I'm running input transformers in my linestage for phase splitting (lundahl LL1676) which is Amorphous core without airgap.. and i started wonder if it would be perferable to still have input cap.. of course they can take a little DC - but how much is too much? also, i'm thinking during startup the offset can be quite high?
You have to connect the transformer and measure. Maybe the offset goes down when you load the output of the Paradise with a low impedance.
Looks good, and it looks like you did the grounding as I talked about in my huge ramblings...... Would be interested to know if you hear any hum!
Great build
alfred
How about powering Paradise and then plugging it in the linestage 10seconds later (the big hump is over then)? It is best anyway to keep it powered up all the time.
I run the transformer in 2:1 step-down so input impedance is approx 200K, so it's an easy load.
I started thinking the best way would maybe be building a output relay delay, and put it on a time i know the output voltage is stabilized.
I'll try shooting Lundahl an email asking this very question - because i'm shure interested to know. The only way otherwise for me to "skip" output cap would be to have balanced output, because i have one XLR input after the transformer.
I started thinking the best way would maybe be building a output relay delay, and put it on a time i know the output voltage is stabilized.
I'll try shooting Lundahl an email asking this very question - because i'm shure interested to know. The only way otherwise for me to "skip" output cap would be to have balanced output, because i have one XLR input after the transformer.
Concerning the offset you have to differentiate here between the AC and DC impedance of your transformer.
The transformers won't get damaged. It is a different question whether a few mV dc can get the cores closer to saturation, but i doubt it.
A 300 ohm load won't change the offset much if at all.
A 300 ohm load won't change the offset much if at all.
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Of course it's DC which is the concern but the question is how much is acceptable? To much can also get the transformer magnetized, and i have heard it is pretty hard to demagnetize it, but have no pratical experience of this..
Anyway, i'll just wait lundahl's answer, and when my unit is finished i'll see if there is any output delay needed during startup.
Anyway, i'll just wait lundahl's answer, and when my unit is finished i'll see if there is any output delay needed during startup.
@shoom;looking forward to your listening impressions.If its hum free I'd be interested as to how you wired as I still have some residual hum with mine which I am struggling to eliminate.
Hi Alfred
Yes read that really useful post and used along with Frans Diagram helped me find a place to start. I’ve seem others use different approaches to grounding but left myself room to change easily if I need to.
TBH I have high hopes for the DDRC.😉
I’m also hoping that Thermo coupling the front end will reduce DC offset still further but I’ll know that tomorrow.
I’ll let you know on the Hummmm once I’ve plugged in. I’ve used a similar scheme before and it worked well so fingers crossed.
Hi Marra
Yes well compare notes on that😎.
My Paradise Built
Here a few pictures of my own Paradise I just completed. The PCB were done months ago, but I was waiting for the proper enclosure. I found two nice metal cases that I reused and I designed custom front and back panels from Front Panel Express. The preamp is black, the pre-reg is silver. Here we go with the pre-regs, dual mono naturally 😉
Here a few pictures of my own Paradise I just completed. The PCB were done months ago, but I was waiting for the proper enclosure. I found two nice metal cases that I reused and I designed custom front and back panels from Front Panel Express. The preamp is black, the pre-reg is silver. Here we go with the pre-regs, dual mono naturally 😉
Attachments
Because my pre-reg supply voltage was a little on the high side, and that the preamp shunt regs were cooking at 50C, I installed a central CRC filter to lower the supply voltage and the noise at the same time. I did it using spare parts I had in stock, nothing fancy. The input voltage drops from 28.2Vdc (ripple 37mv) to 25.4Vdc (ripple 1.8mv) before the shunt reg adjusted at 18V on the preamp PCB. Noise is then lower than 1mv on my DVM. Not bad. I included a clos-up of my preamp PCB.
Attachments
Great work Algar
Your boards look fantastic as does the build.
Looks like you are cap coupling the output?
Your boards look fantastic as does the build.
Looks like you are cap coupling the output?
Hi all
Back for another update.
So with the thermo coupling coppers in place I now have 2.1mv DC offset on both channels with 10R Input load.
looking better all of the time in that front.
next step
Plug in my DC coupled Headphone amp/stunt headphones.🙂
And
One thing I would like to complain about is the hummmmm.😀🙄
Yup I can just about hear it with the volume control maxed so well done Frans and Alfred. That grounding scheme sure works well so far and I’ve no reason to doubt that it will work well in my main set up.
For DC couplers It’s worth noting that the DC offset does take 15-20 mins to stabilise so I’ll just be switching the Paradise on before the rest of the system (all DC coupled with servos in the pre and power with speaker protection).
I’m happy with the results so far and confident that I have almost reached paradise.
Now the switch on and off cycles for the next few days and then some music.
Hopefully some comments on sound next
Back for another update.
So with the thermo coupling coppers in place I now have 2.1mv DC offset on both channels with 10R Input load.
looking better all of the time in that front.
next step
Plug in my DC coupled Headphone amp/stunt headphones.🙂
And
One thing I would like to complain about is the hummmmm.😀🙄
Yup I can just about hear it with the volume control maxed so well done Frans and Alfred. That grounding scheme sure works well so far and I’ve no reason to doubt that it will work well in my main set up.
For DC couplers It’s worth noting that the DC offset does take 15-20 mins to stabilise so I’ll just be switching the Paradise on before the rest of the system (all DC coupled with servos in the pre and power with speaker protection).
I’m happy with the results so far and confident that I have almost reached paradise.
Now the switch on and off cycles for the next few days and then some music.
Hopefully some comments on sound next
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I can see that the Paradise progress since the last time I took a look. Do you where the thermal coupling is mentionned in the thread, as well as the new grounding scheme? I want to implement it into mine for sure.
The coupling caps are a temporary measure to let me test the preamp for a while. The little DC offset worry me a little on some of my amps.
I hope to reach such low DC offset as a few mv, but for now it is rather around 20-30mv. This is why I'm so interested in the latest improvement.
Thanks...
SB
The coupling caps are a temporary measure to let me test the preamp for a while. The little DC offset worry me a little on some of my amps.
I hope to reach such low DC offset as a few mv, but for now it is rather around 20-30mv. This is why I'm so interested in the latest improvement.
Thanks...
SB
Algar, great work.
shoom, the 2mV offset you get now is more or less the offset of the Opamp used as servo.
When you want even better you need to use something like an OPA627 that is specced down to 0.1mV.
shoom, the 2mV offset you get now is more or less the offset of the Opamp used as servo.
When you want even better you need to use something like an OPA627 that is specced down to 0.1mV.