Hello,
I m first time writer here. I m planning to build a phono pre amp using the audio research PH3 schematic. However, I m having problem identifying what is the JFET Q1 and Q2 used in the first stage. It's called *6537* on the schematic.
This advantage of using JFET is to minimize the noise level.
I tried to search products in Fairchild, Toshiba, Vishay etc. and getting nowhere. The closest one I found from products sold in eBay is using Toshiba 2SK170 and I m not sure if this is suitable for this schematic.
You help is very much appreciated.
Attached schematic for your reference.
Regards,
Ken
Vancouver BC Canada🙂
I m first time writer here. I m planning to build a phono pre amp using the audio research PH3 schematic. However, I m having problem identifying what is the JFET Q1 and Q2 used in the first stage. It's called *6537* on the schematic.
This advantage of using JFET is to minimize the noise level.
I tried to search products in Fairchild, Toshiba, Vishay etc. and getting nowhere. The closest one I found from products sold in eBay is using Toshiba 2SK170 and I m not sure if this is suitable for this schematic.
You help is very much appreciated.
Attached schematic for your reference.
Regards,
Ken
Vancouver BC Canada🙂
Attachments
Those *6537* look like in house code numbers. Probably some standard one, hidden. R2 and R3 would contribute enough noise so to undermine any Japanese special fet choice. An uninformed guess would be something like J112 would work. But you need to ask someone who has been actually servicing ARC to really know.
I hate to be all sour and stuff, but the circuit looks kinda like a fustercluck to me. That there are two fets being run in parallel with strangulated drain current (they get a little over 1ma apiece when you count in the contribution of R11, R12, and R18 to the current through R3) tends to indicate that the chosen devices didn't have a lot of transconductance. PN4393s wouldn't work here as they would need a lot more negative gate voltage (read lots more voltage across R3) to hold them back at the operating currents chosen here. You could likely get one piece of selected 2SK170 BL to more or less work. Drain current should be somewhere between 2.3-2.7ma, depending on which of the schematic voltages you actually believe. You want the current to be on the low side of that range so you have some drain voltage fro the fet.
This circuit looks like it's set up for MM cartridges, so I'd be tempted to ditch the original input circuit and use a 2SK170 cascoded with a triode to get rid of the Miller capacitance. If you really as me though, I'd try something like SY's phono circuit without the input transformer first.
This circuit looks like it's set up for MM cartridges, so I'd be tempted to ditch the original input circuit and use a 2SK170 cascoded with a triode to get rid of the Miller capacitance. If you really as me though, I'd try something like SY's phono circuit without the input transformer first.
me , Sir , don't like ARC circs ;
had my share of copying them , when I was young and enthusiastic
had my share of copying them , when I was young and enthusiastic
Do you gents agree that something like J112 could fall into place in that circuit as it is? (I do find that CCT non purposeful enough too by the way).
yes ;
according to datasheets , both J112 and J113 will do ;
as I remember from various schematics - at ARC they were used to adjust resistor values to exact Jfet used in situ .
NB that I didn't play with J112/113
according to datasheets , both J112 and J113 will do ;
as I remember from various schematics - at ARC they were used to adjust resistor values to exact Jfet used in situ .
NB that I didn't play with J112/113
I took a look at the datasheet, and it looks like you could get the J113 to work. They're cheap enough to easily afford a pile for selection purposes (that is, if you want to bother with this circuit in the first place).
At least we answered the original question. I.e. What could that Jfet be or suggest something that works in that circuit as it is.
I have to say I am overwhelmed by all the inputs internationally.
After re thinking about it, I have cold feet to proceed with this schematic.
You are correct that it is weird that ARC would used resistors values such as
31.25K, 518.1K etc. It is impossible to get these values, and it is a pain to connect the resistors in series to come to those values.
But if my interest rekindles I will further seek your help.
Thank you, thank you to you all.
Regards,
Ken
Vancouver Canada
After re thinking about it, I have cold feet to proceed with this schematic.
You are correct that it is weird that ARC would used resistors values such as
31.25K, 518.1K etc. It is impossible to get these values, and it is a pain to connect the resistors in series to come to those values.
But if my interest rekindles I will further seek your help.
Thank you, thank you to you all.
Regards,
Ken
Vancouver Canada
You somewhat misread our intent, or at least mine. The misgivings were about the circuit topology, not its particular implementation (well, maybe that, too). I, for one, have no qualms about combinations of various 1% values to get an exact value for something like an RIAA network. That really wasn't the point. The point was that the overall circuit was kinda wonky, and that you might be better served by building a more recent and elegant circuit.
ARC uses special house numbers for parts that are selected and graded based on specific values. WHAT those values are is proprietary information. at a guess a 2SK170 would probably be a pretty good choice.
I have asked a guy who'd repaired lots of equipments including ARC's, and he said he didn't know what those JFET were. When JFET was broken, he just filed the application for the part to the distributor, and they would send the part to him.
Annoying....
Annoying....
I know this is an old thread, but It works well, but you will need to make a few adjustments in the feedback, mainly the 518.1k resistor needs to be in the 820k range, I haven’t found the exact value but it’s pretty close to that, it gives the proper boost it needs in the bass region. I ran simulations through B2 Spice.
Here’s the data
Attachments
...
You are correct that it is weird that ARC would used resistors values such as
31.25K, 518.1K etc. It is impossible to get these values, and it is a pain to connect the resistors in series to come to those values....
Regards,
Ken
Vancouver Canada[/QUOTE]
My guess is that R3, R5, R7, R11, R13, R18, and R20 are parallel combinations and R12 is parallel + series. But for R18, 171.4K is pretty hard to find. I'll start a separate thread on the hand-drawn vs. drafting department SP-10 phono stage...
You are correct that it is weird that ARC would used resistors values such as
31.25K, 518.1K etc. It is impossible to get these values, and it is a pain to connect the resistors in series to come to those values....
Regards,
Ken
Vancouver Canada[/QUOTE]
My guess is that R3, R5, R7, R11, R13, R18, and R20 are parallel combinations and R12 is parallel + series. But for R18, 171.4K is pretty hard to find. I'll start a separate thread on the hand-drawn vs. drafting department SP-10 phono stage...