ELAM 250/251 vs G7 with CK12 (With Soundfiles)

Ok, I've deiced to try try a ELAM 250 circuit with my Tim Cambell CT12.
I have a G7 in a Nady 1150 body with it at the moment, but I'm not 100% happy with that circuit. (the capsule really shines in omni however)
Besides I want to try something p2p, and try something that was orginally used with the CK12.
I'm gonna try it with a cinemag2480, and a jensen D.I transformer to see if I prefer either one. (I know Gus is not a fan of the 2480)

I'm using a 6072 for the tube too.

Now I've read countless threads on the 250/251 and found the answers for a lot of my questions, so hopefully I'm not asking the same things.

1st off, the 100pf and the 4800pf in the schematic have a voltage rating of 500v and 350v. For a circuit that's kinda around 120v, do they need to be that high?? Coz I can get hold of some Polystyrene caps at 160v(the G7 BOM doesn't need any caps over 160v)
Silver Mica's all seem to be in the 300-500v mark so I could use those, but would Polystyrene be better? What have previous builders used here? Other types of film caps? Are the micas good enough?

2ndly how close to the original cap values do I need to be, coz I can find 4700pf or 5000pf caps all over the place, but 4800pf?
I could just parallel another 100pf..................
And the 20uf. I have found some, but most are motor caps and I don't need 600v rating.......just 6v
Again I could just parallel 2 x 10uf caps, but is a 22uf cap close enough??

3rdly, my G7 PSU is setup for 120v for the ck12 capsule. can I just use that and not use the pattern selector??
Or is there a better option? A better psu?? Should I bother building the one in the schematic.
And for those of you who used a relay for the pattern selection, would you be so kind as to show me how you set yours up? I'm trying to decide if I want to drill into the mic body for switching or just use a relay

And also, have many people noticed a bit of body resonance in their apex 460/nady 1150? Just walking around the room caused mine to "boing" in the low mids a lot.
I dropped the 2.2uf output cap to 1uf in my G7 and that helped to tame it down. but can I put anything inside the mic to control the vibrations? (leaving enough room for the circuit and the heat of it)

I think that's it. Sorry if these have been answered before.............. I did read a lot of threads and internet searches  on this.....

Bumpity bump 

> deiced to try try a 250 ... CT12. ... a G7 in a Nady 1150 ... not 100% ... something p2p... CK12. ...with a cinemag2480

What is this, an arithmetic test?

+250
+CT12
+G7
+1150
+100%
+p2p
+CK12
+2480
====
4013 (according to idiot PC)

I do not know if this answer is in Ohms or Euros.

> in the schematic

Completely lost me. I guess you are doing a tube mike head-amp, but which number?

General speculation to stir an argument:

Silver Mica caps are as perfect as can be. Since you can't easily slice mica real thin, they are traditionally all 500V up past 1,000pFd. (This is changing, as mica gets scarce, tools get sharper, and mass-production gear gets smaller and low-voltage.)

Polystyrene is a man-made plastic, boiled dino fat, not a God-made rock. Aside from that, PS is as perfect as can be (unless your soldering is brutal).

100pFd ceramic is pretty-near "glass", and again as perfect as can be. ("Ceramic" over 5,000pFd is usually a frothy salted stuff and less than perfect.)

If this is where I think it is, it needs to be very-good, but it is hard to find an awful 100pFd cap. Use anything. May need 120V rating.

I can not imagine 4,800 vs 4,700 is a difference. Likewise 22uFd is probably one semitone more bass (probably subsonics) than 20uFd. Both are probably artifacts of "preferred number system" fashion changes (4, 8, 16, 32uFd in the 1930s, then 5, 10, 20uFd in the 1960s, now 4.7, 6.8, 10, 15, 22 uFd). 

> walking around the room caused mine to "boing" in the low mids

You do NOT want to bass-cut the "low mids". Deep-low will vanish. May as well use a dynamic.

Ever see a luthier? Rapping violin or guitar panels? Listening to the tone?

Or a drummer, taping his wallet to the drum skin to damp a nasty tonality?

Tap-rap it, probably with headphones, possibly gutted with a $2 mini-electret inside so you can experiment with rubber ball, fingers, socks.

Are you sure it is not your mike stand? "low mids" seems unlikely for something as small as a mike body, very much in the range of long loaded metal pipe.

Are you sure it is not an unhappy choice of coupling cap and transformer inductance? Have you run frequency response from grid to XLR?

..the 22µF cap in the bias section need only very low voltage rating: 16 or 25 V is fine, I put a 47µF 25V , works perfect,  the PSU will work, but might be too noisy, the mk7 PSU will be much more quiet. A Elam curcuit has a bass roll off ( 8M from grid two ground ) btw

nicholas

e.oelberg said:

..the 22µF cap in the bias section need only very low voltage rating: 16 or 25 V is fine, I put a 47µF 25V , works perfect

Click to expand...

I'd agree with that in general; try not to vastly over-rate voltage for electrolytics.

I've used the Cinemag 2480 in a similar circuit. I think I'd maybe try something else. If you are already dropping quite a bit of cash on this one, I might look at what Oliver Archut is offering. For the record, I found the transformer fairly bright in my circuit (maybe I should say clean, since the response was very flat across and outside the audio band).

for the relays, I use the 6 v from the heater psu. I droppped the voltage to 5 and used pin 3,7 to carry the voltages for the relays. what is your problem soundwise with what you have, maybe it wont change the things you expect. you will have less bass with an elam circuit and you will have more noise !


nicholas

and when did you buy tim capsule, his first batch has pretty scoped mids, I didn"t like that so much. The new batch is fantastic.

e.oelberg said:

what is your problem soundwise with what you have, maybe it wont change the things you expect.

Click to expand...

With cardiod and fig8, the G7 kinda sounds a bit tubby in the low mids. Congested if you will.... And the tops not so bright. I've messed round with heater voltages etc and it's still the same.... Ludahl 1538 out, so it's not a deviation of Jakobs design.
Omni has less bass, as I expect, but the high end is so much nicer.
Even when I EQ something recorded in cardiod or fig 8, the top never sounds as pretty as in omni. And I've tried both sides of the capsule.

A while ago I had a new AKG CK12 capsule in there, and it had the same problem, but when I swapped it over to one of my royer mod mics, suddenly the royer mod was a very bright mic, but I didn't like it. Very siblant. A weird kind of bright.

Tims capsule sounds a million times better in the G7 than the AKG, but I still would like to try it in a different circuit, to see if the change is significant and to my liking.

e.oelberg said:

you will have less bass with an elam circuit and you will have more noise !

Click to expand...

Are you saying that the 251 will have more noise than the G7, using the same psu, or is it a noisy mic with any psu?
Is the G7 psu  noisy by nature?? I would look at building a different psu if I needed to.
Or are you refering to the different ratios of the output transformers and their output level..... lundahls 5:1  vs  the cinemag 12:1

The mic is mainly used for vocals, so I'm not too worried about it having less bass. I end up cutting a lot in the mix anyway. I would rather have more clarity in the high end.

e.oelberg said:

and when did you buy tim capsule

Click to expand...

I bought mine very recentley. Maybe bout a month ago, so I assume it's the 2nd batch. It doesn't sound scooped at all.

rodabod said:

I've used the Cinemag 2480 in a similar circuit. I think I'd maybe try something else

Click to expand...

I've got some on the way already, so I'll give em a go. But I'll try out the Jensen DI transformer too. I saw Gus try it in a similar circuit.
I'd love to try some of Olivers transformers, but I'm not spending too much on this mic, as I've got a lot of the parts here, and I'm just gonna take out the G7 board and slip int the 251 circuit. It's just more of a comparsion thing to see if I prefer a different circuit.

PRR said:

Are you sure it is not an unhappy choice of coupling cap and transformer inductance? Have you run frequency response from grid to XLR?

Click to expand...

No I haven't yet. I usually use the standard PC software like RMAA for testing, bout how would the 300ohm output of my soundcard interact with impedance of the grid? I'm not really sure how to do this with a mic.....
Comps and stuff however are easy to test

Lowfreq said:

PRR said:

Are you sure it is not an unhappy choice of coupling cap and transformer inductance? Have you run frequency response from grid to XLR?

Click to expand...

No I haven't yet. I usually use the standard PC software like RMAA for testing, bout how would the 300ohm output of my soundcard interact with impedance of the grid? I'm not really sure how to do this with a mic.....
Comps and stuff however are easy to test

Click to expand...

Should be fine; just attach your source to the coupling cap on the grid, and adjust the level so as to get away from the (high) noise-floor, but avoid clipping. You could shunt your current grid resistor with a 10K to keep the induced noise/hum down if it is an issue when testing.

Ok. I'll give it a go

Ok, I disconnected the capsule and hooked in where Roddy suggested, did some tests, and here's the frequency response graphs

Here with the standard 2.2uf


And here with the 1uf (I think this made things worse for the top end...... -1.66dB)


And a comparison between both


To my ears, the 1uf controlled the low "boing" I was hearing, but it seems to mess things up otherwise. I'll try it with a different stand and cradle and see what happens.

The dip in the high end bothers me.

Last time I had a piece of equipment measure like this, it was my DAOC compressor, and that was due to cable capacitance, and I could definitley hear it, when I fixed it.

Maybe my valve mic cable is the issue here?? Not the mic??

Do those frequency response plots look a bit off?

PRR said:

====
4013 (according to idiot PC)

I do not know if this answer is in Ohms or Euros.

Click to expand...

Or perhaps in DIL ?

Look at those plots again.

As PRR already hinted, by halving C to 1uF, you have brought the hump of the resonance between the cap and the transformer higher into the audio band.

Not only is the sub-30Hz hump more pronounced, but the next two octaves (up to ca. 120) are lifted as well. Try a 3.3uF, that should smooth things out down there.

A few things

I don't think of circuits as a microphone name I try to think of them as plate out triode gain stage or CF or a mix, then the tube and its specs and all the other things that interact inside a microphone circuit.

What did you use as a load on the output of the microphone when you did the plots.  Try 1K and 2K if possible

I am not sure what the circuit is.  120VDC?  What transformer?

Did you adjust the operation point by adjusting the cathode resistor for the 120VDC B+?

Did you try a different tube?

The Jensen DI transformer sounds OK with the Royer 2001 mod but might not with other builds.

Note that some microphones have damping material around the tube body.


Rethink how you measured the circuit.  What was the load 1K, 2k? What was the signal level at the primary of the transformer?  There is more to think about.

EDIT found a link for tube microphonics
http://www.thevalvepage.com/valvetek/microph/microph.htm

here are some measurements i did with my elam clone ( but 100M Grid to ground !!) with a Haufe T14 and a Pikatron UP 713 the other way round.
soundwise I do prefer the Pikatron it has more bass dynamics, better transients, no saturating bass, I just wonder what this resonance is, and if there is a chance to get rid of it. Please Ignore everything above 30K. The file is a pdf, you may download it to see it bigger,  Nicholas

What did you use as a load on the output of the microphone when you did the plots.  Try 1K and 2K if possible

Click to expand...

Ok, I tried that, and it seemed to make things even crazier. I then measured it going through one of my preamps. The High freq was there, but it now showed a roll off in the bass, which is the opposite of what I'm hearing........

I am not sure what the circuit is.  120VDC?  What transformer?

Click to expand...

At the moment it's a G7 circuit, lundahl 1538, CK12 capsule. PSU is set to give me 120v loaded. Heater voltage sitting round 6.1v

Did you try a different tube?

Click to expand...

Yep, I've got a couple of telefunken EF86s that I've tried, and a Phillips E80f (which messed with the voltages a bit...not such a direct replacement, as I've read.......)

Note that some microphones have damping material around the tube body.

Click to expand...

I'm gonna have a rethink about my capsule mount too. I had to take out the stock one, as it made the capsule sit too high in the head basket. Maybe it's not isolating it from the vibrations enough. Although the stock one, also did the same thing.......... :

But It's definitely the mic and not a stand or shock mount causing the resonance. Holding the mic in one hand & tapping it with the other, it still boings like crazy.........

I'm gonna slip in the different circuit, and see for myself any differences..........rather than bothering you nice people with more questions....

you could make a simple test mount with Plastilin or something similar chewing gum like rubber.

For some reason I could only see your pdf link when I replied and had your post in quotes...

On the plots, the T14/1 actually looks better to me, and it doesn't appear to be bass shy either. A very extended LF response is often not a good thing. I built some circuits that were direct coupled up until the output cap, and the amount of rumble picked up was barely acceptable, so I ended up implementing a 30 Hz low cut. That's why the steeper roll-off of the T14/1 *looks* better to me. Of course I can't see the kind of distortion it produces. The slight 50 Hz resonance on the T14/1 looks benign; I'm not sure about the weird ripple on the Pikatron courve. But maybe that's just a measurement problem. The HF roll-of is due to the plate to ground cap, I suppose? Perhaps you should do another measurement with that cap removed, just to see what it looks like.

Yes Rossi,

the bass goes a bit low on the Pikatron, maybe this causes also this ripple. The highs are perfect, I prefer very offen a rolloff at the very top. It"s going to be truncated finally to 44.1 16 bit, so a rolloff at 18k is fine with me. What you don't see in this graph is that the T14 saturates pretty fast, so bass sounds compressed. The Pikatron has a huge dynamic and much feels much faster if this makes sense. On the other hand on voice the Haufe t14 is just perfect.
with the Pik it's almost to clean, pretty close to the brauner sound btw.
Anyway the Pikatron ÜP 713M is a good contender for mics. In old sitral desks are dozends
of them.


nicholas