This is the amp I just got in. It's from 2004, I think.
The chassis is well built, but the amp (which has crossfeed) is op-amp based.
Other than improving caps and such, any obvious (easy) improvements possible here?
https://web.archive.org/web/20050603012903/http://www.meier-audio.homepage.t-online.de/
https://web.archive.org/web/2006111...o.homepage.t-online.de/bilder/headamp1mk2.gif
https://web.archive.org/web/2006111...mepage.t-online.de/bilder/powersupply1mk2.gif
The chassis is well built, but the amp (which has crossfeed) is op-amp based.
Other than improving caps and such, any obvious (easy) improvements possible here?
https://web.archive.org/web/20050603012903/http://www.meier-audio.homepage.t-online.de/
https://web.archive.org/web/2006111...o.homepage.t-online.de/bilder/headamp1mk2.gif
https://web.archive.org/web/2006111...mepage.t-online.de/bilder/powersupply1mk2.gif
Very low esr paralleled caps next to lm6171 would be good for this beast.Now, if your headphones don't happen to be some exotic very low magneplanar spl audeze, lcd or hifiman the obvious improvement is to lower the supply to +-5...max 10v and remove the buf634 adding just 68 ohm output resistor.That will increase stability.LM6171 can deliver tons of currents on 100 ohms .68+32 =100 ohms.Lm6171 does very well with low supplies like +-5v.7805 and7905 are faster and lower noise regulators than 7815/7915.Most 32 ohms headphones need less than 1.5V rms output.My 250 ohms bayers need 3.5V.600 ohms need around 8V for maximum power so +-10V supply would be absolutely ok for thrm.The lower the supply voltage the lower thermal caused distortions and noise.
It's just my opinion to adjust an amplifier for your preffered headphones so that you get absolute performance .
If you have normal high spl 32...300 ohms headphones you can also leave the +-15v rails untouched and just introduce the 68 ohms resistor inside the feedback loop of lm6171 with better thermal regime, but some circuits don't like that irrespective of load and enough supply headroom.
It's just my opinion to adjust an amplifier for your preffered headphones so that you get absolute performance .
If you have normal high spl 32...300 ohms headphones you can also leave the +-15v rails untouched and just introduce the 68 ohms resistor inside the feedback loop of lm6171 with better thermal regime, but some circuits don't like that irrespective of load and enough supply headroom.
Last edited:
Thanks for your reply, dreamth!
I disagree somewhat that the 6171 can supply enough power. In the head amp community, there is strange but weirdly effective trend to make head amps as powerful as possible. headphones such as beyer dt880 really seem to come to life when carefully powered by a speaker amp.
Anyway, my actual Meier amp -- Corda Mk 2 -- is shown here:
https://web.archive.org/web/20050605010322/http://www.meier-audio.homepage.t-online.de/
Not sure what the exact schematic is but most Meier amps from that vintage are similar.
One strange thing is that for its std 0-ohm putput, I get quite a bit of hiss out of certain 'phone, like my AKG k 371 (50-ohm). So I have to use the Corda's 120-ohm output. The 120-ohm out may also sound better for most 'phones, overall. It certainly has less background hiss on most headphones I own which vary considerbaly in impedance (beyer dt880, Sennheiser 600, Philips Fidelio, etc).
I have modded it quite a bit over the years including opamp "bypass" and main PSU / regulator snubbers. By opamp bypass, I mean adding a additional electro cap + resistor across the opamp psu rails.
I think I replaced most orig Pana FC caps with Pana FM. Also might have upgraded the diodes, too.
https://web.archive.org/web/2006072...mepage.t-online.de/bilder/ha2mk2pcbtop480.jpg
https://web.archive.org/web/2006072...age.t-online.de/bilder/ha2mk2pcbbottom480.jpg
https://web.archive.org/web/2006072...omepage.t-online.de/bilder/ha2mk2front480.jpg
I disagree somewhat that the 6171 can supply enough power. In the head amp community, there is strange but weirdly effective trend to make head amps as powerful as possible. headphones such as beyer dt880 really seem to come to life when carefully powered by a speaker amp.
Anyway, my actual Meier amp -- Corda Mk 2 -- is shown here:
https://web.archive.org/web/20050605010322/http://www.meier-audio.homepage.t-online.de/
Not sure what the exact schematic is but most Meier amps from that vintage are similar.
One strange thing is that for its std 0-ohm putput, I get quite a bit of hiss out of certain 'phone, like my AKG k 371 (50-ohm). So I have to use the Corda's 120-ohm output. The 120-ohm out may also sound better for most 'phones, overall. It certainly has less background hiss on most headphones I own which vary considerbaly in impedance (beyer dt880, Sennheiser 600, Philips Fidelio, etc).
I have modded it quite a bit over the years including opamp "bypass" and main PSU / regulator snubbers. By opamp bypass, I mean adding a additional electro cap + resistor across the opamp psu rails.
I think I replaced most orig Pana FC caps with Pana FM. Also might have upgraded the diodes, too.
https://web.archive.org/web/2006072...mepage.t-online.de/bilder/ha2mk2pcbtop480.jpg
https://web.archive.org/web/2006072...age.t-online.de/bilder/ha2mk2pcbbottom480.jpg
https://web.archive.org/web/2006072...omepage.t-online.de/bilder/ha2mk2front480.jpg
Last edited:
I do have some simple thoughts - and without dissent from the changes made already - but given the abs-massive GBW of the active parts choices - my first suggestion, is really, really simple:
Take both sides of that PCB, and clean it thoroughly - with alcohol, and q-tips or sim, then de-ionised water, then alcohol again ( to dehydrate the PCB surfaces ) - until all the brown flux, and soldering gunge etc is gone, and everything squeaky-clean.
leyt it dry, thoroughly - then perhaps try the '0 ohm ' output again.
Seriously - Jan Meier knew what he was about; and small surface leakage paths given the opamp + buffer choices of parts involved, will really matter/might corrupt more than expected.
Let's just get that all scrubbed clean-as-new, and known-good first; then - perhaps - look where useful alteration to your needs, might be made.
: )
Take both sides of that PCB, and clean it thoroughly - with alcohol, and q-tips or sim, then de-ionised water, then alcohol again ( to dehydrate the PCB surfaces ) - until all the brown flux, and soldering gunge etc is gone, and everything squeaky-clean.
leyt it dry, thoroughly - then perhaps try the '0 ohm ' output again.
Seriously - Jan Meier knew what he was about; and small surface leakage paths given the opamp + buffer choices of parts involved, will really matter/might corrupt more than expected.
Let's just get that all scrubbed clean-as-new, and known-good first; then - perhaps - look where useful alteration to your needs, might be made.
: )
This amp doesn't seem to have the buffers and anyway the input impedance isn't so high to claim such sensitivity to flux conductivity.
The track clearances are really small - it can do no harm to make sure, given existing mods.
ATB.
ATB.
"abs-massive GBW" ??? Huh?
Anyway ... I did try to q-tip alch clean... but much of that resin is really caked in. The mods are in there delicately and I don't want to upset them with such trivial, mechanically-disruptive cleaning efforts. Doesn't look pretty ---but it's on the INSIDE.
What I may do is replace the electro caps with some higher quality ones. I may have wrong in my OP. Those might just be 2004 vintage Pana FC's on the "mains".