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can i change 1 or 2 tubes? that makes sense? or need change only 4 tubes?
Does the HP4 circuit use feedback?
There are 2 sets of driver tubes and output tubes: 2 x 2 = 4 total. The tube sets are matched for each channel (L,R). Therefore the minimum you can change out is 2 (matched).
I would imagine that the HP4 uses feedback (bias), since it is a Class A amp. Send an email to your distributor for forwarding, or else EAR inself (e.g..Tech support/maint.) if interested.
PS I still owe you a PM response. But basically the Neiro clone had too much of a noise floor (buzz) for headphone use and a direct comparison with the HP4.
An amplifier comparison using HiFiMAN HE-6:
HeadAmp GS-X mk2
Bakoon Products HPA-21
Woo Audio WA5
EAR Yoshino HP4
I assume Justin_Time is one of a select few who own and hence have the possibility to compare all these amplifiers.
Since there's seldom much writing about EAR Yoshino HP4 in general and especially comparisons with other amplifiers, I'd like to thank him for his contribution.
Quote (my bolds):
(My) Norwegian thread about the EAR Yoshino HP4 (Google Translate to English (with errors)) has a comprehensive link section in post #2. I haven't found a similar master post or thread on Head-Fi.org.
You will also find:
Observations and impressions including mine
Pictures including my own which has chrome knobs
Most pictures show the model with golden knobs. Here are some pictures of mine with chrome knobs:
As far as HP4 tube rolling goes, I am currently using a matched pair of Philips/Mullard England KLU ECC35 tubes for my inputs, and a matched pair of Philips/Mullard Holland Miniwatt ECC35 (Blackburn single D getter) tubes for my drivers.
One pair of matched input tubes (warm) and one pair of matched output tubes (hot). All four are 6SL7 tubes
You can replace one pair or both pairs.
The chrome knobs are classier looking than the gold knobs, which have more panache
Who bumped this thread after all this time. The EAR HP4 is only one of the finest headphone amps on the planet. IMHO, the HE-6 is more synergistic with a tube amp as opposed to SS but an HP4 can't drive them properly.
This so-called audiophile uses a BAT rated at 55W with all tubes NOS except for the Mig power tubes. The HE-6 plugs into the speaker terminals. Ahhhhh, sonic bliss!
Using the BAT sounds far superior than plugging the He-6 into a Bakoon AMP-11R and that amp actually has the current to drive the HE-6 properly.
Just to correct a possible misunderstanding in an earlier post. The HP-4 is a dedicated headphone amp, and cannot be used as a stand alone pre-amp. The output sockets on the back, balanced or single ended, are straight through and not affected by the HP-4 volume control.
I have been using mine daily for nearly ten years, and currently it is making listening to my Hugo better than digital files have any right to sound. Incomparably better than the Hugo headphone output.
Thought it was about time to resurrect this thread.
At the recent Fujiya AVIC Headphone Festival in Tokyo, I heard a rumour that Tim de Paravincini is thinking about designing a balanced output version of the HP4.
Does anybody have any information at all about this?
EAR Yoshino HP4 is the best headphone amp I ever heard. With Sennheiser HD800 it makes a dream combination.
Have not seen or heard anything about a balanced version yet.
If it comes, I wonder if they will offer an upgrade for the single ended, not sure how much modification the circuit would need. A lot I suspect.
I am currently very into listening to 78rpm records through the HP-4, and if you haven't discovered 78s yet, you'd be amazed how exciting they are.
This is what the man said once when I was first getting my HP4 and inquired:
As to balanced phones. Actually all headphones are basically balanced as the ear pieces are 2 terminal devices and don't know any different. There are usually 4 wires (2 per channel) that are wire at the Jack plug with 2 wires on the earthy or common sleeve of the Jack. The what some call balanced have to be connected to jack plug or adapters to plug in to the HP4. It also is basically balanced but share only the sleeve part of the Jack sockets. The comics have a lot to answer for this confusion.
Thank you Tim de Paravicini.