JJ Audio Dutch

Hi John,


I have started the Plexi Gold series for the Dutch, Akita and my 47


The Dutch 251 and the Dutch 12 now come with a new custom made Plexiglas circuit board and custom headbasket.

The circuit boards are point to point with Gold pins and Silver bearing Solder. The filtering/decoupling is done with ERO Polypropylene and polystyrene capacitors. The resistors are all Mil Spec 1%.



The power supply gets fresh low ESR capacitors bypassed with film capacitors. The PS also has Silver coated Copper stranded Teflon coated wire. The grounding is improved.



As you know the C12 circuit biases the tube with negative voltage from the power supply. To get this voltage I mod the supply like the C12 supply however I make the negative voltage variable so that I can tune the mic to the capsule. With the variety of capsules available this is an important step.



The 251 is biased with a resistor and a bypass capacitor. The bypass capacitor controls the amount of low end in the mic. The stock 251 value is 22uf just like the C24. The Apex uses 100uf with a small film bypass cap. The Sony C800g uses 330uf. Again with the Dutch 251 I will use these capacitors to tune the circuit. I use values of 22uf to 47uf to get the low end right. I had a client recently come into the shop to "tune his mic, I used this technique and changed the transformer coupling capacitor to get the sound he wanted. I use Mil Spec Solid Tantalum for these capacitors.



There are a variety of transformer coupling capacitors that I offer. PIO/MP Polypropylene, and Wet Tantalum



The problem with sending a mic out without the capsule that will be in the mic is, I cant tune the mic properly. Capsules vary within batches.

 I use the AMI T14 transformer in these mics.