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Hifiman EF-5 headphone amplifier mods and rolls - Page 3

post #31 of 71
Thread Starter 
Quote:
Originally Posted by dpump View Post
 


Just some of my thoughts on the EF-5. I purchased mine 3-4 years ago. I'm guessing it's the first revision since my pcb doesn't have a cut out in the front where the volume control is. My pcb appears to have more parts on it than the one shown here. I tried to install an Alps Blue pot and even a smaller more standard size pot such as Radio Shack sells, but neither will fit due to the pcb coming all the way to the front of the cabinet. I have ordered a small Noble carbon pot to try but haven't received it yet. If you want to check your amp to see which pcb you have you can remove the four screws in the front panel and pull the front panel forward to see if your pcb has a cutout such as the amp shown here. The pot which came in my amp is a small Alps which I think is a plastic conductive model and doesn't have the clicks.

 

As far as changing the OP275 opamp, be aware that some other opamps may not be ideal in this amp (or any other amp). The 'audiophile' opamps all need some form of compensation to work in a specific circuit and just replacing an opamp with another opamp that isn't optimized can cause problems. I tried other opamps in my amp but they all ran hot temperature wise which means they may not be totally suitable for this circuit. If you try another opamp or dual opamps, be sure to check the top of the opamp with your finger to see if it is getting hot. Some heat is probably ok but if it is too hot to keep the tip of your finger on then I personlly wouln't leave it in. I have seen an opamp oscillate in a circuit (not this amp) and get red hot in a matter of seconds and it will burn up if the amp is left on. In other words, just replacing one opamp with an 'audiophile approved' opamp is not always a good thing. Since my amp is an older version it may not 'like' other opamps, so the newer version may be fine, but I would check just the same.

 

As far as tubes go, try a 12BH7 or an E80CC/6085. I personally like these better than the 12AU7. Just like opamps just swapping to a different tube number may mean the amp isn't truly optimized for that tube, but it seems to work fine in this amp and won't cause any problems in use. I agree this is a great amp and not as appreciated as it should have been. Head-Fi is often focused on the latest and the greatest at the expense of older amps that are as good or better than the current models. If you can buy an EF-5 used for $250-$300 I don't think you will regret it. I will try to take some pictures of my older version amp when I finish working on it so you can see the difference between mine and the newer version shown here.

Good write up and observation.  The cut out in the pcb of the later version seems to enable users to fit a bigger pot or originally the manufacturer wanted to use an alps pot or similar type as the space is just fit for it.

 

As to the opamp some of them have lower operating voltage thus will heat up or burnt if used in EF-5.  Therefore check datasheet on operating voltage before swap.  I agree that some opamps are less stable and oscillate by themselves if capacitance are not big enough.  Check the data sheet before swapping.  However the one I used is a very good opamp which is very stable and you may wish to try it out.


Edited by inter voice - 8/21/14 at 7:31am
post #32 of 71

the best opamp I have heard so far in the signal circuit was AD797 in analog stage of old arcam alpha 9 (based on dcs ring dac)

 

opa275 is another great opamp in ef-5 but like you wrote before - it all depends on the implementation and specific circuit, opa275+12au7 and mighty transistors seem like perfect combination for my ears

 

is your tube socket extra tight too ? It takes forever to pull it from the socket using minimal force to avoid breaking the glass

 

is your pcb moving a bit when you pulling the tube from the socket ? (saw it in a few ef-5)

 

despite a few flaws I like this amp the best to drive hifimans (he-4 after many auditions)

 

I am gonna have mine in a few days - waiting for newest possible revision from my dealer, I wonder whether there is still resistors ladder volume control or standard VR - I will let you know


Edited by magicman - 8/21/14 at 7:43am
post #33 of 71
Thread Starter 
Quote:
Originally Posted by magicman View Post
 

is your tube socket extra tight too ? It takes forever to pull it from the socket using minimal force to avoid breaking the glass

 

is your pcb moving a bit when you pulling the tube from the socket ? (saw it in a few ef-5)

 

I am gonna have mine in a few days - waiting for newest possible revision from my dealer, I wonder whether there is still resistors ladder volume control or standard VR - I will let you know

i).   Right the tube socket is tight but I can still manage to take it out without too much effort (don't forget to remove the two plastic plates before removing the tube, it makes the job much easier).

 

ii).  No, the pcb did not move when I pull out or insert the tube, though the board may flex up a small bit when pulled.

 

iii).  Actually the stock VR is of low quality and after rotating for some time carbon fines will deposit on the contact surface thus causing cracking noises when turning.  Actually the pot is NOT a resistor ladder volume (just a normal VR) but is designed in such a way that it stops at some pre-set positions using mechanical means.  I suggest you just change the pot to alps if possible.  


Edited by inter voice - 8/21/14 at 8:33am
post #34 of 71
Quote:
Originally Posted by inter voice View Post
 

i).   Right the tube socket is tight but I can still manage to take it out without too much effort (don't forget to remove the two plastic plates before removing the tube, it makes the job much easier).

 

ii).  No, the pcb did not move when I pull out or insert the tube, though the board may flex up a small bit when pulled.

 

iii).  Actually the stock VR is of low quality and after rotating for some time carbon fines will deposit on the contact surface thus causing cracking noises when turning.  Actually the pot is NOT a resistor ladder volume (just a normal VR) but is designed in such a way that it stops at some pre-set positions using mechanical means.  I suggest you just change the pot to alps if possible.  


iii) hahahahah omfg ... this is really pathetic, I had no idea, so what was the point for pre-set positions - just making it hard to find volume sweet spot + lack of ultra precise stepped attenuator (avoiding channel imbalance) - epic nonsense

 

ii) I must have some f*&^ed up piece in the past, I hope the newest revision will be flawless (from my experience I can tell that QC i very poor - I got this amp yesterday but my dealer after opening it to check it for me realised there were many scratches on the amp + some old revision from 2013, total crap + tube didn't have one of the gold pins - wtf is with their QC ?)

 

i) yeah I never did it and that may help a lot, thx

post #35 of 71
I'm glad I found this thread. I was having a hard time finding people who own this amp.

Anywho, I agree that the stepped attenuator isn't the best, but I prefer no channel imbalance over the limitations of the stock setup.

I rolled in a NOS 12FV7, and to my ears, it sounds the best compared to a RCA tube and the stock tube. MIT des heat up a bit more and causes the amp to hum a little, so I try not to listen to it for too long, but the sounds is pretty impressive!
post #36 of 71
Hi. Very nice mods here. I have a Philips Miniwatt (Holland) tube and im waiting for two OPA627 chips plus adaptor for my EF-5.

I dont have any DIY skills, so no chance i will play with capacitors or volume pot. I enjoy this amp with my HE-500, HE-4 and DT990 premiums.
post #37 of 71
Thread Starter 

Hifiman EF-5 is a great amp. having been overlooked by a lot of people including me not until I won the EF-5 and HE500 from a lucky draw.  The stock EF-5 is good and value for the money but with some simple mods it sounds even much better :D.

post #38 of 71
I'd like to, down the road, replace the opamps for a discrete option. It looks like an alternative case will be a must though...

Any suggestions on available options?
post #39 of 71
Thread Starter 
Quote:
Originally Posted by mrscotchguy View Post

I'd like to, down the road, replace the opamps for a discrete option. It looks like an alternative case will be a must though...

Any suggestions on available options?

May be you can try Burson discrete opamp and you may not need to change the case :D.  I used a pair of Burson opamp in my CDP which sound great when compared with the stock ones.

post #40 of 71
Quote:
Originally Posted by inter voice View Post

May be you can try Burson discrete opamp and you may not need to change the case biggrin.gif .  I used a pair of Burson opamp in my CDP which sound great when compared with the stock ones.

Not the one that like 3 inches tall? Right?
post #41 of 71
Thread Starter 
Quote:
Originally Posted by mrscotchguy View Post


Not the one that like 3 inches tall? Right?

I think it is about 2 inches tall and look like the following:

 

http://www.bursonaudio.com/creations/discrete-opamp/

 

You may stack up two IC sockets and the opamp can then be inserted without removing the casing.


Edited by inter voice - 8/28/14 at 4:45pm
post #42 of 71

lol - QC is indeed terrible, my 2nd ef-5 had issue with left channel (something wrong with tube or tube's socket because when I touched a bit tube there was the signal...)

 

but yesterday 3rd try - epic, flawless, newest revision ef-5, after 1 day of listening I am just speechless, comparing to emo or lyr this one chinese amp is total destruction of everything I have heard so far, can't stop surprising me, this amp is gonna stay with me forever, after many other routes now I am 100% sure (I had this amp in the past but was looking for other alternatives)

 

with he-4 there is such amazing depth, flesh, punch - all without losing clarity, grip and transients speed (I have never heard such combination to have it all in spades)

 

for me ef-5 has amazing low end (kick drum kicks like no other amp with he-4) and upper mids (rock guitars - handling metal/hard rock guitar distortion is like on real arena concert, piano) + ultra high resolution

 

keep on great thread, maybe in the future I'll try some other opamps, I tried many other tubes in the past, but in 12au7 family, stock tube is the best for my ears, there were always losing clarity and details having some more smoothnes in the sound so for me just no go ...

 

do you have schematics of the amp ? I would love to reverse-engineer it for the future when it's not available any more to design my own pcb with the rest of elements (voltage gain I guess 12au7 directly, then opa275 driving power output transistors stage ?)


Edited by magicman - 8/30/14 at 2:09am
post #43 of 71
Thread Starter 

You are right that the QC of Hifiman needs improvements.

 

As to the tube being used, I have tried a number of vintage tubes and eventually I settled down with RCA clear top 12AU7.  To my ears it is the best tube to be used in EF-5 and suits my taste most.

 

I have also tried getting hold of the circuit diagram of EF-5 but so far I cannot find anything on it :(. 

post #44 of 71
Quote:
Originally Posted by magicman View Post

lol - QC is indeed terrible, my 2nd ef-5 had issue with left channel (something wrong with tube or tube's socket because when I touched a bit tube there was the signal...)

but yesterday 3rd try - epic, flawless, newest revision ef-5, after 1 day of listening I am just speechless, comparing to emo or lyr this one chinese amp is total destruction of everything I have heard so far, can't stop surprising me, this amp is gonna stay with me forever, after many other routes now I am 100% sure (I had this amp in the past but was looking for other alternatives)

with he-4 there is such amazing depth, flesh, punch - all without losing clarity, grip and transients speed (I have never heard such combination to have it all in spades)

for me ef-5 has amazing low end (kick drum kicks like no other amp with he-4) and upper mids (rock guitars - handling metal/hard rock guitar distortion is like on real arena concert, piano) + ultra high resolution

keep on great thread, maybe in the future I'll try some other opamps, I tried many other tubes in the past, but in 12au7 family, stock tube is the best for my ears, there were always losing clarity and details having some more smoothnes in the sound so for me just no go ...

do you have schematics of the amp ? I would love to reverse-engineer it for the future when it's not available any more to design my own pcb with the rest of elements (voltage gain I guess 12au7 directly, then opa275 driving power output transistors stage ?)

I never quite got that from mine, but since I bout used, the stock tube has probably seen better days.

I pulled the front off and cleaned the stepped attenuator with de-oxyit to help smooth out some of the scratchiness between steps. It made a difference, but didn't clear it up.

At this point, I'm a bit leery about using the 12fv7 tube I it, but it sounds the best, so hopefully it won't kill the amp (or shorten its life).

That said, I'm thinking about getting a Psvane tube for my ef5... Anyone have any experience with these tubes?
post #45 of 71
Thread Starter 
Quote:
Originally Posted by mrscotchguy View Post

At this point, I'm a bit leery about using the 12fv7 tube I it, but it sounds the best, so hopefully it won't kill the amp (or shorten its life).
 

According to the data sheet of 12FV7 the heating element draws much more current than 12AU7 and if prolong used some of the electronic components of the EF-5 will be burnt out sooner or later. I won't take such risk and will stick to 12AU7 for peace of mind. Though 12BH7 draws less current than 12FV7 it still takes more current than 12AU7. 


Edited by inter voice - 8/30/14 at 9:37am
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