High-Value Resistors for Mic Builders and Tempcos for Synths

Construction information for DIY projects, including the MS Mid Side Matrix, Elliptic Equalizer, Mastering Console, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
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mediatechnology
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High-Value Resistors for Mic Builders and Tempcos for Synths

Post by mediatechnology » Mon May 26, 2008 3:37 pm

I'm stocking a couple of hard-to-find resistors that some members here may eventually need.

For the mic builder I currently have a few 2G ohm (for the search engines who visit us 2000 Mohm). I'm almost sold out of these but I have a few 1Gohm on the way with more backordered. These are Vishay RNX0382G00KNLB (2G) and RNX0501G00FNEL (1G). They are 3/8W and 1/2W sizes. (Doubt we'll see that dissipation in a microphone though.)

The other one I stock is the Precision Resistor PT-146 (PT146). This is a 3500 ppm temperature compensating 1K 1% ideal for use in log and anitlog amplifiers. The 1K PT-146-1K and the 2K PT-146-2K (2K available from Music from Outer Space) are often use in DIY synth building. The 2K is a better choice if it's in the feedback loop of an op amp.

Links are here:

http://www.ka-electronics.com/pt146/rnx-2G.htm 2G
http://www.ka-electronics.com/pt146/pt146-35.htm PT-146
http://www.musicfromouterspace.com/cata ... ge=CATALOG PT-146 2K

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mediatechnology
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Temperature ("tempco") Compensation Resistors for Log Amps and VCAs

Post by mediatechnology » Tue Oct 23, 2018 6:16 am

I no longer offer the Gig Ohm GΩ resistors or the PT-146 for sale but I did have to use a PT-146 1KΩ +3500 ppm I had in stock as a replacement for a failed KRL RQ-81 (Tel Labs Q81) found in a Heathkit IG-5238 AC Voltmeter with dB.

Since I did a quick web check on both KRL and Precision Resistor I thought I would post the links here:

Precision Resistor wirewound and SMT temperature compensators: http://www.precisionresistor.com/skin/r ... sators.pdf

KRL Bantry Components: http://krlbantry.com

After replacing the 1979 date code KRL RQ-81 with a PRC PT-146 the dB scale was only about half a needle width off. Now that's precision.

See also: http://microohm.com/temperature/tempmini401.html

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mediatechnology
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Re: Resistors for Mic Builders and Synths

Post by mediatechnology » Sat Aug 21, 2021 8:55 am

Just found a couple of gems in Mouser's in-stock resistor inventory:

1K 3900 ppm/°C linear PTC "tempco" resistor PN 660-LT1/4LT52R102J39: https://www.mouser.com/ProductDetail/LT1-4LT52R102J3900

Not 3300 ppm but in stock. 3600 ppm available from KOA Speer.

Data Sheet 1K 3900 ppm/°C linear PTC resistor PN 660-LT1/4LT52R102J39: https://www.mouser.com/datasheet/2/219/LT-16425.pdf

1GΩ 1/4W Thick Film Resistor:https://www.mouser.com/ProductDetail/279-RGP0207CHK1G0

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mediatechnology
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Re: Resistors for Mic Builders and Synths

Post by mediatechnology » Wed Aug 25, 2021 10:29 am

mediatechnology wrote:
Sat Aug 21, 2021 8:55 am
Just found a couple of gems in Mouser's in-stock resistor inventory:

1K 3900 ppm/°C linear PTC "tempco" resistor PN 660-LT1/4LT52R102J39: https://www.mouser.com/ProductDetail/LT1-4LT52R102J3900

Not 3300 ppm but in stock. 3600 ppm available from KOA Speer.

Data Sheet 1K 3900 ppm/°C linear PTC resistor PN 660-LT1/4LT52R102J39: https://www.mouser.com/datasheet/2/219/LT-16425.pdf

1GΩ 1/4W Thick Film Resistor:https://www.mouser.com/ProductDetail/279-RGP0207CHK1G0
Got the specialty resistors in and had a look at the 1GΩ thick films.

Using the conductance measurement feature of my Fluke 8050A on the 200 nS range I read about 1.07 nS which is about 934MΩ.

I suspect that the tape parallels the other resistors and whoever packed these at Mouser may have touched them and deposited a little bit of oil. Separating the leads on the meter also improved the measurement so there are a lot of variables. Still darn close considering it's in the GΩ range.

Image
Mouser TT Electronics 279-RGP0207CHK1G0 1GΩ Bias Resistor

I'm going to play with the 3900 ppm PTCs next.
After that I make pair a 1GΩ resistor to an LSK170 and see if they're quiet.

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Tempco Resistors

Post by mediatechnology » Mon Aug 30, 2021 3:46 pm

I had a chance to play with the 3900 ppm tempco resistors from KOA Speer.

The response time is really fast.
These are 5% resistors but the 25°C value was almost dead on.

Image
KOA Speer Tempco 1K 3900 ppm Resistor LT1/4LT52R102J3900

The color-coding is kind of unique.
It's "102" (1K brown-black-red) and then "39" (3900 ppm orange-white).

Image

I made a quick xls calculator to see what "fixed" resistor values would be required to make a 3300 or 3400 ppm composite.
I assumed a +/-50 ppm resistor and set its TCR to 0 since its TCR is de minimis compared to the large TCR of the tempco thermistor itself.

The equation I used is TCR = (R1 x TC1 + R2 x TC2) / (R1 + R2).

A 180Ω in series with the 3900 ppm works out to be 3305 ppm with a 25°C value of 1180Ω.

A 150Ω in series with the 3900 ppm works out to be 3391 ppm with a 25°C value of 1150Ω.

When the tempco is padded to lower TCR the voltage divider resistor in a log (R1 below) or expo converter also needs to be scaled by either 1.15 or 1.18.

Image
TI AN30 Log Converters https://www.ti.com/lit/an/snoa641b/snoa641b.pdf

Image
TI AN311 Theory and Applications of Logarithmic Amplifiers https://www.ti.com/lit/an/snoa575b/snoa575b.pdf

I also found this source for tempco resistors: https://synthcube.com/cart/tags/tempco

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