TDA7293 inverting t-network FB point-to-point - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 28th October 2014, 04:03 PM   #1
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
Default TDA7293 inverting t-network FB point-to-point

preface --
with all the fake/clone/pull tda72xx chips to sort out, you know what id did? i finally gave up on them and went all-in with TI Overture series parts; avoided the Spike issues by paralleling enough of them for any given application to run well within the safe operating areas shown on the datasheets. have yet to hear a peep out of Spike.
in any event:
this thread is kept alive for posterity and because some of its contents may be useful.
now, i should say that this thread does not reflect what i've done lately with 7293.
since i found almost no performance differences inverting vs non-inverting i've gone back to using the Fly-xy version http://www.ebay.com/itm/111405494862 of Daniel's favorite board as a starting point and to handle the power and output circuitry, but i omit the slave chip and i build the NFB and input circuit point-to-point on the underside of the board with 1k/30k in a conventional NFB loop (not a t-net). the NFB DC-blocking cap is Elna 220uf. the input cap is 3.3uf 400v panasonic poly. (tube preamp). i also use rail-to-rail bypasses for both sets of power inputs (pins 7 to 8 as well as 13 to 15) .22 uf or .47 uf 100v x7r kemet
non-inverting also has the advantage that the mute circuitry works while inverting breaks the mute function for reasons that are obvious if you look at the tda7293 datasheet. and non-inverting avoids the need for a buffer on the input.

end of preface


the purpose of this thread is to have a discussion of the above-captioned topic and related matters.

goals: equal or exceed datasheet performance, low offset (adjustable), easy-to-replicate, reliable & stable, suitable for XLR-end-to-end-balanced applications, no exotic parts, inverting and non-inverting options, opamp buffer option, balanced input option, balanced input option with tube/valve buffer..
so far there have been no reported errors but please do let me know if you spot one (or have an improvement suggestion of any sort, of course!)

SCHEMATICS: the following link contains schematics. the first one is the simplest but the document also includies optional input buffer and alternative more-complex topologies (most of them use t-net techniques):
https://drive.google.com/file/d/0Bz_...ew?usp=sharing
if you use the buffer it would be after C1 in which case C1 can be smaller valued (ex: 0.47)

some things that are not covered in the schematics:
connect bootstrap capacitor, positive end to chip pin 6, negative end chip pin 12
connect one end of a 100 nf to pin 7*
connect one end of another 100 nf to pin 8*
connect one end of another 100 nf to pin 13*
connect one end of another 100 nf to pin 15*
connect positive end of a 220 uf to pin 7*
connect negative end of another 220 uf to pin 8*
connect positive end of another 220 uf to pin 13*
connect negative end of another 220 uf to pin 15*
join together the unattached ends of capacitors of the 8 preceding steps--this becomes the chip's local power ground star*
the lower end of R2 connects to the power ground star
run power cables to each of pins 7, 8, 13, 15 and the power ground star
connect zoebel network (between power ground star and pin 14)*

BOM -- for inverting t-net version (not including optional input buffer):
1- Authentic TDA7293
1- 50k multiturn cermet minipot (R4 -- used to zero the output DC offset)
1- 3.3uf poly (C1)
2- 10k1 KOA CFS or your favorite type (R1, R3)
1- 22k1 KOA CFS or your favorite type (R5)
1- 10R 1W (R6)
1- gain set (R2) KOA CFS or your favorite type -- choose to select a desired gain > 26db, 100R is typical
1- 100nf x7r 100v (C2 e.g. kemet)
1- 100uf Panasonic FC or Elna 63v (bootstrap cap)
2- FB43 (ferrite beads between input cap and input R)--optional for RFI suppression
4- 220uf 50v low esr (e.g. panasonic FC or a similar nichicon)
4- 100nf 100v x7r (e.g. kemet)
NOTE: you may also also need: stby circuit, PSU, heatsink, case

BOM -- for optional buffer (drawing second row left):
1- 47k KOA CFS or your favorite type (R8)
1-1k0 KOA CFS or your favorite type (R7)
1- NJM4556 or similar unity gain stable audio op amp

proposed optional minimalist diode-based Vs - Vp isolator for power board (drawing top right--one rail shown)
Vp connects at C6 and Vs connects at C8
BOM:
8- diodes each D2 should be schottky. D1 D3 D4: standard 6A? MUR860? BYW98100?
4- 0.1uf 100v x7r (1 at each Vs and Vp pin) C6, C9. C7 and C8 are optional electrolytics
the Vs PSU feeds could be regulated for better PSRR

another approach to vas isolation
Click the image to open in full size.
from:
http://www.diyaudio.com/forums/attac...arate_vpvs.gif



alternate balanced topologies (schematics pic's bottom-most circuits -- the tube-hybrid versions use 6922 or similar)

and lest we forget safety:
Click the image to open in full size.
from: http://www.decdun.me.uk/gc/groundlift3.jpg
__________________
Regards, Steve

Last edited by sfthurber; 1st April 2015 at 04:09 PM.
  Reply With Quote
Old 28th October 2014, 04:49 PM   #2
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
pictorial:
2 !--10k-->3.3uf-->SigIn
2 |--10k-->SigGnd
2 |--10k--------->to:x
3--10k-->SigGnd
14--10k------------>x<--200R--SigGnd
__________________
Regards, Steve
  Reply With Quote
Old 29th October 2014, 08:37 AM   #3
diyAudio Member
 
Mark Whitney's Avatar
 
Join Date: Feb 2013
Location: Netherlands
A schematic would help.
__________________
Regards Mark.
  Reply With Quote
Old 29th October 2014, 04:38 PM   #4
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
schematic v.0.0
https://drive.google.com/file/d/0Bz_...ew?usp=sharing

ok let's start with this and assume initially that the circuits (except for local bypassing) for for pins 1, 7, 8, 12, 14, 15 are on one or more separate modules or PCBs.
all fixed resistors are 10k except R2 (which sets the gain), R4 is 50k linear, and C1 is 3.3uf poly.
let's assume local bypassing TBD for pins 7, 8, 11, 15

then at least we need to add the CCS bootstrap (pin 12 or 14 to pin 6) and zoebel (pin14 to SigoutGnd)

COMMENTS?
__________________
Regards, Steve

Last edited by sfthurber; 29th October 2014 at 04:44 PM.
  Reply With Quote
Old 29th October 2014, 05:57 PM   #5
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
v.0.1
added zoebel and output conn

https://drive.google.com/file/d/0Bz_...ew?usp=sharing
__________________
Regards, Steve
  Reply With Quote
Old 29th October 2014, 06:11 PM   #6
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
v.0.2
correction to output connector

https://drive.google.com/file/d/0Bz_...ew?usp=sharing
__________________
Regards, Steve
  Reply With Quote
Old 29th October 2014, 06:51 PM   #7
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
BOM:

1- TDA7293
1- 50k multiturn cermet minipot
1- 3.3uf poly
1- 10R 1W
3- 10k1 1% CF RN60
1- 100nf x7r 100v (zoebel cap)
1- 220uf FC 63v (bootstrap cap)
2- FB43 (ferrite beads for pins 2 and 3)

also need: bypasses, mute-stby circuit, PSU, heatsink
__________________
Regards, Steve
  Reply With Quote
Old 29th October 2014, 09:19 PM   #8
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
added optional input buffer
u2 is njm4556 or similar

https://drive.google.com/file/d/0Bz_...ew?usp=sharing
__________________
Regards, Steve
  Reply With Quote
Old 30th October 2014, 02:04 PM   #9
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
here is what we have so far--

schematic including optional input buffer:
https://drive.google.com/file/d/0Bz_...ew?usp=sharing

BOM (not including optional input buffer):
1- TDA7293
1- 50k multiturn cermet minipot
1- 3.3uf poly
1- 10R 1W
3- 10k1 1% CF RN60
1- gain set R 1% CF RN60 or multiturn cermet minipot, choose to select a desired gain > 20x
1- 100nf x7r 100v (zoebel cap)
1- 220uf FC 63v (bootstrap cap)
2- FB43 (ferrite beads for input cap)

also need: bypasses, mute-stby circuit, PSU, heatsink
__________________
Regards, Steve
  Reply With Quote
Old 2nd November 2014, 01:37 PM   #10
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
here is what we have so far--

schematic including optional input buffer:
https://drive.google.com/file/d/0Bz_...ew?usp=sharing
if you use the buffer it would be after C1 in which case C1 can be smaller valued (ex: 0.47)

BOM (not including optional input buffer):
1- TDA7293
1- 50k multiturn cermet minipot (R4, used to zero the offset)
1- 3.3uf poly
2- 10k1 1% CF RN60 (R1, R3)
1- 22k1 1% CF RN60
1- 10R 1W (R6)
1- 47k (R7)
1- gain set (R2) 1% CF RN60 -- choose to select a desired gain > 26db, 100R is typical
1- 100nf x7r 100v (C2 e.g. kemet)
1- 100uf FC 63v (bootstrap cap)
2- FB43 (ferrite beads between input cap and input R)
2- rail bypassing: 220uf 50v low esr (e.g. panasonic FC) || 100nf 100v x7r (e.g. kemet)
also need: mute-stby circuit, PSU, heatsink, case
optional buffer:
1- 47k (R8)
1- NJM4556
__________________
Regards, Steve
  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
Lots of craziness (weird noises and osc) happening in point to point 5W EL84 Amp 777funk Instruments and Amps 17 2nd March 2014 06:20 PM
Point 2 Point (no PCB) for TDA7293, TDA7294, TDA7295, TDA7296. danielwritesbac Chip Amps 149 10th July 2013 08:18 PM
F5 Point to Point Power Supply Schematic bassnkeys Pass Labs 15 22nd February 2012 04:32 AM
Anyone use magnet wire for point to point wiring projects? Hybrid fourdoor Parts 10 2nd February 2004 08:11 AM
Audio Note's Kit One done in point-to-point wiring Wram Tubes / Valves 18 29th April 2003 10:59 PM


New To Site? Need Help?

All times are GMT. The time now is 03:12 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2