[murrays]

These are fairly easy to solder up without a circuitboard, as the result is a 2-terminal "device" (this being the DIY forum).
I have done them that way in the past: the 1 JFET + 1 resistor configuration, not for class-A, but for input offset biasing.
There are also commercial "constant current diodes" available which are the same thing packaged up in a standard diode package.
They are manufactured with a range of preset current specifications, so you have to do the maths first, to determine the optimal bias.
With one of those it would be physically the same as using a resistor.

 

[ecohifi]

Quote:

These are fairly easy to solder up without a circuitboard, as the result is a 2-terminal "device" (this being the DIY forum).
I have done them that way in the past: the 1 JFET + 1 resistor configuration, not for class-A, but for input offset biasing.
There are also commercial "constant current diodes" available which are the same thing packaged up in a standard diode package.
They are manufactured with a range of preset current specifications, so you have to do the maths first, to determine the optimal bias.
With one of those it would be physically the same as using a resistor.

+1 agreed!
Murrays,
 
to give Tribbs and me some feedback, how did you find them?  Was there an improvement and was it worthwhile?  And were there drawbacks on heat and reliabilty?  If you dont mine me asking!!
 
Tribbs,
 
you can try this with a breadboard.  I haven't thought about that route, but by all means give it a go! 
 
 
SpudHarris,
 
please accept my apologies if I have upset you, I have no intentions of upseting anyone with my posts, just having fun and knowledge sharing is my game.  Cant live without everyones input!

 
 

 

[murrays]

 
Quote:

+1 agreed!
Murrays,
 
to give Tribbs and me some feedback, how did you find them?  Was there an improvement and was it worthwhile?  And were there drawbacks on heat and reliabilty?  If you dont mine me asking!!

 
I made my DIY current sources for a different purpose. My bipolar input chip had a lot of offset and was fully direct-coupled (no caps) so I needed to apply a slight current bias on the inputs to balance the outputs.  On the input a much lower bias was required (nanoamps rather than milliamps) so the resistor values were many megohms and extra heat is not an issue.  The resistors had to be individually selected to achieve the correct current (one channel need +ve, the other needed -ve).
 
As far as output biasing goes, my DAC is an Adcom GDA-700 which uses class-A biasing of all the opamps as part of the design.  It has a great sound but I haven't tried removing them to see the difference.  Adcom used class-A biasing on their opamps in the 1990's.  However the chips they used (AD711/AD712) had been determined to benefit from it (I think there is a Walt Jung article on it).  They commonly used the J555 2mA device.  Many modern chips have improved output stages that do not benefit so much from the class-A biasing practice.  It may even make things worse.  Experience from others and experimentation will be required.
 
Extra current will always generate more heat.  Some maths (Ohms law) is required.  If you can't hold your fingertip on a chip because of its temperature, then it is too hot.
 
 

 

[ecohifi]

 
 

Thanks Murrays.
 
Tribbs,
 
these articles are referring to transistor input devices and one is dated back 2001,  Try some current Fet input opamps such as AD 825, ADA 4627-1 OPA 827 and OPA 1611 if you have not already done so.  Have a look at there bias currents in the data sheet and compare them to a transistor input opamp such as LMEs.
 

 
 

 

[Mad Max]

 
Quote:

How are you finding 1678/1677?
 

 

[SpudHarris]

Quote:

SpudHarris,
 
please accept my apologies if I have upset you, I have no intentions of upseting anyone with my posts, just having fun and knowledge sharing is my game.  Cant live without everyones input!
 

No, echohifi we are cool I was not addressing that post to you. You seem like a real nice guy. It was addressed to Tribbs who seems very rude considering he was asking for advice.
 

 
 

 

[SpudHarris]

Quote:

How are you finding 1678/1677?
 

Well I love the 1678. They are my new best friend haha.
 
Ron (hiflight) tells me that the 1677 is a different chip. I haven't looked at the specs but I'm told the slew rates amonst other things are not the same. I have had the 1677's for ages and have to say I never really wanted to keep listening to them whereas the 1678's are now in my P4, PB2, Fi-Quest and EF5. They all sound fantastic.
 

 

[Mad Max]

Ah my bad.  I did not like 1677.  1678 has pretty low slew rate.

 

[ecohifi]

Quote:

No, echohifi we are cool I was not addressing that post to you. You seem like a real nice guy. It was addressed to Tribbs who seems very rude considering he was asking for advice.
 

 
 

Thanks SpudHarris, its all cool and I'm flattered,  I need you to keep me in check with my spelling errors LOL, FYI I failed English.  Maybe it was my fault because I dont think I read Tribbs post correctly!
 
Ladies and guys,
 
FYI,  there is an electronics magazine called Silicon Chip in Aust that have published a head amp kit and a pre amp that uses a LM833.  Interestingly they believe that they can achieve a lower distortion figure than the current LME 49720 or LME 49990.  There previous pre amp published in 2005 was based on an OPA 2132/4, this is what I am using to evaluate these 8 legged devices.  Cant post the article here due to copyright, but I have heavily modified it to make it sound better than my full discrete bipolar preamp!  Well to my old ears  I believe it sounds better,
 
While you guys are on the 1677/ 1678 have you two tried the 1122 while we are on the LTs?
 
 

 

[SpudHarris]

Quote:

Thanks SpudHarris, its all cool and I'm flattered,  I need you to keep me in check with my spelling errors LOL, FYI I failed English.  Maybe it was my fault because I dont think I read Tribbs post correctly!
 
Ladies and guys,
 
FYI,  there is an electronics magazine called Silicon Chip in Aust that have published a head amp kit and a pre amp that uses a LM833.  Interestingly they believe that they can achieve a lower distortion figure than the current LME 49720 or LME 49990.  There previous pre amp published in 2005 was based on an OPA 2132/4, this is what I am using to evaluate these 8 legged devices.  Cant post the article here due to copyright, but I have heavily modified it to make it sound better than my full discrete bipolar preamp!  Well to my old ears  I believe it sounds better,
 
While you guys are on the 1677/ 1678 have you two tried the 1122 while we are on the LTs?
 
 

Sounds cool. I like the LME49990 a lot. As with the LT1678 I bought enough to evaluate in my favourite amps and still swap this back into the EF5 now and again as it really shines with my LCD2.
 
I'm sure I have LT1122's in my box. I will have to look and report back. Do you like them?
 

 

[Tribbs]

     Quote:

Originally Posted by murrays /img/forum/go_quote.gif
 
There are also commercial "constant current diodes" available which are the same thing packaged up in a standard diode package.
They are manufactured with a range of preset current specifications, so you have to do the maths first, to determine the optimal bias.
With one of those it would be physically the same as using a resistor.

Constant Curent Diodes or Current-Regulating Diodes (CRDs) introduce a fairly large input capacitance into the signal path.
Yes, they will work but at the expense of the audio.  You would want to avoid adding capacitance into the signal path at all costs.
Again, Warren Young states this in his article. Hence the JFET Cascode.
 
Quote:

Originally Posted by murrays /img/forum/go_quote.gif
 
I have done them that way in the past: the 1 JFET + 1 resistor configuration
 

 
Yup! You made a discret constant current diode.
 
Quote:

Originally Posted by ecohifi /img/forum/go_quote.gif
 
Tribbs,
 
you can try this with a breadboard. I haven't thought about that route, but by all means give it a go!

 
I have it on my list!  I'll try it out and report back when I have the opportunity.
 
Thank's for everyone's feedback.  Including you SpudHarris

  [Don't try to read between the lines.]

 

[ecohifi]

Haven't tried the 1677/78 but the 1122 is nice and dark and the highs are real and complete, I find the 1122 the best out of the LT range because I just really like FET input stages,  I still think the ADA 4627-1 b are hard to beat that is why I invested heavily into them.  I dont have a LCD 2 but a Stax Lamba.  The ADA 4627-1 really shows how its supposed to be done in both the stax and my main rig.  In a EE minmax plus it elevates the soundstage and completes the SQ,  Funny enough when both AD 825 and ADA 4627-1a arrived at the same time I didn't like the 4627, probably because the AD 825 was'nt so detailed and heavy in the bottom end but had this airy transparency that I was craving for that didn't exist on the OPAs.  I had the AD 825 at least 7mths when I decided to swop.  When I fitted the 4627 and cranked up the volume, I realised I misjudge them.  The 4627 was like a AD 825 with guts not to mentioned the  detailed bottom end had returned with balls.

 

[SpudHarris]

I prefered the ADA4637BRZ over the 4627. They are both nice but I guess it's personal preference and application, the 4637 are really nice in my balanced PB2....
 
I haven't got the LT1122 as I thought, I have the LT1124 but I haven't listened to it for ages so can't really comment on it. Of the LT chips I do like the 1363 and 1468. The 1363 are very, very nice and you must try them if you haven't.

 

[SpudHarris]

Can you tell me more about LT1122?
 
I have 4 off in my Farnell shopping basket but wondered how they compare to others like OPA4627/37 / 1611 / 1641 / 602 / LT1678 / LME49990 (all favorites)
 
Cheers

 

[ecohifi]

I like the OPA 1611/ 1612 / 827 better than the LT 1122.  Probably not worth trying and I love the ADA 4627-1 A & B versions
If you get a hold of the LT site you can order these as samples like I did, No cost delivered under research!  Same deal with the Texas Instruments you can get the OPA 1611/1612/827 as samples!
 
With the LTs there are also the 1115,1028 but the 1122 is the better one!  The LT1122 is a new process of manufacturing, just like the OPA 1611/ 1641 / 827.
 
The ADA 4627/4327 is supposed to be the answer for the OPA 627/637,  I have not tried the 4327 or the 637 because they are supposed to support gain of 5>