Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st February 2013, 08:31 AM   #2721
diyAudio Member
 
dchisholm's Avatar
 
Join Date: Mar 2011
Location: St Louis, Mo
Quote:
Originally Posted by Joshua_G View Post
. . . the output stage was posted on post #2593. Both are different from the schematic you posted.
I added the output latchup protection diodes as described in Post #2668. I believe the rest of the circuit topology is identical, unless you see something I have missed.

Resistor values shown in my published schematic were altered to increase parts commonality (fewer BOM line items) or to avoid values not stocked at popular distributors. As mentioned at several points in the thread (e.g., Post #2593 and Post #2432), component selection and values are not critical. As I recall, Scott mentioned that he assembled his concept-validation circuits using parts on-hand rather than the exact engineered values, specifically to verify that component types and values are not critical.

I didn't include the thermal coupling shown in Post #2591. Tight thermal coupling is very difficult, to impossible, with discrete SMT parts. As mentioned in Post #2598 the lack of thermal coupling isn't expected to be a serious disadvantage.

Quote:
Scot's latest front end, or input stage, schematic was posted on post #2643 . . .
THERE IS A DRAFTING ERROR IN THE POST #2643 SCHEMATIC!
The labels for " +in " and " -in " are transposed. You can verify this by (carefully) comparing the topology of Post #2643 to the schematics attached to Post #2409 and Post #1568. This is also apparent when you simulate the Post #2643 schematic.

My published schematic includes an input stage balance adjustment (R28 and associated components). This adjustment was not shown on Scott's schematics but the function was discussed in posts (e.g., Post #2667 and #2668). I selected component values that seemed reasonable.

My published schematic includes the secondary compensation components (C2/R10, and C3/R14). These are shown in the Post #1568 schematic but removed from later versions. I retained the networks to provide the greatest flexibility for customizing the compensation. The locations may be left unpopulated if a simpler compensation strategy is used. The values I show give reasonable simulation results with the models I have for the active devices shown.

Similarly, I made provision for moving the secondary compensation networks between the two sides of the differential input stage. I discussed this in Post #2404 et seq.

My published schematic implements the compensation networks as series RC (i.e., pole-zero) networks. This is consistent with the Post #1568 schematic although only a capacitor is shown in later versions. I retained the RC network to provide the greatest flexibility for customizing the compensation. To implement a capacitor-only compensation scheme, install low-ohm resistors (e.g., 1R0), or zero-ohm jumpers, or found-on-bench (FOB) scraps of hookup wire in place of the resistors.

My schematic uses diode-strapped transistors as the level-shift devices (Q7, Q8, Q9, Q13, Q14, Q15) in the input stage. This is in agreement with Post #1568, but was altered to pure diodes in later versions. No claims of improved performance were made for diodes versus diode-strapped transistors. In practice, the component footprints on the PWB will accept diodes in SOT-23 packages at those locations - e.g., BAL99 or BAL74 depending on the polarity.

The Post #2643 schematic shows an LSK389 matched-pair JFET as the input device. Other versions used 2SK170's or BF862's, and reported acceptable performance. I retained the SOT-23 single devices because the LSK389 is not widely available from hobby suppliers. Also, a PWB designed to use the BF862 in SOT-23 package is compatible with other JFET models in SOT-23, where the LSK389 footprint offers very few (if any) alternatives.

Throughout my implementation I used single transistors in SOT-23 packages. (The output devices may, optionally, be SOT-223 devices.) While using dual devices may improve thermal tracking and save PWB real estate there is a much wider selection of suitable parts available in SOT-23 than in comparable duall-device packages. Again, this approach caters to flexibility in construction on a common PWB.

Considering the above, I believe my implementation is compatible with the Post #2643 and Post #2668 schematics. If you have identified other differences please provide specific details. It is possible I have overlooked or misunderstood some aspect of this circuit.

Dale
  Reply With Quote
Old 24th February 2013, 03:25 PM   #2722
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
Looks pretty good to me... I'd be waiting to hear of a working unit using these pcb's.... you know, bugs flushed out. Thx-RNMarsh
  Reply With Quote
Old 24th February 2013, 05:35 PM   #2723
diyAudio Member
 
grhughes's Avatar
 
Join Date: Mar 2005
Location: Cubicle Sweet Cubicle, Springfield, Missouri, USA
Build it, perfect it, listen to it and report the results! Ray
__________________
" "The fool doth think he is wise, but the wise man knows himself to be nothing but a fool." Will Shakespeare
  Reply With Quote
Old 24th February 2013, 05:49 PM   #2724
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
Quote:
Originally Posted by RNMarsh View Post
I can develop my own thru-hole pcb layout faster than I could wire up the circuit with smd.
I dont believe anyone is forcing you to use SMD, but there is performance improvements in less inductive, physically smaller parts and layout, that would be why they made the first ICs to begin with wouldnt it?

Quote:
Larger size will have No impact on audio. Layout might.
hmm thats why I asked Scott, it will certainly have impact objectively; I just wondered how much in this specific case

Quote:
Do what makes you happy. That's what I do.
I wouldnt expect you to do anything else
  Reply With Quote
Old 25th February 2013, 04:45 AM   #2725
RNMarsh is offline RNMarsh  United States
diyAudio Member
 
RNMarsh's Avatar
 
Join Date: May 2012
Location: 2457 Cascade Trail; Cool, CA. 95614
The lead length from the resistor body to the pcb is pretty short..... that would be the only difference as the pcb trace length and shape will dominate. A smd without leads can be shorter than a leadless one but the pcb traces dominate.

I am not as convinced for audio freq range that if you measured thd, s/n, Im, freq resp et al that they would be different due to sm vs thru-hole. I'm willing to be proven wrong.

Thx-RNMarsh

Last edited by RNMarsh; 25th February 2013 at 04:48 AM.
  Reply With Quote
Old 25th February 2013, 08:03 AM   #2726
diyAudio Member
 
grhughes's Avatar
 
Join Date: Mar 2005
Location: Cubicle Sweet Cubicle, Springfield, Missouri, USA
It just seems to me that SMD is just not for the DIY assembler where he is only making maybe four units for a stereo preamp. It is for the manufacturer that is making hundreds or thousands. What DIYer wants to invest in a 40x stereo assembly microscope and a reflo oven to make 4 units? Also, Scott said the unit wouldn't support being a unity gain follower with the + input grounded. The JE990 will support being a unity gain follower. Ray
__________________
" "The fool doth think he is wise, but the wise man knows himself to be nothing but a fool." Will Shakespeare
  Reply With Quote
Old 25th February 2013, 08:41 AM   #2727
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
none of the parts being used is that small, none of the parts used needs reflow, all are quite solderable with a standard iron and a standard size tip. 40x stereo assembly microscope for this? try a standard 4x $10 illuminated visor if anything at all. SMD is MORE friendly to the DIYer once you get used to it, PCBs are much easier to make if you dont have to punch a heap of holes in them, especially something this size.

fine if you dont want to do SMD, but your reasons as posted do not make a lot of sense IMO. 1x or 1000x its just as suitable.
  Reply With Quote
Old 25th February 2013, 09:36 AM   #2728
bcarso is offline bcarso  United States
diyAudio Member
 
Join Date: May 2005
Location: Canoga Park, California
Agreed. Once you have a little experience, and especially if you are changing out parts at any point, SM is far more tolerant of rework and in many ways desirable.
  Reply With Quote
Old 25th February 2013, 10:41 AM   #2729
miklos is online now miklos  Canada
diyAudio Member
 
miklos's Avatar
 
Join Date: Jul 2004
Location: toronto
Quote:
Originally Posted by grhughes View Post
It just seems to me that SMD is just not for the DIY assembler where he is only making maybe four units for a stereo preamp. It is for the manufacturer that is making hundreds or thousands. What DIYer wants to invest in a 40x stereo assembly microscope and a reflo oven to make 4 units? Also, Scott said the unit wouldn't support being a unity gain follower with the + input grounded. The JE990 will support being a unity gain follower. Ray
I don't think you need a microscope for that kind of job.
Better get used to SMD, soon no through hole components will be available on the market.
__________________
miklos
  Reply With Quote
Old 26th February 2013, 04:53 PM   #2730
rsavas is offline rsavas  Canada
diyAudio Member
 
Join Date: Aug 2012
Location: Ontario
Default soon no through hole components will be available on the market.

Quote:
Better get used to SMD, soon no through hole components will be available on the market.
You can say this about certain newer small signal semiconductors & IC's, but probably not for power semi's nor many passives.
I can solder 0805 & larger without an aid, but use a jewelers loup (10X) for anything smaller.

SMT is advantageous for a smaller PCB area = lower cost & automated assembly but you are usually forced to use a double-sided boards minimally and almost always need vias. Almost everything I design is mixed technology to some degree or another, especially if it is analog, for digital, well that is usually denser, thus SMT, is the primary component choice for so many reasons.

Keep up the good work folks!!
Rick

Last edited by rsavas; 26th February 2013 at 05:00 PM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Discrete OPAMP audio-gd Vendor's Bazaar 27 20th September 2012 04:02 PM
discrete opamp help blackpowderaudio Parts 0 16th December 2009 03:46 PM
THAT transistor headphone amp (250ma discrete opamp) design sanity check. Russ White Headphone Systems 19 13th December 2007 12:52 PM


New To Site? Need Help?

All times are GMT. The time now is 07:31 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2