| jsa_ind |
Hello Everyone,
Is it true that discrete components would sound better then IC's ?
I mean there is so much of advancement in IC's I thought they would at least would be as good as discretes...am I mistaken to have such a perception ?
Certainly http://www.bursonaudio.com/Why_Burson_HDAM.htm thinks otherwise !
Thanks,
Regards,
Junia. |
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| Geek |
| Kind of depends on application. Both have their places, IMO :) |
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| I_Forgot |
There are certain type of components that have no IC equivalent. Transformers, for example. It is hard to duplicate or exceed transformer performance with op-amps, and of course, op-amps require power and other components to function.
IC's are good at making circuits that are flexible, and consistent. The matching of transistors in an IC can be very nearly perfect which can lead to better performance than discrete parts which can't be matched as well. The manufacturing techniques used in IC yield parts that behave pretty consistently from one device to the next.
OTOH, you can make a class A power amp with an IC output stage.
Both discrete and ICs have their uses.
I_F |
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| AndrewT |
Hi,
have a look at Walt Jung's site and you will find that the opamp man even has a discrete buffer in his notes.
Even he recognises that discrete has advantages.
But a plain simple yes would be stretching it a bit. |
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| I_Forgot |
| quote: | Originally posted by I_Forgot
OTOH, you can make a class A power amp with an IC output stage.
I_F |
That was supposed to say "CAN'T".
I_F |
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| jacco vermeulen |
| But you CAN ! |
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| aerius |
| Depends on what you want to do. For something like a small portable headphone amp for an iPod, opamps are the way to go. For a 800W class A monoblock amp, you pretty much have to use discrete parts for everything except the input stage. |
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| AndrewT |
Hi,
even for line drivers, ICs are at their limits. Anything more than a few mA and they are into ClassAB.
600ohm and 75ohm driven to 20dbu is hard going and to 24dbu is nearly impossible for a single IC.
That's why composite topology is being used but then the cost doubles.
Discretes can overcome these current/temperature effects with careful design. |
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| phase_accurate |
If there is not much output current demand like higher- order active filters then you must be very good in analog design to beat good op-amps.
Someone once claimed on this forum that he wasn't able to her the difference between a straight wire and a chain of op-amps used as voltage followers (which is even the worst usage of an op-amp anyway).
Regards
Charles |
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| pinkmouse |
| All I will say is that discrete amps are more fun to build. :) |
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| jcx |
| quote: | Originally posted by AndrewT
Hi,
even for line drivers, ICs are at their limits. Anything more than a few mA and they are into ClassAB.
600ohm and 75ohm driven to 20dbu is hard going and to 24dbu is nearly impossible for a single IC.
That's why composite topology is being used but then the cost doubles.
Discretes can overcome these current/temperature effects with careful design. |
acutually with today's hotter dsl driver op amps a few 10's of mA of Class A current is available from a few parts without external biasing
and you can of course bias pairs of op amp outputs against each other for push-pull Class A up to the power/current limit of the packages
[6x TPA6120 seen edge on, 440mA Class A for real op amp output stage]
My prototype headphone amp is biased to give 440 mA peak in push-pull Class A with TPA6120 output op amps ~ 5 Wrms into 50 Ohms - with nothing but op amps!
http://www6.head-fi.org/forums/showthread.php?t=190991
scroll down to post #6, #13+ for explanation, pics, sims
some newer dsl driver op amps are faster and handle as much current as many of the classic audio driver transistors although op amp V is pretty limited - common source/emitter output stage could be driven by these op amps to just about any practical power level with the output Qs being the only discrete transistors |
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| Johan Potgieter |
Any reply to this will need to be qualified. Economy, mass-production, consistent preformance, all go very much in favour of the right op-amp.
But I mostly use discreet transistors for the following reasons;
In pre-amps, the headroom with +/- 18V maximum rails is often not enough. Many such commercial ampllifiers go to 12 dB; some struggle up to 15dB headroom. This is often not always sufficient. I use 60 - 80V rail voltage on many occasions, to get some 26 - 30dB headroom. I also understand that the best discrete transistors can have lower noise than any i.c. (fewer manufacturing cycles).
Then the high impedance/current topology, especially around the Vas in power amplifiers, can lead to early Cdom influence cutting into the audio spectrum, resulting in unacceptable high-order harmonic presence. To get an open-loop response up to > 20KHz is well nigh impossible with power chips (caveat: I am not knowledgable with the newest ones). But that is required in order to get sufficient NFB stability/low phase angle necessary in excellent amplifiers. Also different compensation techniques than just a single Cdom is required, but the latter is often a given inside the i.c.
Regards |
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| Nordic |
Oom Johan, you don't maybe want to share a schematic for one with a fellow boertjie?, looking for something that could co-habit with a gainclone's +/-35V rails (70V).
What would be the gain limits with such a setup, i.e. is it unity stable...? |
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| Johan Potgieter |
Sorry fellows, something went wrong there.
Nordic, I will reply later. |
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| Nordic |
| lol here too, was drilling a pcb, when the bit snpped and the rest went through my finger tip... The wound is not too serious, I think... Can't look, lol. The problem is if I see my own blood it is like kicking a sick horse, in the nuts very hard,I go down. |
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| Johan Potgieter |
South Africans down!
Just wipe the blood off the pc board, Nordic. If you are a guy with steel in your nerves, there might be left a short. |
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| Nordic |
All seems well... with the PCB, still haven't looked at my finger though.
Going to watch Borat now, and then when I get back I will finaly complete my analog vu meter... thats to say if the diodes I got are a suitable replacement for OA91. |
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| Johan Potgieter |
Getting back to the thread from all this blood (and before a moderator causes more to flow):
Nordic, I do not have a single universal circuit - that is part of the point. For a near unity-gain circuit I simply use the uni-gain complimentary pair, i.e. what is sometimes called a composite emitter follower. That could be given a gain of 1 - 4. Thus perfexctly stable. For gain circuits I in fact mimic a simple op-amp: Long-tailed input pair, Vas, followed by complimentary emitter-follower. Circuit values and compensation are chosen for the application. Open-loop bandwidth is never < 20 KHz, and 100 - 200V transistors are used. If that seems unnecessarily complex, the advantage is one of being free to chose operational parameters best suited to the application.
If you need a specific circuit I suggest you contact me privately; I do not want to hi-jack the thread. Just for completeness (since this thread is not about power amplifiers): There I also start with a long-tailed pair, though NFB not via that - straight to the input. The Vas is a totem-pole because of its linearity and large collector swing capability, with some refinements. This is followed by an emitter-follower (Vas output impedance is very high) driving a full-complimentary output pair. Again the advantage: I can tailor values for best response/phase characteristics/stability, etc.
Regards |
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| Nordic |
| I might just do that, got 3 projects at 80% status at the moment so i should not be too long... are you the same Johan Potgieter who's details are on the Mr Valve newsletter? |
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| lineup |
transistors are semiconductors
once you have learned how to deal with transistors
and put them into circuits
then designing with transistors is much more flexible
there are 1000 of different types of transistors
with all possible and impossible characteristics
operational amplifier and other integrated circuits, IC,
are a bunch of semiconductors, transistors put together in a fixed way
with usually only small adjustments possible from the outside
from the IC PINS
there are however some general purpose IC
that have features that makes them very useful in most any kind of applications
and there are some Audio IC that are special purpose
and with some very good data
that this makes them outperform most any diy transistor circuit
transistors are a tiny bit better performers, in 90% of all situations,
when put together by the hands of a circuit designer with good knowledge
Finally:
99% of all IC can not do without some transistors inside
99% of all transistors can do without IC
typical op-amps can house 30-50 transistors, or even 100
:)
lineup :cool: has become a transistor man - was an op-amp man in beginning |
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| peranders |
| quote: | Originally posted by jsa_ind
Is it true that discrete components would sound better then IC's ?
|
The simple answer is yes and no :nod:
You have to know a part in order understand what it do for you. In IC's you can't make certain parts like good resistors, big caps and certainly not inductors but what you _can_ do is super matched transistors at speeds of 3 GHz or more for the cost of almost nothing. |
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| Bgt |
| LM4562 is getting very close;) |
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| lineup |
| quote: | Originally posted by Bgt
LM4562 is getting very close;) |
LM4562 is a good operational amplifier IC.
Handled properly it may do good audio.
Now, very (... read excessive fast for Audio ) fast Op-Amps can have impressive data,
but some extra care in PCB layout
and other things are often required to avoid oscillations (improve stability in some real loads).
LM4562, and the likes of it, are no challengers to
for example one of my current discrete pre amplifier projects:
+-20 Volt RMS output, using discrete regulated +-75V power supply.
At highest HiFi quality ( ... read 0.005% THD distortion )
With the specified limit of max +-17V supply
LM4562 is very far from it,
it doesn't even come close to my discrete ..
And my discrete amp uses standard low price TO92 higher voltage transistors.
By the way, I do not use, if can be avoided in low power amplifiers
at any time Class B or Class AB designs.
not when it is so easy to setup a True Class A for some mA output at line level.
*****************************************************
I don't know, but ..
what does such a limited wonder,
almost handicapped when comes to compare voltage supply
as LM4562 cost?
Not that I have any plans or needs to buy any Op-Amp.
Not for the moment.
But would interesting for comparing to the cost of
my 150 Volt HiFi amplifier.
:cool: lineup :cool:
Lineup Audio Discrete Class A Designs
http://lineup.awardspace.com/ |
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| novec |
Ok, this is getting really interesting... I'm starting a group buy of the LM4562 opamps for my NewClassD amps and some active crossovers, which are all made for DIP chips. However, I've got a new CD player brewing in the back of my mind, which obviously has no limits in that respect.
Being relatively inexperienced with circuit design and PCB layout, but very "fiddly" and up for a challenge, what are your tips? Concrete examples are much appreciated.
Edit: I'll most likely be using TI's PCM1794 DACs in dual mono for my CD player. |
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| DCPreamp |
Hi lineup,
Why do you need +/-75V rails for your preamp and 20V RMS output? Most commercial, high-end, and even tube amps can be driven to full output with just 2V RMS of input.
When in the 2V RMS world, one would seem very hard-pressed to beat the LM4562 op-amp for noise, distortion, low Z-out, etc. And, at <$3 each, wow, what a performer.
As far as class A vs. class A/B for signal level applications, why would one think the LM4562, or virtually any op-amp, has cross-over distortion or issues with output drive integrity? With distortion and noise being so exceptionally low, I just can't imagine worrying about the output class. If there were improvements to be made, I'm pretty sure their engineers and scientists would be all over it.
Other advantages to monolithic ICs over discrete designs include near-flawless device matching, laser trimming, minimal inter-capacitance and trace inductance, perfect temperature tracking, and the ability to fab very unusual current sources and multi-function circuits/devices.
I have no problems whatsoever with opamps and feel they are near perfect devices (when implemented properly and matched to their intended duties). Naturally, I fully understand op-amps cannot perform at high voltages, high currents, high powers, etc. Plus, most likely 99% of all recorded music you've ever heard was run through op-amps while recording, mixing, mastering, or duplicating. |
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| lineup |
DCPreamp
I thuoght your name, DCPreamp was more like Discrete Pre Amplifiers
.. but we can never know, can we :D
Why I can't use most any Op-Amp
and anything but my own discrete transistor +-75 V DC regulators for my idea and circuit?
Because sometimes, you do experiments and try to see
... if for example transistor voltage amplifiers will benefit from tube like voltage levels as supply.
It has not been done much research in this field.
I know only of a handful of pre-amplifiers with very high voltage operatin.
Besides, to design a 20 V RMS stand alone voltage amplifier
you can definitely not use +-18-20 volt Op-amps, = max 40-45 total voltage.
...
Because, for as anybody know:
20 V RMS requires: +28.3 Volt and -28.3 Volt
and for transistor to work linear, it is not at all bad in my very special amplifier, to add a few voltages
to avoid beginning clipping behavior and also improve other parameters.
This is why the extra added +46.7 and -46.7 volt,
making the supply in total be 150 volt.
It is a tube like transistor voltage amplifier, if you like.
lineup :) has got good reasons, for stay Discrete... this time
PS.
Apex high voltage Op-Amps are too expensive for this experiment
as well as I can not buy even op-amps with 50% of needed volt supply
at least not for normal money ( like I used normal standard 150V and 300 volt small transistors )
and not in my country.
I do never buy from abroad. Not from Other countries.
DS. |
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| Johan Potgieter |
Ouch, Lineup, stop hitting us in the eyes!!:hot:
My addition would be that there is such a thing as headroom, explained before. The volume control is usually at the end of a pre-amp (perhaps only followed by a unity-gain buffer).
What happens before it? Particularly with the wide variation in CD outputs as well as CDs (at least in my experience), I have encountered levels up to 20dB above "normal" (whatever that might mean). If I cater for an output of 2,8Vp, that means a possible 28Vp before the volume control - plus some extra. We then arrive at total 70V odd rail voltage.
I do not think the cost is really a factor, neither is drift. I am not a dc coupled fan - more problems than advantages (if any). And lowest noise (pnp) transistors do have a lower noise factor than i.c.s I know - result of the larger number of manufacturing cycles involved. Then I also do not like the early phase correction in many i.c.s (also as said before) but that may be subjective - I have encountered the odd problem with h.f. overload there. Furthermore I put high and low steep-cut filters in my pre-amps (reason and design for another day), where the +/- 18V lot can definitely hit the rails.
In the end, I find lower distortion (particularly high order) with discrete transistor design under worst conditions, mainly because of the rail voltages. But all this may be a little subjective. One certainly acknowledges the advantages of i.c.s. It depends on the application.
Regards.
Edit: Spelling! |
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| lineup |
| quote: | Originally posted by Johan Potgieter
Ouch, Lineup, stop hitting us in the eyes!!:hot: |
My friends here at diyaudio never 'get hit' by my posts.
If you feel you get hit, it tells more about you, Johan, and your thinking, thoughts in case.
than it does tell anything about my posts.
Nicht waar?
Have a closer look at yourself, from a distance .... and you might see a bit further than your own nose-tip
------------------------------------------------------------------------------------
By the way, lineup friends or not,
take a look into this interesting TOPIC!!!!! we have goin':
started by suzyj
www.littlefishbicycles.com
diy audio projects division ;)
Discrete Guitar Preamp - by Suzy J.
Several interesting discrete JFET circuits,
already in the above little thread!
Regards
to anyone that are willing to take my regards
and all the other ones
lineup
December 2006 |
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| cotdt |
| i agree that op amps have less noise, but a well designed discrete circuit doesn't have any noticeable noise either. anyway, to me a well-designed discrete circuit sounds better, and i've rolled a lot of op amps. they all sound different from each other, so i couldn't imagine how they don't degrade the sound. to me the difference between various op amps even within the same manufacterer is like night and day. people with half-decent ears (like myself) should do a blind test comparing a cascade of op amps to straight wire. that will effectively demonstrate that op amps suck. |
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| jcx |
| quote: | Originally posted by lineup
[B]
...
Besides, to design a 20 V RMS stand alone voltage amplifier
you can definitely not use +-18-20 volt Op-amps, = max 40-45 total voltage...
|
obviously you didn't follow up on my eariler post in this thread http://www.diyaudio.com/forums/show...001#post1041001
the described amp uses a "cascaded" op amp output stage - 2 +/16 V rated op amps run from gnd and +/-30 V respectively, lifting the +/- supply rails of the output op amp for very close to 20 Vrms swing - essentially doubling the V swing capability of the op amps used, in principle 2 of these could then be used with a bridge tied or balanced load for another 2x swing |
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| Johan Potgieter |
| quote: | Originally posted by lineup
My friends here at diyaudio never 'get hit' by my posts.
If you feel you get hit, it tells more about you, Johan, and your thinking, thoughts in case.
than it does tell anything about my posts.
Nicht waar?
Have a closer look at yourself, from a distance .... and you might see a bit further than your own nose-tip |
I don't detect any signs of humour in your post, nor anything but emotion in a technical thread -
So, come on, please Lineup!!
If you paid any attention at all to my previous contributions, you would by now have seen that I often use humour! My remark was simply about your using an increasing script size in order to, "sound louder" - or what? ... and my reply quite light-hearted! Is your own perception such that you required twenty little smileys after that in order to see it for what it was??
Your cryptic CV leaves me at a disadvantage, so let me just say that I have quietly been round the block of both science and life a few times. I certainly still have many shortcomings, but did not deserve your rude personal closing remark above, so please. And if I am not your friend, you qualified that.
Now can we carry on with science while recognising humour where it is intended (especially when followed by an emoticon). You might just possibly have noticed that my design approach agreed with yours.
Regards to all (including Lineup). |
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| AndrewT |
Hi Johan,
he was having a dig at me.
He can't get over being corrected for posting erroneous information. |
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| DCPreamp |
Hi Folks,
DCPreamp = battery powered for ultra-low/zero PS noise. I also run AC coupled as I too don't like DC coupling and don't have irrational fears of caps when they are in their low Xc state.
lineup: I understand using HV for tubes and trying to simulate a tube-transfer function with semiconductors. I'm not questioning that. Tubes do require high supply voltages because of their nature, but semiconductors do not. So I don't think running semiconductors at high voltages automatically means they will sound like tubes, but I digress.
Johan P.: I also understand having plenty of headroom and the requirements of adequate supply rails to allow for it.
However, if you run a 250WPC power amp with 8 ohm speakers, the amp must have approximately 90VDC rails to accomplish the output of 45VRMS. And if your amp has approximately 28dB of gain, it only requires 1.8VRMS to drive the amp to full power output. So now, you drive 20VRMS into the input of the amp with your "high-headroom" preamp, do you think the amp magically produces a 1,000V peak output? Nope - it just severly clips. There's no mystery here - just amp rails and fixed gain. Pretty straightforeword.
But, with the same amp running at a casual 1 or 2 watts listening level, and only requiring 160mV of preamp signal, it can reproduce those 20dB peaks. So again, why does your preamp need to be able to produce 20VRMS? It quickly starts to stink of subjectivism where is "just sounds better and is suposed to be that way" with no scientific reasoning.
Paul |
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| Johan Potgieter |
Hi Paul,
No, sorry - I think there is a misunderstanding. I did say that I was referring to before the volume control, which is usually somewhere near the end of the pre-amp. Thus most of the pre-amp is always subject to "maximum" signal level, if you understand. Obviously as you state you will "output" (from the volume control) no more than the required signal level to clip the main amplifier; your ears will tell you that that point has been reached, so.
The full signal is always present before the volume control, except in rare cases where there is also a ganged pot somewhere earlier in the circuit (thus 4 pots on a spindle for stereo). Thus, you do not drive your power amp with that "20Vrms" - that is only the safety factor for before the volume control. (In fact, I hate these amplifiers with too much gain. Folks mostly seem to think that the amplifier must be powerful if it roars as soon as one touches the volume control - never mind that it runs out of steam a little further up the knob scale. Cheating.) But as I encountered there can be such a variation in level there from different input devices/signal sources, that overdrive can occur - you seem to understand that, you said. Other designers (e.g. Douglas Self, Cherry, Linsley-Hood et al) have stated that for safety they prefer somewhere above 18dB headroom. In my view, once one goes for higher d.c., one might as well go quite safe as higher voltage transistors and transformers do not cost that much more. When you measure distortion (and I mean a full high order analysis/intermod, not the outmoded thd), it does appear to help to stay away from the rails. It is one of the reasons why tube pre-amps are quite "clean", what with usually over 150V of signal swing being available.
Your first paragraph is acknowledged (I was not picking on you because of your pseudonym, just a general comment!). I further agree with your last sentence - there is a lot of "it must sound better because [urban legend]" - more's the pity. I would certainly hope that I am never guilty of that line of thought! But some things call for a judgement call (oops, poor grammar) - people will make different decisions. I have certainly also used op-amps, depending on the application.
Regards |
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| DCPreamp |
Hi Johan,
You had mentioned the pot after the amp, so I missed it and blew that part. I guess I'm not super familiar with that topology, either from a lack of experience, or lack of "true" audiophile knowledge.
I typically use the signal-pot-amp path. I can see some benefits to the signal-amp-pot-buffer idea, but it's double the active circuity. I've seen preamp designs with the pot on the output with no buffer, but with a hi-Z-out, one might as well go passive.
I do agree dicrete can be outstanding if not near flawless when done well. Believe me, I have tons of respect for many, many topologies so long as they don't cross into the subjective realm of woowoo BS and stay in-line with reality. You are definately right there based in reality, and I appreciate your details.
So back to the original "are discrete better than op-amps" question, seems a double-blind showdown between topologies would be would be loads of fun. Some day perhaps. 'Til then, I have an LM4562 I'm just dying "not" to hear. ; ) |
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| Johan Potgieter |
AH! There it is then Paul. :D
You would have seen that one often uses the volume control as late as possible, so that any pre-amp noise gets attenuated with the signal at low settings, etc. The hi-Z out could be tolerated, depending on the power amp input conditions.
In one of my more extensive pre-amps I use all of 10 transistors up to the volume control (2 in unity gain buffer after). Rail voltage is 70V.
On the original question I quickly checked whether I was "safe"! I saw in my post #13 that I did mention the right application. But see what you have done now. I will go right back to my data books and make a proper study of that LM4562, and get hold of one when nobody is looking .......;)
Thanks for the correspondence Go for it! |
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| DCPreamp |
Hello Again Johan,
Feel free to check out: http://www.national.com/pf/LM/LM4562.html
The LM4562 a very impressive device, but there are many impressive op-amps out there and when properly implemented, following very close attention to detail, and utilizing excellent components and topology, I'll bet many op-amps will produce fabulous audio results. My current OPA2604 preamp sounds very good to me.
Let me ask: When you design your own circuit, or copy one, build it, fully measure and implement it, how do you know its true performance? Do you have the facilities for testing IMD, THD, noise floor, etc.? If so, then you can truly have confidence in your designs and have the comfort of using top-notch gear.
Unfortunately, I do not have those tests at my disposal and am limited to bandwidth, noise, Z-in/out, VRMS, and a few others limited by my test equipment and my scrutiny.
So, what I do is use the best parts (within cost and "reality" reasons), use proven designs (typically from data-books and industry related books and journals), use solid and quality construction methods, and ultimately, by listening. Other than that, I could be listening to 5% THD for all I know (I doubt it, though). By following what has been presented by Engineers and Scientists at National Semiconductor (if Bob Pease is an indicator of their skill levels, I feel pretty good about their stuff), Burr-Brown, Linear Technology, and others, I'm pretty sure I'm producing some very good results.
What I also know, is that I have tested and listened to several ADCOM preamps, high-end tube preamps, and my own designs, and mine are at least an order-of-magnitude better on the bench as well as in listening tests. It's enough for me to make some bold claims about my gear and give me pretty good confidence, but I still have a hint of doubt about the ultimate performance. Many would say listening tests are all that is required for DIY audio, as a devout non-subjectivist, I always want to know everything that's going on within the design.
Anyway, I'd enjoy reading your theories about producing a good design and how you test your products.
Regards,
Paul |
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| panomaniac |
I have never understood the massive gain or head room approach in preamps. Certainly have owned and heard preamps that had massive headroom, and they sounded great, but how much of that was due to headroom? I don't know.
Johan was talking about signals that went up to 20dB above average. That's pretty typical on CDs, depending on the type of music. But it might be more useful to see it from the other side. The average signal is 20dB below peak. And what is that peak? About 2V rms or 2.8 peak. That's all you get out of most DACs, about 3V peak. Many have lower values.
So no need to worry about the average music level, if the absolute max is 3V. I would think that +/- 15V rails would be plenty, if you don't need much gain. Say less than 12dB.
Analog sources are not so well defined, but you should be able to figure out the approximate max levels.
As Mr. DCPreamp said, most power amps can run into clipping a 2 volts RMS - so how much line level gain does your preamp really need? 6~9 dB would seem to be more than enough to make up for low signal sources. Meaning 8.5 volts peak output. Or a little more than 1/2 rail voltage. I can't see where you'd ever need 8 volts to drive your amp, unless it's some strange high power/low gain thing.
Gain structure is of huge importance in pro audio where there are so many gain stages, often of high gain. Getting gain structure right in a pro rig can make a big difference to the overall result.
Just my thoughts.... |
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| lineup |
| quote: | Originally posted by panomaniac
Headroom Voltage.
----
So no need to worry about the average music level,
if the absolute max is 3V.
I would think that +/- 15V rails would be plenty,
if you don't need much gain.
Say less than 12dB.
|
Headroom voltage is the reason for my high +/- 75 V DC regulated supply.
For my discrete tube-like & transistor based
voltage amplifier with +/- 28.3 V minimum specified output.
(see my previous posts in this topic!)
This is a headroom of only ~ 3:1
And at same time, consider that my amplifier can be used for no global feedback,
or by choice very low feedback factor.
All in true Class A operation and bias.
-----------------------
Compare this to Operational Amplifiers.
Like panomaniac said:
So no need to worry about the average music level,
if the absolute max is +/- 3V peak.
I would think that +/- 15V rails would be plenty
This is a headroom of ~ 5:1
This is considerably more than my amplifier.
Especially when we consider op-amp has a high global negative feedback factor!
And having an open loop gain of 10.000, or more ....
As most Op-amps have.
This while running at low Class AB bias.
Regards to panomaniac
from
lineup |
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| panomaniac |
Hej Lineup.
I see why you need such high voltage rails if you want +/- 28V out. But why such a high output voltage for a preamp? I run power amps with a lower output voltage than that. :)
Did I miss something? I have run tube pres that were capable of over 100V out, clean. But I doubt I ever got anywhere near that - nowhere close.
BTW, some opamps and even VCAs can be run in Class-A, if it helps. |
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| lineup |
| quote: | Originally posted by panomaniac
Hej Lineup.
I see why you need such high voltage rails if you want +/- 28V out.
But why such a high output voltage for a preamp?
I run power amps with a lower output voltage than that. :)
|
Very right you are again, panomaniac.
If you read my posts carefully,
you see I call not my amplifier for 'preamp'
but 'standalone voltage amplifier'.
If I said anything else, it would not be 100% correct.
The idea is this:
.. as is not very hard to find good power amplifier buffers = voltage followers for loudspeaker loads,
we would need some good voltage amplifiers for those.
A separate input and VAS stage, if you like. (VAS= Voltage Amplification Stage)
Such a voltage amplifier would have output
into a Power Follower buffer, VoltageGain ~ 0.90-0.99
This is why I decided to specication:
Min 20 V RMS into something like >=2kOhm
with very low distortion.
Now put 1 + 1 together!
And you will find you have a very good power amplifier.
Although in two separate stand-alone units.
Regards
lineup
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* fotnote:
Even myself, lineup, have published at forum such a power buffer,
in True Single End Class A, giving out 15-23 W RMS in whole span 4-8 Ohm,
with very low distortion.
I even have attached, along with my schematics and description,
test data from my simulation into different impedances
and I can guarantee stability even at normal capacitive loads!
How many transistors?
For this 20 W RMS(5 Ohm) follower?
+ two MJ21194
+ one BD139, TO126
+ one 2SA970, TO92 for low noise input.
Makes it 4T circuit, only. |
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| panomaniac |
Ah, so...
I thought you might be going in that direction. You are rolling the preamp and power amp voltage gain stage into one circuit, so to speak. Then putting it in one box and the current output stage in another box. Sure, why not? As long as the stages couple well.
Can you send me the files for you SE Class-A power buffer, or point me to the post with them? I'd like to see what you've done.
Thanks! |
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| Johan Potgieter |
DCpreamp (your post #41)
Yes, guess I am overlooking the priviledge of facilities at my disposal. At work all those were available, but lately only for final checking, courtesy of the local university. My main design tool has become Spice, which I have experienced to get pretty close to reality. What I look at are high-order harmonics (or rather the absence of them). One can do worst case design and find where they start to emerge, and try for a happy medium (THD hardly of value there). This is of course more important in power amplifier design. I also try to keep the phase angle low over the whole audio range. [This is a kind of secondary thing and a subject on its own. The gist is the poor behaviour of amplifiers in out-of-sonic ranges where, should anything come along, artifacts can be generated with audible effects. Filter sharply either side of the audio range, and keep your amp in order where there might still be stuff, etc.]
The problem with listening tests is to what and for how long. You would know about something called listener fatigue, sometimes only established after days. The probable source of that is immediately recognisable in e.g. spectrum analyser tests. But as said, not everybody has that priviledge. In that case, tried designs by known designers, absolutely!
Panomaniac, your post #42,
Taking the inverse logic, quite true. But my CD has an average output of about 1,3V. It has an amplifier after the DAC - which general practice, incidentally, I have seen several comments on, with ideas for improvement. Apparently some CD designers are not so good in the analogue area.
You bring up the point: What input sensitivity? My line-ins are 0,5V, and there are also still tape- and phono-ins (the need for which, I accept, will diminish "as we speak"). But also the difference in CD signals (I mean the discs) can be quite dramatic. Then back to what must be tolerated before the volume control, etc. I do, in fact, provide measures for rough adjustment of inputs at the pre-amp input, so that folks can at least set source outputs at the loudspeaker more or less equal.
I would re-iterate that I do not condemn op-amps per se, just prefer discretes in certain cases. Also stating that my power amp maximum input is a high 600mVrms, will further clarify.
Regards |
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| lineup |
| quote: | Originally posted by Johan Potgieter
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I would re-iterate that I do not condemn op-amps per se, just prefer discretes in certain cases.
Also stating that my power amp
maximum input is a high 600mVrms,
will further clarify.
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600mVrms
-------------------------------------
This is to me a good value.
A value that I have found we can count on,
that output level from
an Average CD-recording, or most CD, will live up to.
Of course can be very different for different kinds of music.
Classic music and Rave, Rap music has got different contents of amplitude.
The relationship between Peak Music outputs and Average output level, I mean.
But sure is, we can often not design and use Max 2.0 V RMS, the CD standard
as input sensitivity
at least for normal power amplifier and if we want to play LOUD.
Not even count for 50% 1.0 V RMS will be good always.
-----------------------------------
A target value for input sensitivity I often have used
when make an initial specification of my HeadPhones Amplifiers
is input sensitivity (input voltage level required for close to maximum output, before clipping)
of 0.707 Volt RMS ... which give vPeak input +/-1.0 Volt.
I have got this value from measuring sound level output from some of my typical records.
Typical for the music I listen to most often.
lineup |
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| Johan Potgieter |
| Thanks for info, Lineup |
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| panomaniac |
Bump:
Lineup, I'll ask again.
Can you send me the files for you SE Class-A power buffer, or point me to the post with them? I'd like to see what you've done. |
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| lineup |
sorry
my friend,
panomaniac
I missed your post asking.
( you know I involve myself in so many many topics.
3.600 posts since 2002
once i have said what I think I can say ina subject
i move on to something else
-- that's the way i am :) a bit restless perhaps)
Of course I post the link here.
To me and my other friend's topic.
This topic was started by
a very fast learning! beginner in your own amplifier designs!
Like me he is using Simulation software to check up what looks good.
Before he actually build.
I took his idea - found it interesting!
And we discussed and improved it to very good data.
Very good data, if you consider the simplicity of circuit.
As told it is SINGLE Supply 100% Class A (both mine and jerluwoo amplifiers)
And though simple, it is using two NPN Power Transistors in PUSH-PULL
for better efficiency (=a bit less heatsinking).
Here is jerluwoo topic
diyAudio Forums > Top >Amplifiers >Solid State > My simple class a approach
Be sure to have a look at jerluwoo later version.
He did post several. One after one better than the other
until they were very good Class A power amplifiers.
Hard to say if my posted design is better than his.
They are both okay, I would say.
panomaniac,
can you post a response post in that topic, Please.
Say something, to comment.
This is all I ask from you
when I give you my schematic I attached there.
;) I think jerluwoo will be happy see someone read his posting;)
Many Regards
and thanks for showing interest in some of my works
lineup |
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| panomaniac |
Thanks Lineup! I read the thread. Seems simple enough. 3055s, eh? Hmmm...
I know what you mean about losing threads. I had to search my own posts to find this one again. :xeye: |
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