ART T4 schematics?

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ART T4 schematics?

Postby mruckus » Thu Feb 08, 2018 10:14 am

Hello! Just did the capsule and tranny mod on my T4, but wondering if anyone has a schematic for this mic so I can confirm the cap supplying the transformer? I assume that the 1uf can be exchanged for the 2.2uf for enhanced frequency response? Thanks!
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Joined: Thu Jan 18, 2018 7:28 pm

Re: ART T4 schematics?

Postby Dave Thomas » Thu Feb 22, 2018 8:09 pm

Hello, thanks for the inquiry.

I believe the ART T4 used the standard 460 schematic which is a CCDA circuit. So, you need to use a 6072a tube and not a 12AX7/7025 or 5751.

Make sure there is no C9 or C10 on the circuit board.

Also, the input impedance is much lower and the input capacitance much higher in the original U47 circuit and the CCDA with the 6072a is more Hi Fi (faster transient response).

To get the U47 response you need to use a pentode strapped as a triode like the U47 which creates more harmonic distortion in the lower register like the original U47 because of the ratio between the higher plate output impedance to the triode plate circuit and the BV8 transformer creates this sound.

However, we use our optimized CCDA circuit in our CM47VE and lots of folks prefer it to an original U47 because its more accurate (HiFi) in the low end but it does not sound as "vintage".

The 2.2 ufd will give you a smoother low frequency response down past 25hz while the 1ufd will roll out the Lf response 6db/octave starting at about 50hz like the original U47.

However, this will depend on what transformer you use. The T47 is a more modern version BV8 while our BV08 is more consistent with the transformer in an early U47.

If you use an AMI T47 or our BV08 then you will get a bit more harmonics in the lower register with the 1ufd but an early roll-off like the original U47.

However, our BV8 will also give you the vintage transformer sound with the CCDA circuit.

Our AK47 does the best job of mimicking an original K47 capsule because they are skinned with 6 micron mylar and use a brass surround like the original.
AK47 capsule.jpg
AK47 capsule.jpg (8.01 KiB) Viewed 788 times
K47-U47.jpg (31.61 KiB) Viewed 788 times

We have some original BV08 being wound for us and we will have these on hand and for sale by the middle of April. These are easier to mount than the AMI T47 and will sell for around $75 USD/
Bv08-Bv11.jpg (373.38 KiB) Viewed 788 times

Cheers, Dave
Dave Thomas
Posts: 167
Joined: Mon Dec 30, 2013 2:46 pm

Re: ART T4 schematics?

Postby mruckus » Fri Feb 23, 2018 4:07 pm

Thanks so much for the all the info! I bought the AK47 and BV8 for the mod, they smoothed the frequency response right out, especially in the upper mids; it sounds great now! I put in a 12AY7, it had a 12AX7 originally. I will check into that output cap this weekend. Thanks again!
Posts: 3
Joined: Thu Jan 18, 2018 7:28 pm

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