[shinew]

I've never tried using 2 BUF634s, but I think even 2 BUF634s without connecting the BW pin should be good enough. I just happened to have some chips to spare when I built it so I used 3 for each channel & another 3 for virtual ground. yea, serious over kill for ER-4S!

but hey, i didn't built this amp just for my Etys so it might be useful when I get other phones later.

To my ears, BUF634s running at high BW make little to no difference on my ER-4S. Perhaps each note is a bit more pronouced. Anyway, the difference so subtle that i'm not even sure if i really hear it or it's just my imaginatoin. I built a switch on my amp so that I can run it at low BW when I'm on the road & high BW at home(just because the specs look nicer that way

). You should consult PPL about this. From what I know, he's one of the 1st DIYers who started using BUF634 on Headwize.

 

[topher]

I follow what ppl says very closely. I also pay a
lot of attention when ever someone describes what
they hear when they build something.

Just because I can design a bunch of different
kinds of opamps doesn't mean I have a clue on what
they will sound like.

So I just try to help when I can, and watch for
any clues as to what may lead to improvements in
sound quality.

Thanks for the feedback. I think that external bandwidth switch is a great idea.

I have some AB switch stuff to build as soon as I get my bench up in the new room, and I think that will be one of them.

 

[Daniel Pumphrey]

With lots of years of using the Etymotic ER4 I also believe one 132 or 134 is more than enough power for these phones. Problems could be caused by using one 634 alone without any gain provided by an opamp before. All these concerns relate to the design of the circuit and not only how many 634's are used. It is very possible to build a great amp using one opamp and one buffer with more than enough power to drive almost any phone.
I personally would use the extra money for the 6 634's to buy the best passive parts and especially the input pot as these can make considerable improvements in the sound and noise. I recently realized the improvement which can be attained by using a higher quality pot, and have not even tried the really high quality parts available.
Has anyone tried the digital pot Apheared was working on months back before Headwise went down the first time?
It is quite possible that two to three buff634's could sound better, but it isn't necessary for the tiny ER4 phones and equates to a possible 75 v output with sufficient power supply. I would suspect other problems if one 634 isn't enough for this phone.
Dan

 

[Possum]

I gave one of the digital pots Apheared mentioned, the Dallas Semiconductor DS1802, a shot in my Szekeres amp. I'm not sure if it was my setup or if it was the pot, but I had to limit the input source voltage or I'd get severe clipping. I used a voltage regulator to supply the 5VDC to the chip, from the recommendation of someone here. But there were 2 problems that caused me to give up on this pot circuit I spent ~$25 on (since I somehow blew a chip, or maybe it wasn't blown... read on):

1. Interference from my internal power supply circuit (which only had a few filter and bypass capacitors and a LM350T voltage regulator, and an external regulated PSU that fed DC voltage to this circuit) would cause noise occasionally if something was slightly moved or jostled.

2. The pot didn't seem to "initialize" or reset properly about 70% of the time when the amp was first powered up for the day. Maybe after 30 minutes of a "warmup" time and some fooling with the pot, it would be initialized properly and have normal operation. If not working properly, it would control the volume of one channel or not work at all. Sometimes upon power-up, you could raise the volume to the max, but then you couldn't lower the volume, and the chip would be frozen on this max volume setting - then I'd usually have to wait the 20-30 minutes until something finally clicked and let the chip work.

So after these 2 annoying problems, I decided to scrap that $25 experiment and ended up using a $22 Alps blue pot that I bought from Angela.com with an order of other parts.

BTW, I'm very happy with these Alps blue's, and am also using one in my Apheared #42 amp.