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THAT4301 Analog Engine End of Life. THAT4305 adapter boards.

Posted: Fri Jan 18, 2019 1:14 pm
by mediatechnology

To: All 4301 Customers
From: THAT IC Marketing and Sales
Re: 4301AP20-U, 4301P20-U & 4301W20-U End of Life (EOL)
Date: January 16, 2019

As one of the customers currently purchasing the 4301 part, we are very sorry to tell you that we
must cease production of the 4301 later this year. This applies to the 4301AP20-U, 4301P20-U
and the 4301W20-U.

Why are we discontinuing the 4301?
Our foundry supplier is discontinuing the process in which these products are manufactured.

Will there be a "last time buy" opportunity?
Yes, we will accept new (last-time buy) purchase orders up until May 1, 2019.

All shipments must be taken by May 1, 2020. And, once accepted by us, last-time buy orders
cannot be cancelled, or returned for any reason except those relating to quality.

What alternatives are there to the 4301?
We offer four other Analog Engines: the 4305, 4315, 4316, and 4320. All these are currently in
production and available for immediate shipment. Three of them (the 4305, 4315, and 4320) are
made in our own fab. These products offer a range of price and performance options. The 4305,
in particular, runs from similar power supply voltages as the 4301 and provides the critical VCA
and RMS level detector function of the 4301. It lacks the opamps, but of course there are many
opamps available in the market. We recommend that you consider the 4305 in any redesigns.

In addition, THAT Application Support can offer assistance in adapting one of our other Analog
Engines to fill your requirements.

Where do I go to ask questions?
If you have any questions or concerns regarding the last time buy, please contact Tom Ryan,
Customer Service Supervisor, at 508-478-9200 x138, or via email at
Applications Support can be reached at
pdf here: ... Notice.pdf

Re: THAT4301 Analog Engine End of Life. Last Time Buy May 1, 2019

Posted: Wed Feb 06, 2019 11:45 am
by emrr
I see my inventory are all the 'A' version, and that was discontinued 4-5 years ago. I hardly see a difference, and maybe the current version had improvements that obsoleted the need for two versions. All the relevant project discussions are long gone from here and the other place, remind me again why the 'A' was specified, and does it matter now?

Re: THAT4301 Analog Engine End of Life. Last Time Buy May 1, 2019

Posted: Wed Feb 06, 2019 12:16 pm
by JR.
from looking at the data sheet the 4301A appears to deliver slightly lower THD+N
THAT wrote: In the 4301A, the VCA is selected for low THD at extremely high levels.
So better part for hot levels. Looking at distortion plots, there appears to be a small increase of THD at lower level for selected A parts, but unlikely to be audible or significant.


Re: THAT4301 Analog Engine End of Life. Last Time Buy May 1, 2019

Posted: Wed Feb 06, 2019 1:21 pm
by emrr
Ah yes, I see it now. Thanks.

Re: THAT4301 Analog Engine End of Life. Last Time Buy May 1, 2019

Posted: Wed Feb 06, 2019 2:06 pm
by mediatechnology
I still have a few 4301A that I used in my Pico.
There really isn't much difference in 4301/4301A THD other than at high input levels.

I would definitely score some regular 4301 while you can.
The good news is that there are now 18/tube versus 20 so you don't have to spend quite as much.
The 20 pin DIP over-mold got a little bigger a couple of years ago and tubes shrank by 2 units.

THAT4301 Analog Engine Adapters Using THAT4305

Posted: Thu Nov 10, 2022 4:07 pm
by mediatechnology
Sometime ago I found Profusion's THAT4305 adapter for the THAT4301:

Thought it would be a good idea to post it.

I also have a couple of untested Gerbers for a THAT4305 to THAT4301 adapter and a THAT4305+THAT2181 to 4301 adapter if anyone is interested.
They were sent to me by Rosalfonso Bortoni of THAT.
I'll try and get pdfs of the schematics.


THAT4305 to THAT4301 Adapter

THAT4301 THAT4305 Adapter
(9.5 KiB) Downloaded 77 times
THAT4301 THAT4305 Adapter Schematic
(44.93 KiB) Downloaded 71 times

High performance version with extended DR detector and 2181 VCA.

THAT4301 THAT4305 +2181 High Performance Adapter
(11.24 KiB) Downloaded 66 times
THAT4301 THAT4305 High Performance Adapter
(50.14 KiB) Downloaded 72 times

THAT4301 Analog Engine Adapters Using THAT4305

Posted: Sat Nov 12, 2022 11:34 am
by mediatechnology
I added the schematic pdfs for the THAT4305 to THAT4301 adapters in the post above.

I had a chance to run some quick tests on the extended dynamic range detector and it works very well.
The DR is greater than 100 dB.
At -80 dBu it only had about 1 dB of error.
+20 dBu and all points in-between down to -70 dBu (or better) were spot on.

A wide-range level detector using the THAT4305.

The 4305's internal VCA forms a 2:1 compressor for the RMS detector thus expanding its' dynamic range.
This changes the normal 6 mV/dB scaling of the detector to 3 mV/dB.
U3A scales the 3dB/mV output to the 6 dB/mV of the THAT4301.

Not shown are the "external" series resistor, Rin, and coupling cap for the VCA's current-domain input.
I used a 95K Rin (+10uF) to obtain a 0V output for 0 dBu in.
Ct was 10 uF +10R to ground.

The attack time of the RMS detector, combined with the resulting compressor overshoot, causes a much faster attack time than the RMS detector.
Sims also show a longer release time.
I'm going to investigate this further.

Re: THAT4301 Analog Engine End of Life. THAT4305 adapter boards.

Posted: Tue Nov 15, 2022 4:33 pm
by mediatechnology
I did some measurements of the log conformity of the 4305 High Performance RMS detector.

A wide-range level detector using the THAT4305.

Test conditions:

Rin =20KΩ.
0 dBu in was adjusted to 0V out using a potentiometric trim ahead of the 10 µF Cin.
Ct =10 µF.
T = 23.9°C at device pkg.
No scale factor buffer. (3.1mV/dB)

Input in dBu vs. RMS Out

Cin grounded: -248mV
-80: -240 mV
-70: -213.6
-60: -185.3
-50: -155.2
-40: -124.5
-30: -93.6
-20: -62.3
-10: -31.2
0: +0.01 mV
+10: +31.3
+20: +62.7

Looks like the error is only about 2.6 dB at -80 dBu; 1.3 dB at -70 and 0.7 dB at -60 dBu.

Or, looking at it another way: 80 dB DR with less than 1 dB error; 100 dB DR with <3 dB error.

Since the detector uses a 2:1 feedback compressor to extend dynamic range Ct should be 20 µF, instead of 10 µF, to match the 4301's attack/release characteristics.

Re: THAT4301 Analog Engine End of Life. THAT4305 adapter boards.

Posted: Tue Dec 13, 2022 10:17 pm
by emrr
The attack release changes are interesting. Looks like changing the RMS cap, and trimming the input resistor are both necessary if substituting in an existing build.