I run the bass at 4 for the plexi mode and 2 in tweed mode.
     
  4. Hand of Doom

    Hand of Doom Member

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    Have you linked the channels together?
     
  5. jzucker

    jzucker Supporting Member

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    What is the bassman mod?
     
  6. jzucker

    jzucker Supporting Member

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    Do you know if he uses the extra gain stage as a cathode follower? If so, that's a cool mod. I did that once on a bassman and it was awesome.
     
  7. fr8_trane

    fr8_trane Member

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    No but I don't expect it to sound very good as the two channels are out of phase because they don't have the same number of gain stages. The bass channel has 3 and the normal channel has two. Each gain stage inverts phase so you end up with a mismatch which will cause some nasty sounding (but possibly useful?) phase cancellation.

    I'm not sure. I can tell you (from posts by Mr. Allen on the Weber forums) that the bass channel tone stack is after the first gain stage like typical BF circuits not after the 2nd gain stage like real tweeds and plexis. However, I think he may use a 25k mid resistor to lower insertion loss and increase gain (i'm guessing here). The bass channel uses the first 2 12ax7's which means there are 4 available triodes. Only 3 of them are being used as gain stages which means one of them could indeed be used as a cathode follower. I'm not electrically savvy enough to know for certain but if you really want to know shoot Mr. Allen an email. He's a nice guy and certainly very knowledgable. All techno-babble aside the bass channel sounds sufficently gainy and Marshall-like to cure my gas for any other 50 watt NMV Marshall or clone AND I get a BF clean channel ta boot.
     
  8. Hand of Doom

    Hand of Doom Member

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    What are your settings? What cab/guitar?
     
  9. fr8_trane

    fr8_trane Member

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    Guitars are a 50's MIM tele, MIM strat, and a Yamaha AES620 (dual HB). The cab as I mentioned above is a marshall 4x10.

    Bass Channel settings
    vol: 3-7 (the amp starts to break up at 3 even with the tele's low output pickups and you can get a bluesy grind with humbuckers in tweed mode at the same setting. At 7 your on the "highway to hell" and Angus is riding shotgun. Kick in a boost or OD for a searing lead tone.)

    treble: 5-8 depending on guitar and/or attenuator.

    Bass: 4 in plexi mode. 2 in tweed mode

    Clean channel settings
    volume: 2-6. This channel has alot of headroom and does not breakup until 6-7 depending on the guitar.

    treble: 5-7

    bass:1
     
  10. Hand of Doom

    Hand of Doom Member

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    sorry, I didn't see that post. thanks.
     
  11. Hand of Doom

    Hand of Doom Member

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    The reason I ask is because I have the same mod. I was linking the channels and didn’t like the strange tone. The clean side is great. The drive side has a splattery drive that has a LOT of low end. I like to set mine at around 11 o’clock, the treb at 3 or 4 o’clock and the bass at 7ish. With the deep switch down I ad more bass and vol.

    And now I know not to link the channels…thanks.
     
  12. fr8_trane

    fr8_trane Member

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    Hmmm... I don't hear "splattery" drive. I would take "splattery" to mean uneven, harsh and unmusical. The drive channel on my amp sounds nothing like that. Its not smooth like a MESA or a Fuchs either. Its got more of that open british sound with alot of bite in the upper midrange. With the volume up and in tweed mode (deep switch up) there's a ton of bass but it isn't flabby. It almost makes my 4x10 sound like a 4x12. Plexi mode kills for high volume riffing because of the midrange emphasis and the rolled off bass. YMMV
     
  13. ChrisP

    ChrisP Member

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    if you haven't...email The Man.

    He is very good about customer support.
     
  14. Hand of Doom

    Hand of Doom Member

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    ^ thanks, I will.

    Well that is certainly not what I meant fr8_trane . I guess I am bad with tone terminology. To me, and it may just be my amp and the way I am using it, it has a…..fuzzy tone? I made a few clips of the tone a while back but lost all my files.

    :)
     
  15. twoheadedboy

    twoheadedboy Member

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    I believe I heard the clips of Sangre's Allen modded Bassman. I too can vouch for the splattery tone. It was really loose and unfocused. Maybe a variance in the output transformer or speakers was causing that.
     

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