Whistle Rock Audio ML12 preamp BUILD/HELP thread!

[dribro]

No noise or artifacts, got the eight ml 2520 missing a few condensers so, as soon I'm able they will join the party, but for now the gar are truly great. No issues about the 7th and 8th channel's.

Recommend.

Thanks Mike and everyone else.

 

[TillM]

Hey Guys,
just want to send you a first impression of my WRA ML12 Preamp.
I just wait for the Input and Output transformers, the knobs and the t-pads.
They are at the customs, so they should arrive next week.
Also I wait for Pier Paolos DOA. I'm so impressed from his germanium op-amps that I decided to use two of them in this preamp and also two GAR1731 for the other two preamps.
Some things i've to trick out.
The blue LED is bright as hell, i've to change the 470ohm resistor. I'll try a 1.5k resistor first and see what happend.
Than i've to change one wima capacitor cause I attached it with my soldering iron and it burned at the top. I'm a idiot

Well at last the only thing i've to trick out is that at the doa sockets the "in+" should have 0v but i always measured some millivolts like 0,2v and 0,5v ... don't know why this happens and I hope somebody can give me a advice what could be the mistake.

 

[TillM]

and from top

 

[TillM]

... and a close up

 

[TillM]

Well,
I end up my build. The first test was a disaster, but that was my fault.
After check everything this morning everything works perfect since hours.
I want to thank Mike for this nice layout.
Pier Paolo for his APP14GE that I used on two channels in this Preamp.
Gary Barnett for his nice GAR1731 DOA.
Big thanks to Frank Röllen for the nice panel and enclosure. Always a pleasure to deal with him.
And a big thanks to Andrey (Avdo). His Output and Input transformers are really nice and he is a great guy to deal with, answered all my question even for this project in minutes. Thank you so much.
And last but not least, API

 

[TillM]

Hey guys,
I Need a small advice.
Since the Preamp worked for hours, I get problems with the doas.
After a small Check up. I still have the problem again, that I Measure 0,4v and 0,5v at the -IN DOA pin.
They should be zero.
What can be the problem ?

 

[SV.L]

Is it possible to add a Line Input to this circuit?

 

[dribro]

small update.  After a fews months of some (light) use, i must say the the PT i ended using is not that quiet... Proper orientation and a thin small metal sheet with 3m mumetal mininized issues considerably. But they're not gone at full gain blast in the 2 last channels closest to the traffo. Maybe a shielded traffo  will kill it. Anyway, as i never use things at the maximum gain, this thing rocks. 

In the meantime, a user (Ryan) asked how to hook up the OT 2623.  I used the original AP2623-4 i got from Sahib. Top traffos from a great guy.

It's pretty easy if you look at the Ed Anderson's traffos at CAPI Gear, especifically the EA2623-4 with the same footprint - you'll loose aux outs :
1-rd
3-bl
5-yl
6-or
4-gn
2-br
gy-NA
vl-NA

hope i helped
adriano

 

[neilmctavish]

I'm preparing to build a 4 channel ML12 unit. I have a single channel with small Power Transformer that I bought on the black market to experiment with. I plan to add meters and attenuation. My question for today is what power transformer have people successfully used for their build and would recommend? Mike said a 2x18VAC, 80VA toroidal would be great so I looked some up.

This Hammond 1182N9 transformer came up on Mouser and looked of high quality: https://www.mouser.com/ProductDetail/Hammond-Manufacturing/1182N9/?qs=sGAEpiMZZMvwUzoUXIIvySPCJQuQgm7b0hxT4JmMthH1SkbjcYRrAQ%3d%3d

I was intrigued with this one from Don Audio in Germany. It looked really nice and the store looks like a DIY gem! It is designed for  the PRR 176 Vari Mu design and the transformer has integrated MuMetal shielding. (They sell tape and foil muMetal as well as cans separately, should I find I need it.) I don't know if it would work with the ML12 PSU though as the specs are stated a little differently than in the US. Also, I'm a noob. LOL.
https://www.don-audio.com/prr-176-power-trafo-sec-18v-18v-120v

Thanks all!

Neil

 

[TillM]

The transformer from Don is okay but you don't need the 120v winding.
Take this one from Conrad.

https://www.conrad.de/de/ringkerntransformator-60-va-167-a-rte-602x18-block-710731.html

I use this in my build since months without any issues. You just have to buy a bolt cause the original one is too long for a 1U case.
I used the shield from Don Audio, but it's not necessary.

 

[neilmctavish]

The transformer from Don is okay but you don't need the 120v winding.
Take this one from Conrad.

https://www.conrad.de/de/ringkerntransformator-60-va-167-a-rte-602x18-block-710731.html

I use this in my build since months without any issues. You just have to buy a bolt cause the original one is too long for a 1U case.
I used the shield from Don Audio, but it's not necessary.

Thanks Till! That really helped as it clarified what I need in a transformer. Nice job on your unit, by the way. I think I will buy mine in North America though, but again, thanks for clarifying for me.

I went to the CAPI website and I'm thinking this might be ideal: http://capi-gear.com/catalog/product_info.php?cPath=21_105&products_id=352
I live only a couple of hours drive from CAPI so shipping won't be too much.

Thanks for your help.

Neil

 

[TillM]

Save the money and take this one from mouser.
https://eu.mouser.com/ProductDetail/Triad-Magnetics/VPT36-1390/?qs=sGAEpiMZZMvwUzoUXIIvyTw34uqMHR%252bupIcbHpngzj8%3d

This is perfect for 4 Preamps.
If you want the attenuator buy them with PCB from Jeff, also the 2503 Output Transformer and 2622 Input Transformer from him.
For Metering there is not enough place in the case in my opinion.
The build is pretty straight forward and really easy. The only hard thing was the wiring from the PSU, cause it was the first time I do a preamp that was not a 500-series preamp.
If you have any question, just ask, i will help you as much I can.

I designed the faceplate new, cause i made some faults on my case (I hate drilling metal !!!). Now i've a new front and a new pre drilled bottom plate from Frank. (Frontpanels.de)
I use the smaller switch knobs, that Jeff also sells.
Now I think it looks better and it is more handy, cause the switchknobs was too big for the API Style knobs.
For the attenuator you must use the blue and orange wire from the output transformer and solder it to the attenuator pcb from Jeff.

 

[neilmctavish]

Great tips Till. Thank you.

I looked further at the Whistle Rock website and in the FAQ's Mike recommended the same transformer that you linked to at Mouser. That is the one I will use. Here's the link for others that want to know.
http://www.whistlerockaudio.com/cart/index.php?main_page=page&id=26

Thanks again.

Neil

 

[TillM]

No problem,
this is a great build. The PCB is very good, also Mikes introduction on his homepage.
I worried, that this preamp build get not more attention.
Attached you my front panel designer front.
For the LEDs I use this tiny mounts, if you don't use them you must make the holes smaller.
https://www.dropbox.com/s/1fn8ewogra9ksba/ML12_FP%202TillFinal2.fpd?dl=0

This is with holes for the t-pad.

 

[neilmctavish]

Excellent. Thanks so much Till.

I have a built unit that I bought on the GroupDIY Black Market. Like you, I want to add the attenuator. I also want to add meters as these will be my character preamps.

Looking forward to a lot of fun! LOL.

Thanks again and I'll post updates as I work on this between mixes.

Neil

 

[guyinthevan]

Hey thanks for throwing that on the thread! Your ML12 looks great. I'm at the point of getting the power trafo for my 4 pre's and psu and to be honest, I'm good at reading instructions more than I am electronics. I don't actually know how I'm supposed to hook it to the psu add a switch and apparently a fuse? I was planning on using this old crate power amp chassis and even thought about using the holes they have already placed for i/o but I'm not sure that dealing with drilling metal in a new chassis wouldn't be a smarter idea at this point. I thought I could use the power transformer and switch from the prexisting unit but I suppose not. If anyone with a successful build could shoot me a message so I get out of the way of real DIY'ers during the home stretch that'd be awesome. I'm 2 input, 2 output, and a power tx away from being done, unless I screwed something way up. Either way, I'm too deep in. I may have no idea how I got here, but I'm here and I want to finish! I'd appreciate if anyone could shoot me in the right direction.

 

[TillM]

I would buy a new power transformer for your build.
This would be safer, then take a old one. Especially if you don't know, if it works.
Take the one from Triad Mike supposed earlier in the thead.
Are you in 110v or 220v country ?
U can buy a cheap 1U chassis. and for the most chassis parts you can get predrilled stuff. (Like for the XLR and Fuse)

 

[guyinthevan]

I plan on getting the one he suggested. I'm in the US so it's 110. I mean most literally. From switch to tordial to PSU I'm a babe in the woods. Like I said, everything is populated but a tx or two and the means by which I power. I'll look in to where I might be able to get a decent deal on a pre drilled chassis. There's zero chance I'll be adding any pre's. At least on this build.

 

[bjorn_ake]

Hi everybody.

Anyone would like to share their thoughts/opinions/ experiences on different combinations of input/output transformers?
The  EA2622 / EA2503 would aim towards the API sound, I also would like to try some more clean or uncoloured versions, suggestions? The only I've seen being mentioned is
Cinemag CM-75101APC / CMOQ-2L.

I have some different DOAs as well to try out.

Thanks in advance!
Björn

 

[TillM]

If you want it cleaner, you can also try Jensen Transformers.
I can't compare them in my ML12 build, cause I use the 2622/2503 combination, which is awesome in my opinion.
The only experiences I can give you is with different DOAs.
But also with different DOAs the difference are subtle.
But I've to say, I use my ML12 build just for drums.
I like Pier Paolos Germanium DOAs with my diy U47FET and Kick.
I also like the 992 on my hi hat.
With 1731 I found that the bass response is a bit better, but also with a 2520 it sounds great.
So I don't want to do gearhead talk.
If you have different DOAs, try them and take what you like the best for the source.

If you build four channels, then use two channels with 2622/2503 and two channels with the Cinemags you think about.
But take care about the Zobel.