In the Blowtorch tread they talk about a JC-2 preamp knockoff for $120 plus shipping $ 30. Crazy.
Sorry for threadjack.
Jan
FYI---- later JC added fet follower. That would be the better circuit.... the JC2 could only drive high z loads (100K) with little current for driving long cables (keep to 1m).
-RNM
I notice this amp is very sensitive to changes. I changed out to some nos carbon a while back and it took a while to settle, changed out the 330ohm to Kiwame and it took a little time then to the dual power supply and the new ps needed time but now everything is burning in/settling and the sound is once again cohesive, powerful but realistic bass, with notes, not just bass, and plenty of depth and separation. Very nice.
Has anyone determined the actual output of the amp into different loads? If it has been posted then I either forgot or didn't see it.
Has anyone determined the actual output of the amp into different loads? If it has been posted then I either forgot or didn't see it.
Hello, Lots of good information in this thread 🙂
my Marsh headphone amplifier is under construction - i also integrated DC coupled B1 for volume control in one PCB with optional DC blocking capacitor.
one channel is already soldered , but when I create PCB I made a pretty big mistake - incorrect output transistor pinout(do not believe Google images -Check Data sheets). I use sk170/sj74 + BD outputs. I will re-done PCB again tonight from zero. At least PSU board working fine( 50VA 2x15Vac transformer + linear regulators).
regards,
Oskars
my Marsh headphone amplifier is under construction - i also integrated DC coupled B1 for volume control in one PCB with optional DC blocking capacitor.
one channel is already soldered , but when I create PCB I made a pretty big mistake - incorrect output transistor pinout(do not believe Google images -Check Data sheets). I use sk170/sj74 + BD outputs. I will re-done PCB again tonight from zero. At least PSU board working fine( 50VA 2x15Vac transformer + linear regulators).
regards,
Oskars
Attachments
ok one channel soldered:
seems that everything works: hum 0.05mV with test wiring.
bias - 100ma per channel.
DC offset less then 1mV
20Khz;
90Khz;
clipping @ 9Vrms @13.8V
one channel soldered
i will measure thd with sound-card tomorrow.
seems that everything works: hum 0.05mV with test wiring.
bias - 100ma per channel.
DC offset less then 1mV
20Khz;
90Khz;
clipping @ 9Vrms @13.8V
one channel soldered
i will measure thd with sound-card tomorrow.
Attachments
Yes sir! 😛
The last piece of the puzzle is creating a logic circuit controlled by the headphone jack's switch to switch the power to the CCS-fed shunt reg for the Marsh and also the preamp output to power the Marsh and mute the RCA out when headphones are plugged in.
I look forward to your impressions with the power supply you are using. What caps did you choose?
The PS caps are whatever came on it from China. The inputs are Nichicon, outputs Sanyo.
The Marsh amp has BG's on it.
craigtone,
in your preamp, what are you doing to get the heat out of the headphone amp transistors and the corresponding regulators?
mlloyd1
in your preamp, what are you doing to get the heat out of the headphone amp transistors and the corresponding regulators?
mlloyd1
I think he was referring to the actual devices, as in heat sinks to dissapate heat directily from them.
I wasn't going to use anything ... I'm pretty sure I read a heatsink wasn't needed?
I do have heatsinks en route for the Mesmerize and all of the regulators already have sinks.
I do have heatsinks en route for the Mesmerize and all of the regulators already have sinks.
jamato8 interpreted my question correctly.
actually, i think you WILL need heatsinks for output devices of the marsh headphone amp if you are biasing as in the LA article. MAYBE not if you use 2 diodes instead of three ... MAYBE ...
but why take chances with all that space?
🙂
mlloyd1
actually, i think you WILL need heatsinks for output devices of the marsh headphone amp if you are biasing as in the LA article. MAYBE not if you use 2 diodes instead of three ... MAYBE ...
but why take chances with all that space?
🙂
mlloyd1
I have mine biased with 2 diodes vs 3 and they most likely wouldn't need sinks but I use them anyway. Better safe than sorry as mlloyd1 says. Another builder of the amp took a temp of the output devices and felt that they don't need sinking but again, no harm with them when biased with 2 diodes. And if you bias with all three diodes, without question then need a good sink.
After a while you might want to look into a Goldpoint attenuator. I prefer it to DACT and they are less expensive. DACT actually copied Goldpoint originally and every time Goldpoint makes a change to improve the controls, DACT does the same. Anyway, the quality of sound improves in the mids and high freq with bass about the same as a good plastic or carbon control.
After a while you might want to look into a Goldpoint attenuator. I prefer it to DACT and they are less expensive. DACT actually copied Goldpoint originally and every time Goldpoint makes a change to improve the controls, DACT does the same. Anyway, the quality of sound improves in the mids and high freq with bass about the same as a good plastic or carbon control.
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Hmmm ... regretting my choice of PCB then as this layout is not conducive to heatsinks (devices too close together) ... I was under the impression they would run fine as-is.
Back to eBay for some cheap offshore extrusions! 😛
Back to eBay for some cheap offshore extrusions! 😛