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
High-Value Resistors for Mic Builders and Tempcos for Synths
- mediatechnology
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- Location: Oak Cliff, Texas
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- mediatechnology
- Posts: 5444
- Joined: Sat Aug 11, 2007 2:34 pm
- Location: Oak Cliff, Texas
- Contact:
Temperature ("tempco") Compensation Resistors for Log Amps and VCAs
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
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
- mediatechnology
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- Joined: Sat Aug 11, 2007 2:34 pm
- Location: Oak Cliff, Texas
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Re: Resistors for Mic Builders and Synths
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/KO ... MEzw%3D%3D
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/TE ... LHzw%3D%3D
1K 3900 ppm/°C linear PTC "tempco" resistor PN 660-LT1/4LT52R102J39: https://www.mouser.com/ProductDetail/KO ... MEzw%3D%3D
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/TE ... LHzw%3D%3D
- mediatechnology
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Re: Resistors for Mic Builders and Synths
Got the specialty resistors in and had a look at the 1GΩ thick films.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/KO ... MEzw%3D%3D
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/TE ... LHzw%3D%3D
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](https://proaudiodesignforum.com/images/jpg/Mouser_1G_Ohm_Resistors.jpg)
Mouser TT Electronics 279-RGP0207CHK1G0 1GΩ Bias Resistor
I'm going to play with the 3900 ppm PTCs next.
After that I'll pair a 1GΩ resistor to an LSK170 and see if they're quiet.
- mediatechnology
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Tempco Resistors
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](https://proaudiodesignforum.com/images/jpg/KOA_Speer_Tempco_1K_3900ppm_Resistor_LT1_4LT52R102J3900.jpg)
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](https://proaudiodesignforum.com/images/jpg/KOA_Speer_Tempco_1K_3900ppm_Resistor_LT1_4LT52R102J3900_Closeup.jpg)
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](https://proaudiodesignforum.com/images/jpg/TI_AN30_Log_Amp_Figure_1.JPG)
TI AN30 Log Converters https://www.ti.com/lit/an/snoa641b/snoa641b.pdf
![Image](https://proaudiodesignforum.com/images/jpg/TI_AN311_Expo_Amp_Figure_2.JPG)
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
The response time is really fast.
These are 5% resistors but the 25°C value was almost dead on.
![Image](https://proaudiodesignforum.com/images/jpg/KOA_Speer_Tempco_1K_3900ppm_Resistor_LT1_4LT52R102J3900.jpg)
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](https://proaudiodesignforum.com/images/jpg/KOA_Speer_Tempco_1K_3900ppm_Resistor_LT1_4LT52R102J3900_Closeup.jpg)
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.
TI AN30 Log Converters https://www.ti.com/lit/an/snoa641b/snoa641b.pdf
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