DIY Tube Mic project

[Emmathom]

Hi !

Back on the thread with the building of the second 6AK5 mic but with some mods...

Still a t.bone SC440 USB base but a friend of mine who works metal cut the square hole (for USB) to a round one (for an "aviation connector" named GX16 for 16mm at Ali)

A standard 4cmx6cm perf-board fits (almost) perfectly this mic body > just to file a little

A 1uF SCR tin-foil has replaced the Audiofiler / a t.bone capsule will replace the sE X1S / a Tamura Tx will replace the NTE10/3 (to be tested)

The tube socket is not glue but maintained by hard wires on top & bottom > it stands alright

Tomorrow I'll install the Tamura Tr (10:1) and maybe proceed to some tests...

to be continued...

 

[Emmathom]

Second mic built and volatges tested before installing the capsule and do audio tests : bad tube

I bought the second 6AK5 (Tungsol) on eaby as I did for the first one (Philips, which is operational) but to another seller because out of stock at the first seller : I didn't even powered up HT because the heater glows too much (pale yellow) and volatge drop down from 6,3v (stated for the Philips) to 4,80v

So I decided to buy 2 NOS Mullard 6AK5 at Watford valves (48€ shipp. included) and keep the Philips as spare. I am convinced that this little mic deserves this investment

About the Tamura Tx : it's realy bigger than the NTE10/3 and I have some mechanical mods to make it fit into the body

So no important infos for now...

 

[Emmathom]

HELP NEEDED

I've assembled the mic with the Tamura Tx but no sound...

Tx DC measurements : 150Ω between red & brown / 6,4KΩ between orange & yellow / black to ground

I wired it like this :
primary : orange to 1uF output and yellow + black to ground
secondary : red to audio "+" (xlr pin 2) and brown to audio "-" (xlr pin 3)

Someone has a suggestion ?

Edit : I will put back the Neutrik NTE10/3 to be sure that the mic circuit is full operational > if so, the problem does come from the Tamura Tx

 

[Emmathom]

2 mistakes detected !
- the capsule was connected to cathode and not to grid
- the second grid (pin6) was not connected to plate
how stupid I am...

So audio tests done with SC400 capsule + 1uF tin-foil cap. + Tamura Tx :
* good sound overall
* about +5dB output level compare to Neutrik NTE10/3 (the Tamura comes from a TEAC console and is dedicated to mic input 1:10)
* good balanced capsule

edit : I lowered the audio card level to minimum and shout in the mic from 10cm to check if the mic saturates (especially the output Tx) : no saturation at all

I will keep the Tamura in the 2 mics and now wait for the Mullard tubes from Watford Valves but I can say that this mic is very interesting, rather cheap to assemble and it delivers a really good sound

Will post acoustic guitar samples as soon as I get it back (at the luthier's for the moment) and voiceover as soon as my flu is gone...

Thanks +++ @thor.zmt !

 

[Emmathom]

Second mic assembled (with X1S capsule) and quickly tested : the SC400 capsule appears much more linear to me but I compared with a sample recorded a few days ago because the second PSU is not yet ready.
Anyway it delivers the same pleasant sound as the first one.

I'm waiting now for XLR 5pins to finish the second PSU and for the Mullard tubes : since I get these parts I'll be able to compare the capsules side by side on a unique recording...

 

[rock soderstrom]

@Emmathom, interesting. keep us posted!

 

[Emmathom]

Buying at Watford Valves when living out of UK :
2*EF95 Mullard = 28€
Shipping = 18€ (exaggerated)
+ what was not planned : french customs = 11€ (f***ing Bexit !)
So 57€ for an EF95 pair > too expensive !

 

[Migs 31]

Buying at Watford Valves when living out of UK :
2*EF95 Mullard = 28€
Shipping = 18€ (exaggerated)
+ what was not planned : french customs = 11€ (f***ing Bexit !)
So 57€ for an EF95 pair > too expensive !

That’s why you need a friend who has a UK address and takes the Eurostar frequently to smuggle parts across the Channel... or ship to you as « present » of a value of £5

Thank David Cameron, Theresa & Boris for negotiating badly, Brexit conditions.

€57 is a bit steep, yes. Sorry
M

 

[rock soderstrom]

Buying at Watford Valves when living out of UK :
2*EF95 Mullard = 28€
Shipping = 18€ (exaggerated)
+ what was not planned : french customs = 11€ (f***ing Bexit !)
So 57€ for an EF95 pair > too expensive !

Yep, that's a problem. I know it good. I used to buy a lot of things for our passion on the GB islands, it's not worth it anymore, I already had offers with even more shipping costs and sometimes sellers from the UK don't want to ship to EU anymore in general.

I don't want to judge this politically, I just hope that a better solution can be found in the near future.

 

[rock soderstrom]

Hey Emma, if you want I can sell you 2 of my NOS NIB Telefunken for similar money. They are still sealed and would be a good replacement for the Mullard valves in my opinion. Shipping is not that expensive to France, no custom fees.




Get in touch if you're interested...


PS: this is quasi emergency aid to France, I don't want to sell these tubes otherwise, sorry.

 

[Emmathom]

That’s why you need a friend who has a UK address and takes the Eurostar frequently to smuggle parts across the Channel... or ship to you as « present » of a value of £5

Thank David Cameron, Theresa & Boris for negotiating badly, Brexit conditions.

€57 is a bit steep, yes. Sorry
M

My Son lives in UK... and in that case you paid VAT (20% ?) but yes it's less expensive (I forgot the french customs)

I found a spanich reseller (for those interested) and no customs fee :
https://www.retroamplis.com/epages/...ObjectPath=/Shops/62070367/Products/VAL-5654W

 

[Emmathom]

Hey Emma, if you want I can sell you 2 of my NOS NIB Telefunken for similar money. They are still sealed and would be a good replacement for the Mullard valves in my opinion. Shipping is not that expensive to France, no custom fees.

Get in touch if you're interested...

PS: this is quasi emergency aid to France, I don't want to sell these tubes otherwise, sorry.

Oh Rock, it's very kind, thank you ! but I've already spent money for these Mullard
If I knew before I surely have accepted your offer ! will write you MP

 

[Emmathom]

I received my brand new Mullard 6AK5. I'm waiting for an XLR 5 pin pair to be able to power up the 2 mics at the same time and so conduct a comparative test (acoustic guitar + voiceover) between the one with X1S capsule and the one with SC400.

Will be able to post these 2 samples in a couple of days (hope so !)

 

[rock soderstrom]

I received my brand new Mullard 6AK5. I'm waiting for an XLR 5 pin pair to be able to power up the 2 mics at the same time and so conduct a comparative test (acoustic guitar + voiceover) between the one with X1S capsule and the one with SC400.

Will be able to post these 2 samples in a couple of days (hope so !)

I'm really curious about your experience with the direct comparison of your two microphones. Neutrik vs Tamura, comparison of the capsules with each other and the new tubes? Are the differences big?

 

[Emmathom]

I'm really curious about your experience with the direct comparison of your two microphones. Neutrik vs Tamura, comparison of the capsules with each other and the new tubes? Are the differences big?

I put Tamura in the 2 mics. The comparaison will only be about capsules (but you can refer to mic A of "mic blind test" thread to ear the NTE10/3 + X1S capsule + second-hand Philips tube). Mic A2

I think (?) that the Tamura (which is an input mic mixing console Tx) can handle more level than the tiny NTE10/3

I can't tell about the differences since I'm waiting for 2 XLR to be able to power up the 2 mics at the same time (I could do one by one but a simultanous recording is more accurate, no ?)

 

[rock soderstrom]

I put Tamura in the 2 mics. The comparaison will only be about capsules (but you can refer to mic A of "mic blind test" thread to ear the NTE10/3 + X1S capsule + second-hand Philips tube). Mic A2

I think (?) that the Tamura (which is an input mic mixing console Tx) can handle more level than the tiny NTE10/3

I think you are right, these Tamuras we used as input transformer (are the from a early Yamaha mixer?) and the should withstand more signal than the tiny Neutrik. They have more iron than Neutrik, which should result in more headroom and cleaner bass transmission. But the question is if this plays a role? (Ac. Guitar vs. bass drum) it certainly depends on the source.

I can't tell about the differences since I'm waiting for 2 XLR to be able to power up the 2 mics at the same time (I could do one by one but a simultanous recording is more accurate, no ?)

It's not an easy task to compare microphones fairly. I prefer simultaneous recording. I don't like recording of mastered music via loudspeakers. Your opinion is kind of more interesting to me, as you are there and have a direct comparison.

 

[Emmathom]

I think you are right, these Tamuras we used as input transformer (are the from a early Yamaha mixer?) and the should withstand more signal than the tiny Neutrik. They have more iron than Neutrik, which should result in more headroom and cleaner bass transmission. But the question is if this plays a role? (Ac. Guitar vs. bass drum) it certainly depends on the source.

The guy I bought from said they come from an 2000's TEAC M3 console

It's not an easy task to compare microphones fairly. I prefer simultaneous recording. I don't like recording of mastered music via loudspeakers. Your opinion is kind of more interesting to me, as you are there and have a direct comparison.

As said before, I will record my acoustic guitar and my voice over (no mastered music via loudspeakers)

Got a day free on wednesday : if I haven't got my XLR by then, I will solder wires direct to PSU to take advantage of my day free to record this comparison

 

[Emmathom]

6AK5 Mic samples

Hi folks !
So I recorded the same session with the 2 mics identicaly built except for the capsules. The X1S file is labelled X1S and so with the SC400. At last I found interesting to add a third mic for comparison : a sE2300 in cardio pattern.

About sE2300 : I think the electronic is good (full cms + Tx output) but they put cheap capsules in their mics. I will certainly try to put an Arienne K47 flat in one of the pair to make a test.

Guitar recorded @ +/- 50cm from mic and voice @ +/- 20cm. Recording levels matched to -9dB / -3dB peaks.
At this point I must say that SC400 mic seems more balanced to me.

No need to say that I know I'm not a guitar "virtuose" it's just to have acoustic sound.
Attached is a pict of the gain pot positions to get same recording levels : left is 6AK5-SC400 / center is 6AK5-X1S / right is sE2300. sE2300 has a great output level so it means that the 6AK5 has even more ! (not bad for a little 100v tube)

6AK5 SC400

6AK5 X1S

sE2300 cardio

@ruffrecords @Khron @Wordsushi @kingkorg @k brown @Migs 31 @abbey road d enfer @pinebox @RuudNL @Migs 31 @MidnightArrakis @Recording Engineer @My3gger @MicMan @MicMaven @joulupukki @garp @pmfalcman @thor.zmt @micolas you're welcome to give your opinion. Thanks in advance.

 

[MidnightArrakis]

a sE2300 in cardio pattern.

@MidnightArrakis you're welcome to give your opinion. Thanks in advance.

[a sE2300 in cardio pattern] -- Is this an "sE Electronics" microphone? If so, I have a pair of the "sE 2500" microphones that I have used to record piano with and they sounded terrific!!!

In related news.....if you could send me even just a sketch of your "perfboard PCB" with its mechanical dimensions carefully detailed on it, I could create a PCB-outline CAD-file for you that you could then use to place your microphone circuitry onto. Just a thought.....

/

 

[pmfalcman]

Emmathom,
Very kind of you to include me in the panel of judges.
This time I'll refrain from wine...
Again listening on my phone but
a) I remembered I have an external USB DAC box. Big quality difference.
b) I loaded files into an app which allows me to seamlessly switch between recordings.
Big help.

Anyway, in order SC400, X1S, e2300: dullest, balanced, not enough low/mid - worst.
SC400 sounds muted, lacking upper frequencies. The guitar sounds fine to me but probably as a result of this HF cut - I prefer bass and cello to violin
X1S sounds very well on your voice, best of the three mics. Scale of the guitar seems well rendered. Maybe a bit too much"spikey" in HF but it may be my dislike for higher pitches. Hard to tell not having heard the instrument live. It might be 100% accurate. All in all this mic sounds best.
e2300 - nothing to write home about.