Such a wonderful layout!! But only two jfets in the buffer? I flipped the board over expecting to find 10-15 small buggers. Oh well, I think these two should work well enough 😀
Finished up my stock Iron Pre this afternoon. Sounds really nice so far! Was a breeze to build and setup. I only ever use a single source at a time, and bypassed the relay's and twister for now. As stated in a previous post, I'm using a regular old pot for attenuation to start with, and then hope to swap in the Slegle $200 autoformer pair for attenuation soon. Shooting for an Iron Pumpkin Lite, if you will 🙂
Thanks to ItsAllInMyHead for the free prototype board! I used his BOM for anything I didn't have, and it worked perfectly. I say these are definitely ready for the store.
Last but not least, thanks to ZM for the superb design, layout, and constant help. You're the best!!
Thanks to ItsAllInMyHead for the free prototype board! I used his BOM for anything I didn't have, and it worked perfectly. I say these are definitely ready for the store.
Last but not least, thanks to ZM for the superb design, layout, and constant help. You're the best!!
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Thanks! It was fun doing something small and easy after tackling those high stress monoblocks 🙂 If I measured correctly, I should have room for the two autoformers...
After doing a bit of side-by-side listening with my DAC source, I'm noticing a fair amount of LF roll-off. Is that the norm for these little autoformers? I have a feeling its probably an issue with my build, but haven't spotted anything yet.
That doesn’t sound normal… There is no issues with LF performance on mine, and I have the same transformers.
I may need to double-check resistor values? I kinda feel like it may be an output impedance issue. I was also looking back to see if the Jensen required any clipping, bridging, etc
*Edit* Since I recovered these Jensen's from my F6 boards, also considering the fact that perhaps I boogered up a winding..
*Edit* Since I recovered these Jensen's from my F6 boards, also considering the fact that perhaps I boogered up a winding..
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How is the power transformer wired to the PCB? Do you have any connection to the CT?
How is the PCB grounded to signal ground?
Is the photo in post #1263 the final wiring?
How is the PCB grounded to signal ground?
Is the photo in post #1263 the final wiring?
Hey Jim!
Nothing is hooked up to CT thru holes. The transformer has two 18V secondaries, wired in series to get my 36V. Voltages in the reg are rock solid at +/- 15V. 1263 is the final wiring. Also included a better board shot here. Signal ground is coming from RCA in (confirmed isolated from chassis) to the input. PCB is grounded at a single star point in chassis (via onboard NTC). I confirmed continuity to chassis.
Confirmed correct resistor values in the buffer section.
Out of curiosity, I hooked a powered sub I have. Take a parallel set of RCAs from the pre out to the sub. Normally there’s no detectable change in sound, but this time I noticed what sounded like even more roll-off. The sub had a pretty high input impedance, so not sure how/why it had that impact, but perhaps greater minds will prevail.
Nothing is hooked up to CT thru holes. The transformer has two 18V secondaries, wired in series to get my 36V. Voltages in the reg are rock solid at +/- 15V. 1263 is the final wiring. Also included a better board shot here. Signal ground is coming from RCA in (confirmed isolated from chassis) to the input. PCB is grounded at a single star point in chassis (via onboard NTC). I confirmed continuity to chassis.
Confirmed correct resistor values in the buffer section.
Out of curiosity, I hooked a powered sub I have. Take a parallel set of RCAs from the pre out to the sub. Normally there’s no detectable change in sound, but this time I noticed what sounded like even more roll-off. The sub had a pretty high input impedance, so not sure how/why it had that impact, but perhaps greater minds will prevail.
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I do plan on measuring the output tomorrow to confirm the roll-off. It’s a very real possibility that’s it’s not actually an issue, and I’m just being overly sensitive to a gear change. In other words, may not be worth digging too far into troubleshooting yet. 🙂
Hey, problem solved! 6L6 noticed that I'd tied my two secondaries in series at the transformer, as opposed to running those legs to the CT spot for the series connection. I just made the switch and I've now got full range and full power. Thanks Jim!
I'm really glad that you didn't ( at least that we know of) made so substantial omission, while making monoblocks
say - same situation as going out on jogging, with laces on your joggies ........ unlaced
say - same situation as going out on jogging, with laces on your joggies ........ unlaced
Paaardon, Sirs... Is there a chance to have a Iron Pre beta board? I like very much my B1R2 and I think that would be perfect for my main system: it would be the
you're lucky that we have Hawk Eye Jim around ( thing of Trade, I believe)
I can bet that guiding wannabee Pilots is easier than coping with regular Greedy Boyz
