Hi there! I'm new to these forums so maybe this question has been asked many times. I tried to search, but couldn't find the exact answer... I've been reading threads about phono preamps but still wandering which one is the best...
I don't care about the price of parts. I'm looking for a high quality preamp schematics. Which one of all phono preamps projects mentioned on this forum is the best in terms of sound quality, very low distortion and low noise for MM pickups?
The reason I'm asking this is because I'm planning to build an amp with line and phono inputs, and also be able to use the phono preamps that I'll include in this amplifier as a stand alone devices for recording....
Thanks.
I don't care about the price of parts. I'm looking for a high quality preamp schematics. Which one of all phono preamps projects mentioned on this forum is the best in terms of sound quality, very low distortion and low noise for MM pickups?
The reason I'm asking this is because I'm planning to build an amp with line and phono inputs, and also be able to use the phono preamps that I'll include in this amplifier as a stand alone devices for recording....
Thanks.
Hi thzere....National Semi's website on the LM833 offers an application note for a general RIAA characteristic. In fact there are stacks of ic's suitable for this app, some noisier than others. For moving magnet pickups....the input level and impedances are way different. The simplest solution which Ortofon did with MM types was to supply step-up transformers to match moving coil input eq's. For lowest noise this was the best solution. keep working on it!
rich
rich
I was looking into the Phonoclone and VSPS preamps, and also into many others like those that are included in application notes from different IC manufacturers. I suppose that not only the ICs are the ones that determinate the quality (noise, THD) but the feedback circuits, voltage supply and everything else... Am I correct?
I like the specs of the AD797, but how hard is to modify for example the VSPS or the Phonoclone circuit in order to be able to implement the 797? I like those two phono stages because they are simple, but how about the specs in terms of noise and THD? Thanks.
I like the specs of the AD797, but how hard is to modify for example the VSPS or the Phonoclone circuit in order to be able to implement the 797? I like those two phono stages because they are simple, but how about the specs in terms of noise and THD? Thanks.
The circuit on the lm833 data sheet seems to have alot going for it in comparison to the `one op amp types` normally found in most mixers,integrated amps,not to mention some other manufacturers data sheets ! I have not built this yet , but even for the not very mathematical amongst us the gain can easily be increased at the second stage,the only downside is that from the figues provided and the ones I calculated for a different first stage gain,it always seems to come up with-E96 values of resistors.Seems a good excuse to use the low noise :- very stable welwyn types ! Still if I am to assume correctly that you will be recording your own mixes ; 2 x rotel rq 970 bx (which can be picked up for arround £50 stirling S/H ) running into the mixers line input should give exellent results without the hastle of fabricating your own PCB`s !
Happy mixing !
from soundadvice !
P.S. my soldering is much better than my typing, I do much more of the former than the latter !
Happy mixing !
from soundadvice !
P.S. my soldering is much better than my typing, I do much more of the former than the latter !
AD797, LT1028/LT1115 are three low noise opamps but if you not are going to use any MC pickups you will have many good opamps to choose from. The noise should be less then 10 nV/Hz.
Have you seen this datasheet for inspiration? In the datasheet you have two different kinds of RIAA amps.
http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1154,C1009,C1026,P1293
Datasheet here:
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1026,P1293,D1612
Have you seen this datasheet for inspiration? In the datasheet you have two different kinds of RIAA amps.
http://www.linear.com/pc/productDetail.do?navId=H0,C1,C1154,C1009,C1026,P1293
Datasheet here:
http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1009,C1026,P1293,D1612
Hi,
I'm not going to give you the answer, I can't.
But my thoughts on what to look for.
1. Buffer on the input with a bit of gain (+6 to +10db) before anything gets done to equalise.
2. Split passive equalisation with buffer/gain blocks between stages.
3. Simple passive 75us roll off as last equalisation, achieves noise reduction and maintains single pole to infinity, well almost.
4. Lots of spare voltage overhead at the output buffer and in the intervening gain blocks. Oh and remember all caps have some inductance.
5. If diy find a way to measure your caps to 1% and match channels to 0.5%, resistors to 0.3% accuracy and matching.
regards Andrew T.
I'm not going to give you the answer, I can't.
But my thoughts on what to look for.
1. Buffer on the input with a bit of gain (+6 to +10db) before anything gets done to equalise.
2. Split passive equalisation with buffer/gain blocks between stages.
3. Simple passive 75us roll off as last equalisation, achieves noise reduction and maintains single pole to infinity, well almost.
4. Lots of spare voltage overhead at the output buffer and in the intervening gain blocks. Oh and remember all caps have some inductance.
5. If diy find a way to measure your caps to 1% and match channels to 0.5%, resistors to 0.3% accuracy and matching.
regards Andrew T.
hitachi hca-7500 preamp
Hello all! Can anyone tell me any info at all about this model: hitachi hca-7500 preamp
I've been looking for it on the net but can't seem to find a site in english with any helpful info. If any of you has heard about it or owns one, pls tell me what the features are, your opinion about it, if it's any good, etc etc
I'll really appreaciate it.
Hello all! Can anyone tell me any info at all about this model: hitachi hca-7500 preamp
I've been looking for it on the net but can't seem to find a site in english with any helpful info. If any of you has heard about it or owns one, pls tell me what the features are, your opinion about it, if it's any good, etc etc
I'll really appreaciate it.
The LM833 data sheet (and also an ap-note) is not the
most inspired design or most useful/accurate information.
Nor is that a particularly good amp chip.
For RIAA curve info, see the Lipshitz (sp?) et al papers
in the JAES entitled something like "On RIAA Equalization".
See also the follow-up letters in the JAES.
Doug Self's Wireless World articles on his preamp designs
are worth checking out though the topology he uses is
not my favorite. Also check out Walt Jung's "Audio Op-Amp
Cookbook". There are several reasonable designs on
the web (and others not-so-good)
Designing a decent RIAA phono preamp actually requires some
reasonable amount of analog design skill. The combination
of signal levels, source impedances, RIAA EQ curve, etc.
require the careful tradeoff of conflicting requirements.
You just don't run out and randomly grab a few passive
components and your DIYaudiophile op-amp-du-jour and
throw together a decent circuit.
most inspired design or most useful/accurate information.
Nor is that a particularly good amp chip.
For RIAA curve info, see the Lipshitz (sp?) et al papers
in the JAES entitled something like "On RIAA Equalization".
See also the follow-up letters in the JAES.
Doug Self's Wireless World articles on his preamp designs
are worth checking out though the topology he uses is
not my favorite. Also check out Walt Jung's "Audio Op-Amp
Cookbook". There are several reasonable designs on
the web (and others not-so-good)
Designing a decent RIAA phono preamp actually requires some
reasonable amount of analog design skill. The combination
of signal levels, source impedances, RIAA EQ curve, etc.
require the careful tradeoff of conflicting requirements.
You just don't run out and randomly grab a few passive
components and your DIYaudiophile op-amp-du-jour and
throw together a decent circuit.
richwalters said:
I have built the RIAA amp with the LM833 -- and it sounds great -- you can substitute lower noise preamps if you choose -- the critical elements are the resistors and caps for the RIAA equalization.
if you plug "RIAA" into the search engines at Analog Devices and Linear Technologies you will come up with other designs.
most important, however, is acuracy to the RIAA compensation curve.
email me privately if you need LM833's as I have a bunch left -- and they are "homeless".
Soundadvice said:
I've been looking into LM833's application notes and desided to go that way! However, I really don't know if implementing the AD797s goning to make sense. I don't know if that's really necessary, or I can use the LM833s (or any other standard audio opamp) and not worry about noise issues? I really want my phono preamps to be as best as possible, kinda "audiophile" but still suitable for proffesional studio use.
And yes, I want to use the phono preamps for recording my mixes and also for sampling. The reason I want to build it myself is because I'm actually a student on electronics engineer faculty and I love audio stuff. Thanks.
djaleksei:
Your first question was poorly phrased, so you go a lot of scatter in the replies. Midway through though you specified,
The AD797 only reaches its published performance if certain conditions are met, namely:
From the first point at least you should realise that the AD797 is utterly unsuited for most MM cartridges, and to be honest its a pain-in-the-butt all round.
Let's summarise what's already been posted in this thread:
The LM833 isn't a great choice of op-amp, and the Nat Semi app note isn't the most useful document ever published, but for what you want it'll do the job.
The most ironclad DIY option for those who don't know how to design op-amp circuits is the two stage, passive RIAA, approach along the lines suggested by AndrewT. Insert your flavor-of-the-month IC and chances are it will have low noise and sound pretty decent.
As BrianL eloquently pointed out, more advanced circuits are a delicate set of compromises and to modify them sucessfully you really do have to know what you're doing.
In my limited experience, the reason cheap phono stages sound cheap is they have low quality power supplies often running the opamp in single-supply mode, and the signal goes though several coupling capacitors of low grade ceramic or electrolytic type. Poor grounding and shielding is another typical problem. The actual opamp itself isn't necessarily the culprit, at least if it its an NE5532 or better.
So, to wrap up, don't get hung up on things like noise and distortion. You're going to have enough trouble getting rid of hum, ground loops, noise pickup, and the like no matter which one you pick so save yourself some aggravation and start with something as simple and abuse-tolerent as possible.
-rjm
Your first question was poorly phrased, so you go a lot of scatter in the replies. Midway through though you specified,
The AD797 only reaches its published performance if certain conditions are met, namely:
- The input impedance is less than 600 ohms.
- The input impedance on the inverting and non-inverting inputs are closely matched.
- The AD797 is extremely well bypassed, with a tight ground layout.
- You happen to get very lucky.
From the first point at least you should realise that the AD797 is utterly unsuited for most MM cartridges, and to be honest its a pain-in-the-butt all round.
Let's summarise what's already been posted in this thread:
The LM833 isn't a great choice of op-amp, and the Nat Semi app note isn't the most useful document ever published, but for what you want it'll do the job.
The most ironclad DIY option for those who don't know how to design op-amp circuits is the two stage, passive RIAA, approach along the lines suggested by AndrewT. Insert your flavor-of-the-month IC and chances are it will have low noise and sound pretty decent.
As BrianL eloquently pointed out, more advanced circuits are a delicate set of compromises and to modify them sucessfully you really do have to know what you're doing.
In my limited experience, the reason cheap phono stages sound cheap is they have low quality power supplies often running the opamp in single-supply mode, and the signal goes though several coupling capacitors of low grade ceramic or electrolytic type. Poor grounding and shielding is another typical problem. The actual opamp itself isn't necessarily the culprit, at least if it its an NE5532 or better.
So, to wrap up, don't get hung up on things like noise and distortion. You're going to have enough trouble getting rid of hum, ground loops, noise pickup, and the like no matter which one you pick so save yourself some aggravation and start with something as simple and abuse-tolerent as possible.
-rjm
in defense of the LM833 -- it's noise spec of 4.5nV SQRT Hz is pretty good considering that the chip costs about $0.25 -- the LT1028 (if you can find DIP) is anywhere from $8 to $13, the LT1115 is around $6 -- for DIY it wouldn't make a huge difference (time = money) unless you are an impoverished student, for an OEM it's another matter.
the AD797 -- the mistake people make when using this chip is one of not reading the entire product note.
with a phono cartridge btw -- one of the best ways of reducing distortion is setting the darned thing up correctly !
the AD797 -- the mistake people make when using this chip is one of not reading the entire product note.
with a phono cartridge btw -- one of the best ways of reducing distortion is setting the darned thing up correctly !
Here is a good opamp link to the Douglas Self site. I was just reading this last night. He also talks a bit about phono pre-amp design.
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm
thanks
Brett
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm
thanks
Brett
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