What does a Neve 1073 and a Behringer ADA-8000 Have in common?

Not a lot. Unless of course you are like me and decide to transplant some Neve soul into an ADA-8000.  I have this Behringer ADA-8000 with a burned out power supply anyway …  time to experiment!

BEHRINGER ABA8000 MOD

You are looking at the main section of the Behringer ADA-8000. The red arrow points to the shorting/burned out capacitor that destroyed the transformer. After ordering a new transformer and getting everything to work, I started to tinker.

Tinkerage

In the picture you can see the power supply and the SPDIF to ADAT I/O chips (the Alesis Semiconductor AL1402 ADAT optical decoder and AL1401A ADAT optical encoder – no. 1 and 2 are on left). The clock circuitry is also nearby. One chip is for multiplexing 4 stereo SPDIF channels into a single ADAT out, and the other operates  in reverse, taking a single ADAT Channel and splitting it into 4 stereo SPDIF outs. These are then connected to the actual D/A and A/D converters.

First I thought if I change the opamp on the input section I could get better performance.  Wrong. The old ADA-8000 used a TL074 opamp. The new machine is much better and has a very low noise and high end opamps which are very hard to beat.  At least I tried – this is my input section with a replaced opamp (the bottom right one), the bottom left one is the original. What we have here is the input opamp of 2 sections inputing into an Alesis Semiconductor AL1101 A/D converter (IC17) , it sends a stereo SPDIF signal to the control section (seen above):

BEHRINGER ABA8000 MOD

So the first step really was to find the schematic, After some searching I found it here: http://www.gyraf.dk/schematics/Behringer_ada8000_analouge.PDF Thank you Gyraf Audio for another great job well done!

looking at the input section of the schematic:

Input section of ADA-8000

Input section of ADA-8000

I had a Sowter 9145 transformer lying around – which is equivalent to a Neve P/N 10468 and a spare NEVE BA284 board. The first thought was to bypass the input section completely and transplant the whole BA283 preamp section instead of the existing one. However exmining the existing circuit I noticed that the input section is an ultra low noise class A amplifier – it is a design that has been used in SSL consoles, monolithic preamp chips (such as the SSM2019)  and a very good description of a similar preamp by DIY wiz Rod Eliott is here.  This seems quite decent, so i decide to modify the input section a bit and add just transformer into the soup. Here is the modified schematic as I planned it:

ADA8000 transformer mod

The idea is to feed the fantom power via the center tap thus reducting the noise coming from the +48 supply. The also improved the balance in phantom situations. The 6k resistors are needed to load the trasformers properly, although in initial test I decided (read – lazy) to leave the original ones in place to “see if loading is sufficient”. So now I had the design, and I was ready to tackle the task of modifying the actual hardware! After much dismantling, I managed to seperate the front from the back. The front and back are seperated by cables that carry the preamplified signal to the converters. All the mods are going to run on the front end, so we might as well get to know it.

BEHRINGER ABA8000 MOD

This is the back side of the front panel. After measuring all the components – I determined which ones needed to be soldered and changed:

BEHRINGER ABA8000 MOD

Here u can see the following changes: temporarily removed the XLR to allow access to the components. The caps were removed and the 6.81 resistors changed to send the 48V to the center tap of the transformer. Now the transformer is tacked on:

BEHRINGER ABA8000 MOD

This is the other side of the same board. This is a fully balanced configuration and thus we ground the input center tap. Noise rejection should be very high. Tests conducted after construction revealed noise reduction by at least 20db. The output leads from the transformer go to the vacated caps inputs. The center tap is connected to the +48v input. This configuration works surprisingly well for the non-phantom power situation too, as there is a signal path to ground.  OK now the reassembly:

BEHRINGER ABA8000 MOD

For this project I didnt concern myself with aesthetics and chose to use electrical tape to secure the transformer to the board. The front (class A preamp) and rear board are reconnected using the connectors. Here is a view of the whole project before closing the lid and firing it up:

BEHRINGER ABA8000 with NEVE 1073 PRE MOD

Ok now we need to test this thing! The nice folks at Guitar Center sold me a quality signal splitter cable that I then hooked up to the input sections. Here it is all hooked up and ready to compare the two sections:

DSCN3079

DRUM ROLL…………

ADA 8000 with NEVE transformer white noise sanity check

Hey it works! The levels are a little off because I didn’t properly load the transformer to get the correct gain, also slightly worse noise figures and frequency responses. My ear cant hear 10Hz or 49.99KHz, and neither can the ADA-8000. However, pushing up the levels all the way up to 70db gain there is a 20db drop in broadband noise. A contributing factor is the fact that transformers have a much lower operation band and common mode (hum) rejection is extremely high. Still impressive and useful.

Ok now is the time to actually send in the white noise and compare the signals:

ADA 8000 with and without NEVE transformer channel compare

Hmmmmm… Looks the same! Does that mean that they sound the same? Not in a million years! They may have an identical frequency response  but look at this null test.  (A null test is combining the signals in a way that is suppose to cancel them out so you can detect the difference. In this case it was done with one signal phase inverted):

ADA 8000 with and without NEVE transformer null test channel sweep compare

Now we see the picture! The difference between them is called phase shift. Transformers add an invisible/inaudible component to music called phase shift – for each frequency phase is shifted ever so slightly in a different direction.  This is inaudible by the human ear alone. However: When we mix multiple channels together, the unexpected phase shifts mean a broader mix and less phase cancellations. An overall easier mix by far, hence: Transformer input channels are preferred by studios for better noise rejection, hum rejection and introducing musical phase shifting into the music.

I hope to get my hands soon on a real 1073 and compare the two!


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17 Responses to “What does a Neve 1073 and a Behringer ADA-8000 Have in common?”

  1. newyorkbrass says:

    1. The 48V is sent in through the center tap of the transformer so there is no need for these resistors! i.e.
    + —– || —— +
    ) || (
    +48V ) || (— N.C.
    ) || (
    = —- || ——- –
    2. I found it online or on ebay. I still have a few units – they are useful as extra recording units.

  2. Jim says:

    How are ya? I was reading your thread about moding the ADA800 and found the most information about this unit than anywhere in the last two years.
    I have a couple of questions ,If you would help with them.
    First off what did you use to replace the 6.81 resitors to send the 48v to the transformer? ( yellow and black at the top holes where the resistors were removed )
    secondly where did you solder in the two sets of red and orange wires for the power supply? this thing Toasted on me 2 years ago and could I not find replacement trany nor anyone to repair it.
    The most common reply I recieved was scrap it. this is the second unit that i have had problems with, the first was right out of the box and I don want to buy another.
    I dont have a lot of knowlage in electronics but I do experiment, pictures would be helpfull. and thanks for sharing your information. I would like to save this unit if possible

  3. newyorkbrass says:

    By the way – the phantom power is supplied by a single 2.4K resistor (or the original 2 6.8k resistors in parallel) to the center tap of the external/primary side of the transformer.

  4. newyorkbrass says:

    After much experimentation I find the only real improvement to this device would be to connect a 1073 style preamp to the input, instead of the opamp preamps. i.e. use only the 8 converters for this and then attach preamps bypassing the originals. This is a huge task and involves designing a different board for the front panel etc. not sure it is worth it…. :) although could be fun!

  5. martiaudio says:

    Sorry for previous typing errors..grr

    Also it seems that a simple diy external unit ( for x4 ADA..) to lower VAC main whether it is a 120 or 240 uk VAC is necessary!! it works a lot safer and colder. I lower mine to 215vac instead of 240vac.. as a result the ADA transformer delivers appropriate secondary VAC therefore the power supply for 5, +-15, 48/50vdc works well now. this a very stupid issue from behringer ADA8000 transformer and power supplies design!! Otherwise the unit new or old is quite good and deliver good sound indeed. the ADC and DAC are all right. even better with new coupling caps. my cheapest and best choice in panasonic FC with wimp 0.01uf polypropylene parallel. I am not sure yet that changing quad OP amps should improve significantly the sound but let’s put it that what: I would never use tl074 to design a preamp.. I would design it in +-24vdc with opa2604 at the very least.. so I am hoping to improve with opa1644 otherwise I question if there is a point in modifying the ADA8000 in the first place.
    It is overall a 50/50 reliable unit. so one should not invest too much on a unit. but if modifications can be standardised and proven to works well.. why not!! But not with a sowter transformer though..that is way too expensive per channel basis.

  6. martiaudio says:

    Hi there,
    I am currently numbers of modifications on ADA8000.. some with some without success.
    I am wondering with a different transformer ( no centre tap at secondary ) if I need to have Rload and Cload tapped to ground 0v or can I just have it as one value across the secondary transformer?? AS a tip I am experimenting with a very cheap tranny that might just be very good for Neve 1073 structure.. instead of OEP, it is VTX102-003..the good one!!
    All I need to do is implement it properly and check the sound out.. it is $13ea so with this and soft limiter, relay switch direct line inputs on a scale of 32ch to 48ch ( 4 to 6 units ) I is affordable ish on a grand scale. I am developing a live digital console also live recording. So if it works it would be the poor man’s big and serious set up indeed. What I am after is a little character in my preamp also.. I don’t want pseudo clean ramp of preamps like very digital console even today.

  7. newyorkbrass says:

    You lucked out – I ended up buying a new transformer…

  8. Richard Stanley says:

    Success. I disassembled, and found zero ceramic caps (none anywhere near the transformer. must be the US version or upgraded PMU?). Either way, all I had to replace was the 7815, and 7915 connected to the heat sync. I tested the transformer and it tested OK. Re-caped the two 407uf 35v electrolytics next the heat synced op amps, and 220uf 100v near the transformer (just for good measure). The caps looked “iffy.” Fired it up, and of course everything sounds great (as great as can be without an added input transformer…yet).

    I used the Fairchild replacements for the 7815 and 7915… I might be crazy, but it sounded smoother… still hot as all hell. I’m just going to run it with the top off for now. I want to do the rail mod, I’m already shopping around for those Sowters, on and on and on, and I can see how this little thing can be addicting. I still need to do more “input transformer research.” I learned quite a bit off this. THANKS!! I’ll post with Variac results. These heat syncs are UNTOUCHABLE. But lucky me, I didn’t have a bad transformer… the only two places I could find these transformers was Germany, and Michigan, for around $50.

  9. newyorkbrass says:

    I hear ya! A blown power cap u say? hmmm… i would say fixing stuff that connects to the wall and could potentially kill you – you should think three times before you fiddle with. 100V variac could work – but make sure the machine is grounded before you do anything, or you could kill yourself by mistake. Having said that – on my machine a burnt out cap shorted and killed the transformer:
    See http://www.flickr.com/photos/newyorkbrass/4767031920/.

  10. Richard Stanley says:

    I really hope you respond… With the burnt out power cap and burnt out transformer was the ada8000 still powering up (green lights=yes, but no audio signal pick up) ? I don’t want to spend too much time on a completely dead unit (and complete I mean there is light [which i could assume would come from off the tap] but no audio signal). Any way, maybe I just need to buckle down and take a dive… If you have any recommendations of more then just one cap to replace then that would help. And one last question… would I be able to run a 100V transformer without mod-ing anything else? It would be cheap for me to replace the caps, and buy a $20 variac to run at 100v (or MAYBE find a 100v transformer for internal, and ditch the variac). I look at schematics and go, “oh crap, I need about 4 years of electronics training to REALLY break this down.”

  11. Matti Kari says:

    Hey, thanks for inspiration! I just finished modding my ADA8000: http://mattikari.fi/?p=68

  12. […] this guy (thanks for the inspiration!) my transformers did not have center taps, so I left the former […]

  13. I’d love to pick your brain about performing a similar mod on the output stage of an SM Pro PR8…. email me and let’s talk!

  14. newyorkbrass says:

    I am just a tinkerer…

  15. WalterSear says:

    So jealous of your mad skillz.

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