An input transformer is necessary to unbalance the incoming signal and properly interface it with the op amp, noise-free and at the correct impedance. Since you're building a microphone premplifier, you'd pick one of the microphone input transformers from the table below. However, by using different kinds of input transformers it is possible to build a line-level or instrument-level preamplifier instead.


The designations R7, C3, and R8 refer to termination components connected across the transformer secondary, as shown in the DIY500 mkII schematic. R8 provides loading, and R7+C3 comprise a zobel network, when necessary.

A box containing ------ means leave that component out.
A box left blank means we don't have that information yet.
When in doubt, leave the component out.

The following microphone input transformers mount directly to the DIY500 PCB

PhotoBrandModelTypeTurns RatioGain (dBu)%1 THD+NImpedance Ratio (Ω)R6 (Ω)R7
(Ω)		R8 (Ω)C3 (F)PackagePCB
Location		Tested?Price
(1 piece)		Purchase FromINFO
(transformer pictured here)(any brand)(default base configuration)(any type)(primary:secondary relationship)(passive change in level)(overload point)(reflected impedance)(source Z)(zobel R)(loading)(zobel C)(mounting, shielding, and connection methods)(where to install)(tested by Eisen Audio)(cost)(vendor)(click here for additional information)
AltranC-3402-2mic1:8.16+18.23 (unloaded)?150:10k150------100k------mu-metal can, PCB pins-YesN/A (min. qty. >1)directAltran info
AltranC-4124-100line1:1-1?10k:10k620------20k------mu-metal can, PCB pins-NoN/A (min. qty. >1)directAltran info
-beyerdynamicTR/BV 3.10.0.01.001mic 1:1--200:200200------2k2------metal can, PCB pins-Noundiscloseddistributors/ dealersbeyer info
-CinemagCMMI-2CPCmic 1:2+4.87+8 dBu @ 20Hz150:600150------6k2------metal can, PCB pins-YesundiscloseddirectCinemag info
-CinemagCMMI-3.5CPCmic 1:3.5+9.73+7 dBu @ 20Hz150:1k84150------18k------metal can, PCB pins-YesundiscloseddirectCinemag info
-CinemagCMMI-5CPCmic 1:5+13.8+10 dBu @ 20Hz150:3k7515010k39k220pmetal can, PCB pins-NoundiscloseddirectCinemag info
-CinemagCMMI-7CPCmic 1:7+17+7 dBu @ 20Hz200:9k820030k100k22pmetal can, PCB pins-NoundiscloseddirectCinemag info
-CinemagCMMI-8-PCAmic 1:8+17.8-2 dBu @ 20Hz150:9k615010k100k22pmetal can, PCB pins-NoundiscloseddirectCinemag info
-CinemagCMMI-8B3-PCmic 1:8+17.8-1 dBu @ 20Hz150:9k615015k100k100pmetal can, PCB pins-YesundiscloseddirectCinemag info
-CinemagCMMI-10-PCAmic 1:10+19.75-2 dBu @ 20Hz150:15k150------150k------metal can, PCB pins-NoundiscloseddirectCinemag info
-CinemagCMMI-10B-PCmic 1:10+19.75-1 dBu @ 20Hz150:15k150------150k------metal can, PCB pins-NoundiscloseddirectCinemag info
-CinemagCMMI-10C-PCmic 1:10+19.75+5 dBu @ 20Hz150:15k150------150k------metal can, PCB pins-NoundiscloseddirectCinemag info
-CinemagCM-75101APCmic 1:10~+20dB(?)-2 dBu @ 20Hz (?)150:15k150------150k------metal can, PCB pins-YesundiscloseddirectCinemag info
-CinemagCMQEE-3440APCmic 1:18.26~+25dB(?)-2 dBu @ 20Hz (?)150:50k150------360k------metal can, PCB pins-YesundiscloseddirectCinemag info
-JensenJT-MB-CAmic 1:1-0.26+2 dBu @ 20Hz150:150150------3k------metal can, wire leads-No$60.08 USDdirectJensen info
-JensenJT-MB-CPCAmic 1:1-0.26+2 dBu @ 20Hz150:150150------3k------metal can, PCB pins-No$60.08 USDdirectJensen info
-JensenJT-11K8-APCmic 1:3.5+10.5-2 dBu @ 20Hz150:1k8150------15k------metal can, PCB pins-No$47.06 USDdirectJensen info
-JensenJT-13K6-Cmic 1:4.8+13.3-2 dBu @ 20Hz150:3k4515012k36k220pmetal can, wire leads-No$67.72 USDdirectJensen info
-JensenJT-1110K-HPCmic 1:8+17.8-2 dBu @ 20Hz150:9k615030k100k56pmetal can, PCB pins-Yes$78.51 USDdirectJensen info
-JensenJT-115K-EPCmic 1:10+19.75-2.5 dBu @ 20Hz150:15k150------150k------metal can, PCB pins-Yes$76.36 USDdirectJensen info
-JensenJT-115K-Emic 1:10+19.75-2.5 dBu @ 20Hz150:15k150------150k------metal can, wire leads-Yes$73.32 USDdirectJensen info
-JensenJT-DB-EPCmic (DI in revsere) (in reverse) 1:12~+20.5(?)-3 dBu @ 20Hz(?)150:21k6150------220k------metal can, PCB pins-No$73.08 USDdirectJensen info
-JLM AudioJLM 1:4mic 1:4+9.3-7.6 dBu @ 20Hz600:9k6150------10k------metal can, wire leads-Yes$30 USDdirectJLM info
-LundahlLL1532mic or line 1:1~-1(?)+10 dBu @ 50Hz600:6006202k------1600pmetal can, PCB pins-No$59 USD (K&K)distributors or directLundahl info
-LundahlLL1538mic 1:2.5~+8(?)+10 dBu @ 50Hz200:1K25200------------------metal can, PCB pins-Yes$74 USD (K&K)distributors or directLundahl info
-LundahlLL1538XLmic 1:2.5~+8(?)+13 dBu @ 50Hz200:1K25200------------------metal can, PCB pins-Yes$84 USD (K&K)distributors or directLundahl info
-LundahlLL1576mic 1:3.5~+9.8(?)+12 dBu @ 50Hz200:2K45200------------------metal can, PCB pins-No$72 USD (K&K)distributors or directLundahl info
-LundahlLL1577mic 1:7~+16(?)+6 dBu @ 50Hz50:2K455082k------100pmetal can, PCB pins-No$72 USD (K&K)distributors or directLundahl info
-LundahlLL1578mic 1:5~+13(?)+4 dBu @ 50Hz200:5k200------------------metal can, PCB pins-No-distributors or directLundahl info
-LundahlLL1578XLmic 1:5~+12.5(?)+12 dBu @ 50Hz200:5k200------------------metal can, PCB pins-No$84 USD (K&K)distributors or directLundahl info
-LundahlLL1587mic 1:2~+5(?)+2 dBu @ 50Hz200:800200------10k------metal can, PCB pins-No$59 USD (K&K)distributors or directLundahl info
-NeutrikNTM1 mic1:1~-1(?)?200:200200------2k2------metal can, PCB pins-No£27.98 GBPCanfordNeutrik info
-NeutrikNTM4 mic1:4~+10.5(?)?200:3k2200------27k------metal can, PCB pins-Yes£27.98 GBPCanfordNeutrik info
-OEPA262A2Emic 1:2??150:600150------6k2------plastic box, PCB pins-Yes£9.60 GBP (Canford)Canford, Farnell, RSOEP info
-OEPA262A3Emic 1:6.45??150:6k2150------62k------plastic box, PCB pins-No£9.60 GBP (Canford)Canford, Farnell, RSOEP info
-OEPA262A6Emic 1:1??150:150150------1k5------plastic box, PCB pins-No£9.60 GBP (Canford)Canford, Farnell, RSOEP info
-Pico Electronics23xxx entire range several to choose fromvarious leaded, M8 bushingv1 - present ~$55 USDdirect
-PikatronÜP 3093 M 1:2200 PCB pinsv1 - present €21.40 EURBürklin (part # 80 C 780)
-PikatronÜP 3094 M 1:5200 PCB pinsv1 - present €21 EURBürklin (part # 80 C 782)
-PikatronÜP 3095 M 1:10200 PCB pinsv1 - present €21.40 EURBürklin (part # 80 C 784)
-PikatronÜP 3096 M 1:15200 PCB pinsv1 - present €21.40 EURBürklin (part # 80 C 786)
-Sowter3195-C 1:716.3720025kPCB pinsv1 - present£29.30 GBPdistributors or direct
-Sowter4935-C 1:716.2320030kPCB pinsv1 - present£33.76 GBPdistributors or direct
-Sowter9540-C 1:1-1.85200200PCB pinsv1 - present£33.76 GBPdistributors or direct
-Sowter9610-C 1:1019.2320030kPCB pinsv1 - present£35.12 GBPdistributors or direct

Please Note: The above listed transformers are stock items, available new. Some of these same manufacturers produce OEM, custom, and other non-stock items sharing the same footprints. Granted, there are even more options than we're aware of.


Other microphone input transformers can be mounted through more creative means, such as laying sideways and held down with a cable tie. Below are some examples.

BrandModel Turns RatioVoltage
Gain (dBu)		input Z (Ω)1% THD(+N)R7 (Ω)C2 (F)R8 (Ω)PackageIncluded
on PCB		Fully
Tested?		Source(s)INFO
APIAP2622 1:8.16150 leadsv1 - present used market
Tamura (OEM?)GA80071 leadsv1 - present used marketYamaha PM1000 mic i/p
UTC0-1 1:15.81200 solder lugsv1 - present used or Magnetika
UTC0-2 1:15.81200 solder lugsv1 - present used or Magnetika
UTC0-12 1:1.58~3.5200 solder lugsv1 - present used or Magnetika
UTC0-16 1:14.14250 leadsv1 - present used or Magnetika


Specifications subject to change without notice. GMT