Hi,
I would like to ask a question about set R,recently I bought a board with 10ohm and 21.5ohm, may I ask how much current will set for MOSFET bias? Is 50W power transformer enough for it? Thanks.
I would like to ask a question about set R,recently I bought a board with 10ohm and 21.5ohm, may I ask how much current will set for MOSFET bias? Is 50W power transformer enough for it? Thanks.
50VA transformer is fine for the usual DCB1 settings. 15-0-15 VAC secondary.
Constant current bias of this PSU circuit is determined by voltage drop across the legs of the setting resistance divided by its Ohmic value. Usually 160-175mA for 10 Ohm. Exact voltage drop over the setting resistance depends on some active parts tolerances. Its the reflected difference of three red Leds added forward drop Vf minus the Mosfet Vgs developing between legs 1 and 3.
Constant current bias of this PSU circuit is determined by voltage drop across the legs of the setting resistance divided by its Ohmic value. Usually 160-175mA for 10 Ohm. Exact voltage drop over the setting resistance depends on some active parts tolerances. Its the reflected difference of three red Leds added forward drop Vf minus the Mosfet Vgs developing between legs 1 and 3.
Hi
Just finished my build of the Mezmerize
Tested good until I looked at DC offset
Power 9.76 and -9.78
Volt drop across 64R pair - 1.796 and 1.767
Offset Left 9.1mV and Right 3.3mV
The matched Jfets were 10.64mA, 10.54mA, 10.72mA and 10.85mA shown as the order fitted Left to Right
Where do I go from here all looks good except the 9.1mV offset on the left channel .
When I built this I was lucky to get 200 red led's as specified in the BOM. I didn't do any measurements using them straight from the bag
Just finished my build of the Mezmerize
Tested good until I looked at DC offset
Power 9.76 and -9.78
Volt drop across 64R pair - 1.796 and 1.767
Offset Left 9.1mV and Right 3.3mV
The matched Jfets were 10.64mA, 10.54mA, 10.72mA and 10.85mA shown as the order fitted Left to Right
Where do I go from here all looks good except the 9.1mV offset on the left channel .
When I built this I was lucky to get 200 red led's as specified in the BOM. I didn't do any measurements using them straight from the bag
Your signal JFETs are not so close for IDSS, its normal they show some offset. Exchange their places in the 9.1mV offset pair to see if it will get better or worse.
You can even install female socket pins if you got any.
To can exchange JFETs freely now and in the future.
To can exchange JFETs freely now and in the future.
Hi,
Did as you suggested, swapped jfets over on the 9mv side and it went up to 12.3mv.
I have ordered a length of the sockets you suggested and will fit this and attempt to get both sides down to the 1 or 2mv area
Thanks for your help with this
Regards
Andy
Did as you suggested, swapped jfets over on the 9mv side and it went up to 12.3mv.
I have ordered a length of the sockets you suggested and will fit this and attempt to get both sides down to the 1 or 2mv area
Thanks for your help with this
Regards
Andy
No luck with that pair then. Try a closer matched IDSS pair if you can get one.
Less than 5mV offset is alright and 1-2mV is very good.
Less than 5mV offset is alright and 1-2mV is very good.
I am unable to source 2SK117BL / 2SK170BL / LSK170 in Europe.
I've found some retailers but none of them look trustworthy.
Has anyone recently bought these JFETS in Europe?
Is there an alternative for that trio to use in the PSU area? I already have a matched quad for signal path.
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Choosing a pot.
Would you recommend me getting a 20k ALPS pot or use a 100k TKD pot which I already have. I am aware that I will need to change the RGnd to 1M or so.
I am not sure of the higher impedance effect for the DAC/Phono stage. I keep my interconnects rather short, less than 50cm.
I've found some retailers but none of them look trustworthy.
Has anyone recently bought these JFETS in Europe?
Is there an alternative for that trio to use in the PSU area? I already have a matched quad for signal path.
---
Choosing a pot.
Would you recommend me getting a 20k ALPS pot or use a 100k TKD pot which I already have. I am aware that I will need to change the RGnd to 1M or so.
I am not sure of the higher impedance effect for the DAC/Phono stage. I keep my interconnects rather short, less than 50cm.
Can you solder SMD JFETs on mini-pcb adapters? If yes, get 2SK209-GR from Mouser. They are OK for the PSU section. Very consistent for IDSS from sample to sample also.
The TKD pot is subjectively superior to the ALPS value for value. 100k pot simply narrows the bandwidth vs 20k pot because of the preamp's input capacitance. Fortunately its an intrinsically wide bandwidth circuit because small JFET buffer and it will not overtly slow it down. Higher impedance is also more susceptible to interference.
In few words try your expensive TKD first and if you will feel the music's transients sound rounder than you like get a 20-25k pot of your preference.
Mouser No:
757-2SK209GRTE85LF
For adapter boards search:
SOT23-3 to DIP SIP3 Adapter
The TKD pot is subjectively superior to the ALPS value for value. 100k pot simply narrows the bandwidth vs 20k pot because of the preamp's input capacitance. Fortunately its an intrinsically wide bandwidth circuit because small JFET buffer and it will not overtly slow it down. Higher impedance is also more susceptible to interference.
In few words try your expensive TKD first and if you will feel the music's transients sound rounder than you like get a 20-25k pot of your preference.
Mouser No:
757-2SK209GRTE85LF
For adapter boards search:
SOT23-3 to DIP SIP3 Adapter
Welp, I will go through the list of friends from USA potentially visiting Europe in the upcoming months and can get me LSK170 rather than attempting to solder 2sk209 🙂
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If I need just 3 pairs of inputs, do I still have to solder in all the relays and diodes? I am aware that one can set a stopper on the selector to keep the required number of turns.
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None of the caps suggested on BOM are available on Mouser.
I have come up with these replacements. Do you think these are right matches? First DIY project, might be overthinking this a lot.
UFW1V472MHD - UFW1H472MRD Diameter is larger by 2mm. Might have to solder the legs and move the capacitors outside of the board like the mosfets. Or i might be able just to pull caps closer to the edge by a couple mms
UFG1V101MPM - UFG1H101MPM
EEU-FC1H101B - UFG1V101MPM
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If I need just 3 pairs of inputs, do I still have to solder in all the relays and diodes? I am aware that one can set a stopper on the selector to keep the required number of turns.
---
None of the caps suggested on BOM are available on Mouser.
I have come up with these replacements. Do you think these are right matches? First DIY project, might be overthinking this a lot.
UFW1V472MHD - UFW1H472MRD Diameter is larger by 2mm. Might have to solder the legs and move the capacitors outside of the board like the mosfets. Or i might be able just to pull caps closer to the edge by a couple mms
UFG1V101MPM - UFG1H101MPM
EEU-FC1H101B - UFG1V101MPM
You can solder exactly as many relays and diodes as many inputs you need.
1mm around excess I think it will fit.
Don't move capacitors away from the board. Just Keep them bit higher on the board if their bases would collide with some other nearby part's pin.
1mm around excess I think it will fit.
Don't move capacitors away from the board. Just Keep them bit higher on the board if their bases would collide with some other nearby part's pin.
That is correct. It is the board only. But there is a link to the BOM on the same page. You can buy the matched JFETS from the DIYAudio store but else will come from someplace like Mouser or DigiKey.
PM me with and address and I'll drop one in the mail - or try eBay.
I had to source mine from eBay and based on the fact that my voltage is as expected I believe they are legitimate.
I had to source mine from eBay and based on the fact that my voltage is as expected I believe they are legitimate.
Yes, no problem with using any BC5xx for NPN/PNP instead of 550/560 in this circuit.
BC559C is Mouser number 512-BC559CTA
I have genue matched Toshiba SK117GR for sale ( 2of them in paralel are slight better verson of SK170BL- less capacistance , slight lower impedance, and slight higher gain)