6922/E88CC as impedance converter in microphones?

[rock soderstrom]

What are your experiences with this type of tube as an impedance converter in microphones?

There are some well-known microphones that work with it, but there are also many people who advise against it. What do you think? I would possibly want to use them as a CF. How well does this tube cope with high Rg? Is it perhaps better to use b2b diodes for this?

 

[TLRT]

I think Rode K2 uses that, and the EMI REDD mic with an extra EF86. Not a big fan either of them, K2 sounds very sterile.

 

[rock soderstrom]

I think Rode K2 uses that, and the EMI REDD mic with an extra EF86. Not a big fan either of them, K2 sounds very sterile.

I used the Rode K2 for a long time, but it's not my favourite microphone either. I don't know whether this is due to the tube or the rest of the SS circuitry. The K2 doesn't have a transformer either...

The AT4060 also uses this tube, I think as WCF(?). I have no experience with it, but I know people who like it.

 

[rock soderstrom]

and the EMI REDD mic with an extra EF86.

I haven't seen this before, it seems to be a combination of a REDD47 mic pre plus an additional (?) Ef86. Does anyone have a schematic or gut shots?

 

[capacitorless]

I have limited experience in this area, but the InnerTube Mag Mic MM2000/MM2006 uses an ECC88. I did a little looking when I had to debug mine (it ended up being fixed by drying out the capsule - Stayne was helpful) and it looked like it was a classic plate loaded transformer output. Most of the circuitry was potted and I didn't see markings on the transformer when I had things out.

 

[TimG]

Rode NTK also uses the same tube 6922 for that sound everyone is chasing. Lol.

 

[rock soderstrom]

Rode NTK also uses the same tube 6922 for that sound everyone is chasing. Lol.

 

[vintagelove]

The modern Innertube Audio, Tube 87 insert uses it as well. It’s a mic that when you raise the fader, the vocal jumps to the front of the mix.

Makes for an interesting comparison with a Sony C800G. Definitely in the same family, with the Neumann displaying that classic midrange cut/authority, while the Sony is relaxed in that area, but with an extended high end.

 

[pasarski]

Innertube audio also seems to be selling a tube mic built in a Chinese mini U87. For $2795

https://innertubeaudio.com/mini-87

 

[Accelerator]

@rock soderstrom​

What are your experiences with this type of tube as an impedance converter in microphones?

There are some well-known microphones that work with it, but there are also many people who advise against it. What do you think? I would possibly want to use them as a CF. How well does this tube cope with high Rg? Is it perhaps better to use b2b diodes for this?

Lewitt Audio use the E88CC – ECC88 – 6922 - 6DJ8 valve, for their “Flagship” LCT 1040 (Tube & Fet) Hybrid system microphone (€3.499)…

Till this time in any video(s) that I have watched and Ι heard this LCT 1040 (Tube & Fet) Hybrid system microphone (€3.499), with this “Designed and engineered in Austria” capsule, with the “all the way to the right” choice to Tube Circuit, in the Tube “Clean” and Tube “Saturated” Mode, Ι heard a very “bright” and “Hi-Fi” tone and only in the Tube “Warm” Mode and the Tube “Dark” Mode it “lose up” some of this ultra “brightness” but not this “Hi-Fi” & “Transparent” tone, and (IMHO) because of this “brightness” and this “Hi-Fi” & “Transparent” tone, I didn’t find -in all these Tube Modes- something that I have to like it or to adore it as a Tube vocal microphone…

Their much more economical & “humble” PURE TUBE (Studio Set) cardioid polar pattern microphone (€1.299), with the much more economical & “humble” ECC82 - 12AU7 valve, with all of this “vintage character”, sound like a “tube warmth” Oasis in the desert, in a direct comparison with their “Bright”, “Hi-Fi” & “Transparent” LCT 1040 (Tube & Fet) Hybrid system microphone (€3.499), so if they use the same “Designed and engineered in Austria” capsule in cardioid (only) polar pattern then we have to consider that the very “bright” and “Hi-Fi” & “Transparent” tone comes from the tube characteristics of the E88CC – ECC88 – 6922 - 6DJ8 valve in the LCT 1040 (Tube & Fet) Hybrid system microphone (€3.499) circuit…

 

[mhelin]

Fox Audio Research tried to use this tube in close to VF14 operation point of U47 but in the end it wasn't success. You can read it from here: https://www.foxaudioresearch.ca/6922.htm
Anyway, it works in Rode mics (sans output transformer), so it must be how you use it.

 

[rock soderstrom]

Fox Audio Research tried to use this tube in close to VF14 operation point of U47 but in the end it wasn't success. You can read it from here: https://www.foxaudioresearch.ca/6922.htm
Anyway, it works in Rode mics (sans output transformer), so it must be how you use it.

Yes, I had also read this report. He thinks the E88CC is very good, but after some time he had problems with periodic background noise, which is of course not so good.


It is noticeable that this type of tube is often used in CF circuits.

I think I will only find out whether this type of tube is suitable if I try it out.

That's the plan, I'll build a test mic, Aikido CF with an E88CC. It will be used for loud instruments and overheads.

I am curious....

The modern Innertube Audio, Tube 87 insert uses it as well. It’s a mic that when you raise the fader, the vocal jumps to the front of the mix.

sounds promising!

I have limited experience in this area, but the InnerTube Mag Mic MM2000/MM2006 uses an ECC88. I did a little looking when I had to debug mine (it ended up being fixed by drying out the capsule - Stayne was helpful) and it looked like it was a classic plate loaded transformer output. Most of the circuitry was potted and I didn't see markings on the transformer when I had things out.

I like the creative use of Maglites as mic bodies!

 

[Mr. Moscode]

I've used 6DJ8s in phono and line preamps. They can be microphonic in the upper registers when tapped or jiggled. If they are in a fet /tube hybrid cascode circuit they would be much quieter.

 

[zzzzz]

In my experience with the Rode K2, swapping different makes of 6DJ8 / 6922 makes quite the noticeable difference. Going from EHX 6922 to Amperex (Philips Holland) 6DJ8 was a pretty impressive A/B.

As Mr Moscode notes, many 6DJ8’s I’ve got ended up microphonic. Apparently the USA JAN Philips ones can be reliable. Running a Matsushita right now and it’s fine.

Just posted about some K2 mod stuff here. Rode NTK schematic is pretty much the same. https://groupdiy.com/threads/rode-k2-capsule-suggestions.85520/post-1167169

 

[rock soderstrom]

Just posted about some K2 mod stuff here. Rode NTK schematic is pretty much the same. https://groupdiy.com/threads/rode-k2-capsule-suggestions.85520/post-1167169

Thanks!

In my experience with the Rode K2, swapping different makes of 6DJ8 / 6922 makes quite the noticeable difference. Going from EHX 6922 to Amperex (Philips Holland) 6DJ8 was a pretty impressive A/B.

As Mr Moscode notes, many 6DJ8’s I’ve got ended up microphonic.

Sadly true, I have E88CCs in two of my amps. An HPA and also a line preamp, very fine sounding devices.

I love my Siemens E88CC, but with increasing age they tend more and more towards microphonics.

 

[rock soderstrom]

If they are in a fet /tube hybrid cascode circuit they would be much quieter.

A schematic would be great. Got a link?

 

[Mr. Moscode]

A schematic would be great. Got a link?

Substitute an N-channel Jfet, like a J310 for the bottom triode in a cascode circuit.
You can then bias the grid of the upper half of the cascode to a few volts depending on the normal grid - cathode bias voltage for the desired plate current. In a low mu tube you can tie the grid to ground or to the source resistor of the fet.
If you use a follower off the plate of the tube you can split the follower resistor to give you some negative feedback to the grid and to set the grid voltage. You just have to keep the upper cathode voltage within the max drain to source voltage of the fet.

The main advantage is much lower noise from the tube because:
1. it is the 2nd stage of the cascode and
2. The grid and cathode are in a low impedance circuit which kills (shorts out) tube noise.
3. noise is predominantly from the Jfet.


In this attached circuit the 12AU7 with 0 DC volts on the grid has a cathode voltage of about 7 volts, enough for the J310 in the bottom to work. The NFB is after the output cap voltage divider giving about 10% NFB. With a 250 volt supply this will swing about 30 volts or more RMS nicely.

While the grid has an impedance of about 68K it is an output stage so noise is not an issue.

I don't like running tubes from low supply volts for any reason. They are more linear over a greater voltage swing with 250 v. I've used this circuit with as high as a 350 volt plate supply.

I do have a shopright to the circuit.

 

[rock soderstrom]

Substitute an N-channel Jfet, like a J310 for the bottom triode in a cascode circuit.
You can then bias the grid of the upper half of the cascode to a few volts depending on the normal grid - cathode bias voltage for the desired plate current. In a low mu tube you can tie the grid to ground or to the source resistor of the fet.
If you use a follower off the plate of the tube you can split the follower resistor to give you some negative feedback to the grid and to set the grid voltage. You just have to keep the upper cathode voltage within the max drain to source voltage of the fet.

The main advantage is much lower noise from the tube because:
1. it is the 2nd stage of the cascode and
2. The grid and cathode are in a low impedance circuit which kills (shorts out) tube noise.
3. noise is predominantly from the Jfet.


In this attached circuit the 12AU7 with 0 DC volts on the grid has a cathode voltage of about 7 volts, enough for the J310 in the bottom to work. The NFB is after the output cap voltage divider giving about 10% NFB. With a 250 volt supply this will swing about 30 volts or more RMS nicely.

While the grid has an impedance of about 68K it is an output stage so noise is not an issue.

I don't like running tubes from low supply volts for any reason. They are more linear over a greater voltage swing with 250 v. I've used this circuit with as high as a 350 volt plate supply.

I do have a shopright to the circuit.

Thank you for the detailed explanation - interesting.