LTSpice sim?

[bill0287]

Has anyone built this ("The Honey AMP") in LTSpice? I put it together and I am getting some really odd looking wave forms. Wondering if anyone else has seen this.

[Tassieviking]

Built what exactly

[g1]

Built what exactly

I wondered the same thing.  Then I noticed this is in the 'Honey Amp' section.   

[joecool85]

Has anyone built this ("The Honey AMP") in LTSpice? I put it together and I am getting some really odd looking wave forms. Wondering if anyone else has seen this.

I've been meaning to share this for months and hadn't gotten around to it.  Paul Marossy has actually done just that!  Check out the fourth video here: https://www.ssguitar.com/index.php?topic=5258

[Paul Marossy]

I experienced the same thing. Your LTSpice sim will only be as good as your LM386 model. Almost all of the ones you find on the internet are all hosed up. I actually had to draw up the schematic of the LM386 per the data sheet to get waveforms that look anything like what I would expect to see. Me and a few others worked on this model quite a bit last year when I was doing my ebow resurrection/reverse engineering project. It's about the best possible model with the info that we can obtain. There might be a couple of other components in the IC chip that aren't on the schematic but I don't think it's really an issue for the vast majority of applications.

You can save these files via a word processor & rename/save with the appropriate extension and give it a try.

SUB file:

Code Select Expand

* LM386
*
* Rob S, V1, 2022/12/14
* Does this behaviour show up on the real device?:
* For negative inputs on the NI-input we see
* an inversion on the negative swing.
* Tweaking the gain stage current source helps
* However the primary issue is the NI-input
* buffer will remove base drive from the voltage gain
* stage under large -ve input (say < -0.75V)
* An external workaround is to add a 4k7 resistor
* in series with the NI-input.
*
* Rob S, V2, 2022/12/23
* A fix is to add 220 ohm series base resistors
* to Q3 and Q4.
*
*
* Is = 4.6mA @ Vs=9V
*
***********************************
* IC pins:   DIP8 package order
* Pins: 1 GAIN, 2 INM, 3 INP, 4 GND,
* 5 OUT, 6 VS, 7 BYP, 8 GAIN
.subckt lm386 1 2 3 4 5 6 7 8
***********************************

* input emitter-follower buffers
q1 4 2 11 pn
r1 2 4 50k
q2 4 3 15 pn
r2 3 4 50k

* Base resistors to prevent output inversion
* with strong -ve INP inputs
R33 11 33 220
R34 15 34 220

* differential input stage
q3 13 33 12 pn
q4 14 34 1 pn

* diff amp tail resistors
r3 6 7 15k
r4 7 12 15k

* feedback resistors
r5 12 8 150
r6 8 1 1.35k
r7 1 5 15k

* input stage current mirror
q5 13 13 4 np
q6 14 13 4 np

* voltage gain stage & rolloff cap
q7 18 14 4 np
*c1 18 14 15pf
* 35pF (match -3dB) to 50pF (match 10dB @ 1MHz)
c1 18 14 35p

* Current source for gain stage
* Approx 1.7mA @ Vs=9V
* *** Even with RE added, this source dependency on Vs
* is too high to match the Is vs Vs spec in the datasheet.
* (Also, could derive bias current from through 15k input
*  biasing like LM380.)
R21 21 4  50k
q21 21 21 6 pn
q22 16 21 22 pn 20
R22 6 22  10

* bias diodes
* Set to 2.55mA @ Vs=9V
q11 16 16 17 np 100
q12 17 17 18 np 100

* output stage
q8 6 16 5 np 100
q9 19 18 5 pn
q10 5 19 4 np 100

* Need to rejig with Nc = 1
* generic transistor models generated
* with MicroSim's PARTs utility, using
* default parameters except Bf:
.model np NPN(Is=10f Xti=3 Eg=1.11 Vaf=100
+ Bf=200 Ise=0 Ne=1.5 Ikf=0 Nk=.5 Xtb=1.5 Var=100
+ Br=1 Isc=0 Nc=2 Ikr=0 Rc=0 Cjc=2p Mjc=.3333
+ Vjc=.75 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=100n
+ Tf=1n Itf=1 Xtf=0 Vtf=10)

.model pn PNP(Is=10f Xti=3 Eg=1.11 Vaf=100
+ Bf=100 Ise=0 Ne=1.5 Ikf=0 Nk=.5 Xtb=1.5 Var=100
+ Br=1 Isc=0 Nc=2 Ikr=0 Rc=0 Cjc=2p Mjc=.3333
+ Vjc=.75 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=100n
+ Tf=1n Itf=1 Xtf=0 Vtf=10)

.ends
ASY file:

Code Select Expand

Version 4
SymbolType BLOCK
LINE Normal -48 -63 -48 64
LINE Normal 78 0 -48 -63
LINE Normal -48 64 78 0
LINE Normal -48 -32 -80 -32
LINE Normal -49 32 -80 32
LINE Normal -16 -80 -16 -48
LINE Normal 32 -48 32 -23
LINE Normal -16 79 -16 47
LINE Normal 32 48 32 24
LINE Normal 96 0 78 0
TEXT -64 -40 Left 1 +
TEXT -62 25 Left 1 -
TEXT -42 31 Left 1 3
TEXT -41 -31 Left 1 2
TEXT -9 -53 Left 0 BYP
TEXT -20 -35 Left 1 8
TEXT 27 -13 Left 1 7
TEXT 37 -27 Left 0 Vs
TEXT -12 54 Left 0 GND
TEXT 37 30 Left 0 GND
TEXT -11 32 Left 1 4
TEXT 11 21 Left 1 5
TEXT 52 0 Left 1 6
TEXT -35 -2 Left 1 LM380
PIN -80 -32 NONE 8
PINATTR PinName 2
PINATTR SpiceOrder 2
PIN -80 32 NONE 8
PINATTR PinName 3
PINATTR SpiceOrder 3
PIN -16 80 NONE 8
PINATTR PinName 4
PINATTR SpiceOrder 4
PIN 96 0 NONE 8
PINATTR PinName 6
PINATTR SpiceOrder 6
PIN 32 -48 NONE 8
PINATTR PinName 7
PINATTR SpiceOrder 7
PIN -16 -80 NONE 8
PINATTR PinName 8
PINATTR SpiceOrder 8
PIN 32 48 NONE 8
PINATTR PinName 5
PINATTR SpiceOrder 5
ASC file:

Code Select Expand

Version 4
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IOPIN 240 -544 In
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SYMBOL pnp -528 -144 R0
SYMATTR InstName Q1
SYMATTR Value PN
SYMBOL pnp -224 -256 R0
SYMATTR InstName Q3
SYMATTR Value PN
SYMBOL res -640 48 R0
SYMATTR InstName R1
SYMATTR Value 50K
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SYMATTR InstName Q5
SYMATTR Value NP
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WINDOW 0 0 56 VBottom 2
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SYMATTR InstName R5
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SYMBOL res 192 -352 R90
WINDOW 0 0 56 VBottom 2
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SYMATTR InstName R6
SYMATTR Value 1.35K
SYMBOL npn 272 80 R0
SYMATTR InstName Q6
SYMATTR Value NP
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SYMATTR InstName Q4
SYMATTR Value PN
SYMBOL pnp 704 -48 R180
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SYMATTR InstName Q7
SYMATTR Value NP
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SYMATTR InstName Q8
SYMATTR Value NP AREA=100
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SYMATTR InstName Q9
SYMATTR Value PN
SYMBOL npn 1760 80 R0
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SYMATTR Value NP AREA=100
SYMBOL voltage -1488 48 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 1 2.59K)
SYMBOL cap -1232 -16 R90
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SYMATTR InstName C31
SYMATTR Value 1µF
SYMBOL res -1056 -16 R90
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SYMATTR InstName Q21
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TEXT -1480 -504 Left 2 !.model np NPN(Is=10f Xti=3 Eg=1.11 Vaf=100\n+ Bf=200 Ise=0 Ne=1.5 Ikf=0 Nk=.5 Xtb=1.5 Var=100\n+ Br=1 Isc=0 Nc=2 Ikr=0 Rc=0 Cjc=2p Mjc=.3333\n+ Vjc=.75 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=100n\n+ Tf=1n Itf=1 Xtf=0 Vtf=10)
TEXT -1480 -320 Left 2 !.model PN PNP(Is=10f Xti=3 Eg=1.11 Vaf=100\n+ Bf=100 Ise=0 Ne=1.5 Ikf=0 Nk=.5 Xtb=1.5 Var=100\n+ Br=1 Isc=0 Nc=2 Ikr=0 Rc=0 Cjc=2p Mjc=.3333\n+ Vjc=.75 Fc=.5 Cje=5p Mje=.3333 Vje=.75 Tr=100n\n+ Tf=1n Itf=1 Xtf=0 Vtf=10)
TEXT -112 -1104 Left 2 !.step param Rbb LIST 10k 30k 100k
TEXT -112 -1040 Left 2 ;Adding RE=10 ohm, helps reduce Ic dependcy on Vs but it's still not good enough.\nAs shown, 50k + 10 ohm gives Ic=1.65mA with VS=9V\nIt's possible Q21 is biased via R3, like the LM380
TEXT 1864 -656 Left 2 ;2.5mA bias at 9V
TEXT 1368 368 Left 2 ;35pF matches -3dB\n100pf matches 100dB @ 1MHz
TEXT -1464 -600 Left 2 ;Nc=2 is likely to be a long way off
TEXT 2392 32 Left 2 !;ac dec 300 10 1MEG
TEXT 2392 72 Left 2 !.tran 0 0.3 0.2 10u
TEXT 2400 112 Left 2 !.op
TEXT 2384 -880 Left 2 ;* "Inversion" Problem\n \n- under strong overload on the V+ input\nthe negative output swing inverts\n- High bias current on gain stage\ncurrent source makes this worse\n*** Actual Cause?\nMost obvious cause seems to be\na removal of base drive from the \nvoltage gain transistor when Vin < 0.75V,\n...and that's caused by Q2, Q4\n \n* Fix For Inversion:\n-drop Isource to ~ 1.6mA (Rbb=50k) to \nlargely remove problem.\nPositive drive OK but not much margin.
TEXT 2368 80 Left 2 ;*
TEXT -120 480 Left 2 ;Pins: 1 GAIN, 2 INM, 3 INP, 4 GND, 5 OUT, 6 VS, 7 BYP, 8 GAIN
TEXT 2384 -376 Left 2 ;* Work-around if inversion is real:\n-adding about 4.7K in series with \nthe V+ input Input reduces this effect.\n- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -\n \n* Improvements?:\n- are there input protection diodes missing?\n- reduce dependcy of voltage gain current source\non Vs (This also affects output bias dependcy\non Vs)\n- fix Nc=2 on transistors
TEXT 3024 -880 Left 2 ;LM386 Model\nRob S. Rev 1.0 2022/12/14\n \n* Output Bias Point\n \nOutput: Vs/2 + vbe\n \n* Output Swiing\n \n9V, 8 ohm\noutput is about 3V pk,\n+ ve side clips first.\neg. clips at +3V, -ve swing -3.2V\nclip top has a falling slope\n \n9V 4 ohm\nfrom datasheet about 3.5V p-p\n \n* Current Draw\n \nDS Is: 3.5mA to 4.8mV over 4V to 12V\n      1.3mA change 4.1mA @ 8V\n \nSim: At Vs=9V total current is = 4.6mA\n \n- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - \n \nIf I add RE=10 ohm to the current source transistor\nthe biasing of the gain stage varies about 1.7mA\nWe need enough current there to drive the o/p Qs.\n \nWith this mod o/p/ biases to 2.5mA @ 9V\n(4V to 12V= > 1.3mA to 3.18mA)\nStill too much to change.\nChange due to voltage amp current source varying.
TEXT -1488 -352 Left 2 ;*
TEXT -104 -1152 Left 2 !.lib Lm386-RS1.sub

[joecool85]

Thanks Paul, this should help!  I have to say that I'm surprised there isn't a solid LM386 model out there already though - it's such an old and popular chip, used in so many DIY projects.

[smadin]

Late to this party, but I figured I'd chime in that I also ended up finding I had to make my own LM386 model from the data sheet. I expect Paul's is more correct than mine, so I'm excited to compare them.

[joecool85]

Late to this party, but I figured I'd chime in that I also ended up finding I had to make my own LM386 model from the data sheet. I expect Paul's is more correct than mine, so I'm excited to compare them.

Certainly let us know what you find!