I've hit on an incredibly good sounding mod with the Yamaha HP-50A. ( an understatement )
If I can translate this across other orthos i'm going to need a few crates of tissues to absorb all my tears of blissful joy.
Usually mods on older stuff like this can produce decent results, sure, but nothing that is so far beyond stock and perfect as this.
I've gone through so many I can't keep track of the mod variations through the 50 series variants.
HP-50A are generally the medium levels of low end, HP-50 ( no letter designation , no headband padding ) being generally known as most overtly bassy within the beige lineup.
So with HP-50A in mind it is as follows.
- obvious re-cable and rewiring insides from mono to stereo single sided entry
- remove any of the stock white damping paper material both sides , or whatever is in there stock. Also remove stock foam. Work with bare drivers in bare housing only.
- rear of cups= metal cup hinge divots filled level with Newplast plasticine
- bond drivers to baffle rears using thin Dynamat strips pressed around edge circumferences of drivers ( careful to not reverse the orientation of backside and frontside of drivers, I did do that once yikes...)
- on driver rears, apply Sorbothane ( I used 1/10 inch 30D ) on outer driver areas surrounding the holes. 4 pieces, rounded edges to follow the outer curvatures and inner facing edges of the Sorb are straight edges.. all corners of the Sorbothane should be touching so that you end up with essentially a square free area inside the Sorb application ( think elongated lemon wedge shapes ).
- first damping square pad against the driver rears was HOBBS Rough Silk quilt batting. =THIS LAYER IS KEY . Rough Silk batting is generally not ideal as an immediate damping material as it is fairly porous and transparent, but is has to be doing a little bit I would think.This should be the same dimensions as the square area with the Sorbothane so it is right in the slot against the driver
- next over top of that is a square Arctic Cotton ( I think %100 cotton version ) or another %100 cotton AC quilt batting equivalent. Fits within the sorb area same as the Rough Silk layer. Make this the same square size as the Rough Silk.
- next a very thin disc of foam ( maybe 1-3mm thick ) with notches to fit around/poke through the 4 rear tiny cup riser posts, of course this rests in the cup rears.
- simply snap it all back together, no worries about sealing cup to baffle seam
- new pads here are AKG K518 aftermarket
This mod is so far beyond the earlier ones it's difficult to describe adequately. The key to it was adding in the first damping the driver sees as the Rough Silk batting, which allows the driver some more room for throw( less restriction ) before it encounters the Arctic Cotton layer.
The AC layer is just far enough away now that combined with the cup rear reflections and the AC's own inherent sonic abilities, things are perfectly detailed. No shrill top end but it's not lacking. AC is still in effect even with the added slight distance resulting from the Rough Silk layer.
Spaciousness has gone through the roof.
Separation is incredibly good.
Edges of notes are not blurred.
Distortions must be way down I can follow off tiny vocals and intricacies of note bodies
Nice full grumblings and organic aspects around note edges. Nothing thin. Gorgeous overtones .
Bass quantity up not overbearing.
Bass quality, deep tight, not much left of the slurry Yammie type bass.
=everything in this presentation is even across all volume ranges
^And to my ears it all adds up and integrates perfectly.
Add all that up and it's blissful yes.
Descriptions never do justice to actual experiences.
yeah and all that on what was otherwise an average "lowly" HP series can.
NO LONGER. So get that bias out of your minds for now. I know what you are thinking.
I'll see if can convince a well known friend to try this out, if they are willing to take the time to do so.
just to reinforce that i am not out of my mind.
* No alkeehol or other substances were involved in the making and determining the sound of said mod above.
** This may in fact be one of the much talked about "Desert Island" cans so often mentioned in ancient lore
