Hello,
A closer look at the 2N5457’s and 2N5460’s from Jameco.
The 2N5457’s have a Synertek logo on them. These N JFET’s run about 30% below the minimum IDSS on the datasheet.
Synertek - Wikipedia
The Fairchild labeled 2N5460's test right in the middle of the datasheet.
The thing is, there are no matches to be found between these 2 piles of JFET’s.
Thanks DT
A closer look at the 2N5457’s and 2N5460’s from Jameco.
The 2N5457’s have a Synertek logo on them. These N JFET’s run about 30% below the minimum IDSS on the datasheet.
Synertek - Wikipedia
The Fairchild labeled 2N5460's test right in the middle of the datasheet.
The thing is, there are no matches to be found between these 2 piles of JFET’s.
Thanks DT
Attachments
Comment --- I have found that Fairchilds - real ones - are very good BUT can you get them? Some sources and maybe Jamco, buy from second sources. What i found was that particularly from the internet - eBay et al - they appear to have been sorted already and the ones which did not match dumped on the internet or else where cheap.
THx-RNMarsh
THx-RNMarsh
I tried one a few years back and didn't care for the sound at all.
It sounded too "dark" and "closed in" for my taste regardless of the power amplifier I used with it.
That's the main reason why I built one in the first place since I don't even own a pair of headphones.
I wound up purchasing a Schiit Magni 3 and using it as a preamp. IMHO, the Schiit, which is a CFA, sounds superior to Richard's amp.
Unfortunately, I wound up throwing my example in the trash since it was so disappointing as a preamplifier.
No disrespect to Mr. Marsh intended here. This is just my opinion and of course YMMV.
I tried one a few years back and didn't care for the sound at all.
It sounded too "dark" and "closed in" for my taste regardless of the power amplifier I used with it.
That's the main reason why I built one in the first place since I don't even own a pair of headphones.
I wound up purchasing a Schiit Magni 3 and using it as a preamp. IMHO, the Schiit, which is a CFA, sounds superior to Richard's amp.
Unfortunately, I wound up throwing my example in the trash since it was so disappointing as a preamplifier.
No disrespect to Mr. Marsh intended here. This is just my opinion and of course YMMV.
Thanks for sharing your experience. Some headphone amps double as preamps, but is not always the case. Did not know if it would work well, so I asked.
I built a MHA years ago and thought it worked extremely well with my Audeze LCD-3s. Went on to STAX and DIY Gilmore electrostatic amps. Kept the MHA but cannibalized the PS for another project. Now looking for a preamp and I think you’ve saved me from shelling out for a new PS.
Maybe I should build a new PS anyway and get that MHA back up and running as a designed Headphone Amp again...
Where can I get Fairchild Transistors
I have the a Marsh Headphone board but have not gotten the transistors which seem to difficult now to find known good one's as well as getting properly matched these transistors seem to be the most daunting parts in making this Amp perform at it's best .Anyone out there that can supply the optimal transistor's that will give the best performance from this design.I would willing within reason to pay for this solution.
I have the a Marsh Headphone board but have not gotten the transistors which seem to difficult now to find known good one's as well as getting properly matched these transistors seem to be the most daunting parts in making this Amp perform at it's best .Anyone out there that can supply the optimal transistor's that will give the best performance from this design.I would willing within reason to pay for this solution.
I am about to order components and start my build (after having the PCB in the draw for years).
Does anyone have an ltspice or kicad schematic and models that they can share? The default ltspice does not come with all of the required models.
Also, what are the 2 potentiometers adjusting? I ask as I am not sure what to set them to other than the % value as per schematic image that I have.
Thanks!
Does anyone have an ltspice or kicad schematic and models that they can share? The default ltspice does not come with all of the required models.
Also, what are the 2 potentiometers adjusting? I ask as I am not sure what to set them to other than the % value as per schematic image that I have.
Thanks!
There was only one potentiometer in the original article, then Dr. Marsh suggested an additional to trim the current sources. Start with both midway in their rotation and adjust for minimum DC offset AND THD%
.MODEL 2N5457 NJF(IS=1N VT0=-1.5 BETA=1.125M LAMBDA=2.3M CGD=4PF CGS=5PF)
.model 2N5460 PJF(Is=1.5p Alpha=1e-4 Vk=300 Vto=-3.4 Vtotc=-3m Beta=1.0m Lambda=10m Betatce=-.5 Rd=10 Rs=10 Cgs=5p Cgd=5p Kf=3e-17)
Thanks Jack
I've been reading through a bunch of the pages but wanted to get some clarification. Is sikahr 's power supply the best one to use? What are some other recommendations?
Also, any over current and over voltage protection recommendations? Or do people think they are not needed?
Thanks!
Marsh HPA draws a bit too much current to use Jan Didden's "Silent Switcher" -- you could use a TDK-Lambda DC-DC converter with two outputs. CC10-0512DF-E
My HPA is running with +/-12V derived with a conventional off-line power supply.
Not sure if this helps but I'll be trying some Cap Multipliers with a CRCRC rectified supply (pics below). The CapMX modules are cheap and easy to build and work very well. The development thread for the MX boards is below, SMD version appears in post #613 with schematic and Gerbers in post #621
Juma's Easy-Peasy Capacitance Multiplier
I have also used these Sulzer regulators in a previous build and they worked well -PCB for modified Sulzer regulator – Mini Version | ATL Audio Ltd.
As for protection, AMB do a neat PCB, if you contact Ti Kan directly he will quote cheaper shipping for small orders - The ε12 muting / protect circuit
