Preamp Circuit Question

[tkingen]

If you line up a bunch of different pres from different manufacturers that are based on the same chip (i.e. Burr Brown INA217 OR INA163) are they all going to sound pretty much the same?

 

[Kevin Deschwazi]

I can't give you a full answer 'cos I'm no tech, but yeah there could be differences in sound.

As an example, whether or not the design employed transformers or not could make a pretty big difference.

The DAV BG-1 is interesting in this respect. They say it's an ordinary opamp in a very ordinary circuit design but those who use it (I don't think I've read a negative review on that unit) say there's definitely some sort of mojo going on with the design.

 

[xstatic]

The short answer here.... not really.

Some may sound very similar, some may sound very different. The chip is just the tip of the iceberg.

 

[chessrock]

Much moreso than with most other types of audio equipment. But certainly not entirely.

If you were talking about opamps, then absolutely not. If two different mic pres both use an OP275, what is that going to tell you? Absolutely nothing (other than the designer was at least smart enough to use a really good, inexpensive opamp). If two different mic pres use a 5532, is that going to say a lot? No way.

The instrument amp is a different story, though. And that is really what your question is about.

Now in regards to the instrument amp ... are two designs that use an INA-163 going to be very similar? Not always, but it is very often the case. The very fact that it is based on an instrument amp to begin with -- be it an INA217, SSM2019, or whatever -- automatically puts it in to a general classification. You at least know the basic "type" it's going to be without having to even listen to it (transparent/uncolored, very low distortion in the audible band at reasonable gain, etc.), generally speaking of course.

Although there are certainly other factors involved, most of the stuff that's out there tends to use only minor vairations of the same basic design principle / layout. A company like Grace Design or Earthworks can certainly put a spin on it by using very high-spec'd supporting circuitry; i.e. no electrolytic caps and more expensive film resistors, etc. That in addition to superior grounding, power supply, using better opamps etc. ... any number of things, really. But for the most part, in that type of design, there is no single component in the path that will have as much effect on the sound as the instrument amp.

And it could be further argued that there is no other type of design where one component will play as large of a role in the sound. And for the most part, the mic pres based on those instrument amps tend to be closer to a "standardized" design than most other types of audio equipment.
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[Robert D]

Agreed. The chip does have a contribution to the "sound" of the preamp, but it probably has more of a contribution to the specs, since it is providing all the gain. A lot of the "sound" of a preamp design comes from the supporting circuitry, especially things like transformers, and to a lesser extent, capacitors. Circuit topology is really the biggest factor, followed by components used, assuming reasonable quality components in all cases.

 

[chessrock]

Circuit topology is really the biggest factor, followed by components used, assuming reasonable quality components in all cases.

But would you agree that the use of an instrument amp like the ones in question (i.e. Burr Brown INA, Analog Devices, etc.) will greatly influence the topology?

And would you honestly say that the topologies using an instrument amp at it's core tend to vary wildly from one unit to another? ... or would it be safer to say that they tend to be more similar in their layout than different?

 

[MOFO Pro]

Take the DAV BG-1 for example...

 

[MCI2424]

If you line up a bunch of different pres from different manufacturers that are based on the same chip (i.e. Burr Brown INA217 OR INA163) are they all going to sound pretty much the same?

No. There are dozens of parameters that have to be set by external circuitry to achieve a given result. There is gain, bandwidth. feedback, filtering poles etc. Contrary to popular belief, the chip is only 1 part of the equation and is ultimately configurable. The external circuitry is the magic in whatever sound is achieved in any design. There is much more to a proper design than slapping these chips on a board and firing it up.

 

[dementedchord]

while the opamp can contribute to the sound and whether or not an instrumentation amp is used (if that's what chess is refering to)can also affect the sound... it is by far the least significant considerations overall... circuit topology dominates... quality of supporting components is also higher IMO... it's not just which opamp.. but rather the appropriatness of it's use in that circuit... for instance is it a gain stage or a drive stage??? an opamp with a great GBW and low quiescent current may sound like absolute shit and pop when used as a driver...

 

[chessrock]

while the opamp can contribute to the sound and whether or not an instrumentation amp is used (if that's what chess is refering to)can also affect the sound... it is by far the least significant considerations overall... circuit topology dominates...

Same question I asked RobertD ; If an instrument amp is going to be used, would you agree that the topology is generally going to be somewhat limited, to an extent? Or are there a rich and varied number of possible topologies being used with something like an INA163 or 217, for example?

 

[tkingen]

Hey guys, thank you all for your insights

 

[MCI2424]

Same question I asked RobertD ; If an instrument amp is going to be used, would you agree that the topology is generally going to be somewhat limited, to an extent? Or are there a rich and varied number of possible topologies being used with something like an INA163 or 217, for example?

An instrument amp is a low noise, high bandwidth linear amp designed for accurate analog measurement with excellent resolution. A general amp is designed for applications where bandwidth, low noise or any other tight parameter is not needed (say for comparators etc.)

An "instrument" amp can be set up to be anything the designer wants it to be from shit to diamonds (within the limitations of the actual amp design).

There is no "magic INA163 sound" here. The reason so many cheap pre-amps using either of these chips sound so similar is that the designs use very few external components (cheap to make) and given that, there are only so many configurations that can be made to work (ie: the designs are minimal and similar). A more expensive topology involving decent transformers etc. would add much more $$ to just the parts list alone let alone the design time, board layout, testing and all other things engineering that cost $$.

A monolithic IC chip IS limited to some extent to how well the IC stands manufacturing tolerance (inside the chip). This would be the only reason to question a real expensive design using a monolithic IC. Designers who use discreet components (non-IC) have a much greater advantage as to the parameters that can be set, from bandwidth to dc offsets, and new ideas in the design of the amplifier can be done readily. This costs more $$ in design time and getting it right time than actual components cost. The discreet path is used in the high-end stuff more than ICs.

So, I would not immediately say that Chessrock has no point here, but, I would have to say that not hearing this particular design of amp and just throwing it into the pile of "IC based stuff" is not the fairest evaluation either. People who have them seem to like them so maybe this guy has a unique design with more control over the parameters of the IC. It is possible. Anything is possible.

 

[chessrock]

The reason so many cheap pre-amps using either of these chips sound so similar is that the designs use very few external components (cheap to make) and given that, there are only so many configurations that can be made to work (ie: the designs are minimal and similar).

Great explanation.

A more expensive topology involving decent transformers etc. would add much more $$ to just the parts list alone let alone the design time, board layout, testing and all other things engineering that cost $$.

So would it be safe then to assume that, if a given unit wasn't utilizing a "more expensive topology" ... didn't have a transformer anywhere in the path, and used essentially lower-grade caps and other supporting circuitry ... would it be difficult, then, to justify a significantly higher cost for said unit?

Or, more accurately ... could you at least see where one might raise that question or suspicion, without being totally out of line? Do you think it would be a valid concern, without even having listened to the unit or having direct experience with it? Hypothetically speaking, of course.
.

 

[apl]

Isn't someone modding Behri rack pres by replacing the chip and other components with startling results?

 

[rory]

Or, more accurately ... could you at least see where one might raise that question or suspicion, without being totally out of line? Do you think it would be a valid concern, without even having listened to the unit or having direct experience with it? Hypothetically speaking, of course.
.

You're funny mr. chessrock.

 

[Big Kenny]

I'm waiting for the "AH HA"

 

[Kevin Deschwazi]

So would it be safe then to assume that, if a given unit wasn't utilizing a "more expensive topology" ... didn't have a transformer anywhere in the path, and used essentially lower-grade caps and other supporting circuitry ... would it be difficult, then, to justify a significantly higher cost for said unit?

I'm gonna go out on a limb and assume you're talking about the DAV pres.

I'm not sure it's fair to say they use 'lower grade caps', I've seen a few pics of the guts and the metallised poly caps are Evox Rifas- good caps.

 

[MCI2424]

Great explanation.




So would it be safe then to assume that, if a given unit wasn't utilizing a "more expensive topology" ... didn't have a transformer anywhere in the path, and used essentially lower-grade caps and other supporting circuitry ... would it be difficult, then, to justify a significantly higher cost for said unit?

Or, more accurately ... could you at least see where one might raise that question or suspicion, without being totally out of line? Do you think it would be a valid concern, without even having listened to the unit or having direct experience with it? Hypothetically speaking, of course.
.

Raising questions based on a single piece of info (such as a popular IC) is not out of line if you are to assume that the design is a common one amongst it's peers. IF the unit's design was minimal, then the cost would certainly not be in the components but in the labor and cost of manufacturing (and the desired profit margin tagged on). I did say in another post that if you were to, for example, build an exact copy (sic) of a behringer pre-amp in a lot of 1 that the cost could be 5-10 times higher only because of the lower cost of mass production/high quantity parts. Boutique manufacturers have to charge substantially more and that is why they generally stay away from IC based designs. For them to compete in the market, they must have a substantial design/performance advantage to even exist.

Again. I am unfamiliar with the DAV-1 and cannot provide an opinion about design/build/performance, but IF it uses a unique design that includes expensive components/quality parts all around and has a great sound, then I suppose it is worth whatever people are willing to pay.

Does this make any sense?

 

[Robert D]

But would you agree that the use of an instrument amp like the ones in question (i.e. Burr Brown INA, Analog Devices, etc.) will greatly influence the topology?

And would you honestly say that the topologies using an instrument amp at it's core tend to vary wildly from one unit to another? ... or would it be safer to say that they tend to be more similar in their layout than different?

Sorry I'm late getting back to the party. Lot's of good answers already, and a great discussion. I'm up to my ass in alligators at work today, so I'm going to refer you all to this PDF on the 990 discreet op-amp, which discusses some of the design tradoffs inherent with a monolithic op-amp.
http://www.johnhardyco.com/pdf/990.pdf

Capacitive coupled, transformer coupled, servo coupled, etc.... there are plenty of things that can be done to differentiate different preamps based on the same IC, though the market might expect that higher end products should be discrete designs.

 

[LeeRosario]

If you line up a bunch of different pres from different manufacturers that are based on the same chip (i.e. Burr Brown INA217 OR INA163) are they all going to sound pretty much the same?

specify what chip?

Thats like asking, "if all cars had a V8, would they all run the same?"

Sorry, not trying to be a smart ass.