Need help with BA283 DIY preamp with op-amps

[ashankan]

since this is my first post and thread i'll make an introduction as well.

i am a twenty year old male from norway(north-europe).
my profession (can't realy call it that since i don't make any money of it yet) is sound-engineering, illustrator, and
everything multi-media stuff.
i do everything from designing computer-cooling, chasis, creating comics and music, animation, etc, etc.
you get the idea.

i'm in the beginners phase of things, so i have alot of projects/ideas but almost none are finished.



The neve 1073 project...

about three years ago i read this book called "make mine music" by bruce swedin.
for those who don't know, he has mixed alot of michael jackson's albums.
in his book he "praises" the 1073.
it was the first time i heard of it, but i knew at once that i wanted one.
so i went to my friend google and began researching on how to build one.
after a couple of months i put the project on hold understanding that i
did not have the knowledge to pull it off.

in the years between then and now i have taken up the project just to put it down again,
but have allways learnt something new.

and now it's time to start again.
this time i feel alot more confident.
about half a year ago i got past some kind of barrier. i have allways learnt and understood things fast,
but after i got past that barrier i got to a complete other level of understanding.
i have no problems digesting information/knowledge and resonating it.

enough about me.


i soon realised that building a 1073 was to ambicious, so i wanted to simplify it.

so i ended up with an idea of just using the ba283 board as preamp.

but then the problem is pricing, switches and transformers are expensive.

my idea is to build the ba283 board with op-amp circuitry instead of transformers,
and using unstacked switches at each gain stage and one on the transformer/op-amp input
since these are at 1/10 the price of stacked once.
i also want to build a psu that powers the ba283, and op-amps.

if i could build this i would have a cheap neve based preamp that easily can be upgraded to a true neve replica.

it is also a good project to find the actual difference between op-amps and transormers.

this project probably has many flaws, thats why i post it here (duhu) so it can become flawless.

here are the link for the ba283 board http://members.nuvox.net/~zt.robgrow/circuits/neve/neveba283.html
here are the link for the ba283 board preamp http://members.nuvox.net/~zt.robgrow/circuits/neve/nevemicpre.html

for the the transformer substitute i thought of using an ESP project http://sound.westhost.com/project87.htm
i don't know if the input impedance are right though?

for phantom powering i thought of using this ESP project http://sound.westhost.com/project96.htm

for powering the op-amps i would use this ESP project http://sound.westhost.com/project05.htm

would it be possible to use the same circuit above for the 24v just switching the transistors to -24 and +24 ?

on the ba283 M, and N pins are connected to +24VDC
A, and V pins are connected to common.
is common 0volt the center pin of the transformer?, or is it -24VDC?
i also want a pot on the output to tune the output down if i want to gain alot.
what values should that pot be? 10k?


this wil be my first "real" DIY electronics project, i have seen some projects that resembles this one but not quite like it.

so any help, links, etc would be gratefully accepted.

if you know of a better solution for some of this please tell.




ashankan

 

[Kev]

put the 1073 project aside for the time being

if the project is any good and you haven't made a mess of it
then it will live one day in the future when you have more skills

Simple ... start again with a beginner project

The Green Mk1 is still the one project that has low cost and can completely made by yourself and without a kit
http://www.diyfactory.com/projects/green/green.htm


if the PCB is still a issue then one of the kits is a cool idea

obviously I will recommend a JLM and at this stage a Baby Animal looks like a easy choice
add to that a JLM Power Supply and it could all be safely working on the kitchen bench with out a box around it

even in a plastic box ... with an external switch mode or an internal analog supply this should be a very impressive mic-pre

with any of the trafo options OR opamp, Gain block or Hybrid amps ... and then there is output trafo options
... including ... no trafo

http://www.groupdiy.com/index.php?topic=13739

 

[ashankan]

the problem is that i don't want to do another project right now.
if you want a stratocaster you don't get a les paul.

i don't see why there should be a problem making the ba283 board either.
i'm not a completely noob i have more than enough soldering experience, if only the schematics and connections are right i can do the job.

but thanks for the encouraging post :wink:

 

[Sammas]

[quote author="ashankan"]the problem is that i don't want to do another project right now.
if you want a stratocaster you don't get a les paul.

i don't see why there should be a problem making the ba283 board either.
i'm not a completely noob i have more than enough soldering experience, if only the schematics and connections are right i can do the job.

but thanks for the encouraging post :wink:[/quote]



aargh... building a "ba283 board with op-amp circuitry instead of transformers" will be more like getting a fender practice amp when you are expecting a wall of marshalls...

A crucial part of the neve sound is the transformers they use. You won't get a neve sound with the transformers.

Copied straight from the JLM website "The JLM99V is more like a Neve Class A Preamp on major Steroids". I'd take a look at a JLM audio kits or the SCA N72 kit.

There is no point trying to redesign the wheel... If you really want that stratocaster you should put the 1073 project aside until you can get all the appropriate transformers and switches.

 

[soundguy]

much of the sound of the circuit, like MUCH, is the sound the transformers in part on the thing. You will not have a very "neve" sounding circuit if you omit (or substitute) the specified transformers. If you decide to use an electronically balanced output you still will need to attach an inductor to the 283 to get it to work or you'll have to redesign the circuit itself. After screwing with that circuit for a while, I have often thought that the circuit was just some thing that neve came up with to drive the transformers. Im sure thats not the case, but thats my impression of it... If you wind up building it, on my website there is a solution for the gain switch as well as on JLM audio's website. Joe has probably the clearest wiring diagram ffor the 283 card that is on the internet, you'd be smart to look at that as a guide. The 283 itself is very simple and could easily be wired on perfboard if you want to save money on a pcb. Do note that many of the caps on the board are tantalum and you would be smart to stick with tants in the specified positions if you are going after THAT sound. Neve used phillips electrolytics (which are available now from BC), some tants and the rest were polystyrene. There is a fellow here who has some NOS motorolla transistors which some say sound different than modern substitutes, I havent personally tried to report either way. Before you go through the trouble of building anything you've got to realize that the sound you are going after is entirely tied to the presence of a transformer, there is no transformerless circuit that I have ever heard that will get you anywhere near that ballpark. There are many many good sounding transformerless circuits but its just an entirely different idea. Ive listened to the 283 without the output transformer and it does sound very nice however it is most certainly not the idea, all the weight of that circuit comes from that output transformer. The closest sounding modern replacement is made by carnhill. Sowter makes a replacement as well, but it is a bit clearer sounding than what was originally used back in the day.

good luck

dave

 

[ashankan]

thank you for the feedback.

if i ever get to build it i am going to use transformers.
but the op-amps are for the sake of trying it, and if everything goes to hell
and it doesn't work or something like that i at least hasn't wasted 100+USD on transformers.
but the idea is to build something cheap that i can uppgrade to something good and expensive.

what i need to know is if the op-amps will work, and if common is 0volt(center pin), or if it is -24vdc.

i know i'm stupid for making this project when i know so little.
but i'm shure you guys know exactly how it is

 

[mikep]

[quote author="ashankan"]
if you want a stratocaster you don't get a les paul.
[/quote]

If this is how you feel then do NOT skip the transformers. it would actually sound more like a neve if you skip the B283 and put a couple of opamps between the legit iron i/o! but if you are really dead set on frankensteining a neve pre to make it cheaper IMO you should substitute out the input stage for something like a green pre and use the B283 line driver +L01166 for output. that won't *really* do it either, but it will likely sound cool. IMO the vintage-N sound isn't just the low order distortions it produces, it is also the LACK of other kinds of distortion.

mike p

 

[ashankan]

i just want to build a BA283 preamp with op-amps until i can afford some real transformators.......
and also, this is an experiment wich i think i can learn alot from.
i think i sorted things out very clearly in the first post?

 

[soundguy]

what you are perhaps not realizing is that Im virtually positive that you'll need an inductor to put in place of the output transformer because of the way the power is used by the amplifier, it is routed through the transformer, you cant just take it out of the circuit so far as I understand. A vintage marinair inductor is going to be pricey enough to pretty much justify purchasing a regular output transformer in the first place. You can leave the front end transformerless if you want. This circuit is not a good candidate to do transformerless not only because of the sound of the thing but because you need to have some iron in there or some way of dealing with the power supply, look at joes' drawing on his page.

perhaps someone who understands the circuit a bit more lucidly than myself can explain this a little better.

dave

 

[Kev]

[quote author="ashankan"]i just want to build a BA283 preamp with op-amps until i can afford some real transformators.......
and also, this is an experiment wich i think i can learn alot from.
i think i sorted things out very clearly in the first post?[/quote]

OK
I'm going to say what the others have been too polite to say

" I just want to build a BA283 preamp with op-amps "
you can't

" this is an experiment wich i think i can learn alot from. "
experimenting with proven projects is a great learning experience

" ... i think i sorted things out very clearly in the first post? "
and in your first post you mentioned
http://sound.westhost.com/project05.htm

a dual 15 volt supply supply ... perfect for the Green or the JLM units we mentioned

the JLM power supply has the phantom already on the PCB so you don't kneed the
http://sound.westhost.com/project96.htm
and SO DO the power supply PCB's for Keef and Fabio and many of the others here


the BA283 requires a Gapped Core output transformer and it's not going to work well ... or even easy to make use of ... without one


The Full 1073 Mic-pre requires the extra gain stage to be added to the BA283 card and does require a triple layer rotary switch
yes a dual can be used and the various sites noted above can help
:roll:
much easier to just add the JLM Switch Kit
http://www.jlmaudio.com/JLM%201272%20Switch%20Kit.htm

to cap it off some people do find themselves with hum problems with a BA283 or 1073 project because of strange power supply and chassis mounting techniques

I could go on

" I just want to build a ..... preamp with op-amps "
and no transformers

simple
Green MK1 or the JLM Baby Animal with the simple op-amp option

I'll shut up now

 

[rascalseven]

The 283AM output stage REQUIRES an inductive load between pins B and M to be happy. Even if you don't use transformers, you will have to chase down a T1310 inductor (which looks like a transformer, BTW... it ain't small). This will likely run you in the neighborhood of $30 from most suppliers (vintage parts dudes), and you cannot successfully build this circuit without it.

No, you cannot substitute an op amp for this function... you MUST use a proper (large!!) inductor, specifically the T1310 or equivalent (don't ask me what an equivalent is... I have no idea... the thing is pretty large, and I don't know of another option). If you find a T1310, then you can take your unbalanced audio out off of pin F (through an electrolytic cap) to your opamp stage for balancing.

You can use op amps for the front end if you want, but that might require a more complex power supply, unless you plan to power the opamp with +24 and -0v, which might work, but that in itself is a compromise.

When all is said and done you will likely have had much more trouble-shooting and lots of time wasted than if you just built the normal transformer-balanced circuit with any of the various transformer combinations that are well-documented on this forum (check the Neve META). When you are finally finished you will have a good preamp, no doubt, but you will have a rather odd Les Paul (an Epiphone at that!) instead of the Strat you were hoping for. :?

I understand your desire to make what you want spending less money, but I am reasonably certain that this simply won't work out the way you hope. I don't mean to be a downer, none of us do, but there are lots of experienced voices here trying to help you find the straightest path to your goal (and actually help define what your goal really is), so I hope you choose to listen.

I also appreciate your willingness to boldly ask questions... lots of newbies are too self-concious to do that. I believe you will find, as I think we all have, lots of knowledgeable and kind people here willing to help you along the way as you grow in knowledge.

Truly.... if a Neve is what you want, why try to reinvent the wheel? You may succeed in making a new wheel, but it'll be longer path for you, and when you're done you still won't be much closer to actually achieving what you said at the outset you really wanted... a class-A Neve (or at least something that SOUNDS like a class-A Neve).

If all you want is an experiment, then have at it, and I'm sure many people here will offer their assistance.... it will no doubt be quite a learning experience for all.

I wish you well.

JC

 

[Kev]

[quote author="Kev"] ... I could go on ... [/quote]
:shock:
and it looks like rascalseven did
good stuff JC

 

[ashankan]

ok.

i'll just settle for something simple to begin with, like the green pre, some DI's, and an ssl-comp.

so what specs would a replacemnet for the T1310 need to have?
you couldn't just toss in a switchrelay inductor( or what it's called) with the same mh values as the T1310 as long as it is rated for the voltages going through it?

would there for example be any point in just using the first amp-stage?

is there any other neve preamp boards that you would suggest building that doesn't need the LO1166/T1310?

 

[Kev]

the inductor will need to deal with the same things the trafo does
the DC offset and the total current capability of the T03 output

not all Neves are equal ...
you could use the AB output of the 1080/81 which uses the other group of DOA's
see the DIY81 and countless other pages

the older Neve stuff is complex and varied and there is much out there on the net
people here have tried to simplify a couple of chosen unit but it is not easy to run across ALL units here and redesign them in a simple post on a forum
Geoff Tanner is tryiong to answer many questions ... try his forum

The Neve IC approach of the 51 series is a possible BUT it is very different to what you have been talking about
see JLM for a simple NeveIC circuit

AS for the simple first stage opamp ... the JLM Switch Kits is as simple as it is going to get
OR
the very small units from the JLM1290Micro

JLM BAX83NV & BAX83AM PCBs are both 1.6" (32.7mm) wide x 1" (25.4mm) high. Modules come fully assembled and tested. With the BAX83AM module trim pot preset for Neve LO1166 & JLM111DC output transformers.

http://www.jlmaudio.com/JLMmicro1290.htm


I tend to believe much of the twist in sound for many of the Mic-pres comes from the initial step-up and early gain section
so there may be some merrit in just using the first stage
HOWEVER
the ClassA output and that transformer does make a sound when pushed to higher levels and the output section is currying some current.

this is why Dan Kennedy made his NV unit in the way he did ... go to 3dB to have a listen to the interview with Lynn F.


:shock:
why am I here ?
I said I was going... 'shut up' ... now :?

 

[Family Hoof]

the inductance in the pins B-M loop of BA183/283AM should be at least 1H, preferably closer to 2H, and gapped to handle 80mA DC. Gap lowers inductance, therefor it's got to have a fairly large core to compensate.

Yeah you can use a NV stage and follow it with some other output section to get your current gain. But then what is the point?

 

[soundguy]

you can build an amp out of 340's and 440's liek neve used in the 3415, 1081, 33114, etc. Neve designed consoles with class A inputs like 1073's and then used 3415's for buss amps, so the amp as a whole is no slouch. I personally prefer them over the class A stuff if I had to chose between the two, thats just me and Im a wierdo.

Again, this reverts back to your original post, once you remove the transformers you really no longer have a neve sounding circuit and there are plenty of people out there that know opamps who will tell you that the 340/440 is really nothing special in the least bit. Like I said before, I always get the impression listening to a 283 that it was just some circuit neve came up with that had some braun to drive the transformer.

Anyhow, just build yourself any old single opamp circuit, the api 312 is the one everyone around here seems obsessed with. You can electronically balance it or use it unbalanced or put any transformers on it you want. Edcors for instance are cheap and people seem to like them, I have no experience with them. For a little more you can get cinemag outs which for general use are much more sensible of a choice than the cloudy neve stuff. IMO, a 312 circuit with a 990 opamp and marinair input/output transformers will give you more of the neve "sound" than if you were to take an early 70's neve circuit and use it transformerless as is, let alone hook up some ic to its output to balance it.

As long as you chose a circuit that doesnt require DC to be fed through a winding of the output transformer, you can pretty much do exactly what you want. There is not a long list of preamps requiring a gapped core transformer, you just happened to chose one on the short list. You can include UA1108, langevin am16 on this list as well. Maybe the calrec pq14 too, but I havent studied the schem on that one, certianly sounds like it though from listening. anyway, so thats like 3 or 4 circuits you cant build and basically every other solid state circuit discussed here that you can build and modify as you desire.

My one suggestion, if you care to go transformerless, is to look into building something with fred forssell 993 or 992 opamps. they are fet opamps, so very much not in the neve direction to start with, but fred designed these opamps to be used specifically transformerless. Most any opamp will work, but those were "optimized" in a transformerless circuit so it might be worth some time to investigate those if you like. In listening, the 992 has a more pronounced midrange to my ear while the 993 is flatter and produces somewhat of a bigger soundstage as a result. All that is subjective though.

dave

 

[mikep]

[quote author="soundguy"]you can build an amp out of 340's and 440's liek neve used in the ...[/quote]

this reminds me, I have the application "handbook" for the 338/340 that the Neve engineering department drew up when they developed those amps. It is not the standard 338 documentation, this is something like 10-15 pages long. it contains a full discussion of the circuit, hand plotted curves and example circuits to help the designers get started applying the new amps. one of the circuits, that Ive never seen anywhere else, is a balanced but non-floating push pull output stage using 2x b338. it was never used in a production design that I know of. I don't have the document handy, it is in storage right now, but from memory it consists of a diff-amp (like the first stage of a standard 3 opamp instrumentation amp) with one input grounded and adjusted resistor values to make the output symetrical. who knows what it sounds like, but it shure would be cheaper to build than the LO1166 stage.

I don't want to seem like a tease, Id gladly offer the document up to the group if anyone is interested, but I won't be able to get it out of storage till july. Ill do my best to remember and offer it up when the time comes.

mike p

 

[soundguy]

interested!!!!!

duh, hehe

dave

 

[Family Hoof]

Mike P,

Do you remember the name or number of this document? I could probably dig it up a LOT sooner than you can if I knew what to look for.

-Jens

P.S. Great advice, soundguy! This is what DIY is all about. Build something competitively cool-sounding, functional, and complete, while staying within the realms of reality and budget constraint.

 

[ciminosound]

[quote author="mikep"][quote author="soundguy"]you can build an amp out of 340's and 440's liek neve used in the ...[/quote]

this reminds me, I have the application "handbook" for the 338/340 that the Neve engineering department drew up when they developed those amps.

I don't want to seem like a tease, Id gladly offer the document up to the group if anyone is interested, but I won't be able to get it out of storage till july. Ill do my best to remember and offer it up when the time comes.

mike p[/quote]

Don't worry, someone here will remind you, I'm sure! :green: