What makes Neve preamps so great? Neve clone teardown

the neve preamp has got to be the most famous most legendary you name it vintage preamp of all time and what i'm going to talk about today is what's inside so i've got a golden age pre pre-73 um and i'm gonna walk through the circuit i've already got the lid off and we're just gonna go part by part and talk about what's in it and what does it do okay so we got the preamp here let's just kind of do some some quick orientation from the outside so on the back we have our inputs line mic um insert and then our outputs here sorry it's a little messed up xlr trs really nice complement of uh inputs and outputs here not quite sure why you'd want a combo mic jack but uh who knows um and then we've got power coming in on a barrel connector there uh and then on the front kind of standard uh 1073 controls we've got a power switch another uh instrument input here which is nice di phantom power impedance control z means impedance fyi and then neve's kind of distinctive eccentric volume control here with the line to indicate unity gain and then gain settings to the right attenuation to not to the right clockwise and then attenuation counterclockwise and then an output trim so you can drive the output hard and then attenuate uh and then uh phase over here polarity rather for some reason and uh clip up here got a nice little meter so now that we're oriented let's take a look at the guts so let's start with power so we come in uh because this is a budget preamp we come in on a barrel connector and it's a it's actually an ac barrel connector um so we actually we have to do the um rectifying to dc in here so that's what these uh this looks like a bridge rectifier here or maybe it's these discrete diodes i'm not sure but basically there's a some sort of bridge rectifier that changes that ac into dc and then these caps provide kind of reservoir so spare power if if something needs current really quickly they also do filtering to reduce the noise of the power supply and then we get to regulators um so neve preamps well all the kind of 70s neve circuits ran on plus 24 volts so we should see yep here it is we see a little 24 volt header going to the main board and then of course since it's a preamp there will be a phantom power and that's this 48 volt header here so that's the power supply section nothing too surprising or interesting there but boy is it about to get weird um so neve preamps are just such a one-of-a-kind they're just really their own beast and so that's what we're going to see here let's start with what's kind of normal about them and then i'll get into what's unique so normal is input transformers output transformer uh these are what take in the balance signal here with the inputs and gives out the balanced output on the output so somebody asked me a really great question on instagram the other day which is in balanced audio gear does the does the signal say about stay balanced the whole time through the unit or does it get unbalanced at the input and then everything is uh unbalanced inside and then balanced again at the output and the answer is the latter in 99 of cases you what all you're looking at in in the audio path except for the very input and the very output is unbalanced or single ended and that's just because well first you'd have to duplicate everything to do it balanced you'd have to have one signal path for the hot and one for the cold and also any non-linearities that you introduced in the audio path wouldn't be common mode so they wouldn't be cancelled out which is kind of the point of balanced input and output so uh just thought i'd address that question so we have a mic input transformer and a line input transformer and then we get into the preamp stage so this looks like a lot of parts and it is a fair amount of parts but the neve preamps and and when we're talking about neve preamps most the time we're talking about this circuit which was in the 1073 it was also in the 1272 it was the the basic circuit of their 80 series consoles in the 1970s and the distinguishing characteristics of this circuit is that it's class a it's totally discrete and it's based on very few transistors actually so the the circuit had two parts an input stage which we would call the preamp i know this whole thing is the preamp but even within the circuit there's a preamp stage and then an amp stage so this preamp stage is just three transistors so you can see here there are six transistors are these little black uh kind of ones with a rounded side and you should count six there uh on this kind of from here down and i don't know exactly what's going on here i don't i don't have the schematic i don't know this circuit i'm looking at at the same time you are but i can kind of read it i can look at it and kind of read this is the preamp section and the preamp amplifier the pre-amplifier is only three transistors it's incredible um and there are two of them in one output amp section which is this one here which is just three more transistors so let me see one two and then this yes this is a transistor it's it's just ten times bigger than all the other ones and it gets its own uh cage here because it's so powerful uh it's like a super it's um it's like the hannibal lecter of transistors it's got uh it's no that that doesn't work at all but it is in a cage and it likes uh fava beans and a nice chianti um but this is the the output kind of power transistor that provides the current to uh send the signal to the outside world as we call it this is all the inside world and then the outside world is whatever it's going to uh be going out to um so let's let's say we're a mic signal here we're coming into the mic um transformer here for uh to get unbalanced and then we go to the preamp stage and the way that the gain switch works and now we're getting into weird stuff well we've already it's already gotten a little bit weird uh but now is where the neve preamp gets quite unique because the way that the gain switch works underneath preamp isn't like your typical preamp volume control usually you just have a pot or potentiometer which is what this is and where you just have uh it's basically two resistors and as you turn it one gets bigger the other gets smaller in proportion to each other and that's not what we have here we have this switch that does actually some pretty complex switching um for example at lower gain you're only using this first preamp stage and then at higher gain it the second one kicks in i believe the third one is always engaged for current gain um but yeah so that's a that's kind of why neve preamps are part of why they're difficult to make really well and they're never their name they never can be as cheap as other things is because they require this huge honking multi-pole switch and these things are just not cheap to make well um so that's so where our mic signal we're going into the preamp we're getting involved in all this complicated routing and then we go to this output stage um so you heard me mention current gain a minute ago what we generally are talking about with preamp and output amplifier stages is that the preamp stage is there to do voltage gain and roughly speaking in analog audio voltage is volume or amplitude so the preamp stage does the volume increase but then you can't just have voltage with no current because then you don't have enough power to drive the next stage in the outside world so this next stage is our current gain and that's what gives us the current to kind of it's like the rocket fuel that allows us to push our voltage at that higher volume into the next stage so you can just think of it that way it's the same in um guitar amps you often hear about the preamp tube and the power tube or the output tube exactly like this you have voltage gain aka volume first this is the more delicate stage this is where most of the tone comes from usually and then the output stage which is kind of the the muscle it's there to provide the the booster for the voltage to get into the next device um and in this case we're also it's also going through this big transformer which requires a bit of power on its own just to get a nice clean signal through there so that's a basic you know i know that's very macro but that's a basic walkthrough of the kind of the topology but what what makes this special why are never preamps so coveted so legendary um it really comes down to the choice of parts because there are so few components in here i know it doesn't look like that few but there are what do we say six nine transistors in this entire circuit your typical op-amp uh in fact there's one right here this is an ic i'm sure this is not in the audio circuit it's just here to drive this meter but your typical ic op amp like that has at least 20 25 transistors so you can imagine this whole thing is is significantly less complex than a single chip and most pre-amps that you'll find now have you know five chips to ten you know many many chips so this is actually a very primitive not primitive it's very clever it's very ingenious in very smartly designed but it's very simple and when things are very simple every part matters a lot especially the transistors because the transistors are in class a which means they're working all the time they're not sharing the load between each other and they're working kind of on the borderline of their linear range meaning most parts uh especially transistors are specked for a certain distortion and noise um spec when they're operated in a certain range these are kind of pushing that once you get beyond that range is when things get fuzzy and and needy and that's what's going on here so it's very very critical that you choose the right transistors so that's really where the art and labor of of replicating a neve circuit comes in same with the tran uh transformers very very critical um and from a user experience perspective how good this switch is and um and and the rest of the switches are very important so that is kind of what makes or breaks a neve preamp um and also kind of what makes them so magic and special is it's just a few really particular parts doing their thing and um some reason we in the audio world have just fallen in love with that thing that they do so um there you have it there's the neve circuit if you've made it this far in the video i hate to break it to you but you are a nerd and uh thank you for following along uh if this that kind of stuff is interesting to you check out uh our website diyrecordingequipment.com we make audio kits so you can build your own stuff and do more of this kind of uh well the opposite of a tear down you can do a build up so thanks for tuning in uh i'm really excited about doing these kind of tear downs the last one got a great response this is really fun i would love to hear comments uh requests of things you would like to see the with the lid off and a little bit of a walk through like this so thanks for tuning in

Channel: DIY Recording Equipment

Views: 32,075

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Id: JMCPL-iBDw4

Length: 13min 37sec (817 seconds)

Published: Thu Jul 16 2020