Fender Blues Jr IV Vs III – 7 Differences You Need To Know

Is the Fender Blues Jr IV worth an upgrades over the III? I would say probably not but if you were deciding between the two, the IV is definitely the winner.

The main difference between Fender Blues Junior iv vs iii is the significant jump in sound quality. The Fender Blues jr IV exhibit a stronger bass and a more responsive reverb than the III. It also differs in the quality of the speakers and the cabinet built quality.

These differences are listed below for more specific descriptions:

  1. Bass: IV has a stronger, rounder and clearer bass, especially when you used distortion. This is the main difference that is obvious on the first hearing. Fender has clearly made this change to answer critics who wasn’t happy with III’s bass handling.
  2. Reverb: IV has rearranged the reverb in a different part of the circuit, resulting in a more warn sounding reverb as III is a bit wash out
  3. Gain: IV has stronger and even louder gain. When you compare the two side by side, the IV sounds fuller
  4. Sound Brightness: III is well known for having a brighter sound and it is still valid, even against IV
  5. Pedals: The IV has made using pedals even more easy. This an effort to make the amp more versatile to keep up with the times.
  6. Cabinet: Suppose to be lighter but can’t really tell
  7. Speakers: IV uses the Celestion A-Type while III uses the “lighting bolt” speaker

For the more technical incline, here are some additional differences in terms of actual component change from III to IV:

  • C8 preamp caps is upgraded from 0.0022uF to 0.022uF
  • Bias is still fixed with the factory resistors being 33k for R51 (unchanged) and 27k for R52 (increased from 22k)
  • Reverb position has been changed
  • Things that remain unchanged includes: large filter cap, output transformer, C2 preamp caps, tone stack.

Despite the improvements in IV, there are still problems that exist

  • Volume still doubles when you dial it from 1 to 1.0001. This is a known problem since III but it looks like it wasn’t fixed in IV.
  • Build quality is still the same from something in this price range. The wood used is not the best and if you moved it around very frequently, you might need to resoldier certain items.
  • Cabinet design still lacks depth. It will be perfect if it was 1-2 inch deeper. That would help to remove the ‘boxy’ sound that some have complaint about.

Which Fender Blue Jr model is the best

The decision to go for Fender Blue Junior IV or III depends on the context that you are using it:

  • If you like brighter and woodier tone: go for III. I would say the older Fender supporters will likely prefer this tone rather than the IV’s darker tone.
  • For stage gigs: the III model has a brighter sound so you might want to choose this. However, both amps are actually sufficient powerful to handle small gigs and yet are not too loud for a small venue.
  • For versatility: the IV has made the usage of pedals more easy and integrated. If you are the type who likes to play with different tones and styles via the pedal, the IV definitely is the better choice.

Blues Junior Iv Humboldt edition vs regular

For IV, there is a regular version and the Humboldt edition. Their differences are:

  • Speakers: The Humboldt edition features the Hotrod Hempster speaker by Eminenc while the regular has the Celestion A speaker
  • Cabinet material: The Humboldt used cab plywood vs the particle used by the regular version
  • Price: The Humboldt edition is about $50 more than the regular version.

So, which version should you get?

My recommendation is the regular version because I can’t really tell much difference from the two, when I listen to their demos online.


Best setting for Fender Blue Jr

Be it for the III or IV, you need to adjust the right setting to get the best of these machines.

  • Dial the master volume all the way up
  • Control the volume via the volume dial
  • Eq to taste, especially you want more clean tone or natural guitar sound

Doing the above will give you so much better tone quality and even reduces some of the boxed sound that result from a shallow cabinet.

The common mistake made by most guys is to do the reverse. They dial the master really low and set the gains pretty high. What this does is to cause the amp to overdrive but at the same time, choking the amp due to low master.



The Fender Blues Jr IV is an upgrade of the more classic sounding III. Side by side, the overall sound from IV is definitely fuller, so I can say the sound improvement is significant.

However, there are also some fundamental changes which might divide the Fender crowd.

The Fender supporters who like the classic tone might still prefer III. For folks who like more bass and have more versatility in playing styles, the IV offers exactly that.

5 Comments Posted

  1. i have the blues jr. LTD in brown tolex, i installed a eminence wizard speaker, 58 oz. magnet, also installed standby switch, new jj tubes all around, dampening rings so tubes do not rattle, and a custom leather handle, my amp sounds awesome, not boxy at all, not like my blues deluxe, but both my fenders sound great, and i use many pedals, i think if tomorrow every one stopped making amps fender would always be in business.

    • And what if I’ve neither the know-how nor the money for such mods; would you still go with the JR 4 or something else (Vox, Supro, DSL20, etc)? Thanks

  2. I have a bj II, bought it used, had new JJ tubes, has the accutronix reverb, plywood for the baffle and bottom of amp, put a celestion super 65 speaker in that a friend gave me, this tightened the bottom end a little, a little more clarity overall. I think if I were to obsess more about the sound I might cut a baffle that centers the speaker in the cabinet(not sure why the offset) one wouldn’t build a speaker cabinet that way on purpose. I might try the frommel supreme kit since I’m not gigging and mainly place bass and drums. I think if I spent a lot of time thinking about the sound I would just save, sell something else if need be and get a a deluxe reverb

  3. The amount of opinions on this amp is staggering
    For an amp that was introduce in the mid 90’s it’s hard to fathom the abundant amount of tweaking and moding this amp has undergone. I am bewildered by the fact that a product costing as much as these would require so much after market attention. Why would you buy an amp and then swap out the apparently cheap speakers and tubes Up here in Canada the amp is costly and for almost $900 you’d think they could make it worth the money.

  4. So I’m suppose to base my decision on the fact you listened to both blues jr.on line and could not tell the difference in sound? Wow.

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