TDA7293 inverting t-network FB point-to-point - diyAudio
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Old 28th October 2014, 05:03 PM   #1
diyAudio Member
 
Join Date: Jun 2014
Location: Tysons Corner VA (near D.C.)
Default TDA7293 inverting t-network FB point-to-point

the purpose of this thread is to have a discussion of the above-captioned topic and related matters.
any contents of this thread posted by me is for DIY-use only and commercial use is expressly prohibited.
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!)

schematic including optional input buffer and alternative topologies (most 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)

7293 Step-by-step for master or solo chip (there is a 3886 step-by-step below)
================================================== ==========
optional first step: slip a small protoboard onto the odd-numbered pins then using the board as a lever, bend the pins to have a lateral offset so that the even-numbered pins slip into the board one row behind the even-numbered pins.
alternative first step: trim the pins so the even-numbered pins are about 1 cm overall and trim the odd-numbered ones to about 1 cm after the first bend. optionally: slip one stripboard each on a) the odd numbered pins and 2) the even-numbered pins
connect 3-conductor mute-standby controls cable to chip pins 1, 9 and 10 (in inverting 7293, mute is not used -- ie: always unmuted).
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*
connect a power cable to each of pins 7, 8, 13, 15 and the power ground star
connect zoebel network (between power ground star and pin 14)*
[if building the balanced version that has no tube then connect Rfb (R15) between pin 14 and pin 2*]
connect the +IN Rshunt between pins 3 and 4 (see R4, R13, R21, R28, R39)
mount the chip (silicon greased) with a tab bolt or a crossbar (NOTE: insulate either the chip or the heatsink)
connect speaker return line to power ground star
connect speaker out line to pin 14
connect input network miniboard connections to pins 2, 3, 4 and, if building a non-balanced version, then to pin 14 also
mount input network miniboard to standoff or to chip mounting crossbar
(input network miniboard options and build instructions forthcoming)

3886 Steps for solo chip
===============
remove NC pins 2, 6, and 11
connect pin 5 to pin 1 (v+)
connect bypasses to pins 4 (v-) and 1/5 (v+) then join the two loose ends of the bypasses to form the power ground star
connect power&control lines to pin 4 (V-), pin 1/5 (v+), pin 7, pin 8, and the power ground star
install input and fb network to pins 3, 9, 10 and run a wire (or loop-breaker) from sig-gnd to power ground star
(the input and fb network is the same as the 7293 version
connect out-sig-return line to the power ground star
connect out-sig line (or thiele) to pin 3
connect zoebel between pin 3 and power ground star

7293 -- Steps to Add a Slave
===================
optional first step: slip a small protoboard onto the odd-numbered pins then using the board as a lever, bend the pins to have a lateral offset so that the even-numbered pins slip into the board one row behind the even-numbered pins.
alternative first step: trim the pins so the even-numbered pins are about 1 cm overall and trim the odd-numbered ones to about 1 cm after the first bend.
connect pins 1, 6, 9, 10, 11 and 12 to master pins of the same numbers
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*
connect a power cable to each of pins 7, 8, 13, 15 and the power ground star
connect zoebel network (between power ground star and pin 14)*
connect pins 2, 3, and 4 to pin 8
mount the chip (silicon greased) with a tab bolt or a crossbar (insulate the chip or the heatsink)
connect speaker return line to power ground star
connect speaker out line to 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- 47k KOA CFS or your favorite type (R7)
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 axial FC 63v (bootstrap cap)
2- FB43 (ferrite beads between input cap and input R)
4- 220uf 50v low esr (e.g. panasonic FC ora similar nichicon)
4- 100nf 100v x7r (e.g. kemet)
also need: stby circuit, PSU, heatsink, case

optional buffer (drawing middle left):
1- 47k KOA CFS or your favorite type (R8)
1- NJM4556

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 non-inverting topo (drawing 2nd row right)
BOM:
Authentic TDA7293
C3 nichicon muse bipolar 100uf or larger
C5 3.3uf poly
Resistors, datasheet values, KOA CFS or your favorite type
1- 100nf x7r 100v (C2 e.g. kemet)
1- 100uf axial FC 63v (bootstrap cap)
2- FB43 (ferrite beads between input cap and input R)
4- 220uf 50v low esr (e.g. panasonic FC ora similar nichicon)
4- 100nf 100v x7r (e.g. kemet)
also need: stby circuit, PSU, heatsink, case


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; 26th November 2014 at 07:49 PM.
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Old 28th October 2014, 05:49 PM   #2
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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
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Old 29th October 2014, 09:37 AM   #3
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Location: Netherlands
A schematic would help.
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Old 29th October 2014, 05:38 PM   #4
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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?
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Last edited by sfthurber; 29th October 2014 at 05:44 PM.
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Old 29th October 2014, 06:57 PM   #5
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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
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Old 29th October 2014, 07:11 PM   #6
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Location: Tysons Corner VA (near D.C.)
v.0.2
correction to output connector

https://drive.google.com/file/d/0Bz_...ew?usp=sharing
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Old 29th October 2014, 07:51 PM   #7
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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
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Old 29th October 2014, 10:19 PM   #8
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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
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Regards, Steve
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Old 30th October 2014, 03:04 PM   #9
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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
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Old 2nd November 2014, 02:37 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
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