DIY Front End 2022

[MJPAudio]

Thoughts on running higher bias and drive a 300ohm headphone?

 

[Zen Mod]

yeah

evident shortage of headphone amps, of lately

 

[profiguy]

What a great contribution to the diy crowd! This may be possibly the new Swiss army knife line stage circuit I was looking for. Many thanks to you Mr Pass for this!

Hmmm, I have a stack of J113s. This looks like it could be a very useful balanced line converter, RIAA or output buffer for eq and active xover.

Any precautions one could take to safeguard the fets in case of input without B+ present? How close do the input fets need to be matched?

 

[BeardyWan]

Any issue in replacing R3 with a pot for us as a volume knob?

 

[Zen Mod]

if you need to ask, take care to observe presented schm as Black Box;

whatever you want to add, it goes either in front of Black Box, or after Black Box

so, in short - No.

Volume pot goes in front of Black Box
main reason - R1 is defining part of circuit, gain wise and impedance wise; R3 also being important ........... and - in case of resorting to single rail arrangement, there is substantial DC potential across R3

 

[BeardyWan]

OK thx

 

[lineup]

A little under 3 ma and 9 ma. Approximate, but not at all critical.

My simulation shows 6mA for Q4.
My J113 then is IDSS 18mA

 

[lineup]

Nelson Pass has got a point - J113 is plenty to buy.
It often comes down to if we can find and buy.
Otherwise not anybody can build.

 

[Nelson Pass]

I guess ~40k for R3/R4 for 4x gain?

I vote for that.

 

[Stanislav]

Do 2 x 2 x 2sk170 in parallel (2 on either side) on the differential input at front end.
Haven't personally played with 2sk145BL but I am confident the combination above should easily beat it.

2sk369 fits that bill handsomely.
the only problem for most folk might be it is even harder to find than 2sk170

 

[william2001]

I vote for that.

So for transformer drive... replace R5 with a jumper? (FE will be near load) Make C3 100X bigger? Crank the output current to ~15mA and don't put your tongue on Q4,Q5? (I have some little clip-on heatsinks)

 

[stonegreen]

How are the values of the resistors for the J113 determined?
=> R7, R8 matched to Vp of J113

Anyone have an explanation?

thanks
(If you don't ask, you remain stupid!)

 

[2 picoDumbs]

So for transformer drive... replace R5 with a jumper? (FE will be near load) Make C3 100X bigger? Crank the output current to ~15mA and don't put your tongue on Q4,Q5? (I have some little clip-on heatsinks)

Depending on voltage, 15mA could be a little excessive.
You might get away with it with heatsink attached.

 

[william2001]

Currently my rails are 22.7V. I thought about doing a CLC with active bridge later that will bring the rails up quite a bit. I guess you get into needing to parallel some more outputs or something.... Would be nice to see a schematic of how to do this properly...

 

[jackinnj]

2sk369 fits that bill handsomely.
the only problem for most folk might be it is even harder to find than 2sk170

2sk3557 perhaps...gm 35mS, Idss 10-32mA, Ciss 10pF

 

[cubicincher]

Good possibility!
2SK3557 - JFets do a very good sounding job in two of my WaynesLineStage-variants. But max. voltage rating D-S of 2SK3557 is much lower (15 V max) than J113. Cascoding to the rescue?
No. The J113 can do a really great sounding job! Pretty cheap and available.
Greets
Dirk

 

[geoturbo]

This looks very interesting, thank you Papa.

 

[tombo56]

2sk369 fits that bill handsomely.
the only problem for most folk might be it is even harder to find than 2sk170

Watanabe san has them, though V grade. I bought a batch and measured Idss was in 18 - 20 mA range.

2SK369V

 

[william2001]

This might be beyond my pay grade... Came up with this current sink to replace Q4. Replace Q5 with a KSA1220. Would this work to get more output stage current for a difficult load? Or am I forever banished from the site for blatant ignorance....

 

[grataku]

Watanabe san has them, though V grade. I bought a batch and measured Idss was in 18 - 20 mA range.

2SK369V

are the V grade amenable?