500 series mic Pre build suggestions please :)

[okgb]

For those of us who are cheap [ and have a few 2520's around ]
Have you tried it much with other opamps ?

 

[Echo North]

I've tried it with the gar2520's and gar1731 and it worked fine, no change in performance in the AP (oscillation, distortion...).  I haven't done much listening yet but there are no red flags. 

I'm going to be testing more of the DIY opamps you see around the forum in the next 6 weeks.  They are a bargin!

 

[mitsos]

I guess I need to read up a bit on the topology. RE: other trafos, you can fit the lundahl 1538XL, cinemag(altran, EA2622) and OEP all within the lundahl footprint, which should fit under the EA10468, if you have bare board under the 10468. Or you could make some sort of adapter PCB like the edcor->lundahl footprint for the Gpultec. anyway, keep us updated.

 

[buildafriend]

Does this allow for combining the use of two different op amps resulting in a mix of the two?

 

[buildafriend]

Hey Mike, do you have any parts kits left for peter purpose's LA3 build?

 

[Echo North]

I guess I need to read up a bit on the topology. RE: other trafos, you can fit the lundahl 1538XL, cinemag(altran, EA2622) and OEP all within the lundahl footprint, which should fit under the EA10468, if you have bare board under the 10468. Or you could make some sort of adapter PCB like the edcor->lundahl footprint for the Gpultec. anyway, keep us updated.

I'll have a look tonight.  My only concern is that I'm super paranoid about testing PCBs before production.  If it's an easy add then it should be ok.  If I have to move a few traces around I'll most likely want to do another proto run.

 

[Echo North]

Does this allow for combining the use of two different op amps resulting in a mix of the two?

I don't think it would give you what you're looking for.  You need a two gain stage pre for that.

 

[Echo North]

Hey Mike, do you have any parts kits left for peter purpose's LA3 build?

Yes I should still have the transformer bundle on my site.

I should probably maybe start a Lola build thread and stop hijacking this one

 

[Echo North]

I guess I need to read up a bit on the topology. RE: other trafos, you can fit the lundahl 1538XL, cinemag(altran, EA2622) and OEP all within the lundahl footprint, which should fit under the EA10468, if you have bare board under the 10468. Or you could make some sort of adapter PCB like the edcor->lundahl footprint for the Gpultec. anyway, keep us updated.

Looking at it, I think the best solution is an adaptor PCB that mounts on the little stand-offs on the 10468 mounting holes.  I can be set up so builders can decide between par/ser primaries.  I'd like to avoid pads/traces pressed under the transformer.  Having an adaptor should work well.

Edit: Woud also be a super easy thing to do on perf board.  I'll post dimensions.  I'll also be posting self etch PDFs on the release date because I like to encourage DIY insanity.

 

[buildafriend]

Mike, sorry to be a kiss *** but since I am in the brewery I just want to let you know that I think it's awesome that you are in this thread.

Anyway... I have never waited for international parts before and now I am with nothing to do while I wait for Peter purpose's LA-3 kits and for my sowter trafos for my 1 bottles.

The 1290 kits seem cool but they also seem like they would cost twice as much as the VP26's. I heard a sound sample if the VP26 on guitar and it sold me on the quality.. It sucks that they are sold out. It made me cave on my no API rule. I had no idea that it was an even older circuit than the 312! Tape Ops review made it seem very cool.

I wish JLM made a kit for the TG500. At 1000 dollars I would just buy the Chandler Germanium.

So many DIY kits... So little time!! I need to just pick something and go with it. I want a rockin Pre for heavy thick rock guitars. Lots of Depth of field.. But affordable.

Thanks

 

[Stagefright13]

Mike I have time to test A lola pre prototype at my studio. I am very familiar with 990's just not 2 in one circuit. Will need it for about 4 days and will send it back. Very interested tho. I also have gar 2520's and the new 512 late model 2520's from Api to test if ya want. And all the regular test sources. It works at regular +- 16 Lunchbox voltage ok?



John

 

[Echo North]

Mike I have time to test A lola pre prototype at my studio. I am very familiar with 990's just not 2 in one circuit. Will need it for about 4 days and will send it back. Very interested tho. I also have gar 2520's and the new 512 late model 2520's from Api to test if ya want. And all the regular test sources. It works at regular +- 16 Lunchbox voltage ok???


John

Hi John,

I sent you a PM.  Yes it's designed for +/- 16V.  Having two 990's in what amounts to parallel, will give you many of the benefits of +/- 24V rails in addition to a few others.

Mike

 

[Stagefright13]

K I get it. Sounds kick ass. Hard to beat A 990 at what they do. But testing is always good.


John

 

[Stagefright13]

Sounds great. On the 25th I am recording one of the best acoustic guitar guys I know on A Martin. His guitar is A dream to record. Forget what model and 2 different Vocal types plus some bass guitar. It has A DI for the bass? If so can test that also.

Thanks,
John

 

[Echo North]

It has a DI yes.  I've used it for bass, rhodes and guitar.  The DI goes through the input transformer and is differential through the pre just like the mic in.  It has a pair of FET impedance buffers before the input transformer.

 

[buildafriend]

Why differential (also considered "class B" I think?)

 

[gemini86]

Topology and biasing are two different things. A push pull amp can still be operated in class a.

 

[Echo North]

Why differential (also considered "class B" I think?)

No it's class A.

It's really, at the end of the day, two single op-amp pres (like say the 312) in parallel.  In the classic single op-amp pre the signal will be single ended after the input transformer and be converted back to differential after the output transformer.  Using two in parallel allows you to run the signal fully differential through the whole pre.  Both the + and - signal having their own gain stage. 

This topology allows for higher CMRR (almost -100dB in my case) which means lower noise and takes advantage of the excellent balance of the 10468 design.  It also provides higher output drive current which will lower distortion and improve output transforme performance.  This is especially important when you consider the 1166 output is a step up transformer so it has a very low primary impedance.  You can aslo get rid of a few caps needed in the single ended design.

have a look at the block:
http://www.hairballaudio.com/diy_images/Lola-Block.jpg

If you delete Op-amp 2 and connect the 3 hanging leads to ground, you'd have a classic single op-amp design.

Hopefully that helps!

Thanks,

Mike