Apex 460 DIY Mod Advanced Audio Forum

[Papa Tango Charly]

On the copie of the advanced forum
https://groupdiy.com/threads/advanced-audio-forum-is-down.81107/It says "5-connect pin 8 to ground through a 270k resistor and tie a 2.2/250v capacitor to pin 8. The other side of this capacitor feeds the red wire of the output transformer."
I'm doing a simple Apex Mod Advanced audio
Can someone confirm that this capacitor 2.2/250v goes on C8
Thanks


It

 

[Rybow]

Yes. The 2.2/250v cap would replace the C8 capacitor. Those instructions read as if you were building the mic from scratch point to point

 

[Papa Tango Charly]

Thanks

 

[Papa Tango Charly]

Yes. The 2.2/250v cap would replace the C8 capacitor. Those instructions read as if you were building the mic from scratch point to point

Have you got any other advise for this mod i would like to put a 6.5.1 transformer from 3U and make a 47ich kind of mic. thank you

 

[Rybow]

That transformer is nearly half the ratio of the stock transformer as well as suggested replacements. I am certainly no expert, but it might cause impedance issues. That being said I read an article about the CCDA circuit in the Apex 460 allows for a lower impedance, so it could be totally fine! No harm in trying it out

From what I understand, a lot of the 47 vibe is from the capsule and head basket design. The transformer plays a smaller role on the tone equation.

 

[Papa Tango Charly]

Thanks Rybow

 

[fsalter]

i have modded a few 460's, and the stock transformer is actually very good It is flat to 20hz, and changing it does not offer any advantage. Go see the write up at Fox Audio Research. The most important mods are capsule and changing the 12ax7 tube to a 12at7 or a 6072.

 

[Papa Tango Charly]

Ok Thank You

 

[Nen'O]

Hi,
I have 2 Apex 460/Badaax T11 A modded with Advanced Audio Apex 460 Mod Pack.
Changing 2x 62V zener diodes in power supply is crucial for this mod, you can keep stock capsule but AK12 capsule is waay better, smoother. C10 and C9 caps have to go out. 2.2uFd PIO works much better for C8.
12ax7 will overload transformer, EH 6072 does the job, you can probably use lower output tubes as well 12at7/12au7/12ay7. BV 18 transformer is much much better option than BV 11 for this mod and it's only few $ more. Stock transformer does the job same as capsule if you want to save some $$ and have decent tube mic, but IMO AA 460 pack is great value for money, you get top notch microphone for an amazing price and they are great people to work with.
Cheers

 

[neowalla]

Hi,
I have 2 Apex 460/Badaax T11 A modded with Advanced Audio Apex 460 Mod Pack.
Changing 2x 62V zener diodes in power supply is crucial for this mod, you can keep stock capsule but AK12 capsule is waay better, smoother. C10 and C9 caps have to go out. 2.2uFd PIO works much better for C8.
12ax7 will overload transformer, EH 6072 does the job, you can probably use lower output tubes as well 12at7/12au7/12ay7. BV 18 transformer is much much better option than BV 11 for this mod and it's only few $ more. Stock transformer does the job same as capsule if you want to save some $$ and have decent tube mic, but IMO AA 460 pack is great value for money, you get top notch microphone for an amazing price and they are great people to work with.
Cheers

Is their mod pack a DIY kit that you can install? On their website it looked more like you had to send the mic to them to be modded. I'm kind of hoping the former. I live in Canada and the shipping is much cheaper than going with the Microphone-Parts mod kit shipping from the US.

 

[kingkorg]

Is their mod pack a DIY kit that you can install? On their website it looked more like you had to send the mic to them to be modded. I'm kind of hoping the former. I live in Canada and the shipping is much cheaper than going with the Microphone-Parts mod kit shipping from the US.

I managed to dig this up from WBM. This applies to the Apex as well.

Hi Sevin, upgrading a tcm 1050 to our CM47ve microphone is a fairly simple procedure.
Now, some of the very early 1050 microphones had the 12AX7 tube soldered into the circuit board and replacement of the tube in this version is much more difficult and requires a bit of "extreme" electronic techniques.

It is impossible to heat all 9 pins at once without setting the circuit board on fire. The only way to remove the 12AX7 is to don eye protection, put a rag on the tube and smash it with a hammer over the dust bin. Then cut away all the pieces and unsolder each of the pins one at a time. Then clean out the 9 pin holes with a solder sucker and solder wick. Then you can solder back in a PRE-TESTED 6072a tube. Make sure it is thoroughly tested before soldering it back in!!!!

The later tcm1050 microphones all have a tube socket which makes the tube replacement much easier.

The following changes should be made to the 1050 circuit.

1) C9 & C10 should be removed. They can be cut out and are not required into today's modern world. C9 & C10 where meant as RF filter from the days of Taxi cab's operating their 2-way radios on the upper AM radio frequencies.
These capacitor values were spec'd to low in the 1050. So, C9 & C10 in parallel to ground causes the distortion at 11khz to increase 4 times because of the inherent resonance between these capacitors and the low buget output transformer.
SIMPLY REMOVE THESE CAPACITORS...DO NOT...STRAP THEM WITH A WIRE JUMPER AS THIS WILL SHORT THE OUTPUT OF THE TRANSFORMER TO GROUND.

2) C6 & C7 should be removed. These bypass the cathode resistor in the 1st stage. However, they are not necessary in the 1050 circuit and only necessary in a single stage C12 type circuit.
Once properly modified the 1050 circuit is superior to any single plate output circuit. With C6&C7 removed the circuit is more linear without any LF roll-off. The gain drops 4db but this increases the headroom and signal to noise ratio by 4db.
AGAIN SIMPLY REMOVE THESE CAPACITORS...DO NOT... STRAP THEM WITH WIRE JUMPERS AS YOU WILL SHORT OUT THE CATHODE BIAS RESISTOR.

3) Replace C8 the 1ufd outut electrolytic coupling capacitor with a 2.2ufd metal film. This will place any resonance between C8 and the output transformer down into the sub-sonics where it will not negatively effect the audio signal.

4) Replace the 12AX7 with a 6072a this lowers the gain another 2db but the output impedance on the first plate is much lower. A new Sovtek 6072a selling for around the $20 is more than adequate in this clever CCDA type circuit.

Now, you will have optimized the 1050 circuit which is a 2-stage CCDA (constant current draw amplifier) with an output impedance 10 times lower than the venerable original U47 circuit.

5) Replace the stock economy transformer which has a 10.5:1 turns ratio with our BV8 having a 6.5:1 ratio. The green wire goes to pin 6 and the black wire to pin 5 on the 7 pin connector. The white wire goes to pin 4&7 on the 7 pin.
The red wire is attached to the red wire that goes to the output of C8. Remember, the gain has dropped by nearly 6db in the front end but the BV8 has 5db less loss than the economy 10.5:1 transformer.

6) The economy 32mm (k67) type capsule with its 3-5 micron thick diaphragms is replaced by our AK47 capsule which is a single back-plate w/dual 6 micron diaphragms having identical specs to the original K47 used in the U47 & M49.
The K47 will fit onto the existing saddle but will mount either 2mm closer to the front or the rear. I prefer to move it back 2mm.

7) Next replace Z5 & Z6 sometimes noted D5 & D6 inside the power supply with two 62v Zener diodes. This will drop the power supply B+ voltage to 124v dc + and - 2%. These supplies are usually set for 144v dc and this will place about 70v dc on the capsule. The AK47 and the original K47 capsule seem to give optimum results when they are polarized between 55 and 60v which is what you will get from a 124v dc supply. These are located behind the pattern switch on the board.

That's it!!! If this is all done correctly then the microphone should fire up and sound like a WORLD CLASS MICROPHONE.

I will try and take some pictures of the next 1050 we get in for upgrade.

Cheers, Dave

And here's the schematic of another variant of the mod with plate out.

http://www.mark-o-matic.com/media/apex460-c12-mod.jpg

 

[neowalla]

Yeah I going to try this one. If this is seriously all it takes, then there's no sense spending $250 on a new PCB and parts that aren't needed to do a "Fox 460" mod.

 

[kingkorg]

Yeah I going to try this one. If this is seriously all it takes, then there's no sense spending $250 on a new PCB and parts that aren't needed to do a "Fox 460" mod.

Yes as far as i know, according to what he describes on his site. You can go either plate out (c12) or what he calls "ccda", although some people more knowledgeable than me say it isn't true ccda.

 

[neowalla]

I've modded (rebuilt, really) one 460 with Microphone-Parts.com "Fox 460" circuit kit, and I'm just finishing another 460 with Dany's D251 PCB, and BOM, and styros from vintagemicrophonepcbkit.com. A third 460 I'll do the above mod and compare them all. I keep seeing used Apex 460's for sale and I can't resist this addiction.
I've ordered the parts listed above from Mouser already. Maybe at some point I'll record some samples with each one and post them if anyone is interested.

 

[Nen'O]

Is their mod pack a DIY kit that you can install? On their website it looked more like you had to send the mic to them to be modded. I'm kind of hoping the former. I live in Canada and the shipping is much cheaper than going with the Microphone-Parts mod kit shipping from the US.

Hi,
i’m on 5th mic modded with parts and help from AA guys. Never had to send mic to them.
I can see mood pack is still available on their website
you can drop them a message.
https://advancedaudio.ca/products/apex-460-mod-pack

 

[Rybow]

I've modded (rebuilt, really) one 460 with Microphone-Parts.com "Fox 460" circuit kit, and I'm just finishing another 460 with Dany's D251 PCB, and BOM, and styros from vintagemicrophonepcbkit.com. A third 460 I'll do the above mod and compare them all. I keep seeing used Apex 460's for sale and I can't resist this addiction.
I've ordered the parts listed above from Mouser already. Maybe at some point I'll record some samples with each one and post them if anyone is interested.

You’ll have to post once you fire up that D251 460. That’s next on my list. When funds allow I’d like to mod my 460 to “ultra premium”. Then watch as the gold records cover my wall

Just got a Nady TCM1150 for the low price of $0.00. It’s missing its 7 pin cable and shock mount. Tested with my 460 cable, and it works just fine! I used the 1150 to confirm the EH 6072a I ordered from the tube store is no good.

I didn’t remove C6 & C7 in my 460. Might be worth a try?

One issue I came across in my 460 was the polarization voltage to the rear diaphragm was half what it should have been. In figure 8, I measured around 60V that would then drop 10V almost immediately. Replacing the capacitor and resistor in the power supply that are right after the pattern switch fixed that issue.

 

[neowalla]

You’ll have to post once you fire up that D251 460. That’s next on my list. When funds allow I’d like to mod my 460 to “ultra premium”. Then watch as the gold records cover my wall

I plugged it in to give it a quick test and I have to say it is very underwhelming. Sibilant, not particularly quiet, worse than stock honestly. I'm going to go through the build thread and try to do some troubleshooting, but I have to say there is definitely value in the kits that Matt offers at Microphone-parts.com. The instructions leave nothing to guess at and search for some random forum thread from 10 years ago, all the parts you need are there, and as long as you can follow directions and aren't a complete hack, you will end up with a great mic. Lesson learned.

 

[Gus]

I would reinstall the two RF caps however, use a lower value matched pair. The cap matching helps with CMRR.
A simple adjustment that you don't see posted by "Mic gurus" for this circuit is the simple use of a LPF cap between the stage.
I did post a schematic years ago at an older version of this forum.
You can install a 12at7 the LPF cap plate to ground and adjust the RF caps values with every thing else stock. Sometimes electrolytic caps can sound good as the output coupling cap location.

 

[neowalla]

Hi,
i’m on 5th mic modded with parts and help from AA guys. Never had to send mic to them.
I can see mood pack is still available on their website
you fan drop them a message.
https://advancedaudio.ca/products/apex-460-mod-pack

I'll give it a try. I bought one of their AK12 capsules for another build and it sounds good.

 

[Rybow]

I plugged it in to give it a quick test and I have to say it is very underwhelming. Sibilant, not particularly quiet, worse than stock honestly. I'm going to go through the build thread and try to do some troubleshooting, but I have to say there is definitely value in the kits that Matt offers at Microphone-parts.com. The instructions leave nothing to guess at and search for some random forum thread from 10 years ago, all the parts you need are there, and as long as you can follow directions and aren't a complete hack, you will end up with a great mic. Lesson learned.

To be honest this is not what I expected you to say. Hopefully a little troubleshooting is all that is needed! Are you still using the stock capsule?
Whenever a mic I’ve worked on is noisy, a good cleaning with a flux remover pen often solves the issue.
Microphone parts stuff is pretty good. I have an RK47 capsule from the first batch they had in a FET847 mic. Sounds unreal

I would reinstall the two RF caps however, use a lower value matched pair. The cap matching helps with CMRR.
A simple adjustment that you don't see posted by "Mic gurus" for this circuit is the simple use of a LPF cap between the stage.
I did post a schematic years ago at an older version of this forum.
You can install a 12at7 the LPF cap plate to ground and adjust the RF caps values with every thing else stock. Sometimes electrolytic caps can sound good as the output coupling cap location.

Aha! That’s some good info Gus. If I’m reading this right, lowering and matching C9 & C10 will take care of the resonance issue, and lower the noise when using a 12AT7. I have a 12AT7 in mine right now, and while there is some hiss it’s not unusable.

I’ve got a 200pF cap plate to ground. I haven’t been able to put this mic through it’s paces yet, I can say that the sound has smoothed out quite a bit from stock