Question: Transformer for c800-G

[JessJackson]

According to the attached document the c800g is 7:1

Oliver from TAB suggested to me a UM351 but I was leaning towards the T67 or the T47 for this application.

Any suggestions for the best matched to 6au6a?

Cheers

J

 

[Melodeath00]

Maybe ask JJ Audio? I think they are using the same transformer as the C800G in their Akita, or at least the same brand, maybe?

 

[Gus]

I built a C800G 6au6 like circuit sometime ago to check out what people liked about it.

I had to burn in then selected tubes for low noise and the power supply needs to be low noise

IMO is not a good DIY project

 

[Pip]

I would take Oliver at his word personally. He does this stuff a lot.

The C800G mic is a very unique and special animal. That Peltier junction is critical to the sound of the mic as is the oil bath that surrounds the tube. I see much of a path to try and recreate this machine in a DIY package. Also it is still under manufacture keep that in mind.

It is also not what I would call a go to mic it has its uses but they are very specific voice timbres I have discovered. I had a chance to buy one years ago and kicked myself for a long while untill I realized that I probably wouldn't use it that much.

Maybe a C37a?

 

[JessJackson]

I would take Oliver at his word personally. He does this stuff a lot.

The C800G mic is a very unique and special animal. That Peltier junction is critical to the sound of the mic as is the oil bath that surrounds the tube. I see much of a path to try and recreate this machine in a DIY package. Also it is still under manufacture keep that in mind.

It is also not what I would call a go to mic it has its uses but they are very specific voice timbres I have discovered. I had a chance to buy one years ago and kicked myself for a long while untill I realized that I probably wouldn't use it that much.

Maybe a C37a?

I should have given a little more background before writing my specific post.

I own two c800-g's and have some spare populated replacement boards that I ordered from sony a while ago, all i need to add is housing, tube capsule (k67) and transformer. I will use original neumann capsule and add filter 100pf cap. if top end is still not smooth i will try replacing the electrolytic caps one by one.

I've never been happy with the top end of my sony's and instead of modding and ruining resale value of mic, I will build a hacked one, trying different types of components until top end is smooth.

Your wrong about Peltier section though, it doesn't contribute to the sound of the mic, it is purely to keep tube slightly cooler, there is no oil bath, its a small amount of silicone paste between the Peltier and the tube to help the heat transference..  its a complete gimmick and definitely not necessary in the build.

cheers J

 

[Pip]

I would take Oliver at his word personally. He does this stuff a lot.

The C800G mic is a very unique and special animal. That Peltier junction is critical to the sound of the mic as is the oil bath that surrounds the tube. I see much of a path to try and recreate this machine in a DIY package. Also it is still under manufacture keep that in mind.

It is also not what I would call a go to mic it has its uses but they are very specific voice timbres I have discovered. I had a chance to buy one years ago and kicked myself for a long while untill I realized that I probably wouldn't use it that much.

Maybe a C37a?

I should have given a little more background before writing my specific post.

I own two c800-g's and have some spare populated replacement boards that I ordered from sony a while ago, all i need to add is housing, tube capsule (k67) and transformer. I will use original neumann capsule and add filter 100pf cap. if top end is still not smooth i will try replacing the electrolytic caps one by one.

I've never been happy with the top end of my sony's and instead of modding and ruining resale value of mic, I will build a hacked one, trying different types of components until top end is smooth.

Your wrong about Peltier section though, it doesn't contribute to the sound of the mic, it is purely to keep tube slightly cooler, there is no oil bath, its a small amount of silicone paste between the Peltier and the tube to help the heat transference..  its a complete gimmick and definitely not necessary in the build.

cheers J

Ah ha! I would still go with Oliver on this as I said he has a lot of experience. If memory serves me right the original C800 had oil in the heat tube that pulled heat away into the radiator housing. As it was described to me by a Sony tech at AES, it kinetically flowed back and forth by natural fluid dynamic properties. Could be hype I guess!? But about 10 years ago Sony took the mic off of its line for over a year to re-tool it to meet ISO 9000 environmental standards. Maybe that changed then. I won't debate whether or not cooling a tube makes for less noise or not. I have never A/B'ed a mic while cooling its tube! ;D

 

[Moby]

That Peltier junction is critical to the sound of the mic as is the oil bath that surrounds the tube

Just to add comment about this. No, there is no oil inside, just the silicone paste and thin copper foil around tube to ensure better  cooling. Btw, I don't see any problem with recreating this in the DiY. I'm not sure about transformer winding scheme/inductance, but I'm sure that one of the vintage Neumann BV tx will drop in. At last, measuring primary inductance of the original transformer can be a good start.

 

[Gus]

I have not been inside a C800G however the PCB mounted parts in the pictures I saw on the web look fine.

The 6AU6 circuit I built based on the schematic does not have a harsh high end it is a textbook plate out circuit.  It does have a higher plate current than some other tube microphones. 
I tried different capsules and different heater voltages.

What types of preamps are you using, transformer or transformerless?

It is important that the heater power supply section is low noise. 

 

[Moby]

I used c800g many tmes, also I repaired one with faulty tubes. Yes, mic is very specific, sounds huge and yes, it has some hf "boost" but I like it on some vocals, specially male. It matched well with vintage isa focusrite blue, but it worked for me with other preamps like Neve, etc.... I think that main hf character comes frommcapsule, but I just guess :/

 

[Triode-Joe]

FWIW

I have a Telefunken (Schoeps) CM 51/U that uses a 6AU6 (EF94), this is one of my favorite microphones.
The transformer is a T44/2, it's the same size as a T14 but has a turns ratio of 9:1. It looks like the AMI T13 would be a very close match.

Joe

 

[gyraf]

The C800G tube is probably not an ordinary 6AU6 - if you take a close look, it's longer than a real 6AU6. My best guess is that it is the Russian near-equivalent (forgot the number, is it 6J4P?) - and using those, you get fewer rejects when checking for microphonability.

Btw, the rejects can be used in the PSU (and if you're in a pinch, you can use a tube from the PSU in the mic)

Jakob E.

See also:
http://www.groupdiy.com/index.php?topic=23666.0
http://www.groupdiy.com/index.php?topic=49521.0

 

[Moby]

The C800G tube is probably not an ordinary 6AU6 - if you take a close look, it's longer than a real 6AU6. My best guess is that it is the Russian near-equivalent (forgot the number, is it 6J4P?) - and using those, you get fewer rejects when checking for microphonability.

Btw, the rejects can be used in the PSU (and if you're in a pinch, you can use a tube from the PSU in the mic)

Jakob E.

See also:
http://www.groupdiy.com/index.php?topic=23666.0
http://www.groupdiy.com/index.php?topic=49521.0

Russian 6AU6 is 6Ж4П. If I remember correctly original tube was marked as "Sony 6AU6" but dimensionally it's same as 6Ж4П. So I replaced the dead tube with Russian. In the PSU are American 6AU6's and yes, they can work inside mic but sounds bit different.
EF94 is also possible replacement but I never tried those.

 

[JessJackson]

Yes Russian 6J4P is the best replacement tube. Ive been using them for years and they don't have any complaints. In fact I have two sony's. one with original 6au6a and one with russian tube. you won't be able to tell the difference sonically. To my ear, there is no difference.

My power supply will have no rectifier tubes in it. This design was a bit pointless.. yeah right.. slow ramp up.. tube life lol

 

[Melodeath00]

Very interesting about the tube. I'd love to eventually see a GroupDiY C800G build.

JJ Audio I believe is using 8:1 transformers made by a company that also made them for Sony. Or maybe the 8:1 was a mistake, and they have actual 7:1 C800G transformers?

They also specify that the transformer coupling cap in the C800G is a Vishay, and that they specifically use a "Vishay (ERO) MKP 1840" in the Akita. Whether or not that is the same exact cap, I have no idea. I've never used let alone opened a C800G.

 

[Gus]

Very interesting about the tube. I'd love to eventually see a GroupDiY C800G build.

Why?

Also look in the microphone meta
Why clone something do something different.

 

[JessJackson]

Very interesting about the tube. I'd love to eventually see a GroupDiY C800G build.

Why?

Also look in the microphone meta
Why clone something do something different.

I agree, I think there are ways to improve easily on this design. It was Sony's quick way of getting their own u67 out there.

Heres some pics of the boards I have. You can see that the output cap is a ERO MKP1841, I read that Vishay took over this name. I also heard the vishay MKT 1822 is a GREAT audio cap.

 

[Melodeath00]

Very interesting about the tube. I'd love to eventually see a GroupDiY C800G build.

Why?

Also look in the microphone meta
Why clone something do something different.

Well, not everyone wants to design or redesign mic circuits. I'm happy enough just building them. I am fascinated by mic circuits, but I am not currently at the stage where I want to mess with them. Building copies is enough for me, right now. I don't think I could do better than Sony. Plus, building a clone would be a lot cheaper than a real C800G, no matter how you look at it.

What do you mean by "microphone meta"

 

[Melodeath00]

Jess, what transformer did you end up going with?

 

[JessJackson]

Jess, what transformer did you end up going with?

sorry for bringing this thread back from so long ago, I just came across it. I ended up going with a UTC A-24 wired backwards