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Preamp and A/D converter ideas

hello,

I have a question for you guys.
For our archive digitizing works, we are currently using a couple of Neve 1073DPD.
We will be needing 4 new channels, which would mean 2 other 1073 for around 5000$.
So I was wondering if you guys would have any ideas of some other gear that could do the trick for a little less money.
It could be an interface (all included), some other preamp+converter (standalone) or even preamps and converters (separately).
I mean, I love the 1073, but it start to add up in terms of money and I was wondering if there would not be a cheaper alternative.

Thanks for your time.

N.

Comments

Kurt Foster Sat, 09/22/2018 - 12:40

no. actually i've retired mostly because my ears aren't so good anymore. but they've had lots of great reviews on all their stuff by people who have the originals.

the thing to consider is even between 2 or 3 different original vintage pieces, you will most probably hear slight differences because components will drift at different rates. manufacturers generally shoot for the "in the neighborhood" or a "flavor". consensus is the Warm gear is right in there.

if i could get around and hear as well as i did when i was younger, i would build a studio around a collection of Warm equipment and a MARA Machines refurbished MCI 1" eight track and 2 track along with one of the new versions of the Tanner or Tree Audio consoles available.

there's a big move back to analog and recording live off the floor these days.

http://auroraaudio.net/company/history#

niclaus Sat, 09/22/2018 - 13:40

I had no idea you retired. How long ago did you stop?

Actually, I don’t the console part of things. I just need some good pres and ADC.

Do you think the RME stuff could do the trick?
I mean how would you rate their pres and converters in 2018 compare to some more expensive stuff (such as the 1073DPD which has a really good conversion stage.).
Would the RME Fireface UC, for example, be a real step down compare to what I get from the 1073?
It has the advantage of being an interface as well which would save me some bucks too.

But while some people seem to love them, some say they are not that great.

N.

Kurt Foster Sat, 09/22/2018 - 13:58

RME has been a good investment for a lot of people probably some of the best "affordable"pre amp / converters. not Nevish though. Completly different animals. RME has "no hair" to speak.

i retired about 2005. i closed KFRS in 2001 and moved to the McKenzie River Valley. I installed a smallish but well equipped computer based home studio in my house but i soon learned that there was not really any demand for recording services in Eugene Oregon. plus, i really didn't like the sound of mixing in the box and everyone has a computer. i really regret having to sell my MCI 636.

i would be available to produce if any one wanted my help but i would absolutely need to have an assistant / engineer with great hearing. i don't hear much of over 10 k any longer.

Happily, things are beginning to change. a lot of people are beginning to understand home studios don't cut the mustard for the most part. big rooms, hi volts are a must and and recording live off the floor is often the key to great records.

there are some things i really like that are done one or two tracks at a a time or midi / vsti based like

'">Thunderclouds

, but for the most part i still prefer real music played on real instruments by real people at the same time.

that coupled with increasing age and the ensuing slight loss of hearing as well as the ability to stoop kneel and in general put up with clients it was time to retire. i had a very good run, left some footprints in the snow. i'm-a-happy. :LOL:

Boswell Sun, 09/23/2018 - 06:19

niclaus, post: 459092, member: 33719 wrote: We will be needing 4 new channels, which would mean 2 other 1073 for around 5000$. So I was wondering if you guys would have any ideas of some other gear that could do the trick for a little less money. It could be an interface (all included), some other preamp+converter (standalone) or even preamps and converters (separately). I mean, I love the 1073, but it start to add up in terms of money and I was wondering if there would not be a cheaper alternative.

Hi Niclaus,

Other than implying that another pair of Neve 1073s would be too expensive, you don't give a budget for a new pre-amp/converter.

From what you say about your project, it sounds as though something like a Focusrite ISA428 with optional ADC card would work well for you. That box has 4 transformer-coupled mic preamps, plus 4 ADC line inputs that would accept the outputs of your existing 1073s. All you would need then is a simple audio interface card such as an RME PCIe board that would receive a pair of ADAT light pipes to give you 8 channels at 96Khz. Marco (@pcrecord) might be able to offer a better user's view on the ISA than I could.

At the next level lower (in budget terms), the Audient ASP880 would do a similar job, but with 8 native mic pre-amps, each with balanced inserts that give a direct ADC route in for external pre-amps.

kmetal Sun, 09/23/2018 - 22:38

You could use the ISA 828 as well. For more neve style BAE is highly respected and even sourced the st Ives xformers I believe from the original factory. The grace m108 is 3k and has 8 Pres and AD, stereo out DA, and is remote controllable. A high performance unit for the price, and its pristine, transparent sound mast be better suited to archiving than the colorful have, or at least a nice alternative.

pcrecord Mon, 09/24/2018 - 05:27

Boswell, post: 459107, member: 29034 wrote: From what you say about your project, it sounds as though something like a Focusrite ISA428 with optional ADC card would work well for you. That box has 4 transformer-coupled mic preamps, plus 4 ADC line inputs that would accept the outputs of your existing 1073s. All you would need then is a simple audio interface card such as an RME PCIe board that would receive a pair of ADAT light pipes to give you 8 channels at 96Khz. Marco (@pcrecord) might be able to offer a better user's view on the ISA than I could.

The ISA 428 gets a lot of love at my studio, I had 2 ISA Two prior buying the 428, so I was already spoiled.
ISA preamps have a Rupert neve design if you didn't know. They are not 1073 but sounds as good with maybe less mojo and more transparency.
Getting the 428 with the optionnal digital card gets you 4 preamps giving 80db of noiseless gain and 4 extra line-in with direct path to the converter.
So you could have transparent conversion for archiving and still have 4 preamps in case you also want to record mics...

niclaus, post: 459096, member: 33719 wrote: Would the RME Fireface UC, for example, be a real step down compare to what I get from the 1073?

RME firefaces are excellent audio interface. Their onboard preamps are very honnest and fonctionnal but they aren't 1073 nor ISAs.
Since we don't know much about your archiving needs and workflow, it's a bit hard to tell you what to get. .
But if transparency is the priority, Kmetal's suggestions for grace is right on point as preamps goes.

audiokid Mon, 09/24/2018 - 23:15

niclaus, post: 459096, member: 33719 wrote: I had no idea you retired. How long ago did you stop?

Actually, I don’t the console part of things. I just need some good pres and ADC.

Do you think the RME stuff could do the trick?
I mean how would you rate their pres and converters in 2018 compare to some more expensive stuff (such as the 1073DPD which has a really good conversion stage.).
Would the RME Fireface UC, for example, be a real step down compare to what I get from the 1073?
It has the advantage of being an interface as well which would save me some bucks too.

But while some people seem to love them, some say they are not that great.

N.

Rme makes good converters and interfacing but their preamps are not worth investing. I haven’t heard all their pres but I’ve owned a few and wouldn’t buy them for their preamps.

DonnyThompson Thu, 09/27/2018 - 05:31

If you want clean and pristine - which it doesn’t sound like you do, LOL, you might want to consider Grace or Apogee.
While no pre is 100% “transparent” - that’s a term that gets thrown around a lot these days - they are likely as clean as you’re going to get.
But because they are, you’re not gonna get any mojo out of them...
Apogee makes great converters, too.
I love my Focusrite ISA pre’s. They’re not as clean as those above, they do have a “sound”, but they’re nowhere near as edgy as a Neve. Then again, guys who like Neve lijevthem hecause they are edgy, and have a sonic signature of their own.
For alternates to Neve, you may want to look into BAR or Heritage - I’ve worked with real Neve gear in the past, but I’ve never worked with those “knockoffs”, so I can’t say how they sound in terms of accuracy or being authentic; but I’ve heard comments from those who have who have been very happy with them as a less expensive Neve alternative. Then again, as I’m sure you already know, you could have several 1073’s next to each other and each can sound different from the others...
If I recall, I think I read that the BAE pres have either Carnhill or St Ives XFO’s, and both of those have been used in a lot of Neve pres and consoles over the years. Though, while the XFO’s are an important contributor to the sound, they’re not the only thing that determines it.
You may want to research them and see ( or hear) what you can find out, because they certainly are cheaper than real 1073’s.

niclaus Thu, 09/27/2018 - 08:00

Hey!
Sorry I have been traveling a lot lately and I did not noticed all of your replies.
So thank you guys for all your good advices.
I will sure look into all of them.

I did not gave a budget because I don’t really have one, just wondering what would be good for no more (or hopefully a little better) than what we already have.

Donny, yes, what we are looking for is clean and pristine, I am not sure if that was a joke or not but I do think the neve ADC is really good.
Yes, that is true that the preamp stage might not be of the more “cleanish” but we don’t, obviously, push them hard in the archiving work, it is only used for leveling of the different output of the different machines. And then we can use them when in need of mics recording that would call for a Neve-ish kind of sound.

So if I understood correctly I could use something like a RME for interfacing and for their ADC that seem good but would need something else, like an ISA, for leveling.
Anyway, I will take a look at all that.

Again, thanks a lot for your replies , this is much appreciated.
And sorry for the late reply.

N.

niclaus Thu, 09/27/2018 - 08:45

Just took a look at all that and specially at the grace m108.
It looks great! Especially for that price.
I have never been able to work with grace stuff but from all I read and from what you all say, I shouldn’t be disappointed.
I could use it as a stand alone box and then just send it’s digital outputs to some RME fireface on each protools rig. That way I can use all converters at the same time and route them to the different rigs, and use the Firefaces DAC for monitoring.

The apogee x 6 looks great too but probably harder to be used that way.

Thanks a lot for your advices.

pcrecord Thu, 09/27/2018 - 11:46

niclaus, post: 459149, member: 33719 wrote: So if I understood correctly I could use something like a RME for interfacing and for their ADC that seem good but would need something else, like an ISA, for leveling.
Anyway, I will take a look at all that.

That's the thing, we don't really know what are the sources you are achiving. If it was already line leveled, no preamps are needed.
Also we don't know what you are archiving to. If it's a pc, the leveling can be done in the DAW..
All in all I think the ISAs came out because they are clean and give a ton of gain without noise but also because the ISA428 and 828 have optionnal ADC card. So you could have it all in one box. The all you need is any interface with ADAT inputs...

What's to be avoided is interfaces that only have preamp inputs. even if they can be switched to line level, the signal still go throught a part of the preamp circuit and therefor it can alter the sound. When investing for Neve Grace ISA or other highend preamps, the last thing you want is to color them with another preamp... (my humble opinion)

Hope this help ;)

niclaus Thu, 09/27/2018 - 12:01

And your humble opinion is totally agreed upon
Thank you for that.
They would be used to digitize optical, magnetic, 35, 16mm,..., soundtracks mostly.
The machine are supposed to output line level signals but you never know what is going to happen with those old soundtracks, if you know what I mean. Sometimes we still need a pretty decent amount of gain for reasons we do not control and because of decisions that were made 60 years ago...

DonnyThompson Thu, 09/27/2018 - 13:26

If the audio content is already line level; you might look at a unit that allows you to bypass the pre section and go right to the conversion stage.
If it’s not line level, I’d be looking at a very clean preamp with great converters. Apogee fits this description, as does Grace in terms of clean pres ( though the M Series has no conversion, they may make a combination pre/converter, I don’t know). I’ve heard good things about RME from others, but I’ve never used any of their gear ( at least not that I can recall) so I can’t comment either way.
But.. it would help to know a bit more about what you’re doing.
Even if you’re not “pushing” the Neve, you still very likely be picking up more coloration and the character that Neve is known for... More so than something like the Grace or The Apogee.
Both of those units are very beefy in gain as well, should you want that for future use with low output dynamics and Ribbons, though for that scenario, I really like the Focusrite ISA because it has great gain (78db? Maybe it’s 80db... we could ask Marco about that, though I don’t think that +/- 2db will really matter (@pcrecord). What I really like about the ISA stuff is that it has selectable impedance(s), which can be very important with moving coil/ ribbon mics.
If transferring is all you are planning to do, and you currently like the sound of the Neves you have, then you may want to look into some of the Neve “clones” that have emerged, like BAE or Heritage Audio, though these are strictly pres and don’t have conversion stages.
:)

audiokid Fri, 09/28/2018 - 07:10

kmetal, post: 459115, member: 37533 wrote: You could use the ISA 828 as well. For more neve style BAE is highly respected and even sourced the st Ives xformers I believe from the original factory. The grace m108 is 3k and has 8 Pres and AD, stereo out DA, and is remote controllable. A high performance unit for the price, and its pristine, transparent sound mast be better suited to archiving than the colorful have, or at least a nice alternative.

Yeah... m108 looks really nice.

kmetal Sun, 09/30/2018 - 02:10

If you only need stereo adc, you could go with mytek Brooklyn which if I recall correctly has a 129db dynamic range, and def does 382k sample rate. Which may be better for future proof archiving. It's priced at 2k, and is a high end unit.

https://mytekdigital.com/storeus/catalog/product/view/id/241/s/brkl-adc-b/category/35/

You could also go the RME adi pro which is a stereo ad/da with something like a 123db ad Dynsmic range and 126db DA dynamic range, and goes up to 764khz sample rate! It's got a $2k price tag as well.

You could also use the lymx e44 or e22 pcie converters which are 4 ch snd 2 ch adda cards with something g around a 117db ad Dynamic range, and 121db DA dynamic range. They are $650, and $850 or close to that, from JRR Shop.com

DonnyThompson Sun, 09/30/2018 - 04:18

bouldersound, post: 459182, member: 38959 wrote: I get to use some Grace M101 preamps. They are quite nice sounding, silky smooth.

My own take on the Grace 101, based on the experiences of the three occasions I was able to use them, is that the M101 shines - but not because of any character or sonic coloring that other preamps are known for - but because it allows the mics you are using, (and the sources you are capturing), to sound the way they are supposed to sound; without adding any character of its own.
On one session I was working on a few years ago at a colleague’s studio, we used a ribbon mic (Royer 121) as a second/distant mic on a very nice-sounding Marshall (tube) guitar amp; and that gain-chain of the Marshall, the Royer, and the M101 sounded fantastic.
IMO, it was due to the guitar amp and the 121. The beauty of the Grace is that it allowed the mic and amp to sound as they were supposed to. Usually, I like the combination of a dynamic and a ribbon on a guitar amp, but on that session, we ended up not even using the dynamic mic (421) that I had placed in-tight on the speakers. It sounded great - using just the ribbon mic that I set back a few feet off the amp.
The other great feature that the Grace M-101 has, (similar to other clean pres I’ve used, like the Focusrite ISA-1 and the Millennia HP-35) is that it offers LOADS of available gain ( and it also has a +10db boost function for Ribbons and low-output Dynamics), yet it is also incredibly quiet, too.
I’ve used the Grace with other mics as well. For one session, at the same studio several months later, I brought my pair of 414 EB’s to a drum tracking session, and we used two 101’s with the 414’s for drum OH’s. The top end was indeed silky smooth; but I credit that more to the 414EB’s (and the drums, cymbals, and the room) But... the 101’s were wonderful, and a perfect choice, because they allowed the mics (and the drums) to sound the way they were meant to sound.
(FWIW, I recall having to do very little afterwards with those tracks, using that gain chain.)
IMO, that’s the real magic of Grace preamps, and where they truly shine: they “stay out of the way” of the other links in the gain-chain that do add their own form of color/character.
Based on my own - albeit limited -experience with them, that’s really what I came away thinking that this is what the M101’s really do best.
IMHO, of course.
:)

Boswell Sun, 09/30/2018 - 06:09

Donny's right on the money about the Grace M101, and most of what he said can be applied to other top-quality transparent pre-amps.

However, the other side of the coin is that pre-amps of this type won't hide a poor-sounding microphone, and this doesn't necessarily mean that the microphone is inherently bad, simply that it may be being used in an application for which it's not suited. That leads us on to the result that there are very few top-end microphones that work well in almost any situation. The AKG C414 that Donny mentioned is one of the few. In the realm of dynamics, the Shure SM57/58 is up there as well.

DonnyThompson Sun, 09/30/2018 - 07:07

Lol, yeah... I neglected to mention that the Grace is so neutral, that it will very accurately capture bad sounds, too; as Bos (@Boswell) mentioned. Whether that’s caused by a wrong mic choice, or placement, or a poor-sounding vocal, instrument, amp...or even a poor sounding room, the Grace will capture those things accurately.
There are preamps that offer their own unique type of coloration, ( most are known for their character and are chosen because of it) and sometimes, these sonically colored pre’s can be a bit more forgiving, when it comes to tones that don’t sound as good as others. Sometimes you can “hide”- or distract attention away from - poor sounding frequencies, by driving a colored preamp hotter ... models that are known for their color and character, such as Neve’s, Avalon, API’s, or other preamps that can drastically change in tone as you ramp the gain up on them.
But, that’s not really a “fix”, and is not advised. You’ll very likely end up working a lot harder to get those “not so good” sounding tracks to sit nicely in a mix, and most of the time, it doesn’t really work.
You’re always better off to capture your sound sources as close to the fidelity that you want to work with. Recordings that sound good to begin with are far easier ( and more satisfying) to work with, than captures that will require a lot of processing in an attempt to make them sound “passable”.
This may require a different mic, or a different mic placement...but it can also be the source itself that can sound bad to begin with.
I love my AKG 414EB’s, and as Bos mentioned, those mics are known for sounding good on pretty much any application. But, I could use them, along with the Grace, on a terrible sounding kit of drums, or in a poor sounding room, and it’s not gonna matter.
Your capture is what matters first and foremost. The Grace is a great pre to use for tracking, but because of its transparency, it will accurately capture both good and bad-sounding sources.
;)

niclaus Sun, 09/30/2018 - 12:14

Wow I had no ideas that thread was gonna go this far deep into the grace pre’s.
Thank you so much guys for all you good words and advices.
Now I definitely want one!!

More seriously, I really think, from the fonctionnalities, and from everything you just wrote that this is the way to go for us.
Thank you so much.

It is not going to happen before a few months as it will be used in our new premises but as soon as we will be all set up, I will definitely need one!

pcrecord Mon, 10/01/2018 - 05:20

DonnyThompson, post: 459190, member: 46114 wrote: Grace is so neutral, that it will very accurately capture bad sounds, too;

This is what many newcomer will experience and lead them to say preamps do not mather.
They start recording with cheap mics and interface and at some point try a Highend preamp and it sounds bad.
Why? because the highend pre reveals more of the source / mic / room than the equipement they are usually using.
Many of them fail to realise, they need to be better at mic placement and every other aspect of recording including ear-training before they can appreciate highend gear.
When I switched from a live mixer to ISA and UA preamps, I had a hard time adjusting and needed to re-think my whole approach to mic choices and placement.
The ISA preamp made me re-evaluate each of my mics and relearn their behaviour.
This was a period when I learned a lot and I'm thankfull I did put the time!

(I thought it needed to be said in case someone finds this thread from a google search.. ;) )

kmetal Tue, 10/02/2018 - 06:34

pcrecord, post: 459200, member: 46460 wrote: This is what many newcomer will experience and lead them to say preamps do not mather.
They start recording with cheap mics and interface and at some point try a Highend preamp and it sounds bad.
Why? because the highend pre reveals more of the source / mic / room than the equipement they are usually using.
Many of them fail to realise, they need to be better at mic placement and every other aspect of recording including ear-training before they can appreciate highend gear.
When I switched from a live mixer to ISA and UA preamps, I had a hard time adjusting and needed to re-think my whole approach to mic choices and placement.
The ISA preamp made me re-evaluate each of my mics and relearn their behaviour.
This was a period when I learned a lot and I'm thankfull I did put the time!

(I thought it needed to be said in case someone finds this thread from a google search.. ;) )

Ditto for me when I got my 414. I realized how bad my room sounded.

DonnyThompson Tue, 10/02/2018 - 11:21

Marco’s (@pcrecord ) experience with working with high end preamps mirrors that of my own. Working with high end pres for the first time made me recognize the other factors involved, putting more focus on things I hadn’t considered beforehand: mic quality, mic placement, how different rooms can play a major factor in the sound quality of what you are capturing within that space, as well as conversion... though when I first came to these realizations, I didn’t think about conversion quality, because I was still working in analog; but it’s definitely a factor with digital.
And, I think Marco is totally correct about first time users of high quality preamps not being very impressed, because they look at those high quality preamps as being some kind of “instant fix”, or “silver bullet” answer to what they’ve experienced previously with cheaper preamps.
I’m not saying the quality of preamps doesn’t matter, because it absolutely does... but I think many beginners expect high quality preamps to be “the” answer to a poor sounding room, or using a cheap sounding microphones.
The TOTAL gain-chain matters - and I’m including the very first step in that chain as being the sound of the instrument/voice, the room where the recording is being done; and then onto the mics, the pre, and the conversion. The chain will only ever be as good as its weakest link.
;)

Kurt Foster Tue, 10/02/2018 - 12:57

there are many different approaches to building high end mic pres. some employ lots of transformers and discreet components, some have op amp designs of varying types and some can even be surface mount tech. they can all preform wonderfully in spite of them all being very different in design. some may be better suited to certain applications like a requirement for more gain and the ability to switch input impedance as required for ribbon mics.

there is however, one very important thing that all great designs have in common and it is very easy to tell if a mic pre has or not. that is the POWER SUPPLY.

all mics generate very low voltages and require a lot of power to boost gain to line level. even more so for older ribbon mics that need a lot of gain and low impedance's to function to their specification. not only does a power supply for a mic pre need to provide plenty of power but it also has to be well regulated CLEAN POWER. it's not cheap to build a powerful well regulated clean power supply and i suspect that dealing with varying voltages required for international use only exacerbates difficulty.

some claim a 9 volt wall wart power, oblivious to polarity as employed in rack crap like BARFINGHER or ARRENNPEE electronically step up voltages to acceptable levels but that's at the cost of amperage. there is no free lunch. both high amperage and voltage are necessary.

niclaus Wed, 10/03/2018 - 01:26

The chain will only ever be as good as its weakest link.

So true but every time I read that, I am wondering if it ain’t me who is the weakest link!

Anyway, I got the approval of the COO. We are going to go with the grace m108.
A big thank you to all of you for your time and advices.
Great thread!

I will let you how I like it once everything is set up!

DonnyThompson Wed, 10/03/2018 - 02:01

@Kurt Foster

Great point, Kurt.

Is there a recommended minimum voltage that you like to see for mic preamps; a voltage level that can power all mics sufficiently?
And, besides “sufficiently”, what would your recommended optimum voltage be on a mic pre?
(For example, let’s say you’re working in recording scenarios where low output dynamics and ribbons are being used)...

(Lol, I think we can leave out the 9v wall-wart as an option). ;)
-d.

kmetal Wed, 10/03/2018 - 04:07

Kurt Foster, post: 459227, member: 7836 wrote: there are many different approaches to building high end mic pres. some employ lots of transformers and discreet components, some have op amp designs of varying types and some can even be surface mount tech. they can all preform wonderfully in spite of them all being very different in design. some may be better suited to certain applications like a requirement for more gain and the ability to switch input impedance as required for ribbon mics.

there is however, one very important thing that all great designs have in common and it is very easy to tell if a mic pre has or not. that is the POWER SUPPLY.

all mics generate very low voltages and require a lot of power to boost gain to line level. even more so for older ribbon mics that need a lot of gain and low impedance's to function to their specification. not only does a power supply for a mic pre need to provide plenty of power but it also has to be well regulated CLEAN POWER. it's not cheap to build a powerful well regulated clean power supply and i suspect that dealing with varying voltages required for international use only exacerbates difficulty.

some claim a 9 volt wall wart power, oblivious to polarity as employed in rack crap like BARFINGHER or ARRENNPEE electronically step up voltages to acceptable levels but that's at the cost of amperage. there is no free lunch. both high amperage and voltage are necessary.

I think this holds true across the board with electronics. When u see pultec emulations for $500 youve got yo wonder why.

Boswell Wed, 10/03/2018 - 05:17

DonnyThompson, post: 459245, member: 46114 wrote: @Kurt Foster

Great point, Kurt.

Is there a recommended minimum voltage that you like to see for mic preamps; a voltage level that can power all mics sufficiently?
And, besides “sufficiently”, what would your recommended optimum voltage be on a mic pre?
(For example, let’s say you’re working in recording scenarios where low output dynamics and ribbons are being used)...

(Lol, I think we can leave out the 9v wall-wart as an option).

This is where I put my professional designer's hat on. Apologies in advance.

The reason that commercial wall-warts have (rightly) got such a bad name for audio units is that they are designed to be cheap, and that means skimping in all aspects of design, component selection and production. There is no reason in voltage terms why even very high end pre-amps could not be powered by a wall-wart supply, 48V phantom power (PP) and all, if the same standard of design and production that went into the pre-amp also was applied to the wall-wart.

The specification for studio-standard phantom power is 48V +/- 4V. The spec also says that a 48V PP microphone has to be connected via 6K8 resistors from the two signal output lines to the PP supply. This implies a maximum short-circuit current of about 15.3 mA, so the pre-amp has to be capable of supplying that to at least one input connector without overheating or other failure. It's not in the specification that the non-shorted inputs must still be at 48V, so most pre-amps are able to supply about 6mA per channel without the PP voltage falling below specification. This puts a total current and hence an overall power specification on the circuitry that generates the PP, whether that be a separate line from the power supply or is generated by an inverter from one of the other internal power rails. PP generation is one of the trickier aspects of pre-amp design, both from a specification point of view and also in terms of keeping the inverter switching noise out of the audio signal paths and EMC radiation from the cabling.

I could go on. Sorry.

Boswell Wed, 10/03/2018 - 07:58

Kurt Foster, post: 459255, member: 7836 wrote: please do go on Bos. i'm positive you know a lot more about it that i do.

i believe that a bi polar power supply of at least+/- 15 volts is a good rule of thumb minimum and yes a line lump can do that but once again it would need to deliver well regulated +/= 15 volts of clean power.

I give a wry smile these days whenever I see the integrated circuit manufacturers calling the ±15V to ±18V rails high voltage. I am guessing it's because the largest quantity of devices currently sold have a maximum supply voltage of ±5V or less.

In several of the audio designs I have done, I used carefully-regulated ±17.5V rails in order to get the largest voltage swings I could out of devices that had absolute maximum ratings of ±18V. Without exception, in all the designs of this type I used internal power supplies rather than wall wart or cord lump types. However, it has been only relatively recently that I have managed to find reliable switching PSUs that are electrically quiet enough to power professional audio gear. Before that, I was still designing in 50/60Hz mains transformers, sometimes specified with overwinds if a 48V output was needed.

One of the designs I was most pleased with used ±45V rails. The front-end circuitry was made up of discrete devices, but since there are op-amps available that will run off that voltage, I used a few of them as well in the later stages. The transient performance of that unit was amazing, partly helped by having no coupling capacitors in the signal path. It was a real pity that the company who comissioned the design got taken over before the unit got to market, so only the pre-production prototypes got built before the new owner canned it.

DonnyThompson, post: 459257, member: 46114 wrote: So, you are saying that it’s not that a wall wart couldn’t be of sufficient and consistent voltage, it’s just that the manufactures take shortcuts in that component - to keep the pricing down -so that by and large, they are not usually capable of delivering either. Have I got that right?

They were developed for a particular market sector, and it was not the audio one. The lower-end audio people seized on them as a way of saving production costs.

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