lowest possible, if your sources are having enough cojones
25K is safe bet
shunt resistor from gate of JFet buffer is defining input impedance
keep it at least 10 times higher than value of volume pot
or even higher
no problem even with 470K .......... it's there practically just in case of pot wiper loosing contact, once in future
25K is safe bet
shunt resistor from gate of JFet buffer is defining input impedance
keep it at least 10 times higher than value of volume pot
or even higher
no problem even with 470K .......... it's there practically just in case of pot wiper loosing contact, once in future
Tomorrow my balanced Iron Pre chassis should be here, and I can start on that. To that end, I assume a reread of this thread and Iron pre build guide is in order.
I have built two Iron Pres, one was a beta build, second was with modushop chassis, twister and all. I sort of glossed over info on balanced versions.
Any suggestions to avoid pitfalls with this similar, but a touch different balanced Iron Pre? Looks pretty straight forward.
Russellc
I have built two Iron Pres, one was a beta build, second was with modushop chassis, twister and all. I sort of glossed over info on balanced versions.
Any suggestions to avoid pitfalls with this similar, but a touch different balanced Iron Pre? Looks pretty straight forward.
Russellc
Will do, looks straight forward enough. I am however, capable of anvil destruction using only rubber hammer....still can't believe I foolishly tore up xa 252.
^ You'll be totally fine. Biggest change is setting current through buffer (one more set of pots per board to fiddle and twiddle).
Other than that... build two boards and wire 'em up. 🙂 Enjoy!
Edited to add - OH! I can't remember what version you built previously - Don't forget the jumper (J1 or J5.... can't remember) if you're not using logic controls. That's the #1 issue I see with reports of "everything looks good, but I get no sound". 2nd to that is forgetting to install jumper caps after nulling offset. Don't mix up the TO-92s...
Other than that... build two boards and wire 'em up. 🙂 Enjoy!
Edited to add - OH! I can't remember what version you built previously - Don't forget the jumper (J1 or J5.... can't remember) if you're not using logic controls. That's the #1 issue I see with reports of "everything looks good, but I get no sound". 2nd to that is forgetting to install jumper caps after nulling offset. Don't mix up the TO-92s...
@ItsAllInMyHead is a force to be recconed with. As is ZM and many others here. So fear not 🙂.
If you are using modushops chassis I highly recommend thir perforated inner bottom plate as an add on. I found it fantastic to use for cable dressing and fastening of components.
If you are using modushops chassis I highly recommend thir perforated inner bottom plate as an add on. I found it fantastic to use for cable dressing and fastening of components.
Another Iron Pre is singing! Wow this is truly an awesome gift, huge shoutout and thank you to Zen Mod, ItsAllInMy Head, Mr Pass and all the helpful people on this forum! It is dead quiet, but the sound it produces is clean, detailed, and very engaging. I am somewhat new to diy audio, the build guide and the threads were extremely helpful. I learned a lot on this build, a lot of firsts for me.
Thank again for this wonderful gift!
Thank again for this wonderful gift!
Attachments
Not a kit, but I can't help but share me enthusiasm for this wonderful preamp.
Built from earlier boards from Jim. Cutting and welding involved of a clapped out crest power amp chassis. AC routed through 12 gage square tube. That's what I had.... Ultra isolated power supply with lots of steel. Hifi collective shunt attenuator really was an incredible shift in SQ. Uncanny. Aside from iron, is there a better circuit to attenuate? 2 resistors. Well 4 total bal. Zfoils in the right places. Perfect.
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Built from earlier boards from Jim. Cutting and welding involved of a clapped out crest power amp chassis. AC routed through 12 gage square tube. That's what I had.... Ultra isolated power supply with lots of steel. Hifi collective shunt attenuator really was an incredible shift in SQ. Uncanny. Aside from iron, is there a better circuit to attenuate? 2 resistors. Well 4 total bal. Zfoils in the right places. Perfect.
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Here's mine. This was really fun to build. Sounds great.... dead quiet. Thanks to everyone on this thread for the tips and entertainment.
I completed my boards and was toning things out before firing up the Iron Pre for the first time when I noticed both of the Out pads, plus and minus, are going to ground. This is the situation on both of my boards, jumpers on and jumpers off. I am not finding any solder bridges or misplaced parts on my boards. I can’t tell from the schematic or from the “eagle” board traces pict if this is the normal situation when the boards are powered off.
BTW, I noticed a lot of builders leaving the snubbers out on these later boards. I Quasimodo’d my Antek AN0218 with the standard C values and found R to be 34.5 ohms.
Thanks in advance for any guidance provided.
-Glen
BTW, I noticed a lot of builders leaving the snubbers out on these later boards. I Quasimodo’d my Antek AN0218 with the standard C values and found R to be 34.5 ohms.
Thanks in advance for any guidance provided.
-Glen
Hi Glen -
When you're measuring ... exactly where are you measuring to and from?
Edited to add - ZM beat me to it... LOL!
When you're measuring ... exactly where are you measuring to and from?
Edited to add - ZM beat me to it... LOL!