inductor load?
Hey I've been following this thread.
The original circuit by Nelson Pass looks like typical tube self bias linestage. It came to my mind that maybe we can use inductor replacing 2.2K at the drain? I thought this way 12V SLA battery can be used, assuming DCR of inductor is lower than 2.2K and yet giving more voltage swing. SImply because I have some 12V battery and charger.
I think the possible distortion when turning up the volume pot is simply because the input signal voltage from CD player exceeds the source-gate voltage. In tube circuit the equivalent is cathode-grid bias, normally kept over 2.0V to take the typical CD player output.
Or am I totally minunderstood? Where can I buy 2SK170?
Cheers
Hey I've been following this thread.
The original circuit by Nelson Pass looks like typical tube self bias linestage. It came to my mind that maybe we can use inductor replacing 2.2K at the drain? I thought this way 12V SLA battery can be used, assuming DCR of inductor is lower than 2.2K and yet giving more voltage swing. SImply because I have some 12V battery and charger.
I think the possible distortion when turning up the volume pot is simply because the input signal voltage from CD player exceeds the source-gate voltage. In tube circuit the equivalent is cathode-grid bias, normally kept over 2.0V to take the typical CD player output.
Or am I totally minunderstood?
Where can I buy 2SK170?Cheers
Re: inductor load?
you understood correctly ;
yes - you can use choke load ,if you need drekload of gain
2SK170................dunno
Chul said:Hey I've been following this thread.
The original circuit by Nelson Pass looks like typical tube self bias linestage. It came to my mind that maybe we can use inductor replacing 2.2K at the drain? I thought this way 12V SLA battery can be used, assuming DCR of inductor is lower than 2.2K and yet giving more voltage swing. SImply because I have some 12V battery and charger.
I think the possible distortion when turning up the volume pot is simply because the input signal voltage from CD player exceeds the source-gate voltage. In tube circuit the equivalent is cathode-grid bias, normally kept over 2.0V to take the typical CD player output.
Or am I totally minunderstood?
Cheers
you understood correctly ;
yes - you can use choke load ,if you need drekload of gain
2SK170................dunno
Re: inductor load?
Yes, of course you can, but you are still accomplishing the same
sort of thing, but with more expensive hardware.
This is justified in the output stage of a power amplifier, but it
not usually economical with a line-level stage, as the inductor
must be quite large. Much easier to use a constant current
source for the same effect.
Or a resistor, if you don't need that much gain.
Chul said:
Yes, of course you can, but you are still accomplishing the same
sort of thing, but with more expensive hardware.
This is justified in the output stage of a power amplifier, but it
not usually economical with a line-level stage, as the inductor
must be quite large. Much easier to use a constant current
source for the same effect.
Or a resistor, if you don't need that much gain.
Vix said:
Nice job Vix, and the perfect box for the job
I am off to the supermarket to find a suitable cookiebox...mpmarino said:HeY! The freakin little thing works.
Sounds pretty good too!
Ya surprised?
The great thing about a simple circuit like this (except for the sound) is that more people are building it and actually succeeds. Here: http://www.tech-diy.com/smallsignal.htm
Steen
steenoe said:
Nice job Vix, and the perfect box for the job
Thanks! It is going a bit slow, I won't have time for this till Sunday...but then I hope I won't need more than two hours to finish it
You can find various nice and unusual boxes in the supermarket. It is also funny. When I was choosing mine, I was looking for the prettiest (Choky translation: Ugliest
) box, didn't care much about the content! O bit OT, this is some chipamp that I made while I was a student (Didn't know about Pass Labs then)...
Regards,
Vix
Attachments
Vix said:
Thanks! It is going a bit slow, I won't have time for this till Sunday...but then I hope I won't need more than two hours to finish it
You can find various nice and unusual boxes in the supermarket. It is also funny. When I was choosing mine, I was looking for the prettiest (Choky translation: Ugliest
O bit OT, this is some chipamp that I made while I was a student (Didn't know about Pass Labs then)...
Regards,
Vix
Two hours should do
Nice chipamp, does it have a sweet smell to it?Steen
Could you elaborate on how the source gate voltage is related to the power supply voltage (and gain if at all)?
I plan to use the Jfet BOZ as a frontend for an F4 and drive the whole thing with a behringer dcx2496 passively through a TVC. I may need very little gain since the ak4393 outputs 4.8V (and my speakers are 97db efficient) but the ak4393 is unlikely to be too happy driving the TVC nearly full open.
TIA
Giulio
Thank you Mr.Pass, Choky and Steeno 
Hi, Giulio I do not know how to 'quote' in this forum.
My assumtion was based on tube stage, with calculation that the current 7mA and the source resistor make the bias voltage like V=IR. 0.07V. With tube linestage they usually keep this around 2V or higher.
But I do not know the difference of tube and JFET.
If I think the 'tube way' the input volume pot here is rather a trim pot and we need to find the range that can work like normal attenuation volume. That's all I know but by properly dividing voltage this can be solved.
What H*LL I am building this one someday anyway.
BTW I also love TVC, I have one from Sowter. Normally I use 12AX7 full balanced linestage (transformer input and output) with F1.
Cheers
Hi, Giulio I do not know how to 'quote' in this forum.
My assumtion was based on tube stage, with calculation that the current 7mA and the source resistor make the bias voltage like V=IR. 0.07V. With tube linestage they usually keep this around 2V or higher.
But I do not know the difference of tube and JFET.
If I think the 'tube way' the input volume pot here is rather a trim pot and we need to find the range that can work like normal attenuation volume. That's all I know but by properly dividing voltage this can be solved.
What H*LL I am building this one someday anyway.
BTW I also love TVC, I have one from Sowter. Normally I use 12AX7 full balanced linestage (transformer input and output) with F1.
Cheers
steenoe said:
Ya surprised?
Steen
Actually Mr Steen
, yes I am surprised. Most of my escapades end in failure - mostly due to time constraints(read-lack of knowledge ). Your right tho, the simplicity is key.Ya know, I think this little circuit could be considered like a "Lego", a building block of something great.
Thanks Pap....well, I already had a great Papa - the name is already used for me. Thanks Mr Pass - and Mr. Mod
/ Manu / Steen
O.K. That is one way, other ways would employ a couple of BJTs or a BJT+LED, BJT+Zener Diode etc.,
I asked because some here have more experience knowing the characteristics, frequency response, noise figures and sonic artefacts of different types of CCS and I was wondering which of these would best suit the JFETBOZ.
I asked because some here have more experience knowing the characteristics, frequency response, noise figures and sonic artefacts of different types of CCS and I was wondering which of these would best suit the JFETBOZ.
Re: Re: Re:Constant Current Source
Maybe I am just being overcautious, but with that solution (which I agree with since it is both obvious and simple) shouldn't one take some care to either match the JFETs or otherwise make sure to use the one with lower IDSS for the CCS? (If they differ only a little in IDSS, I could imagine an argument for doing it the other way around, though).
Nelson Pass said:
How about another JFET with the Gate and Source tied together?
Maybe I am just being overcautious, but with that solution (which I agree with since it is both obvious and simple) shouldn't one take some care to either match the JFETs or otherwise make sure to use the one with lower IDSS for the CCS? (If they differ only a little in IDSS, I could imagine an argument for doing it the other way around, though).
Yes, adding a resistor is the standard way to lower the current. However, there is still the question of the relationship between CCS current and IDSS of the lower JFET. Inserting a resistor big enough to safely set the CCS current below IDSS (of the lower device) is a safe way, and would be along the line of what I suggested above. On the other hand, the further below IDSS we go, the lower the gm, so unless we take into account the characteristics of the particular JFET individual we use, this might be wasteful solution. Further, JFETs can usually take a slifght forward bias on the gate-channel junction, which is one possible way to push up the gm, hence my comment above that one might want to do it the other way around.
Anyway, the point of my post was twofold. On the one hand I wanted to alert builders that maybe they cannot just throw in two arbitrarily choosen JFET individuals and that it might be necessary to either match them or take their individual characteristics into account. On the other hand I was also curious to hear what Nelson had in mind since he didn't caution about this.
Anyway, the point of my post was twofold. On the one hand I wanted to alert builders that maybe they cannot just throw in two arbitrarily choosen JFET individuals and that it might be necessary to either match them or take their individual characteristics into account. On the other hand I was also curious to hear what Nelson had in mind since he didn't caution about this.