[till]

Whoops! No, the jacks are not isolated. I have to admit that I totally forgot about the ground channel. OK, I guess I'll look for new jacks... thank you for the hint, MisterX!

 

[en480c4]

A little different than a lot of the builds in this thread, but here are the DIY woody cups I made for my HF-1's.

I turned a 4x4 section of Mahogany on a lathe into these:

They came out great, and initial sonic impressions are very positive. I'll keep the thread in the Headphone Forum updated with back-to-back comparisons with stock HF-1's.

 

[jerb]

did you turn those on a lathe? I was going to try making some out of a chunk of bloodwood/paudak I have sitting in the garage but I havent gotten around to it yet.

 

[en480c4]

Yup, a lathe it was. It went really well for my first woodworking project like this. It was definitely time well spent.

 

[doobooloo]

Very nice lathe job!

Do you hear any increased bass extension or upper midrange resonance from the longer chamber? I ask because I remember those two to be what were so staggeringly different about the MS-Pros compared to the "regular sized" Grados...

 

[en480c4]

I would have to say there is an increase in bass extension. The treble seems to have smoothed out a bit, too, but without a loss in detail. I haven't noticed any change in the mids, but I'm going to be doing a direct comparison to the stock HF-1 soon and will let you know.

[edit]

From my thread in the Headphone Forum:
Quote:

The sound of the woodied HF-1's is definitely different than the stock ones. I had a chance to sit down with Nate's stock HF-1's and my modded ones. There's definitely more bass extension and seems to be more bass detail as well. The treble has smoothed out considerably, and while they definitely don't have any less detail, there seems to be a little less treble "sparkle." They are definitely a little easier to listen to. And the mid-range is fuller with more body. I find the biggest difference in male and female vocals, and thick walls of heavy, distorted guitar. So I would have to say I'm very pleased with the changes made.

So

sums things up pretty well!

[/edit]

 

[ryanjun]

i've built a PPA with a diamond buffer module plus bass extension and gain switches.. the buffer module is basically Walt Jung's discrete buffer circuit. the output stage is pretty much stacked - 6 rows of BC327/337 transistors each channel - full A class operation even with low impedence cans.

unlike the original PPA, it's got no ground channel b/c it's powered from external discrete dual pwr supply unit(semi-Kubota ps). i think this can drive some efficient speaker units, but i haven't tried yet.

 

[Banfi T.]

Nice work!

(Those BJTs wouldn't survive the current demand (and the resulting heat dissipation) of a speaker, so do not try that configuration...)

 

[ryanjun]

Quote:

Originally Posted by Banfi T. (Those BJTs wouldn't survive the current demand (and the resulting heat dissipation) of a speaker, so do not try that configuration...)

thanx for compliment as well as warning..

 

[boodi]

nice faceplate design .. congrats on the choice

does it make justice to the hungry k501 ?

 

[amb]

ryanjun, congratulations on a nice and professional looking amp. While you may have gotten your inspiration from a PPA, your amp is not built on a PPA pcb, nor does it have 3 channels which is an important defining characteristic for the PPA. You had not published a schematic so I don't know how else your amp deviates from that of a PPA, but from just those things alone I'd call it something else rather than a PPA.

 

[ryanjun]

Quote:

Originally Posted by boodi nice faceplate design .. congrats on the choice does it make justice to the hungry k501 ?

i've made several other amps w/Jung's discrete buffers and tried many kinds of TRs for output stages and various resistor values for biasing currents.. mje15030/mje150331 pair was among them.. and these can draw current up to about 1.2W(just on paper). the current spec of BC337 and BC327 is 800mA, so it's 4.8W total. (just on paper spec) the result i got is paralleling output trs gets more dynamics with K501 - i am not sure why; could be more A-class bias current or less impedence. with a decent powerful power supply(it's not a good idea to run this with batteries) i think this one pulls most of the potential K501's got. what i like the most is that it drives K501 right whatever the source is - portable, wall-wart CDP, or whatever.

Quote:

Originally Posted by amb ryanjun, congratulations on a nice and professional looking amp. While you may have gotten your inspiration from a PPA, your amp is not built on a PPA pcb, nor does it have 3 channels which is an important defining characteristic for the PPA. You had not published a schematic so I don't know how else your amp deviates from that of a PPA, but from just those things alone I'd call it something else rather than a PPA.

You're right. as i mentioned, it's pretty far from original in terms of pwr supply. unlike the original, this one has neither a virtual gnd circuit nor a gnd channel to isolate the power rails completely.

people in HAS, a Koream head-fi DIY forum, thought if the amp could be supplied from a dual supply, while the original gets powered from a single DC supply(STEPS), those components could be omitted. in fact, a discrete pwr supply has more performance in terms of ripple current than STEPS, which employs a regulator, and with a dual DC supply unit which has a FIRM ground, u don't need to add a gnd channel to stablize the gnd circuitry.

well, for these reason, when this first came out, members of HAS called it 'JPPA' b/c it was first revised by Jee. but now most people call this a revised PPA or just PPA b/c giving credits to the PPA team is more appropriate in this case. btw, i think the source of PCB has nothing to do with the identity of this amp, b/c PPA is an open scheme.

 

[amb]

Quote:

Originally Posted by ryanjun ... with a dual DC supply unit which has a FIRM ground, u don't need to add a gnd channel to stablize the gnd circuitry.

This is not the right place to discuss the technical merits, but suffice to say that I have done much exploration and testing in this area, and that "firm" ground you speak of in a dual supply is not as firm as you might think, when the headphone load return current is dumped into it.

 

[ryanjun]

Quote:

Originally Posted by amb This is not the right place to discuss the technical merits, but suffice to say that I have done much exploration and testing in this area, and that "firm" ground you speak of in a dual supply is not as firm as you might think, when the headphone load return current is dumped into it.

when ppl built this amp, it was portable in nature at the first place. i think wall-walt operation w/dual pwr supply can be different.. but as you said, this is not a right place.. so why not leave it controversial? all i was trying to do was to explain the reason i think this is a PPA, not something else. btw, i have a PPA with a gnd channel as well.

 

[Banfi T.]

Quote:

Originally Posted by amb This is not the right place to discuss the technical merits, but suffice to say that I have done much exploration and testing in this area, and that "firm" ground you speak of in a dual supply is not as firm as you might think, when the headphone load return current is dumped into it.

I rarely discussed (or mentioned) merit of having a balanced drive. No common ground, no common return path. Very important indeed! (Think again dual mono with common ground...)