Hello all
I would like to thank you for the interest you have shown in the opamp-poweramp design. I'm afraid that, not for the first time, I'm showing up rather late for the party, but pressure of business, you know...
I'd like to say that this is a wholly serious project, that does exactly what it says in terms of performance, but it also has its light-hearted aspect. I hardly think it is going to revolutionise the whole field of audio amplifier design, but I do believe it at least provides a new way to look at the subject, and if it triggers off some other interesting designs based on the same concept, I shall be more than happy.
I can't attempt to answer all the points raised in this discussion, but here are a few thoughts that occur:
As suggested, it might be possible to get lower distortion by operating the output stage opamp array with shunt feedback. The problems are:
1) It adds two resistors per opamp section (ie four per package) and that is a lot of extra components. The voltage-follower could hardly be simpler.
2) The input impedance of the output stage opamp array will now be MUCH lower, if reasonably low feedback resistor values are used, and it will be harder to drive it with very low distortion.
3) The voltage-followers have very accurate unity gain. Using shunt feedback adds in two resistor tolerances and might cause trouble with current-sharing.
An idea that was put forward in the Elektor forum was the possibility of closing a feedback loop around the output stage voltage-follower array; that is probably a sounder notion than shunt-feedback. However, the distortion of the voltage-followers is already very low, and I did not consider it necessary- in a first design at least- to try to close another feedback loop around them. That eliminated possible stability problems and made the design very straightforward.
In fact, the major challenge was designing the gain stage so it had distortion low enough to be comparable with that of the voltage-followers. That job could probably be done with a single LM4562, which has extremely low distortion, but that does rather lose the "all-5532" philosophy, which was part of the point of the project- 5532s are I think, now the cheapest opamps around and it intrigued me to see what could be done using nothing else. (I'm not counting those supply regulators)
I can't tell you much about the "electrolytic capacitor issue" as that occurred and was dealt with at Elektor
IMPORTANT Please be aware that my website is now at The Douglas Self Site (douglas-self.com)
Please pass this info on to anyone you think might be interested. The address should not change again.
I would like to thank you for the interest you have shown in the opamp-poweramp design. I'm afraid that, not for the first time, I'm showing up rather late for the party, but pressure of business, you know...
I'd like to say that this is a wholly serious project, that does exactly what it says in terms of performance, but it also has its light-hearted aspect. I hardly think it is going to revolutionise the whole field of audio amplifier design, but I do believe it at least provides a new way to look at the subject, and if it triggers off some other interesting designs based on the same concept, I shall be more than happy.
I can't attempt to answer all the points raised in this discussion, but here are a few thoughts that occur:
As suggested, it might be possible to get lower distortion by operating the output stage opamp array with shunt feedback. The problems are:
1) It adds two resistors per opamp section (ie four per package) and that is a lot of extra components. The voltage-follower could hardly be simpler.
2) The input impedance of the output stage opamp array will now be MUCH lower, if reasonably low feedback resistor values are used, and it will be harder to drive it with very low distortion.
3) The voltage-followers have very accurate unity gain. Using shunt feedback adds in two resistor tolerances and might cause trouble with current-sharing.
An idea that was put forward in the Elektor forum was the possibility of closing a feedback loop around the output stage voltage-follower array; that is probably a sounder notion than shunt-feedback. However, the distortion of the voltage-followers is already very low, and I did not consider it necessary- in a first design at least- to try to close another feedback loop around them. That eliminated possible stability problems and made the design very straightforward.
In fact, the major challenge was designing the gain stage so it had distortion low enough to be comparable with that of the voltage-followers. That job could probably be done with a single LM4562, which has extremely low distortion, but that does rather lose the "all-5532" philosophy, which was part of the point of the project- 5532s are I think, now the cheapest opamps around and it intrigued me to see what could be done using nothing else. (I'm not counting those supply regulators)
I can't tell you much about the "electrolytic capacitor issue" as that occurred and was dealt with at Elektor
IMPORTANT Please be aware that my website is now at The Douglas Self Site (douglas-self.com)
Please pass this info on to anyone you think might be interested. The address should not change again.
Doug Self NE5532 PowerAmp deserves a lot of attention. The measured THD + Noise performance is better than one might expect, despite the enormous common-mode input voltage. This should legitimate the unity gain buffer approach. Beyond this I would like to investigate the class AB operation, graphing the instantaneous supply currents for determining if the NE5532 is driving the internal output transistors using hard-switching class AB, soft-switching class AB or soft non-switching class AB. I would like to measure the behaviour when using an inductive and a capacitive load. I would like to measure the power supply rejection from 10 Hz to 100 kHz, determining if inexpensive laptop power supplies delivering 18V DC can make a good fit. I would like to measure the temperature effects on THD and noise, comparing thermal modulation between through-hole packaging and SMD packaging.
I would like to compare various NE5532 makers like Fairchild, OnSemi, NJR, JRC, Philips, Signetics. There may be interesting differences.
I would like to compare the NE5532 results with other audio opamps like :
LM4562
LME49725
LME49880
MC33078
OPA1612
OPA1642
OPA2134
OPA2227
OPA2228
OPA2604
Using parallelization, an interesting lane is to see what's happening to power supply rejection, THD and subjective results when applying discrete bias currents to the internal ouput stages like Jan Meier did 10 years ago.
Beyond the pure NE5532 concept, there may be interesting findings using a grid of 16 Kuroda amp cells, each fitted with 150 MHz 60V output transistors and a soft non-switching class AB polarization. I really would like to taste something like this.
Cooling using off-the-shelf processor heatsinks and fans would ease the construction and enable features like Peltier cooling, thermal pipe cooling, water cooling and liquid nitrogen cooling using off-the-shelf PC tuning components.
At the end of the process you get a very interesting compound of technologies.
This is a brand new world, indeed.
Are audio-opamps Blameless ?
I would like to compare various NE5532 makers like Fairchild, OnSemi, NJR, JRC, Philips, Signetics. There may be interesting differences.
I would like to compare the NE5532 results with other audio opamps like :
LM4562
LME49725
LME49880
MC33078
OPA1612
OPA1642
OPA2134
OPA2227
OPA2228
OPA2604
Using parallelization, an interesting lane is to see what's happening to power supply rejection, THD and subjective results when applying discrete bias currents to the internal ouput stages like Jan Meier did 10 years ago.
Beyond the pure NE5532 concept, there may be interesting findings using a grid of 16 Kuroda amp cells, each fitted with 150 MHz 60V output transistors and a soft non-switching class AB polarization. I really would like to taste something like this.
Cooling using off-the-shelf processor heatsinks and fans would ease the construction and enable features like Peltier cooling, thermal pipe cooling, water cooling and liquid nitrogen cooling using off-the-shelf PC tuning components.
At the end of the process you get a very interesting compound of technologies.
This is a brand new world, indeed.
Are audio-opamps Blameless ?
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The PCB layout is available as a free download from the Elektor site:
The 5532 OpAmplifier, part 1 - ELEKTOR.com | Electronics: Microcontrollers Embedded Audio Digital Analogue Test Measurement
Thanks Don, I registered a few years back with Elektor. Tried the free download... no good! Then remembered I had signed up before so logged on and completed the registration process, and find I have 10 free credits. Had to log off and back on to "buy" the article with the freebie and then the download worked for free.
A set of boards arrived last thursday, half an hour before i took off to France for the ETF.
Ordered them the moment Elektor had them online, took +1 month to arrive, nice enough that Elektor is willing to offer such small demand items.
I can do up to 16" boards at home, but drilling ~1K holes to save a few bucks is totally bonkers.
Shame the agenda is too stuffed right now for amp time.
Ordered them the moment Elektor had them online, took +1 month to arrive, nice enough that Elektor is willing to offer such small demand items.
I can do up to 16" boards at home, but drilling ~1K holes to save a few bucks is totally bonkers.
Shame the agenda is too stuffed right now for amp time.
Attachments
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Vix,
Myself and several others heard this amp at Burning Amp, driving Nelson Pass' wideband Lowters in a HUGE open baffle. Sounded very good to me and others.
We also tried it on another baffle with a wideband driver assisted by a 15 inch woofer but that was not so hot, probably because the wideband and the woofer were not well integrated/crossed over.
IOW, as 15-watters go, a pretty good amp, interesting concept and relatively low cost to build.
jan didden
It's funny to me to see all of this discussion about parallel followers as outputs. I've been building headphone amps like that for 20 years. I use some opamps that were tossed out as obsolete video amps in CATV decoders.
They are quad opamps and I use 4 per channel for a total of 16. They current limit at 20ma per opamp and have power supply limits of +/- 15.
I use a dual opamp of the same type for the voltage gain, one section for each channel.
Power supply is simple lm317/337.
I'm not going to quote numbesr because it's been so long since I measured one I don't remember, but it does sound good, mostly I can't hear the amp at all. I just use local feadback in the gain stage. The output follower is 100% feedback.
Have fun BZ
They are quad opamps and I use 4 per channel for a total of 16. They current limit at 20ma per opamp and have power supply limits of +/- 15.
I use a dual opamp of the same type for the voltage gain, one section for each channel.
Power supply is simple lm317/337.
I'm not going to quote numbesr because it's been so long since I measured one I don't remember, but it does sound good, mostly I can't hear the amp at all. I just use local feadback in the gain stage. The output follower is 100% feedback.
Have fun BZ
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Hi all -
Sorry for a stupid question, but I'm having trouble finding some of the capacitors listed in the parts list for this pre-amp. Can someone tell me what type of capacitors these are? When nothing more is given what type should I assume?
C17-C25,C42-C50 = 100nF 100V, 10%, lead spacing 7.5mm
C51 = 470nF 100V, 10%, lead spacing 7.5mm
C52,C53 = 100µF 25V, 20%, diam. 6.3mm, lead spacing 2.5mm
Most are clearly specified, but when they are not, I don't want to guess. Mouser.com in the states has a lot of the components, but many are not coming up. Is there a secret to this? Thanks.
Sorry for a stupid question, but I'm having trouble finding some of the capacitors listed in the parts list for this pre-amp. Can someone tell me what type of capacitors these are? When nothing more is given what type should I assume?
C17-C25,C42-C50 = 100nF 100V, 10%, lead spacing 7.5mm
C51 = 470nF 100V, 10%, lead spacing 7.5mm
C52,C53 = 100µF 25V, 20%, diam. 6.3mm, lead spacing 2.5mm
Most are clearly specified, but when they are not, I don't want to guess. Mouser.com in the states has a lot of the components, but many are not coming up. Is there a secret to this? Thanks.
Looking quickly at the photo of the amp (and it's a power amp not a preamp 
) C17 is a polystyrene "suflex" type. These tend to be very expensive nowadays.
You want ones that physically fit the PCB if you are using that, otherwise any good small poly film type would be fine. The 470nf are available as films quite cheaply.
Don't use ceramics for this.
These are the "suflex" type,
http://cpc.farnell.com/lcr-componen...citor-160v-100pf/dp/CA05853?in_merch=Products From This Range
Very expensive.
) C17 is a polystyrene "suflex" type. These tend to be very expensive nowadays.You want ones that physically fit the PCB if you are using that, otherwise any good small poly film type would be fine. The 470nf are available as films quite cheaply.
Don't use ceramics for this.
These are the "suflex" type,
http://cpc.farnell.com/lcr-componen...citor-160v-100pf/dp/CA05853?in_merch=Products From This Range
Very expensive.
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How would the uninformed about the nuances of capacitors know that? I am getting the PCBs, so lead spacing is important to me as well. But that is hard to find sometime, even from the data sheet. I like to have the proper size for fit-n-finish of the board - not to mention the proper type of capacitor for the circuit design. I'm finding the pots are really expensive, and, yet again, hard to find - so far. It would be nice to get everything from one supplier, but I know that's not a realistic goal.Looking quickly at the photo of the amp (and it's a power amp not a preamp
You want ones that physically fit the PCB if you are using that, otherwise any good small poly film type would be fine. The 470nf are available as films quite cheaply.
Don't use ceramics for this.
These are the "suflex" type,
FSC 160V 100PF 2.5% - LCR COMPONENTS - CAPACITOR, 160V 100PF | CPC From This Range
Very expensive.
Urgh There were some polystyrene called out, but others not, so that led to my confusion.
Yeah, I'm in the wrong alley alright.
I know just enough to be dangerous. That's why I ask. I did preface it with ..stupid question... just to cover the rhetorical comments. I don't eat and sleep capacitors.
Mylar (polyester) for the 100nF + 470nF, you'll find it hard to source other than MKT for a 7.5 lead spacing.
For the two 100uF/25V/2.5mm radial electrolytics, Mouser will have a range of manufacturers to pick from.
(the various lingo Elektor editions sometimes differ with naming part types, one may specify a material type and the other not, local ease of sourcing components thing i guess)
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