Ultra Amplifier Build Thread

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#64
On onsemi's website, KSA1381ESTU has a status of "Lifetime". I emailed them for clarification and received this:

This part is in end-of-life status. This means it is being discontinued. Active means the device still exist in our system and is an orderable part. This device you are referencing has a last time buy date of Jan 5, 2025 and a last time ship date of July 5, 2025.
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#67
The ideal devices for this design should be high gain, with matched gain between N and P devices, low capacitance and robust.

Based on sims, this is the order of devices I found to work with the design in order for best to least. This is all described in the build guide.
  1. 2SC3503E / 2SA1381E
  2. KSC3503D / KSA1381E
  3. TTC004B / TTA004B
  4. BD139 / BD140
I looked at MJE243 / MJE253 and MJE340 / MJE350 as well, but cannot recommend them due to the performance and DC offset.

If device availability becomes an issue, I think the logical path forward would be to look at a design with a two-device VAS that mitigates the VAS requirements of the current design. However, as you add more devices, the design begins look more like Bob Cordell's Hafler DH-220C.
 
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#69
I received a question on the impact of VAS device matching and selecting between 2SC3503E / 2SA1381E and KSC3503D / KSA1381E.

So, I ran some sims to compare. I seem, to remember assessing this early on and thought that complementary 2SC3503E / 2SA1381E would perform better. Must have been expectation bias. You can see from these results that there is very little difference between these. Note that the VAS degeneration resistors are asymmetrical for KSC3503D / KSA1381E to account for the higher gain of the P channel.

In addition, this shows that matching the VAS devices is not necessary. The main impact of mismatch is DC offset. However VR2 allows you to trim this out. This only becomes an issue if the untrimmed DC offset is excessive (like 50mV or more).

I'll work on updating the build guide to cover this.

1kHz into 8R
2SC3503E / 2SA1381E: 1W 0.0011% / 25W 0.0050%
KSC3503D / KSA1381E: 1W 0.0011% / 25W 0.0049%

20kHz into 8R
2SC3503E / 2SA1381E: 1W 0.0041% / 25W 0.0599%
KSC3503D / KSA1381E: 1W 0.0041% / 25W 0.0603%
 
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#70
Thought I would add TTC004B / TTA004B to the analysis. THD performance is a bit worse, but they do offer much better slew rate symmetry. If you look at the build guide, the degeneration on these is heavier than with SC3503 / SA1381. This is to maintain the same thermal stability. You could ease this and improve the performance a bit, the tradeoff doesn't seem worth it to me.

1kHz into 8R
TTC004B / TTA004B: 1W 0.0017% / 25W 0.0081%

20kHz into 8R
TTC004B / TTA004B: 1W 0.0039% / 25W 0.0737%
 
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#71
Well, I dug into TTC004B / TTA004B a bit more. The original build really focused on SC3503 / SA1381 with other devices almost an afterthought. I think I went in assuming these would be the logical best choice. I decided to reassess this.

I tinkered with the VAS degeneration to see if it can use the same R8/R9 values as 2SC3503E / 2SA1381E. To maintain the same VAS current, R4/R5 change to 1.27K. The higher gain of the TTC004B / TTA004B means you give up some thermal stability vs SC3503 / SA1381 when the degeneration is the same. The affect of this is that the output biasing will run 10% to 20% low until the outputs heat up. DC offset looks OK.

I then assessed gain margin. I found that the compensation caps C3/C4 can be lowered from 15p to 10p and maintain the same gain margin and bandwidth.

These are the revised sims. I also compared the TO-247 vs TO-264 devices for those interested in their impact on 8R loads. With these tweaks, TTC004B / TTA004B may be preferred over SC3503 / SA1381. Especially when you look at slew rate, which shows better symmetry. This also confirms that their is little advantage to the double-die devices unless you anticipate a more difficult load.

1kHz into 8R
TTC004B / TTA004B (TO-247): 1W 0.0017% / 25W 0.0079%
TTC004B / TTA004B (TO-264): 1W 0.0017% / 25W 0.0078%

20kHz into 8R
TTC004B / TTA004B (TO-247): 1W 0.0028% / 25W 0.0487%
TTC004B / TTA004B (TO-264): 1W 0.0029% / 25W 0.0411%

Time to update the build guide!
 
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#72
brian92fs said:
Thank you for the acknowledgment. It took several months to complete. But it something I've wanted to do for several years now and this design was a good outlet for that. The excellent Wolverine guide and @Bonsai's HiFiSonix guides inspired me. I hope someone out there finds it helpful.
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Your build guide (as well as the examples you mentioned) was a pleasure to read even if I didn't build the amp.
My "how to do it right" reference examples for manuals are (still) the Users Manuals for the old APT 1 Power amp and APT Holman Preamp.
 
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#73
@brian92fs and @lineup , it seems the LSJ689 is not easy (or at all) to get now. I played with other FETs in LTSpice and the combo of J201 and J175 is looking great. Because those are single FTEs, the layout(s) existing will not work. Also, matching might be needed, I suppose (although the LSJ489/LSJ689 are not matched officially also, I think).
Anything I might be missing or can J201 and J175 a be a good alternative?
 
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#79
@brian92fs can you share the models for the TTA004B/TTC004B? I am getting much worse THD than you in spice using those.
I am using the Toshiba models.

Code: 
*********************************************************************
*  (C)  Copyright  TOSHIBA CORPORATION  2016
*  Date                 :21/08/2016
*  File Name            :TTA004B.lib
*  Part Number          :TTA004B
*  Parameter Ver.       :Ver.2
*  Simulator            :PSpice
*  Model Call Name      :TTA004B
*  TNOM                 :25 degree
*  Pin Assign           :1=Collector 2=Base 3=Emitter
*********************************************************************
.MODEL TTA004B_BJT PNP(
+ LEVEL = 1
+ TNOM = 25
+ IS = 7.5e-014
+ BF = 190
+ IKF = 0.47
+ ISE = 5e-011
+ NE = 2.4
+ NK = 0.63
+ XTB = 1
+ XTI = 2
+ TRC1 = 0.003
+ NF = 1
+ VAF = 6.8
+ VAR = 50
+ BR = 6
+ IKR = 5
+ ISC = 1.0e-21
+ NR = 1.015
+ NC = 1
+ RB = 4
+ RC = 0.125
+ RE = 0.05
+ CJC = 4.09E-011
+ MJC = 0.33
+ VJC = 0.75
+ CJE = 1e-11
+ MJE = 0.33
+ VJE = 0.75
+ EG = 1.11
+ TR = 1E-009
+ TF = 1.59E-009)

*********************************************************************
*  (C)  Copyright  TOSHIBA CORPORATION  2016
*  Date                 :05/08/2016
*  File Name            :TTC004B.lib
*  Part Number          :TTC004B
*  Parameter Ver.       :Ver.1
*  Simulator            :PSpice
*  Model Call Name      :TTC004B
*  TNOM                 :25 degree
*  Pin Assign           :1=Collector 2=Base 3=Emitter
*********************************************************************
.MODEL TTC004B_BJT NPN(
+ LEVEL = 1
+ TNOM = 25
+ IS = 1.374e-013
+ BF = 137.2
+ NF = 1
+ VAF = 11.95
+ IKF = 0.5057
+ ISE = 8.098e-013
+ NE = 1.8
+ BR = 35.11
+ NR = 1
+ VAR = 1000
+ IKR = 10
+ ISC = 1.916e-011
+ NC = 1.5
+ NK = 0.55
+ RE = 0.115
+ RB = 0.885
+ RC = 0.0709
+ CJE = 5.78E-011
+ VJE = 0.75
+ MJE = 0.33
+ CJC = 2.89E-011
+ VJC = 0.75
+ MJC = 0.33
+ FC = 0.5
+ TF = 1.545E-009
+ XTF = 1
+ VTF = 1
+ ITF = 1
+ PTF = 0
+ TR = 0
+ EG = 1.11
+ XTB = 1.4
+ XTI = 6.467)
 
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