Recently I have received a pair of HE-500 and Hifiman EF-5 headphone amplifier through a prize draw - lucky me  .
 
On first hearing I can say they are well matched gears BUT I think if the performance of the EF-5 can be improved further I am sure there should be a jump in the overall SQ.
 
Having gone through the web there had not much been said about how to mod EF-5 except mentioning some simple upgrades such as changing the tube with different maker and change an opamp with better ones.
 
I hope this thread can attract comments and share their experience to improve the performance of EF-5. The following picture shows what I have got from the prize draw. 
 

 
This is how the stock PCB looks:
 

 
 
As a start I have done the following simple mods:
 
Changed the stock Full Music 12AU7 tube with RCA Grey Plate 12AU7 tube; and
Changed the two opamps (OPA275 and NE5533) with LM4562NA and inserted 0.22uF MKP decoupling capacitors over legs 4 and 8 of the two opamps.
 
I noticed that after the above changes the music is more clear and dynamic to my ears.  Very noticeable improvements can be heard.
 
What I will do soon is to change the 6 pcs of power supply smoothing caps with Panasonic FR (low ESR) caps of 2200uF and 1000uF.  Unfortunately the available space inside the casing is too small else I can fit bigger caps inside. I will also change the 4 stock diode with schottky diodes. I hope there will be further improvements to the SQ the EF-5 produces.
 
I will take some photos when they are done.
 
If you have done some mods on EF-5 before please share your experience with us. 

OK, my caps have arrived and I spent some time today to change the 6 numbers of stock smoothing caps to Panasonic FR and 2 decoupling caps by Rubycon ZLH.  The picture shows the PCD with new caps on. You can also see the two opamps have also changed to LM4562NA with 0.22uF decoupling caps on the supply.  I have also changed the stock diodes to Schottky diodes with faster response.

 

 
I have also cut short the low voltage AC power lead to ensure better current flow.  The stock fuse is changed to audiophile quality silver fuse.  The following picture shows the backside of EF-5. You can also see the two damping rings in red fitted onto the 12AU7 vacuum tube.
 

 
 

After all the above mods there is no change in the appearance of EF-5. See the following picture.

 
Due to space constraints I am unable to carry out further mods but I have just ordered one SYLVANIA 6189W to replace the RCA 12AU7 (Grey Plate) that I am now using.
 
As to the sound, on first hearing my impression is that the EF-5 is now more clean, punchy, bass is extended and tighter as well as with better soundstaging and musical separations.  Overall the music is very smooth while the high frequencies are non-fatiguing. 
 
What I will do now is to burn in the EF-5 and the HE-500 for 100hrs and after that I will carry out a review on this combination and compared it with my other headphone amplifiers as well as HD-800 and LCD-X.
 

Awesome mods mate, glad you are enjoying it.

Oh, I forgot to mention the prize was given out by Frank of Toxic Cables.
 
Thank you Frank .

Now the modified EF-5 has been running in for about 40 hrs.  Thought the SQ of this EF-5 out performed the stock headphone amplifier yet I am exploring if further modification can be done.  Having looked into the PCB I found the +12V DC from the 7812 voltage regulator is suppying current to quite a number of circuits thus making the 7812 very warm.  I doubt this 7812 has sufficient capacity to ensure enough current supplying all the circuits as the max current output of the regulator is only 1A.  I understand that the source to the opamps should be of very low noise level and must be very stable to guarantee opamps' best performance. With that in mind I decided to change this 7812 with Fidelity Audio's +12V sPower.  This regulator can supply 5A current and with extremely low noise level though a bit expensive (costing about £50 for one). 
 
After changing the 7812 with a +12V sPower I immediately notice that the music is much much more smooth and clear. The soundstaging has improved, the LF and HF are more extended and tight without harsh feelings in the highs.  This should be the result of having a very stable source and with extremely low noise level.  I am really happy with the outcome. Unfortunately I did not take a photo before I boxed everything up and share it with readers here.  I think I have done all the possible mods to the EF-5.  Any further mods might need changing the casing to provide more space for the added electronic components.
 
I am still waiting for my NOS SYLVANIA 6189W which is one of the best tube available in the market.  I will further report the performance of my completed EF-5 after replacing the 12AU7 with the SYLVANIA.

My NOS SYLVANIA 6189W has arrived and I then replaced the RCA 12AU7 (Grey plate) in my EF-5 with this tube.  After heating it up for a few hours I then have an initial audition.
 
I can confirm that the SYLVANIA provides better overall SQ than the RCA.  The bass is puncher and the music is more smooth, in particular on the vocals.  Certainly this is the best replacement tube I have tried so far.
 
Later on I will carry out a detailed comparison between Audeze LCD-X, the Senn. HD800 and the Hifiman HE-500 using this EF-5 as headphone amplifier.
 
Well, the modification and rolling of my Hifiman EF-5 has come to a conclusion and thanks for the looking.

 
I have completed modifying my Hifiman EF-5 and details of my work can be found in my previous threads.
 
The performance of this modded EF-5 performs much better than the stock amplifier.  To give you an idea of its performance I can say it performs neck to neck with my Yulong A18 headphone amplifier.  As I love smooth and warm music I prefer using both of them marginally over my other Fidelity Audio HPA-200 SE which is an honest headphone amplifier with extremely good dynamics and no added coloration.
 
The Comparison
 
Now the modded Hifiman EF-5 has been run-in for about 80 hrs and I then compared its performance using my Audeze LCD-X (with Toxic cables Silver Widow); Senn. HD-800 (with Toxic Cables Scorpion) and Hifiman HE-500 (with Toxic Cables Black Widow).   The source used is my heavily modded Marantz CD63 KI (using top of the range components costing me more than £1,000) which performs better than any CDP of more than £3,500 including my previously owned Leema Antila IIs Eco.
 
I ran 30 sec. of track in repeated mode on each of the following pieces of music and compared the music using each of the above mentioned headphones in a number of runs.  To make the story short the following is my impression:
 

1. “The more I see you” by Nat King Cole (basically vocals)

LCD-X:  Nat King Cole’s voice is very real, clear and pleasant to hear.  I can feel his emotion. The background is very clean.
HD-800: The pitch of Nat’s vocal has raised by a small amount and making it less natural than LCD-X . Don’t make me wrong the difference can only be identified in head to head comparison otherwise it is un-noticeable.  HD-800 reveals more HFs but with lesser bass when compared with LCD-X.
HE-500: Bass is comparable to LCD-X but muddy.  The overall presentation is a bit dark and the background is less clean.  The soundstaging is much less than the other two CANs.
 
Verdict:  I prefer using LCD-X for vocals and follow by HD-800.  
 

1. Cino De Abril  (Tango music with lots of musical instruments, Latin America style music)

LCD-X: All musical instruments can be clearly heard, the guitars are clear and lively.  Good soundstaging. The music overall is very natural and pleasant to my ears.
HD-800: Excellent soundstaging and excellent musical instrument separation. Music is very clear and dynamic.  All minor details can be heard.
HE-500: The music is generally pleasant to listen but seems to be veiled and lacks clarity when compared with the other two CANs. Overall the music is less smooth.
 
Verdict:  Here I prefer HD-800 and follow by LCD-X.
 

1. The Great Gate at Kiew (Classical music with strong bass)

LCD-X: Bass has high impact, good soundstaging however musical instrument separation can be improved.
HD-800: Very good musical instrument separation; excellent soundstaging though with less bass impact than LCD-X.
HE-500: Bass has insufficient impact than LCD-X.  Average musical instrument separation and lacks soundstaging.  The overall presentation is dark, a bit veil and muddy.  The background of the music is not clear.
 
Verdict: I love the music from HD-800 more and then follow by LCD-X.
 

1. Sunshine in Taskkurgan (Performed using “Balakvoc Fredman” violin of 1730)

LCD-X: The music from the violin is very lively and is very real.  I can feel the emotions and feelings of the musician.  The sound from the violin is very sweet, smooth and is extremely pleasant to hear. The background is very clean.
HD-800:  The violin is not as sweet as LCD-X though not far off due to a bit increase in overall pitch.  If there is no head to head comparison with LCD-X I may not be able to spot the difference.
HE-500: The violin is not as lively and pleasant to hear. The presentation is a bit dull.
 
Verdict:  I love the presentation of the 1730 “Balakvoc Fredman” violin from LCD-X but HE-800 is not far off.
 
Conclusion
The result of the above comparison is just my impression on the performance of three different CANs using Hifiman EF-5 as their amplifier bearing in mind that the frequency response of the ears of individual is not of the same.  Different people will have their own impression and preferences on how a piece of music is being presented.
 
In conclusion it is hard to come to a very definite conclusion that LCD-X and HE-800 are better than HE-500 noting that the price tags of the three CANs are very different.  They are of different leagues.  From personal likings I will use LCD-X for jazz, blues and vocals while HD800 mostly on classical music in particular on orchestral music. Well the HE-500 will be for general leisure listening.  

edited...dont want to cause waves...my apologies

well done.

hifimanrookie said:

edited...dont want to cause waves...my apologies

well done.

Click to expand...

YOU don't want to cause waves..... (ROFL!!)
 
Nice Job Inter Voice! Thanks for the impressions!

longbowbbs said:

YOU don't want to cause waves.....  (ROFL!!)

Nice Job Inter Voice! Thanks for the impressions!

Click to expand...

x2

I have just ordered an Alps Blue Velvet 10K Dual Potentiometer to replace the stock VR for volume control.  According to my measurement the available space is just sufficient to accommodate it and I will post a photo after I have made the change.
 
Hope there is some improvement in SQ .  

Well, the Alps Blue Velvet Dual Potentiometer arrived last week and today I spent some time to complete the last modding work to the EF-5.
 
The Alps VR is much bigger than the stock VR and I need to carry out some modifications to the front panel in order to fix it in the right position.
 
The work is not difficult and EF-5 has just sufficient space to accommodate this bigger VR.  Please see the photo uploaded below for reference.
 

 
The casing of EF-5 has just sufficient space to accommodate the Alps VR.
 

The stock VR is small and of low quality.
 
Now with the new Potentiometer fitted the volume control is much more smooth and I can adjust the amplifier output at will.  You may wish to know that the stock VR is of stepped control and thus making it difficult to adjust the output level to suit your listening. This is certainly an advantage when the Potentionmeter is changed.
 
With the new Alps potentionmeter fitted I noticed the overall SQ is more smooth when compared with the stock VR.
 
Now I have done everything that I could to improve the performance of this Hifiman EF-5 and I don't think I can do anything much more without changing the casing.
 
I hope my experience is useful to those who also own one Hifiman-EF5.
 
I have one last remark about the performance of this modded Hifiman EF-5 with my headphones.  I have tried this EF-5 with Hifiman He-500; Senn HD-800 and Audeze LCD-X.  My conclusion is that EF-5 matches particularly well with Audeze LCD-X.  I love the music reproduced by EF-5 with LCD-X more than the other two. 

 
As can be seen from the back view of the EF-5 the 18V AC power is fed from the transformer in the lower unit into the main headphone amplifier (the upper unit) using a connector cable with two plugs at both ends.
To ensure the flow of current is not restricted, yesterday I removed the power supply plug to the amplifier unit and soldered it directly onto the PCB.  Only one connector plug remains (to enable the two separate units can be taken apart).  

Awesome upgrades mate, i have to think about wiring my power supply directly on the units, never thought of this before.

I have taken a photo to show the new back side view of the EF-5.  You can see there is only one plug on the connector cable.