So we need to "select" the Idss for the B1 buffer stage. So if we select two devices for each channel of the B1, should we select them to be similar Idss, if so, would not one say that we are "matching" the Idss of each device? Or could I "select" one at 7.6mA and "select" another at 8.9mA Idss and that would be OK? Because there is no "matching" required, then that would be fine, is that what you are saying?
Also, if I may ask another question, what is "Idss", current from drain to source, what is the extra "s" for, source grounded?
Ian.
DQ: I'm not an engineer, so I can't do the maths for you, but I "reckon" you should be alright to do that. The lightspeed is a tiny load, so represents a very small extra current draw on that winding. I have often used such transformers for say, 2 positive supplies, and each will have a different load. An example would be to supply the analogue and digital parts of a DAC separately.
In any case, what you are proposing, thats exactly what I will be doing with mine.
Ian, I believe what you are saying is correct - once the values are roughly the same, you should be ok - AFAIK, all you really need are all to be similar for the B1. On the other hand, while you don;t need to match at all for the shunt reg, I think it was designed for sk170 in the 7-10mA range, rather than lower than this. Having said all that, many people do use matched pairs (say a few percent) for the B1.
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I fired mine up last night and it works perfectly, no hum or buzz, just clean sounds. Need to do a few more bits of tidying up before bringing it into the main system.
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Salas: re the 10R rather than 68R - I have some 3W 10R here - would I get away with using those rather than the 5W you mentioned?
Fran
In any case, what you are proposing, thats exactly what I will be doing with mine.
Ian, I believe what you are saying is correct - once the values are roughly the same, you should be ok - AFAIK, all you really need are all to be similar for the B1. On the other hand, while you don;t need to match at all for the shunt reg, I think it was designed for sk170 in the 7-10mA range, rather than lower than this. Having said all that, many people do use matched pairs (say a few percent) for the B1.
******************************
I fired mine up last night and it works perfectly, no hum or buzz, just clean sounds. Need to do a few more bits of tidying up before bringing it into the main system.
**********************************************
Salas: re the 10R rather than 68R - I have some 3W 10R here - would I get away with using those rather than the 5W you mentioned?
Fran
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select Idss to be similar.
The B1 is designed to run the active device at Idss. That requires the CCS device to pass the same or similar Idss.
If you have a pair of 8.15mA and 8.23mA then that is a selected pair. they are within 1% Idss. You could use <2% tolerance Idss. I suspect you could even use <5% tolerance Idss, but I do not know which should be the higher and which should be lower. There are science reasons for NOT running the active device at well above it's Idss but some builders are reporting that they prefer the sound when the active device is running at >100% of Idss. I will ALWAYS run <=100% Idss. I will NOT try >100% Idss.
But, that selection MUST BE DONE at the SAME temperature. This must be checked when both jFETs are supplied and measured at the same time and they are thermally coupled together.
The B1 is designed to run the active device at Idss. That requires the CCS device to pass the same or similar Idss.
If you have a pair of 8.15mA and 8.23mA then that is a selected pair. they are within 1% Idss. You could use <2% tolerance Idss. I suspect you could even use <5% tolerance Idss, but I do not know which should be the higher and which should be lower. There are science reasons for NOT running the active device at well above it's Idss but some builders are reporting that they prefer the sound when the active device is running at >100% of Idss. I will ALWAYS run <=100% Idss. I will NOT try >100% Idss.
But, that selection MUST BE DONE at the SAME temperature. This must be checked when both jFETs are supplied and measured at the same time and they are thermally coupled together.
Thanks a lot guys.
Uriah, do you mean I should use one pair of bridges and one cap from the DCB1 PSU to feed both the LS's 7805 LDO as well as half of the DCB1? My intention was to use separate bridges + cap for the LS, not those in the DCB1. Your post answers this but my English is not good enough to be sure I got it well.
Yes, billyk, either sharing the transformer only or sharing both the transformer, 2 bridges and 1 cap. From Uriah I understand the second option is correct.
Uriah, do you mean I should use one pair of bridges and one cap from the DCB1 PSU to feed both the LS's 7805 LDO as well as half of the DCB1? My intention was to use separate bridges + cap for the LS, not those in the DCB1. Your post answers this but my English is not good enough to be sure I got it well.
Yes, billyk, either sharing the transformer only or sharing both the transformer, 2 bridges and 1 cap. From Uriah I understand the second option is correct.
I've spent some time tonight listening to my DCB1. This was a direct comparison to my regular B1, with LS. The DCB1 has an ebay stepped pot, 50k.
I don't want to comment too much on the sonics as really, my DCB1 is not yet finished. I have a LS ready to go into it, and there is also the matter of upping the current through the shunts to try out as well. Theres a few other finishing touches needed as well.
The long and the short of it though is that I'm a very happy camper. It seems more dynamic than the B1, and definitely seems to have more controled bass and kick. The presentation is different too, with vocals more forward than my regular B1. Theres one or two things I would like to sort out but then this is still a work in progress. It will be very interesting to see how it settles in over the next few days and weeks, but we are starting from a high point I reckon.
So, in short this is a great preamp!!
Again, thanks to Salas, CRT, Teabag and of course papa himself.
Fran
I don't want to comment too much on the sonics as really, my DCB1 is not yet finished. I have a LS ready to go into it, and there is also the matter of upping the current through the shunts to try out as well. Theres a few other finishing touches needed as well.
The long and the short of it though is that I'm a very happy camper. It seems more dynamic than the B1, and definitely seems to have more controled bass and kick. The presentation is different too, with vocals more forward than my regular B1. Theres one or two things I would like to sort out but then this is still a work in progress. It will be very interesting to see how it settles in over the next few days and weeks, but we are starting from a high point I reckon.
So, in short this is a great preamp!!
Again, thanks to Salas, CRT, Teabag and of course papa himself.
Fran
Cheers. Up your 220k across audio input to 560k if you are to use the 50k pot enough more. More resolution to come in a couple of days.
If your trafos won't get enough primary voltage any time soon, get a 2X15 100VA because at 200-250mA the current ones gonna duck more for secondary voltage. Constant current is demanding on the cores. Maybe go 8R2 2W directly for R1. 250mA is even better. There is a gm curve benefit for 9240's/240's around there. Mount the power resistor upright.
If your trafos won't get enough primary voltage any time soon, get a 2X15 100VA because at 200-250mA the current ones gonna duck more for secondary voltage. Constant current is demanding on the cores. Maybe go 8R2 2W directly for R1. 250mA is even better. There is a gm curve benefit for 9240's/240's around there. Mount the power resistor upright.
Thanks Salas,
in fact I might just do that soon, as that would be a more fair comparison then to the lightspeed. As it is, the stepped pot has to be underperforming. No changes though for another few days I think, let it settle a bit more. In case I wasn't clear in my post above, I am impressed!
Speaking of lightspeed, heres my one ready to go in:
in fact I might just do that soon, as that would be a more fair comparison then to the lightspeed. As it is, the stepped pot has to be underperforming. No changes though for another few days I think, let it settle a bit more. In case I wasn't clear in my post above, I am impressed!
Speaking of lightspeed, heres my one ready to go in:
Attachments
) ask here if having any questions.
Do you guys think an IEC inlet EMI filter is a worth while addition the the dcb1? or just a waste of $$ ?
Here's a couple I was looking at ;
Schaffner EMC - IEC Inlet filters
Here's a couple I was looking at ;
Schaffner EMC - IEC Inlet filters