Soon I will start building my bal Iron Pre.
I have two matched pairs of j74/2SK370 for one channel and two matched pairs of j74/LSK170 for the other channel.
Is the LSK170 usable without changing any other parts?
Is it a bad idea to have this jfet being different between two channels?
I have two matched pairs of j74/2SK370 for one channel and two matched pairs of j74/LSK170 for the other channel.
Is the LSK170 usable without changing any other parts?
Is it a bad idea to have this jfet being different between two channels?
if you got them as that from Store, just go for it
JFets are from Pa, for both batches of kits
JFets are from Pa, for both batches of kits
Just finished stuffing the boards. Still missing my volume pot and inputs haven't been connected. I dialed in 15+ and 15- with 0mv DC offset no problem. Hooked up the ribbon cables for the selector and the LED doesn't light up, measured 19 volts on both sides of all the resistors. Not sure if I reversed the cables or what I did.
How would I go about if I would like to reduce the gain on one of the balanced inputs? There is no way of reducing the dac's output. Would a voltage divider (say 6k8/3k3) work, assuming the dac's output can take this?
Looking good!
Just for my sanity and bad eyes, would you double check the orientation of your JFETs, please.
In particular, I am concerned with what I think I see for J3 (one of your 370s) on the top board.
Edited to add b/c of accidentally posting ... (not enough coffee) 🙂
- What resistors are you measuring 19V on both sides? Can you explain exactly where you have placed the probes, please.
- Did you make your 14-pin cables?
- I know it is already mounted, but could you take a quick picture of the exposed side of the twister board. From what little I can see, it looks correct, but it would be good to confirm.
Edited ... again... see schematic... I don't see solder or anything in place for J5. If you're using your own logic solution, it's not needed, but ... I don't think you are. 🙂 Ask if you need clarity.
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Must be age that I cannot find it but what is the (recommended) place to connect the power for relays and leds?
that one pic is not showing cables at all
check what IAIMH said
are you dealing strictly with Balanced source(s), or your'e using SE sources too?
everything is onboard, switcher LEDs are getting power through flat cable
in that case, just remove autoformer and short appropriate xformer pads, to have direct route from buffers to output pads
Forgive me jumping in the middle, but I believe Robin would like to reduce the gain for only one out of a possible five balanced sources, a DAC, and using digital attenuation is off the table.
then he is in problem, if plural (sources) is in the case
introducing any sort of additional resistive attenuating is simply against any premise of Iron Pre, standard resistive volume attenuator is already enough of compromise
of course, some trickery with additional relays ( actuated for one input only) and some work with exacto knife, to exclude autoformer from circuit for said input ....... that's possible
introducing any sort of additional resistive attenuating is simply against any premise of Iron Pre, standard resistive volume attenuator is already enough of compromise
of course, some trickery with additional relays ( actuated for one input only) and some work with exacto knife, to exclude autoformer from circuit for said input ....... that's possible
^ Agreed... That's why I didn't even remotely try to come up with a solution ... I leave the tough stuff to the mighty one. 🙂
@Robin De Wolf - Why is digital attenuation not an option for you? Did I misunderstand when you said below?
@Robin De Wolf - Why is digital attenuation not an option for you? Did I misunderstand when you said below?
Am I correct that you only want to have a relatively lower volume for this one source?
Well let me explain in a bit more detail. Say I want to use IP bal solely as buffer for single source. Having no volume pots whatsoever, and using the dac's digital attenuation.
Ideally I would like to have the buffer bring it in the right volume "range" as to not attenuate too much in digital domain.
I thought or wondered if a voltage divider would be a simple yet clean solution?
Ideally I would like to have the buffer bring it in the right volume "range" as to not attenuate too much in digital domain.
I thought or wondered if a voltage divider would be a simple yet clean solution?
then, simple as :
I believe I already covered exclusion of xformer with appropriate sketches , several pages back
I believe I already covered exclusion of xformer with appropriate sketches , several pages back
Yes IAIMH was right, thanks for catching that my J3 was flipped on the one board. I also missed installing the jumper at J5. Once I installed that jumper the relays and selector switch appear to be working properly. Just waiting for my 4 gang volume pot and the last pair of relays.
Thank you for the clarification, Robin. Apologies for my error. I thought you wanted to use more than one input/source and just have the lower gain for one of the inputs (the DAC).
Cheers!
Cheers!
Using a 10kohm volume pot, is it still suggested to change r27, r28 to 100k ohm instead of the 220k listed in the BOM? ZM any thoughts on what damage I did by having the sk370 backwards at j3. I tested it using the diode tester with my dmm and it appears to pass that test assuming I did it right.
either 100K or 220K
everything OK with 2SK370, it's symmetrical and gate is mid pin; just solder it properly
I was not clear😅 but the question still remains: is there another clean solution to lower the gain before the IP bal buffer. As ZM mentioned, skip autoformer and solder proper pads is 1:1. What if I would like to halve the dac's output before the buffer?
altering source signal yes = your problem - use resistor L cell -6db, -9db, -12db,whatever
removing autoformer on output leave you with 0db gain of Iron Pre
where you're going to mount physically that resistor L pad - your choice - ditto on XLR connector in Iron Pre or in source itself
practically entire issue is irrelevant to Iron Pre, except tossing Iron out - because you don't need gain nor you need SE/BAL conversion function
removing autoformer on output leave you with 0db gain of Iron Pre
where you're going to mount physically that resistor L pad - your choice - ditto on XLR connector in Iron Pre or in source itself
practically entire issue is irrelevant to Iron Pre, except tossing Iron out - because you don't need gain nor you need SE/BAL conversion function