| Franz G |
Hi Carlos
I use now 2x10000uF and 2x2200uF per channel (in fact, just 6100uF per rail), following by 1uF, 0,1 uF foil and 0,1uF ceramics direct at the pins. Cheap electrolytics (Jamicon and Philips).
No C in the signal path, at all. No zobel, no LR network, nothing at all. 2x22VAC 225VA torroid.
Nothing inverted, no buffer, no cap between the inverted input and the ground. Just a resistor.
Franz |
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| PMA |
| And here are currents through upper and lower output transistor, and output voltage and output current. You can see that only the upper transistor conducts. Increasing input voltage for this load (1.6k) the lower transistor will start to conduct as well. for higher load resistance it will be true class A for all output voltages. |
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| PMA |
| Finally, hereby the schematic with nod numbers to identify the voltages and currents. |
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| carlosfm |
| quote: | Originally posted by Franz G
I use now 2x10000uF and 2x2200uF per channel (in fact, just 6100uF per rail)... |
With one PSU for two channels that is 12,200uf per rail.
That doesn't sound good to me, but you may have other oppinion.
Don't take first impressions for granted, listen to the amps, compare.
Anyway, I'm not going to deeply discuss these matters anymore.
I opened this thread to share my experience with the OPA627.
I hope it's useful for someone. |
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| aHobbit |
| quote: | Originally posted by Franz G
Hi Carlos
I use now 2x10000uF and 2x2200uF per channel (in fact, just 6100uF per rail), following by 1uF, 0,1 uF foil and 0,1uF ceramics direct at the pins. Cheap electrolytics (Jamicon and Philips).
No C in the signal path, at all. No zobel, no LR network, nothing at all. 2x22VAC 225VA torroid.
Nothing inverted, no buffer, no cap between the inverted input and the ground. Just a resistor.
Franz |
Hi Franz!
Am contemplating to do just what you did, but I lacked the time, and instead made those that have been tested by carlosfm et. Al. Correct me if I am wrong on the impression I got from your post:
(1) you are using NIGC
(2) unregulated PSU
(3) no pre-amp (no buffer)
(4) 5 capacitors in the power rail
- 2x 10k uF
- 2x 2.2k uF
- foil 2x 1uF and 0.1uF
- ceramic 2x 0.1uF
(5) Your impression: this config is better than the buffered regulated IGC [or is it NIGC] (in your own assessment).
Thanks. |
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| garbage |
| quote: | Originally posted by Nuuk
I think you are referring to the album 'The Girl In The Other Room'! But on some of her other recordings, I have found that her voice is not precisely located and I have assumed this is due to her voice being picked up by both her mike and the mike in the piano. |
yes, that's the album i was referring to. her other recordings seem to have her located slightly to the right... at least that's what i feel.
| quote: | Originally posted by carlosfm
Listen to Jacintha "Jacintha is her name" and in a while you'll be crying.:bawling:
:cool: |
hmm... not much news abt Jacintha locally though... she had a few albums that made it into the international audiophile reviews. was actually surprised that a Singapore album can achieve that. |
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| Franz G |
aHobitt:
Thats right, the configuration you write, I compare it to a buffered regulated IGC.
The above configuration is correct, but don't forget: just "normal" diodes, nothing ultrafast (they dont need any bridging with caps).
The result is very good and I need some more time to compare it to other solutions.
Carlos: 2x10000uF in series is 5000uF, 2x2200uF in series = 1100uF, this 5000uF and the 1100uF in parallel = 6100uF are working per rail.
All other calculations are just "marketing".
Franz |
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| Nuuk |
| quote: | | yes, that's the album i was referring to. her other recordings seem to have her located slightly to the right... at least that's what i feel. |
Exactly what I find. On the 'A NIght in in Paris' CD, on track 10, at the beginning her voice seems to move more to the right and then back toward the centre. I played that track just after building my first GC and thought it was a problem with the amp! |
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| aHobbit |
Thanks FranzG.
I am not using ultrafast diode - just the typical ones.
If infact this will sound good comparable or better than the regulated GC, I will have the amp in my NEC A-10II in my next mod. This route will be easier for me. |
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| carlosfm |
| quote: | Originally posted by Franz G
Carlos: 2x10000uF in series is 5000uF, 2x2200uF in series = 1100uF, this 5000uF and the 1100uF in parallel = 6100uF are working per rail. |
In series?:confused:
In parallel?:confused:
If you are feeding two channels from one PSU aren't all the caps in one rail in parallel?
Maby if you post a schematic... I'm a little confused...
| quote: | Originally posted by Franz G
All other calculations are just "marketing". |
Calculations are marketing?:confused: |
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| X.G. |
HI,Carlosfm
I had introduced your excellent experiences to my friends.But... two of them told me not to get the expected better results:dead:
sounds smoother,the bass better,but the definition worse,some weak sounds lost.
| quote: | Originally posted by carlosfm
I must say that I don't have biasing into class-A on my OPA627+BUF634 pre |
Oh,my god!
I just read your post:bawling: :bawling:
their amps are OPA627+BUF634T!:cannotbe:
| quote: | Originally posted by Nuuk
Slightly OT but can anyone identify this chip for me?
A search on Google doesn't bring anything up. I would guess it is a dual but I found three of them on the output of an old Pioneer CDP. |
Hi,Nuuk
The IC is M5238,produced by Japanese company(Misu????)which the Logo showed.
Here is one of the link I just searched
http://www.talkaudio.co.uk/vbb/showthread.php?t=59742 |
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| Nuuk |
| quote: | | The IC is M5238,produced by Japanese company(Misu????)which the Logo showed. |
Thanks X.G. May I ask what search engine came up with that link? It didn't show up in Google. :confused: |
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| Joe Rasmussen |
| quote: | Originally posted by carlosfm
Calculations are marketing?:confused: |
I thought it was mathematics? :confused: |
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| Franz G |
I mean by "marketing calculation": just add all capacitance in an amp and write about the sum in the flyer :xeye:
Here is the PSU schematics:
The testamp looks like this:
It is important to say: this amp sounds different than the buffered version. I am sure, bass is better.
But I can not tell you up to now, wich amp I prefer. Give me one or two weeks of comparing them.
Carlos: please dont forget we use different speakers: I drive fullrange speakers in backloaded horns. I NEVER use more than 1W output!
Franz |
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| carlosfm |
| quote: | Originally posted by Franz G
Carlos: please dont forget we use different speakers: I drive fullrange speakers in backloaded horns. I NEVER use more than 1W output!
Franz |
Ah, that's a completely different story.
With those easy to drive speakers you may not need to regulate.
The unregulated amp will give good results, although I like it with much less capacitance.
The capacitance you have gives better bass but affects midband and treble, it throws away the "magic" of these chips.
The unreg. amp will give very good results with your speakers, but if you test it with "normal" speakers you'll find out that the reg. amp will drive them much better. The result is tighter and better bass and you'll follow the music much better, everything is more defined.
You make the amp that you need. If unreg. gives better results for you, go for it.
BTW with those speakers you can even use the LM1875, wich is IMHO very good. |
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| tbla |
| quote: | | With those easy to drive speakers you may not need to regulate. |
regulation is not only a matter of the abillity to drive speakers - it has other "good things" too.......(Carlos, the krell has landed ;) ) |
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| Nuuk |
| quote: | | I use google too, the Key words is 'M5238'+'PDF' |
Amazing how just one letter 'M' can make the difference! ;)
I must try this new Blinkx thingie! :bigeyes: |
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| carlosfm |
| quote: | Originally posted by tbla
regulation is not only a matter of the abillity to drive speakers - it has other "good things" too....... |
:D
| quote: | Originally posted by tbla
Carlos, the krell has landed ;) ) |
No...
Am I understanding right?
You mean K < your work of art?;)
:cool: |
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| Sunsun22 |
I've soldered a 1.8K resistor on top of a "high leg" dip socket because I don't want to make further damage to the PCB "IF" this is no good. The pre-amp I am using is ML38S and the opamp in test is OPA627BP
When I turned on the system right after the installation, I am really amazed to hear the system really sings. I used to test many systems with Maria Callas "La Mamma Morta" and her mouth, in the previous system, doesn't open wide enough. However, with the installation of resistors, her mouth is now wide open!! The base is deepened and the high is extended. I really like to see how it works after a day or two.
One question. The OPA627 was used to run at 37 degree C but now it sometimes goes up to 45 degree C. Do I need headsinks?
Sunny |
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| carlosfm |
| quote: | Originally posted by Sunsun22
When I turned on the system right after the installation, I am really amazed to hear the system really sings. I used to test many systems with Maria Callas "La Mamma Morta" and her mouth, in the previous system, doesn't open wide enough. However, with the installation of resistors, her mouth is now wide open!! The base is deepened and the high is extended. I really like to see how it works after a day or two. |
My initial feelings about these ML preamps seam to confirm.:rolleyes: :dead:
Oh, I like this part:| quote: | Originally posted by Sunsun22
However, with the installation of resistors, her mouth is now wide open!! |
:D
| quote: | Originally posted by Sunsun22
One question. The OPA627 was used to run at 37 degree C but now it sometimes goes up to 45 degree C. Do I need headsinks?
Sunny |
If you have them, you can use them.
But don't bother, that's not hot.:hot: |
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| Nuuk |
| quote: | | However, with the installation of resistors, her mouth is now wide open! |
My dentist is interested in this mod! ;) |
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| carlosfm |
| quote: | Originally posted by Nuuk
My dentist is interested in this mod! ;) |
I was not thinking on the dentist, but I'm naughty.:D |
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| Rambi |
| quote: | Originally posted by carlosfm
I was not thinking on the dentist, but I'm naughty.:D |
Considering that she died over 25 years ago; naughty is not the first word that comes to mind... :dead:
(It's a joke, I know ;)) Remco |
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| Franz G |
Nothing about class a, but forgive me, here my story continues:
I compared the "overcaped" NIGC with the buffered and regulated version (class a/b for the opa627) tonight.
The regulated version shows in fact more "musicality" than the overcaped version. More details, good soundstage.
But my favourite tonight (at the left):
Two times 2 Watt valve amp, single end, class A.
May be in future I will use chipamps just for subwoofers...
Franz |
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| carlosfm |
Franz, your 'overcaped' version is not the correct way to use these chips, as I said.
Anyway, with your speakers your 2w valve amp may please more to you.
Even then, it's a question of taste, and I don't discuss that.
But if you had "normal" speakers instead of your full-range horns you couldn't even bare to listen to that valve amp.
You seam to have a good match between amp and speakers, and for your musical tastes, so no need to fiddle.
Don't discard chipamps just because you have a better choice on your system.
I've heard lots of things, lots of them I have no money to buy, and believe me, these chips are very good, I have lots of pleasure listening to music.
BTW, I made my sub amp with chips.:D
2 // OPA549s. |
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| aHobbit |
| quote: | Originally posted by Franz G
Carlos: please dont forget we use different speakers: I drive fullrange speakers in backloaded horns. I NEVER use more than 1W output!
Franz |
I agree with carlosfm. For a 1W output, even the 10k uF seems to be an overkill, and would just tend to give you more potential problem. Removing those 10k uF will save you amp cost and space.
But I agree with you, that on a 1W, what you did might really sound better.
I wonder if anyone did experiment the AN1192 for LM3886, using the capacitors:
- 2x 1200uF in the PSU board
- 2x 10k uF, 2x 470uF, 2x 0.1uF near the power pins
These are multiple bypassing which FranzG nearly implemented, but would give out more power (of course with buffer circuit).
Thanks for posting your observations. |
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| Sunsun22 |
Hi Carlos, here she is: -
DOB April 23 1923
Are you still interested to go naughty with her today? ;)
By the way, after listening for the whole night (I just can't stop), I can say the amp is having more punch at the low and more details at the high. The vocal is especially good. So good that I'm wondering does Class A biasing introduced some MSG?
When I compare to the change of sound stage by changing the caps to BG, BG caps are shifting the spectrum to the high while biasing to Class A is expanding the spectrum. I think my PCB has to go through another surgery to solder these resistors on it permanently.
Sunny |
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| Franz G |
Carlos, you wrote:
"BTW, I made my sub amp with chips.
2 // OPA549s."
So, you use subwoofers?
Maybe, thats why you dont miss the lacking bass in the regulated chipamp with just 33uF nearby the chip?
Franz |
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| carlosfm |
| quote: | Originally posted by Franz G
Carlos, you wrote:
"BTW, I made my sub amp with chips.
2 // OPA549s."
So, you use subwoofers?
Maybe, thats why you dont miss the lacking bass in the regulated chipamp with just 33uF nearby the chip?
Franz |
All the tests I make are without the sub.
And I know my speakers very well without the sub.
There's no lack of bass with 33uf caps on the chip.
Maby there is on your implementation, with your PCB.
You recognized that the PCB traces may be a little thin.
Don't concentrate just on a frequency band, listen to the music as a whole.
I don't like the result of having big caps near the chip, with regulated PSU.
Pay attention to bass quality and tightness, midband, treble, detail, "air", speed.
When I mean big, I'm saing more than around 100uf.
From 33 to 100uf gave the best results when I tested it. |
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| carlosfm |
| quote: | Originally posted by Sunsun22
When I compare to the change of sound stage by changing the caps to BG, BG caps are shifting the spectrum to the high while biasing to Class A is expanding the spectrum. I think my PCB has to go through another surgery to solder these resistors on it permanently.
Sunny |
So you're saying that a cheap resistor on the right place brings more improvement than fancy BG caps?
I'm not surprized.
Sometimes it happens.:D |
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| soundNERD |
sorry for interrupting, but I would just like to know how much power can be obtained from an amp using the OPA627.
Thanks! |
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| Zombie |
| Power: an OPA627 can deliver 70mA...40mW into 8R? |
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| soundNERD |
| Sorry again for changing the topic, but what good is it if it only produces so little power? headphone amp? |
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| carlosfm |
| quote: | Originally posted by soundNERD
sorry for interrupting, but I would just like to know how much power can be obtained from an amp using the OPA627.
Thanks! |
The same.:D |
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| carlmart |
| quote: | Originally posted by soundNERD
Sorry again for changing the topic, but what good is it if it only produces so little power? headphone amp? |
It is good for small signal amplifying applications only. Very limited power.
Audio electronics is where specialization is very much used. It's less problematic to have several stages, each doing a specific task, instead of one doing it all.
Even so, inside a small signal chip (e.g.: OPA627) or a large signal chip (e.g.: LM3886) there are sub-stages that also different tasks.
But as a rule, small signal chips specialize in doing low-noise amplification or fast signal handling, having limited power capability to drive it.
That's why in this forum the combination OPA627/BUF634 became quite popular, each chip doing a specific task.
Carlos E. Martinez |
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| Franz G |
I am on the way to try this:
... drive the EL84 SE tubes with an OPA627, instead of the ECC82.
Franz |
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| mikelm |
| quote: | Originally posted by carlosfm
Don't concentrate just on a frequency band, listen to the music as a whole.
I don't like the result of having big caps near the chip, with regulated PSU.
Pay attention to bass quality and tightness, midband, treble, detail, "air", speed.
When I mean big, I'm saing more than around 100uf.
From 33 to 100uf gave the best results when I tested it. |
Hi Carlos,
Sorry if I have missed something earlier but I am just experimenting with various types of regulation and caps on a couple of chip amps.
what regulators are you using ? and what type of caps do you prefer ?
Is there a thread which covers this ?
cheers
mike |
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| Nuuk |
| quote: | | Is there a thread which covers this ? |
Mike - don't ask ! :bawling:
This may be of help to you though! ;) |
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| GregGC |
| quote: | Originally posted by Franz G
[B]I mean by "marketing calculation": just add all capacitance in an amp and write about the sum in the flyer :xeye:
Here is the PSU schematics:
The testamp looks like this:
It is important to say: this amp sounds different than the buffered version. I am sure, bass is better.
But I can not tell you up to now, wich amp I prefer. Give me one or two weeks of comparing them.
Carlos: please dont forget we use different speakers: I drive fullrange speakers in backloaded horns. I NEVER use more than 1W output!
|
Franz G,
May I suggest something, if you haven't tried it yet?
How about decreasing the gain to around 11-15 instead of 27-30. LM’s have very good frequency response, so a bit more NFB may be a good thing in your case. This way you'll have much lower distortions and you won't have to attenuate the input signal that much (you said you use only 1W). I'm sure the sound will be different and hopefully better. I remember experimenting with the gain and I liked gain of 22 better than gain of 30. It was smoother but not lacking detail.
I'm very curious to hear what you'd find. I'm looking into building full range speakers with about 94dB/m sensitivity and driving them with GC (no buffers at all).
/Greg |
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| carlmart |
| quote: | Originally posted by GregGC
How about decreasing the gain to around 11-15 instead of 27-30. LM’s have very good frequency response, so a bit more NFB may be a good thing in your case. This way you'll have much lower distortions and you won't have to attenuate the input signal that much (you said you use only 1W). I'm sure the sound will be different and hopefully better. I remember experimenting with the gain and I liked gain of 22 better than gain of 30. It was smoother but not lacking detail.
|
Now that is something I would be very much interested in knowing about too! Perhaps a switch or even a pot would allow some tests in that area.
| quote: |
I'm very curious to hear what you'd find. I'm looking into building full range speakers with about 94dB/m sensitivity and driving them with GC (no buffers at all).
|
If you plan on using a NIGC that should be fine. For an IGC that might work if you are feeding a signal that's already buffered and with some output control, like on a Marantz CD player.
If not Joe Rasmussen's explanations on how different pots and different pot positions affect your response on an IGC are in order. A buffer should improve things, tube or solid-state.
Carlos |
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| carlosfm |
| quote: | Originally posted by Franz G
I am on the way to try this:
... drive the EL84 SE tubes with an OPA627, instead of the ECC82.
Franz |
Ah, now you're talking.:D
Don't forget the resistor!:cool: |
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| carlosfm |
| quote: | Originally posted by mikelm
Hi Carlos,
Sorry if I have missed something earlier but I am just experimenting with various types of regulation and caps on a couple of chip amps.
what regulators are you using ? and what type of caps do you prefer? |
Hi Mike!
Here's the full package!:cool: |
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| GregGC |
| quote: | Originally posted by carlmart
Now that is something I would be very much interested in knowing about too! Perhaps a switch or even a pot would allow some tests in that area.
If you plan on using a NIGC that should be fine. For an IGC that might work if you are feeding a signal that's already buffered and with some output control, like on a Marantz CD player.
If not Joe Rasmussen's explanations on how different pots and different pot positions affect your response on an IGC are in order. A buffer should improve things, tube or solid-state.
Carlos |
Carlos,
I'm planing on NIGC (no buffers, because I believe that they have their own sound, good or bad). A high input impedance NIGC (47-100kOhm Zin) should eliminate the need for a buffer. I have even a PCB that can be used for High Z IGC, NIGC, Parallel or Bridge configuration. Really universal one, using single sided PCB and trough-hole components.
Will see when I'm gonna have time to try it.
/Greg |
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| PMA |
| That's the 100k pot that changes the sound in most significant way. |
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| GregGC |
| quote: | Originally posted by PMA
That's the 100k pot that changes the sound in most significant way. |
Replace it with a descrete resistors attenuator, then. When I build my first GC I tried it with a pot and attenuator and I didn't find a difference. The first GC I build was 2 separate monoblocks. Now I think that that's an overkill (for me, others may think otherwise) and I'm considering using single PSU for both chanels and a stereo pot (from a Yamaha receiver) for the volume ctrl. My GC attenuators started making cracking noise (not very good switches I guess) after 3 mths of use and my Yamaha is 10 years old and the pot works verry well. So, I'm considering a good ($25CAN) stereo pot. seriously. At the end I think one of the original design GC's uses a sliding pot. also, so it can't be that bad. Mind you I subscribe to "Less is more" line of thinking.
/Greg |
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| matjans |
| quote: | | Mind you I subscribe to "Less is more" line of thinking. |
What is less? a pot or a stepped (ladder) attenuator? ;)
a stepped ladder is no more than a discrete pot (stepped voltage divider).
I seem to remember that a 4717 shigaraki (the small one) uses an alps slider. |
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| carlosfm |
No matter what slider, those things usually attract dust inside like hell.:bawling:
Contact spray is a very good friend of slider pots.:D |
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| analog_sa |
hmmm...yeah. Sortof. It's certainly more musical than a passive attenuator but not so obvious compared to a good active pre. One of these days i should try a TVC in a double buffered active arrangement. Could be the best of both worlds (or worst :)) |
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| carlosfm |
| quote: | Originally posted by tbla
TVC rules.......:D |
...at a price.:bawling:
This cheap thing is really attracting me:
http://www.diyaudio.com/forums/show...&threadid=39258
Yes, for me a good active pre is better, but it still needs a pot or some way to control the volume, and it should be a good one.:bawling:
If there's a cheap and good solution, I want it.:D |
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| ABO |
This week I tried biasing the OPA627's in my PMA-buffer preamp. As suggested by Carlos I used 2k resistors from the output to the negative rails of each opamp.
I really didn't expect much of a difference because, in this application, the OPA's are not really loaded and hence are in class A already.
The differences are small, but they're there. I notice a slight increase in resolution. Some instruments and particularly female voices seem to have more body.
You gotta love these kinds of tweaks. I don't know if anybody else has tried it, but one couldn't ask for more bang for buck!
ABo |
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| Franz G |
As I wrote a few days before in another context:
| quote: | The amp now has asymetry, wich results in higher harmonic distortion because of asymetric cancellation. And you seem to like it.
BTW: The same effect happens, when you use an opamp with "class a bias". And many people like it. |
But I wrote also:
| quote: | Harmonic distortions are the reason for many people, including me, to build single ended tube amps!
Many very low distortion amps don't satisfy in a musical aspect. So, the real art is, to use this "amount" of distortion, to make the user happy!
|
:D
Franz
BTW: I am wondering about the results from Carlos FM with the tube (sorry, valve) buffer, compared to the OPA627! No news, Carlos? |
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| carlosfm |
| quote: | Originally posted by ABO
The differences are small, but they're there. I notice a slight increase in resolution. Some instruments and particularly female voices seem to have more body. |
I never felt there was a need to do this when using the buffers.
The OPA627+BUF634 board I took out from my pre is here looking at me.
Now you make me curious... gotta try it.:D
| quote: | Originally posted by ABO
You gotta love these kinds of tweaks. I don't know if anybody else has tried it, but one couldn't ask for more bang for buck!
ABo |
That is exactly my oppinion.
This op-amp can make you :bawling:, when you know how to make it sing.
And it really sings.:cool:
| quote: | Originally posted by Franz G
BTW: I am wondering about the results from Carlos FM with the tube (sorry, valve) buffer, compared to the OPA627! No news, Carlos? |
Franz, you can call me Carlos, or Carlosfm, whatever you like.
FM in capitals separated from my name seams like Frequency Modulation.:D
No, I didn't have the chance yet, I've just finished an amp for a friend...
I need time, as I am now testing something new, I've been etching an hour ago.;)
I will then make the valve circuit and test it.
Stay tuned to 97.8 FM.:cool: |
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| Franz G |
97.8 mHz? Nothing, absolutely nothing...
But FM is still better than AM, isn't it?
Sorry, Carlosfm :)
Franz |
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| carlosfm |
| quote: | Originally posted by Franz G
97.8 mHz? Nothing, absolutely nothing... |
Radar FM here.:cool:
Alternative.
Not commercial ****.
| quote: | Originally posted by Franz G
But FM is still better than AM, isn't it? |
Absolutely.
More bandwidth. :angel:
| quote: | Originally posted by Franz G
Sorry, Carlosfm :) |
Of couse, I was joking.;) |
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| Dr.H |
Y'all should still consider trying either THS4061 or AD8610. Tried the former in a buffered (BUF634) preamp ala pavel macura and found it to be a more open, cleaner and engaging presentation. 627 is good, detailed, but quite dark.
627 plays good music, THS4061, unbiased I might add, makes it seem more live, especially on the highs, which have more air.
Another candidate is the AD8610. Currently trying this in a DAC IV stage (DAC is SAA 7350 of Theta DS Pro Pime) and again, seems more involving vs an unbiased 627. Also, bass and highs seem to have more extension vs 627. Only issue is that supply max is +-13V.
At some stage, will try Resistor and JFET biasing of both 4061 and 8610. |
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| carlosfm |
Ryan, the THS4061 is too noisy for my taste, and it also has high input offset voltage.
Much more appealing, and I suggest that you give it a try, is the THS4031/2.
IMHO.
The THS4031/2 has:
- Much lower input offset voltage.
- Much lower noise (1.6nv/sqHz compared to 14nv/sqHz :eek: of the 61/2).
- Much lower distortion.
In my oppinion, the parameters where the 31/2 have inferior specs are not so important.
The only thing is that the 31/2 is stable at gains of 2 or -1, but for a line or headphone preamp this is no problem. |
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| Peter Daniel |
| quote: | Originally posted by Dr.H
Another candidate is the AD8610. Currently trying this in a DAC IV stage (DAC is SAA 7350 of Theta DS Pro Pime) and again, seems more involving vs an unbiased 627. Also, bass and highs seem to have more extension vs 627. Only issue is that supply max is +-13V.
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I was using AD8610 for some time in my preamp. It is indeed more open and more involving than OPA627, but for some reason it never sounded completely natural. The highs seem a bit artificial (sort of proccessed). I was running it at +/- 15V rails (as ML preamp provides only that) so maybe that was influencing the sound somehow. But during constant operation at higher voltage for at least a month, I didn't get any problems.
I'm back to OPA627 and I think it can be made to sound fine. At the moment I'm using 4.7 BG N additional bypasses directly on the pins. It seems to be slightly better than previous 0.01u film caps, but nothing really major. |
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| carlosfm |
This is a little off-topic here, but anyway the thread is mine:D and I think this may be of interest.
I spent some good moments this night playing with my small battery-powered preamp, one that I made some years ago for tests.
One input, one output, an input pot, very minimalist.
+/- 16V with 4x7.2V nicad 300ma batteries.
The voltage at the op-amps is around +/-13V.
The circuit is very small, the pot is on the circuit and the board has around 4x4cm.
Talk about small signal path...:)
It uses a double op-amp.
I use it with my favourite double op-amp: the LM6172.
Tonight I opened this thing and started testing op-amps, again.
Here's what I tested:
- LM6172
- OPA2132
- NE5532 :eek: (from Signetics)
- THS4062
- AD826
- AD8620
And the winner is: LM6172.:D
It beats the OPA2132 by a very small margin, it's almost on par, you have to be an experient listener to pick the differences.
The THS4062 made my speakers move with the movement of the pot.:dead: As I predicted, it has input DC-offset. Not bad sounding, but there's better and I think this is not indicated for audio use, it has some peculiarities for a voltage-feedback op-amp.
The Signetics NE5532 is not bad at all, but... nah. A little synthetic sounding.
The AD826 has a common characteristic usually found on AD op-amps: a recessed midband. Not neutral, veiled midband, not for me.
The AD8620 confirmed my first test some time ago: a "thin" treble, it lacks "body" and harmonics, it's a girl treble.:clown:
Now it's late, bed it is.
The pre is here, charging the batteries.:D |
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| carlosfm |
| quote: | Originally posted by Peter Daniel
I was using AD8610 for some time in my preamp. It is indeed more open and more involving than OPA627, but for some reason it never sounded completely natural. The highs seem a bit artificial (sort of proccessed). I was running it at +/- 15V rails (as ML preamp provides only that) so maybe that was influencing the sound somehow. But during constant operation at higher voltage for at least a month, I didn't get any problems. |
Yes, Peter, read my previous post.
It's the treble, it's the treble...:D
| quote: | Originally posted by Peter Daniel
I'm back to OPA627 and I think it can be made to sound fine. At the moment I'm using 4.7 BG N additional bypasses directly on the pins. It seems to be slightly better than previous 0.01u film caps, but nothing really major. |
Go higher capacitance.
From 22 to 100uf, use a value that fits best.
The 627 will thank you.;) |
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| Dr.H |
Peter,
Your results mirror those reported elsewhere, i.e. operating Ad8610 at +-15V gave a thin top-end. I am running mine at +-13V.
http://db.audioasylum.com/cgi/m.mpl...,+8610&session=
Carlosfm,
I find the use of the Goudreau triplet very beneficial. Maybe your THS4062/1 was needing this. It certainly lowers the perceived noise floor for all op-amps. |
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| analog_sa |
| Thin top end on 8610? Never noticed it when used with a buf634. Without it - maybe thin bass. |
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| carlosfm |
I tested the AD8620, the double version of the 8610.
It was used alone, at around +/- 13V, at a gain of aound 3x.
It has a thin top-end, not exactly aggressive, but thin.
I don't know how to better describe this...
Results may be different with the BUF634. |
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| rha61 |
Finally , choosing an op amp depends on your taste
i'm not pleased with Burr Brown op amp presentation
I prefer the AD ( except AD8620 ) , particularly the 826
I 've spent my last two weeks testing op amps on a UCD180 buffer stage ( hypex module , classD)
the second choice was the 5532 in Philips version , which is an op amp with a beautiful distorsion spectrum ( this op amp is coming back , you can see it on the last Accuphase DP65 or last McIntosh preamps or DAC MDA1000 )
alain |
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| carlosfm |
I've heard very bad sounds from Burr-Brown OPAs whith less than ideal PSU bypass and layout.
On the same circuit the NE5532 wins hands down to the OPA2604 and OPA2132.
When I make it my way, the OPAs (and others) win.
So, I must say that op-amps are not just drop-in replacements as they should be.
Some modern op-amps demand more attention, and then they deliver.
This is my experience, take it or leave it, everyone.:angel: |
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| ryssen |
| quote: | | Thin top end on 8610? Never noticed it when used with a buf634. Without it - maybe thin bass. |
Do you have a schema,maybe I could use it to drive my headphones? |
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| KBK |
| Why is it that I never hear much about people using a shunt volume? If a volume pot is bad, and switched attenuators are expensive..then why not use the pot in a shunt volume arrangement? |
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| audiocrow |
I've used the opamp Class A polarisation in my opa2604 Arcam's Alpha 7SE output (original opamp was rc2114 -I think that's a tweacked version of ne5532).
I also try that mod in my opa2604 Arcam's Alpha 9 integrated amp in pre amp section (original opamp was tl072 :apathic: - now you know why they sounded lazzy and with that valve-like sound...yeahhh...).
I also use opa134 in DC servo- it really amazes face to ne5534 (at least in that position, but that will be another topic :) ).
My opinion:
I think opa604 series are a bit of to mutch WARMMMM. Sometimes they sounded harsh and to mutch processed...meaning not good and very fatigating.
With class A polarization they still sound a bit warm but mutch more correct, plenty of bass, great highs, cleaner vocals, plenty of air, but I think (might me sugestion of mine) a bit less dinamic - maybe just less distorced and/or agressive.
Just my opinion!
Feedback is welcome! |
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| audiocrow |
Does anyone know where can I learn more about biasing a opamp to Class A?
Thank You. |
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| xcel |
Guys,
Really nice thread, I can say (or confirm) that the OPA really sings when in class A. I´ve used it in an number of my (professional)designs, and when the power supply is excellent, you will get truly outstanding performance.
I'm selling my OPA 627AP and BP, as well as many other audiophile opamps. Check my post in the trading post forum.
I think this will give more DIY ers the chance to experiment with these opamps without having to pay the ludicrous prices that local shops are charching them (I've seen as much as 45 euro for an OPA 627 BP !!!!!).
with regards,
Xcel |
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| demogorgon |
up here at my local suplyer they cost 24 euro. insane!
i have 8 of'em, not that i paid though..
hopefully, they'l be singing soon too. |
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| El_Will |
| When using 2 x OPA627AP on a Brown Dog adapter to replace a NE5532, do you put one resistor on the adapter or must you use two resistors, one on every OPA627? |
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| KP11520 |
Hello all,
At the beginning of this thread, Carlosfm talks about adding the proper value resistor between pin 4 (-V) and pin 6 (output) to bias to Class A. Although it is not a perfect situation under load, he suggested to try it and assured everyone that this is all you need to do and don't make it harder than it needs to be.. Looks easy enough, why not. It would be nice to make the OPA627AP op amps do even more.
To figure out the value you need to apply the voltage to the formula. Everyone spoke of voltages like 12 volts and 18 volts. When I test pin 3 (+In) OR PIN 2 (-In) and common I get 2.6 volts and 6 volts on pin 6 (output) to common on my Rotel CD Player with new OPA627AP op amps. Am I doing something wrong or measuring at the wrong place? Any help would be appreciated! Thanks!
Regards//Keith |
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| jarthel |
| is there a schematic for this opa627? thank you |
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| KP11520 |
Hello, jarthel,
Thank you for taking an interest!!!!!!!
Here is the hyperlink to the TI specifications pages for the OPA627AP: http://focus.ti.com/lit/ds/symlink/opa627.pdf
Hopefully this can help! I will post the related part of the RCD-965BX schematic next!
Regards//Keith |
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| KP11520 |
Here is the area of the schematic diagram for the op amps this came with NE5534s, I already have replaced them with new OPA627APs. I hope this also helps!
Regards//Keith |
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| zei |
Hi KP11520
I have,nt read this thread all the way through... But.
Try and messure pin 4 and 7 wich is the supply pins.. I bet you will get different results :)
/Z |
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| av-trouvaille |
Hello,
In this thread I did not read about the experience of Hietbrink or fmak at Audio Asylum (AA) already in 2003. As fmak said: ‘In an AA- post on modifications to the SCD777ES, jhietbrink mentioned the use of the LM6172 bypassed by a 0.1 uF NPO ceramic betweeen V= and V- as the I/V opamp...Without the 0.1 uF cap, the sound was thin and unacceptable. Placing a 0.1 uF Rifa PPS cap across pins 4 and 8 'calmed' the sonics although the incisive trable quality was still there. Putting a 0.01 uF stacked 7XR cap in its place made matters worse. However, mounting the 0.1uF NPO has made the 6172 sound clear and yet with warmth. Timing is excellent and the mid range is much better than a current loaded AD826.The cap is not cheap though, and more expensive than the opamp! Amazing change in the behaviour of the 6172 which is otherwise well decoupled between V+, V- and ground.‘. You can read more here (and in associated posts):
http://www.audioasylum.com/forums/h...ges/156269.html
A review of someone else: ‘Believe it or not - the LM6172 actually sounds lush with the NPO ceramic caps in place. The bass is ample and powerful - and far more articulate than the bass of the OPA2604. The treble is extended and smooth - no hard edges. Cymbals shimmer and every brush movement can be traced. Now I know that some of you are thinking that this can't be a description of the LM6172 - or that I'm partially deaf. But what the LM6172 sounds like all depends on the bypassing. Without the right caps in the right configuration, the LM6172 can sound lightweight with a hard treble and diminished mid-bass. But with the right caps - the sound is glorious - at least for an op amp.’
Such NPO-caps seem to be advised by National and are for instance the Kemet Goldenmax brand in the C350 case size, Radial NPO 100V .1 uF (available from Mouser or Newark). I did not order them yet, and if someone would buy a bunch I would be interested.
A question about post 56 where Joe Rasmussen seems to have included a picture. Somehow I cannot see that picture. Am I the only one?
Best regards, Arjen. |
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| av-trouvaille |
Forgot to add the question on the first part of my post: could the experience with the decoupling of the LM6172 be of interest to apply on the OPA627?
Best, Arjen. |
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| KP11520 |
Hello Zei,
Thank you very much for saving the front of my head and face:headbash: :headbash:
You were right!!! I measured the correct pins and got 30.1 volts on each op amp! Now I can figure the calculations to know which value resistor!
Any suggestions on which type of resistor or will a Radio Shack cheap one do?
I'll probably be back asking how to check to see if it is operating at what Carlosfm suggested, 5 to 10 ma.
Arjen, I am interested also to the answer to your question.
Regards//Keith |
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| zei |
Any cheap metalfilm resistor will proberly do just fine.
When you know that it works you can experiment with different types and see if you get different results.. :)
Oh.. i am pretty shure you should calculate the value of that resistor based on the Voltage 15V and not 30V.
/Z |
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| KP11520 |
Thanks again Zei, can' wait to play!
Looks like a 1.8K will do the trick! I will report back!
Regards//Keith |
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| KP11520 |
| PS does the wattage or tolerance matter on this application? |
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| zei |
| quote: | | PS does the wattage or tolerance matter on this application? |
No.. :)
Mmm.. come to think of it,, the tolerence matters. However you could go with a 1% or even a 5% resistor and just messure it to make shure you got the correct value..
You know 0,1% resistors are (Or can be..) up to 0,1% "Wrong"
So, just go with a normal 1% metalfilm and messure it ;)
/Z |
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| KSTR |
Has anyone seen this before? I'm sure someone already invented this before I did...
A pretty simple concept, basically. Run two identical OpAmp in parallel, symmetrically offset them a little -- by injecting offset currents into the -INs --, and combine the outputs with current sharing resistors. As long as less current than +-Iq is drawn from the output, OP1 will always source current and OP2 will always sink current. When more current is drawn, only one amplifier's output current changes polarity, running through its crossover section. Choosing Ibias and Riso requires some thought in an actual implementation.
Although only a simple closed-loop inverting example is shown, this can be easily extended to high AC gains as a quasi-open-loop building block, e.g. for composite amplifiers.
I've tried this arrangement on both small-signal duals/quads and power OpAmps with great success. It can be further extended to more than two amplifiers and also to different class A to B crossover breakpoints / different quiescent currents for each one, resulting in a gradual class A to B transition for the whole circuit. Thus, output characteristics are greatly smoothed when only one amplifier at a time changes its output current direction and when every amplifier runs at a different internal operation point, current-wise.
Among other options, one can make the biasing somewhat signal dependent (e.g. sensing the output current and/or input voltage), reducing idle state power consumption in power amplifiers.
pros:
- high output current
- wide class-A range
- smoother, piecewise class A to B transition
- lower noise
cons:
- decreased output voltage headroom
- increased Zout (though this is seldom a real problem)
- requires multiple and matched networks/amplifiers
regards,
Klaus |
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| KSTR |
By lucky accident, I found someone who did this stuff before, and guess who? Nelson Pass! Sort of a best-case reference, I think...
And yes, I *did* search the forums before I wrote the previous post.
http://www.diyaudio.com/forums/show...3526#post423526
(see circuit #4)
Regards,
Klaus |
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| Tolu |
| Has anyone tried to bias a LME49710 or LM4562? |
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| Terry Demol |
| quote: | Originally posted by KSTR
Has anyone seen this before? I'm sure someone already invented this before I did...
A pretty simple concept, basically. Run two identical OpAmp in parallel, symmetrically offset them a little -- by injecting offset currents into the -INs --, and combine the outputs with current sharing resistors. As long as less current than +-Iq is drawn from the output, OP1 will always source current and OP2 will always sink current. When more current is drawn, only one amplifier's output current changes polarity, running through its crossover section. Choosing Ibias and Riso requires some thought in an actual implementation.
Although only a simple closed-loop inverting example is shown, this can be easily extended to high AC gains as a quasi-open-loop building block, e.g. for composite amplifiers.
I've tried this arrangement on both small-signal duals/quads and power OpAmps with great success. It can be further extended to more than two amplifiers and also to different class A to B crossover breakpoints / different quiescent currents for each one, resulting in a gradual class A to B transition for the whole circuit. Thus, output characteristics are greatly smoothed when only one amplifier at a time changes its output current direction and when every amplifier runs at a different internal operation point, current-wise.
Among other options, one can make the biasing somewhat signal dependent (e.g. sensing the output current and/or input voltage), reducing idle state power consumption in power amplifiers.
regards,
Klaus |
I believe Rupert Neve (pro console design legend) may have
beeen one of if not the first to implement this scheme or
something very close to it.
Terry |
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| AndrewT |
| quote: | Originally posted by KSTR
A pretty simple concept, basically. Run two identical OpAmp in parallel, symmetrically offset them a little -- by injecting offset currents into the -INs --, and combine the outputs with current sharing resistors. As long as less current than +-Iq is drawn from the output, OP1 will always source current and OP2 will always sink current. When more current is drawn, only one amplifier's output current changes polarity, running through its crossover section. Choosing Ibias and Riso requires some thought in an actual implementation.
Although only a simple closed-loop inverting example is shown, this can be easily extended to high AC gains as a quasi-open-loop building block, e.g. for composite amplifiers.
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Hi,
is this a variation on what Doug Self is doing in some of the new Cambridge power amps? |
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| av-trouvaille |
Hello,
My question about post 56 did not yet yield a response, so another try: Joe Rasmussen seems to have included a picture in that post. Somehow I cannot see that picture. Attachments of other posts are visible. Am I the only one that cannot detect it in post 56? If so, can someone mail it PM?
Best, Arjen. |
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| Gordy |
| quote: | Originally posted by av-trouvaille
Am I the only one that cannot detect it in post 56?
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It is not there. |
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| KSTR |
Hi Terry & Andrew,
Actually I don't know if these audio legends (Mr.Self and Mr.Neve) did this but I strongly speculate they did...
I was thinking about the offset problems with paralleled chip amps (and thus the necessity of current sharing resistors in the outputs) and then I went hey, why not use offset deliberately to get the outputs into class A? With chip amps one needs to parallel quite a few anyway, to drive low impedance speakers during transients (like Andrew has pointed out elsewhere).
Further thinking lead me to use different points where the individual amps change their output current polarity which will result in a rather smooth class A to B transition when output current demand increases above pure class A levels.
Finally I realized that class A, from a PSRR standpoint (often critical with chip amps / op amps), is only beneficial in a fully balanced mode (single ended only the sum of supply currents is constant in class A but not the individual currents). Again the transition points give a smooth characteristic when going into class B in small increments, not all at once. As GND becomes a pure reference potential a single supply is sufficient (which has some other nice effects).
One might call this "Balanced Piecewise Class A" or "Balanced Segmented Class A".
Regards, Klaus |
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| AndrewT |
Hi Kstr,
forcing an opamp into ClassA is only used due to the inside of the ClassAB output stage being inaccessible to tweaking.
The output stage can be converted to single ended by shutting down either the upper half or the lower half of the ClassAB push pull pair. Often the output stage is a quasi stage and designed for optimum IC characteristics.
When one converts the stage to single ended we end up with a very inefficient ClassA stage that has heat directly proportional to ClassA bias current.
Assume the opamp normally sends a maximum of 2Vac (2.8Vpk) into a 5k load. This equates to 0.56mApk output current. A single ended stage must have bias set to exceed the output current for all normal signals. If you want some headroom then bias must be set to some factor over the normal maximum.
Lets adopt Ib=2mA giving 11db of headroom.
The dissipation inside the IC is now +-Vsupply * 2mA ~=30*0.002=60mW on top of what is dissipated in the earlier stages. We have probably got close to doubling the dissipation in the IC for a Class A output of 7Vac into 5k and no capacitance on the load.
Some of the advantages that make opamp ClassA output also apply to a chipamp so your question is not unreasonable.
Now do the same calculations for a chipamp.
Wait a very short while for it to blow up. |
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| analog_sa |
| quote: | Originally posted by AndrewT
Wait a very short while for it to blow up. |
Don't be so pesimistic - these chips have great protection - how else would they survive in the hands of diyers :) The output power may even be enough to power some cans. |
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| KSTR |
Thanks for commenting on this, Andrew. Because I designed a lot of electronics with power op amps at work (ATE stuff) I'm quite aware of the dissipation/SOA related problems, especially with reactive loads. I'm not about to run 1A bias with LM3886's on +-35V supplies...:hot:
The actual amp concept will use about a dozen of them per channel, running on a low supply and with (partly) dynamic biasing. It's not class A over the full output range, as I feel the benefits of class A is mainly in the low level range. And it's a composite amp (the chip amps only act as precision output transistors of sorts for an grounded input 2 OpAmp diff with current mode xformer signal coupling), not the typical GainClone/PA/BPA design.
Regards, Klaus |
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| tiltedhalo |
I have run an LM3875 class A with a power JFET on a low volt supply +/- 16VDC and had good outcomes, surprisingly 1st harmonic distortion increased, 3rd decreased and 2nd harmonics increased, but the overall sound quality was somewhat more laid back with good control, I dare say more "tube like"taking the edge off. The LM3875 liked 1.0 to 1.2A bias, I slide from as low as the chips internal to as high as 1.5A output is low around 10W.
My overall thought on biasing a chip into A was not worth it, measurements are worse, dissipation is "HOT" and power output low. The LM overture series all use a well designed internal Quasi output, and pushing them into one side operation is just not worth the drawbacks, IMHO. |
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| Tolu |
| Would it be possible/profitable to use bias in that preamp circuit? |
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| KSTR |
@Tolu:
I think those very good LME497x0's won't profit much from output bias in such a low gain setup. One surely will need a high noise gain circuit (like x1000) to see a change with normal measurement equipment. I would prefer a setup with two OpAmps as I described to passive biasing with a resistor/CCS.
The benefits of class A will become greater the higher a gain we use -- making composite amp front-ends running (almost) open loop the most interesting candidates (AFAIR people like Walt Jung frequently use(d) this).
@tiltedhalo:
Yes, the only way to find out if it works is to try it out. Thanks for your valuable comments on the LM3875.
Regards, Klaus |
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