8 Channel, 3U NEVE 1073 completed

[DIYnoob!]

Hey just wondering what transformers 3nity used for his build? I know they were cinemags...anyone know which exact ones?

 

[madriaanse]

Hello,

I didn't see anything on Cinemag's (or Jensen's) website that really fits the bill.

You can use:
Carnhill VTB9049
Carnhill VTB1148
Carnhill VTB1847
Sowter 8751
Sowter 9160
Lundahl LL2734 (I think, not confirmed)

HTH,

M.

 

[muffy1975]

Hey Team,

thanks for the help with the pSU. I have ordered a new PSU so I can have 48v.

Guys, has anyone built the Great River MP-2 aswell?? Does the EZ1290 have less top end than the Mp-2? What are people finding?

Thanks

XOX

 

[Whoops]

Hey just wondering what transformers 3nity used for his build? I know they were cinemags...anyone know which exact ones?

using the "Search" function I got this:

Cinemag CMMI-2C and CMOQ-2SG

 

[mitsos]

using the "Search" function I got this:

Cinemag CMMI-2C and CMOQ-2SG

I've talked to Cinemag about these.  You'd most likely want the CMOQ-1SG.

The CMOQ-2 is a 625EI core, (API 2503 size), while the CMOQ-1 is a larger core, (same size as the Carnhill?) which should give you better bass (or less distortion at the same levels).  FWIW, all the CMOQ are quadfilar wound, meaning 4 equal windings, so not exactly what Neve originally used, but they will work.  When I spoke to Cinemag, they mentioned the Carnhills had some phase distortion which Cinemag got rid of in theirs. Marketing speak?  Don't know since I have not used them, but some people say they are cleaner.

 

[madriaanse]

Hi Mitsos,

I'm not sure what turns ratio the CMOQ-1SG has, but if it's like the other CMOQ-1's that are on their website it's not an exact match for LO1166. LO1166, as wired in a 1073, is a 200 : 600 (1 : 1.73). You definitely want gapped (unless you go the LO2567 / T1310 coil route but that's a whole different story).

Best,

M.

 

[mitsos]

Hi Martin,

It's not an exact match to the St Ives/Marinair/Carnhills, but it is a good transformer for the circuit, if GAPPED (that's what the G suffix means, the S means steel core).  As far as I understand, all the CMOQ are quadfilar, meaning 4 equal windings. It works like the API 2503, you can run 1:2 or 1:3 (or 1:1, I suppose).  I guess the closest would be running 1:2 which will give you a bit more gain, but I wonder if that .27 is discernible... Anyway, it's good this info is out there since these are easier to get on the west side of the pond.

 

[madriaanse]

Interesting. Do you know what Cinemag recommends for the RC network on the output? I'd like to hear an AB of original vs CMOQ-1SG. I might order a few to do so.

M.

 

[mitsos]

We didn't get that far into the discussion. happened to get tom r on the phone and started talking all kinds of stuff. I know that for the APIs there is no RC network on the output, I can't be 100% sure it's the same here. 

 

[statzern]

My pre is almost done. I have been having a hell of a time fighting with this braided shielding. Most of my work has always been with guitar amps - not a lot of shielded anything going on in there.

Things are getting awfully crowded on the front panel. Perhaps too many bells and whistles. I am having a tough time getting things into the terminal blocks on the JLM GoBetween - they're too full.

Testing the main board and (hopefully) biasing tonite. At least the power is ok - the lights come on. Woo.  :

 

[statzern]

Hey guys, so testing has started... annnnnd.... problems. When I input a 1kHz sine wave, it comes out looking something like this:

Looks OK, but not exactly right. Maybe I am doing something wrong? I connected the signal generator to the shield and one of the wires that go to the input transformer. At very low levels, the output looks like a perfect sine wave. As I increase the amplitude, it turns into the picture above. Though turning the bias pot does seem to change things, it never really gets symmetrical. Notice that the tops and bottoms are not flat. Wonder why?? The wave is not necessarily the same shape at all frequencies, either. Any ideas?

OK, so here's some really effed up stuff - If you continue to increase the amplitude of the sine wave further, the power to the whole preamp will start to pulse. Could this be some sort of thermal shutdown? I don't know exactly how "big" the wave is, but it's likely bigger than anything that would be coming from a microphone in terms of amplitude.

If any more info would be helpful, let me know and I will try to get it to you asap! Thanks guys.

 

[madriaanse]

Hmm, how's your scope hooked up? (Probe to 5, ground clip to 8 - on LO1166).

Voltages ok? http://s3.amazonaws.com/EZ1290/transistor_voltages.pdf

This pre should swing some +26dBu before going splat. Pretty crazy stuff.

Make sure the 2N3055 screws are very tight.

LM317's on the PSU have big heatsinks on them, right?

Got any (very detailed) build pics to share?

M.

 

[statzern]

Hey Martin, thanks for the response. I am going to get some bigger heatsinks for the PSU. I checked and it is delivering 140mA on the 24V line, and the regulator is getting kinda hot, even at such a low current. Also, I checked voltages on the transistors and some are perfect (all the transistors in the output section are dead on), and some are not. I will have to recheck them once the power supply has been taken care of, because things start out OK, then if the power supply starts struggling it all goes haywire. If that doesn't take care of it, what does the transistor voltages being off suggest? Is it that the transistors are no good? Possibly overheated while installing?

To answer your other questions, the scope is hooked up correctly, and I will post some build pics when I get home.

Thanks everyone,
Nick

 

[desol]

Has the probe been calibrated with a square wave? ie: on the front of the scope?

 

[statzern]

Hm, no it hasn't. Thanks desol, I will make sure to do that.

 

[3nity]

I didnt use any R load on my outputs..
Off course i planned to try them but never did!
I have less gain on my pres than the regular Bluzzi Carnhill units...
But come on i have more than enough though..!

 

[New Soul Rebel]

Jeesssusss! the mind boggles!!!

Wow, Adria that is just unbelievably nice build mate. What does it sound like! Incredible i bet! Very inspiring to see what is possible! 8)

Matt

 

[statzern]

Hey guys - all is well with the pre! It just turned out to be a PSU issue. I mounted the regulators to the chassis and everything is operational!

Waves are nice and even now, frequency response is very flat all the way from about 32 Hz out to about 65-70 kHz. Wow! The only things that I am still having an issue with are the VU meters (needle is not moving??) and I have these lights for the +48 indicators... they're not working either. They are not the LEDs included in the package. I need to go back and study the JLM GoBetween schematic, I guess.

Anyway, the pre sounds great so far! Really clear and very quiet. Will do more testing soon!
;D

 

[mitsos]

I didnt use any R load on my outputs..
I have less gain on my pres than the regular Carnhill units...

Hi 3nity, your output is wired 1:1?  You should have a little less than 5dB (4.6dB) less gain then?  Did you use 2 windings in series for primary and 2 for secondary?

 

[snipsnip]

Hey Guys,

Looking at build pics, it seems some people have filled the PCB trace 'jumpers' and some have not.

Should these be filled or left open?

Thanks
Jake