Hi-Fi News HFN009 (Headcase) restoration.
Apr 22, 2006 17:46:30 GMT
Post by PinkFloyd on Apr 22, 2006 17:46:30 GMT
I picked this old Hi-Fi News HFN009 headphone amp up a few months ago from ebay and just thought I'd share the restoration in case anyone else who owns one wants to give it a boost.
Designed by Tim De Paravicini in 1987 the Headcase is one hell of a good sounding head amp and well worth the buying if you ever come across one. It's resolution and "grunt" are just jaw droppingly good (after recapping etc.) and this amp will easily give todays "beasts" one damned good run for their money!
OK. Onto the restoration. I wanted to keep it as close to the original as possible so basically just recapped it (fitted an extra 4400uF to the PSU section) fitted new resistors, transistors, Gold plated phono sockets and tarted up the bodywork a bit.
As you can see from the following pictures it was far from "discreet" looking when it first arrived.... in fact, it looked like a black coffin for a dead stoat!
The innards weren't much better either with dried out caps and pretty dire looking resistors:
First on the agenda was the MDF enclosure. I stripped off the coat of vinyl veneer and gave it a good sanding down:
Next I sized the enclosure up with 3 parts water to 1 part UPVA (10 coats!) Sanded the enclosure down and then spray painted with Grey paint.
Left the paint to settle for a few weeks and got on with the inside of the amp. I have since decided to remove the ALPS RK27 I fitted and have used the original type that came with the amp to keep it as original as possible (hand matched for perfect accuracy)
New NIC low ESR caps, new gold plated head socket, new diodes and Blue LED.
New resistors, transistors and ALPS RK27 pot (now replaced with one of the original types)
Overhead view
Whilst waiting for the paint to dry so I could give it a good buff up and mirror like finish I contacted the designer, Tim De Paravicini, and here's what he had to say:
Me: I recently bought a Hi-Fi news "headcase" HFN-009 headphone amplifier which I believe you designed?
Tim: Correct.
Me: I totally stripped the board and have replaced the carbon film resistors with metal film types and replaced the original capacitors with low ESR types, it sounds pretty damned good but I'm sure there's a bit more performance to be squeezed out of it and wonder if you, 20 years after designing it, have any little tips or tweaks up your sleeve which I could apply to the headcase? The volco positioned adjacent to the phono sockets is a very good idea and I wish more designers would implement this idea, it keeps the PSU separate from the amp proper and the connecting rod just adds a touch of peculiarity to the amp.
Tim: Not peculiar, Just very logical!
Me: Checked the DC offset at the output and it was pretty large (267mV & -78mV respectively) so I decided to fit 1000uF output caps in series with the output to null any offset present on the output. I also fitted an extra 4400uF capacitance to the PSU section which made a slight improvement especially to the dynamics and general "drive" of the amp.
Tim: As to offset, this is due to the opamp. Do not put output caps in, as this does effect the sound. 20 mV is more than good enough. See next comment.
Me: I'm not too sure if it's a good idea to remove the 120 ohm output resistors and replace them with zero ohm links, what do you think? I know 120 ohm was industry standard 20 years ago but many amp designers seems to think zero impedance is the best way to go, your comments appreciated.
Tim: The 120 Ohm is there for a good reason. This is so that virtually all dynamic headphones with impedances from 8 to 600 Ohm have similar volume levels and to prevent serious overdriving of low impedance types with serious hearing loss and damage to the drivers. Also the amplifier operating on about plus minus 10 volt (if memory serves me) does not have the current ability to drive full voltage into 8 Ohms of about 12 watts. The 120 Ohm limits the power to a few tens of milliwatts. Do you see my point?
Me: Could you possibly tell me what function the TL082 opamp undertakes and if there are any better modern chips I could use in its place? I have literally hundreds of assorted dual chips but won't roll them in just for the sake of it unless I'm doing the amp any justice.
Tim: The TL082 was cost effective, likewise the carbon film resistors. If the unit had been another £100, would you have purchased it? I doubt it. The OPA2134 would be best in current times. did not exist 20 years ago. This is history you know. Hindsight is wonderful. Once I have completed a design I move on to the next thing, In all my 40 plus years there are lots of product out there. Everybody thinks they know more than me but reinventing the wheel is tough. I don't have a copy of the circuit, sorry about that.
Sincerely yours, Tim de Paravicini.
Very nice reply
So, the paint has dried and here she is in her full glory (still looks like a coffin for a dead stoat but a grey one instead of a black one!)
The enclosure is fully shielded with aluminium foil.
A few pics of the inside:
Original type of potentiometer fitted in place of the RK27
One of the nicest (and beefiest) headamps I have heard and WELL worth picking up if you see one going cheap. Easy to work on and a sonic Gem.
More on this particular build @ www6.head-fi.org/forums/showthread.php?t=158126&highlight=ugliest+amp
Designed by Tim De Paravicini in 1987 the Headcase is one hell of a good sounding head amp and well worth the buying if you ever come across one. It's resolution and "grunt" are just jaw droppingly good (after recapping etc.) and this amp will easily give todays "beasts" one damned good run for their money!
OK. Onto the restoration. I wanted to keep it as close to the original as possible so basically just recapped it (fitted an extra 4400uF to the PSU section) fitted new resistors, transistors, Gold plated phono sockets and tarted up the bodywork a bit.
As you can see from the following pictures it was far from "discreet" looking when it first arrived.... in fact, it looked like a black coffin for a dead stoat!
The innards weren't much better either with dried out caps and pretty dire looking resistors:
First on the agenda was the MDF enclosure. I stripped off the coat of vinyl veneer and gave it a good sanding down:
Next I sized the enclosure up with 3 parts water to 1 part UPVA (10 coats!) Sanded the enclosure down and then spray painted with Grey paint.
Left the paint to settle for a few weeks and got on with the inside of the amp. I have since decided to remove the ALPS RK27 I fitted and have used the original type that came with the amp to keep it as original as possible (hand matched for perfect accuracy)
New NIC low ESR caps, new gold plated head socket, new diodes and Blue LED.
New resistors, transistors and ALPS RK27 pot (now replaced with one of the original types)
Overhead view
Whilst waiting for the paint to dry so I could give it a good buff up and mirror like finish I contacted the designer, Tim De Paravicini, and here's what he had to say:
Me: I recently bought a Hi-Fi news "headcase" HFN-009 headphone amplifier which I believe you designed?
Tim: Correct.
Me: I totally stripped the board and have replaced the carbon film resistors with metal film types and replaced the original capacitors with low ESR types, it sounds pretty damned good but I'm sure there's a bit more performance to be squeezed out of it and wonder if you, 20 years after designing it, have any little tips or tweaks up your sleeve which I could apply to the headcase? The volco positioned adjacent to the phono sockets is a very good idea and I wish more designers would implement this idea, it keeps the PSU separate from the amp proper and the connecting rod just adds a touch of peculiarity to the amp.
Tim: Not peculiar, Just very logical!
Me: Checked the DC offset at the output and it was pretty large (267mV & -78mV respectively) so I decided to fit 1000uF output caps in series with the output to null any offset present on the output. I also fitted an extra 4400uF capacitance to the PSU section which made a slight improvement especially to the dynamics and general "drive" of the amp.
Tim: As to offset, this is due to the opamp. Do not put output caps in, as this does effect the sound. 20 mV is more than good enough. See next comment.
Me: I'm not too sure if it's a good idea to remove the 120 ohm output resistors and replace them with zero ohm links, what do you think? I know 120 ohm was industry standard 20 years ago but many amp designers seems to think zero impedance is the best way to go, your comments appreciated.
Tim: The 120 Ohm is there for a good reason. This is so that virtually all dynamic headphones with impedances from 8 to 600 Ohm have similar volume levels and to prevent serious overdriving of low impedance types with serious hearing loss and damage to the drivers. Also the amplifier operating on about plus minus 10 volt (if memory serves me) does not have the current ability to drive full voltage into 8 Ohms of about 12 watts. The 120 Ohm limits the power to a few tens of milliwatts. Do you see my point?
Me: Could you possibly tell me what function the TL082 opamp undertakes and if there are any better modern chips I could use in its place? I have literally hundreds of assorted dual chips but won't roll them in just for the sake of it unless I'm doing the amp any justice.
Tim: The TL082 was cost effective, likewise the carbon film resistors. If the unit had been another £100, would you have purchased it? I doubt it. The OPA2134 would be best in current times. did not exist 20 years ago. This is history you know. Hindsight is wonderful. Once I have completed a design I move on to the next thing, In all my 40 plus years there are lots of product out there. Everybody thinks they know more than me but reinventing the wheel is tough. I don't have a copy of the circuit, sorry about that.
Sincerely yours, Tim de Paravicini.
Very nice reply
So, the paint has dried and here she is in her full glory (still looks like a coffin for a dead stoat but a grey one instead of a black one!)
The enclosure is fully shielded with aluminium foil.
A few pics of the inside:
Original type of potentiometer fitted in place of the RK27
One of the nicest (and beefiest) headamps I have heard and WELL worth picking up if you see one going cheap. Easy to work on and a sonic Gem.
More on this particular build @ www6.head-fi.org/forums/showthread.php?t=158126&highlight=ugliest+amp