Thank you for the help , I just received parts for the other board , I’ll try to rebuild that one and check what's going on.
When testing I’ve had some trouble with USB charger plugged in the same room, there was lot of interference on the scope .
I spoke to one of the guys at work and I might be able to borrow better probe later this week.
All the best
Just checked and you're 100% correct , when switched off all stays the same , thank you
Can you share some info on what and how to test apart from voltage test points. Both boards are ready , I have offset on the outputs around 4mV , all test points now similar , no oscillations but I would like to check bit more ie RIAA accuracy .
Heres my final run down, assuming your using Calvin's with 8.5r on the shunt and have psu rails at 25.5-26.5v
Plug your cart in and dial down the input offset as measured across your cart loading resistor. If you dont have a four figure DVM you'll need to adjust it in small increments, like 5 degrees at a time, leaving to settle for 30 seconds each time until you find the points where -0.1 and + 0.1mv first start showing on your meter, then set it at the mid point on the trim pot. This is easier than trying to shoot for 0.0mv offset directly if you dont have a super accurate DVM.
Doing this accurately will reduce the output offset considerably.
Then make a little cardboard house to go over your input transistors. Nothing fancy just a folded cardboard half box to stop air flow disturbing the input stage and any subsequent output offset adjustment.
With that done, then it's time to adjust offset on the Calvin's. Put your probes between in and out on the Calvin's and do the same adjustment as before, make sure you give it time to settle between each adjustment.
At the same time as doing this adjust the two trim pots under the Calvin's on the main board. Annoyingly adjusting these knocks your output offset, but it is possible to end up with bang on 18v on each rail from the shunt and 0.1mv or better offset between in and out on the Calvin's.
All the above assumes great matching on all your transistors on the main board and on the Calvin's. If you've matched them within a handful on hfe great, if you've curve traced them under operating conditions even better.
If you can hit 0.1mv offset with the lid off you're cooking on gas as the servo will easily take care of that, infact even if it didnt it's not worth worrying about.
Matching the rails exactly like this I can usually get the voltage at all test points to match +/- within 1mv or so on each board and across channels. Do that and you'll be gifted remarkable stereo imagery, stage depth and width. If its built correctly timbre and dynamics will take care of themselves.
Re riaa stage I just match all the caps to within few pf across both boards and I generally build with 0.1,% resistors anyway. I've never done an inverse riaa, I'm not bothered about chasing percentage points on riaa accuracy, itll be swamped by personal preference in cart loading anyway.
Plug your cart in and dial down the input offset as measured across your cart loading resistor. If you dont have a four figure DVM you'll need to adjust it in small increments, like 5 degrees at a time, leaving to settle for 30 seconds each time until you find the points where -0.1 and + 0.1mv first start showing on your meter, then set it at the mid point on the trim pot. This is easier than trying to shoot for 0.0mv offset directly if you dont have a super accurate DVM.
Doing this accurately will reduce the output offset considerably.
Then make a little cardboard house to go over your input transistors. Nothing fancy just a folded cardboard half box to stop air flow disturbing the input stage and any subsequent output offset adjustment.
With that done, then it's time to adjust offset on the Calvin's. Put your probes between in and out on the Calvin's and do the same adjustment as before, make sure you give it time to settle between each adjustment.
At the same time as doing this adjust the two trim pots under the Calvin's on the main board. Annoyingly adjusting these knocks your output offset, but it is possible to end up with bang on 18v on each rail from the shunt and 0.1mv or better offset between in and out on the Calvin's.
All the above assumes great matching on all your transistors on the main board and on the Calvin's. If you've matched them within a handful on hfe great, if you've curve traced them under operating conditions even better.
If you can hit 0.1mv offset with the lid off you're cooking on gas as the servo will easily take care of that, infact even if it didnt it's not worth worrying about.
Matching the rails exactly like this I can usually get the voltage at all test points to match +/- within 1mv or so on each board and across channels. Do that and you'll be gifted remarkable stereo imagery, stage depth and width. If its built correctly timbre and dynamics will take care of themselves.
Re riaa stage I just match all the caps to within few pf across both boards and I generally build with 0.1,% resistors anyway. I've never done an inverse riaa, I'm not bothered about chasing percentage points on riaa accuracy, itll be swamped by personal preference in cart loading anyway.
Thanks for this ,
looks like I'm almost there without little house over transistors (good idea that) ,I plug small resistor for final adjustment something like 10ohm as I'm bit worried about my Zyx 4D cartridge .
all this is DC conditions what about checking more real life conditions with signal generator ,
good board wasn't far out but was showing oscillations on the output and I'm bit worried that just voltmeter won't cut with such a complicated circuit .
looks like I'm almost there without little house over transistors (good idea that) ,I plug small resistor for final adjustment something like 10ohm as I'm bit worried about my Zyx 4D cartridge .
all this is DC conditions what about checking more real life conditions with signal generator ,
good board wasn't far out but was showing oscillations on the output and I'm bit worried that just voltmeter won't cut with such a complicated circuit .
To be fair the circuit is super simple (elegantly so), it's the psu that's the PITA. Once that's solid the actual amp stage is foolproof, assuming no bad parts.
If you feel the need run a few tones through it. 10hz to 100khz in decades and check them on a scope. Give it a 10k square wave for ***** and giggles. It's impossible to damage your cart with a Paradise even if its oscillating so no need to worry. Of course you could fry your pre though....
If you feel the need run a few tones through it. 10hz to 100khz in decades and check them on a scope. Give it a 10k square wave for ***** and giggles. It's impossible to damage your cart with a Paradise even if its oscillating so no need to worry. Of course you could fry your pre though....
Having a Polish Wife I have seen quite a lot of the country. We both much prefer Gdansk to Krakow. It's beautiful and interesting too but not completely overrun with tourists . PM me if you want to know more.
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Si,
Should the cart be connected for setting the input offset? I've always done the tweak with nothing connected.
With cartridge connected you won't see much as majority of MC cartridges have very low internal resistance , to zero offset on the input you need somehow higher sensing resistor . You might need to start with something like 10k as assembly guide states .
Last night I tested both boards with computer based signal generator , looks good , any specific tests to make ?
It seems reason for that varying voltage on 8R2 was that bad/underated 100uF capacitor , all resistors measure 1.25V .I've checked current draw on all rails and is quite consistent ~155mA .
Also I'm not sure how to test frequency response , RIAA accuracy , anyone?
While away I might start reading this thread from beginning I might find something I have missed first time .
I looked over you Flickr again and in some builds you seem to stuff 220R resistors into build-in buffer but you use Calvin buffers , any reason to do that ?
You might also need to check that build with LED's taken out of the regulator main board and fitted to what it seems to be bottom of casing, you use like few cm extension wires and I remember someone saying that it would affect HF performance of PSU , seems like you might need to use oscilloscope after all
Pete, The LEDs to the case bottom are on 5cm leads, taken from the middle LED of each string. I don't recall any speculation re effects on the psu bandwidth. Seeing as I couldn't measure a difference between two identically built boards, one with the lifted led and the other without I was happy to build them that way.
I stuff the 220r because the first half dozen I built didn't use Calvin buffers and I just got into the habit, they don't need removing as there's no transistors connecting them up, so nothing flowing through them. I just never got round to removing them from my Mouser BOM either.
Similar story with the 2sk170 and diode in the top current mirror, they're not needed in the circuit at all, but everyone still built their Paradises with those in place.
Chilly,
I always do my final set-up with the cart connected, just in case it has poorly matched coils.
I stuff the 220r because the first half dozen I built didn't use Calvin buffers and I just got into the habit, they don't need removing as there's no transistors connecting them up, so nothing flowing through them. I just never got round to removing them from my Mouser BOM either.
Similar story with the 2sk170 and diode in the top current mirror, they're not needed in the circuit at all, but everyone still built their Paradises with those in place.
Chilly,
I always do my final set-up with the cart connected, just in case it has poorly matched coils.
Post 274
Quote:
Originally Posted by brozatus View Post
As we have lots of leds on the pcb I ask if it
is allowed to use one of them as a power on
indicator on the front of the case, cabeled to
the front.
We have green leds, but for this one I will have
a red led.
Does this matter or bring any harm to the circuit?
Thanks,
Christoph
Quote:
Originally Posted by brozatus View Post
As we have lots of leds on the pcb I ask if it
is allowed to use one of them as a power on
indicator on the front of the case, cabeled to
the front.
We have green leds, but for this one I will have
a red led.
Does this matter or bring any harm to the circuit?
Thanks,
Christoph
But you can take a bit of light-conducting cable and bring the light to the front-panel.