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Old 10th April 2003, 02:01 PM   #1
miguel2 is offline miguel2  Portugal
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Default gainclone and jeff rowland

Hi,

I think I got the gainclone bug

Digging on the web I saw that the jeff rowland concentra uses some concepts that are mentioned in this forum regarding the gainklones, like the use of LM3886 and battery supply. Taking a look at

http://www.jeffrowland.com/review16b.htm

we can see that:

1 - input is through a tranformer and an AD815

2 - output are 6 x LM3886

TI has an application ("Complete Audio Amplifier") where they use a OPA134 input opamp, that serves to make the treble and bass controls, and then a simple OPA548 (replaceable by the usual suspects).

My question/thoughts are if these more elaborated designs can be better than the gainclone. And if there is a point in converting an unbalanced signal to balanced signal inside the amp to send it to the further stages. And if the transformer is necessary or the input opamp can do it.

Miguel
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Old 10th April 2003, 03:32 PM   #2
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Default Re: gainclone and jeff rowland

Hehehe. I like how their marketing literature tries to mislead people, referring to a power opamp as an "Intelligent Power Transistor with Gain" and implies that these devices are simply replacing the typical output transistors in an amplifier. 47 Labs has some laughable marketing verbiage too, but at least they call a spade a spade when it comes to the Gaincard being based on a power opamp.

Quote:
Originally posted by miguel2
My question/thoughts are if these more elaborated designs can be better than the gainclone. And if there is a point in converting an unbalanced signal to balanced signal inside the amp to send it to the further stages. And if the transformer is necessary or the input opamp can do it.
Well, the Concentra will certainly give you power power than a Gainclone using a single power opamp. Other than that, I don't see any particular advantage.

As for converting an unbalanced signal to a balanced signal inside the amp, well, seeing as the Concentra uses a bridged output scheme, you need to produce a symmetrical signal to drive the two halves.

As for the transformer, I'm not sure what you mean by the input opamp doing it. Not sure what the "it" is that you're referring to. An opamp certianly can't provide electrical isolation. It can't offer as good common-mode rejection performance from balanced sources without trimming of the output impedances of the source to make sure they're as matched as possible and it can't give you anywhere near the common-mode rejection that a transformer can when fed from unbalanced sources.

I've been using power opamps in my own amps for over a dozen years. While the power opamps I've used have changed over the years, the basic configuration has always been input transformer/power opamp. It's worked well for me.

My amps have all been just power amps though. However you could simply put a pot or swtiched attenuator between the transformer and the power opamp. However this would only work using the power opamp in non-inverting mode. Otherwise, the attenuator would need to be upstream from the input transformer.

se
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Old 10th April 2003, 04:12 PM   #3
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Question single ended to balanced...

hi steve,

wouldn't you say that using a DRV134 from Ti as the input device, could be a very good idea...? perhaps JEFF ROWLAND is allready doing this in his poweramps - there is certanly no input transformer inside...?

best regards,
troels



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Old 10th April 2003, 04:31 PM   #4
tiroth is offline tiroth  United States
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A transformer is still better...in some ways.
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Old 10th April 2003, 05:08 PM   #5
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This has already been discussed previously. I think R Jones owns a JR 3886 based amp and he used it as reference while working with the STK modules. Apparently this particular JR is not that great sounding. But i would imagine the sound is different and in some ways better than a gaincard. The multiple parallel devices will certainly improve drive of more difficult loads and generally bass quality. The bridging will further improve dynamics and bass as it solves problems of ground currents/psu well. Arguably the best way to implement bridging is using a quality transformer for the phase inversion. I think JR uses Jensen. So it may be a very valid exercise to improve on some sonic aspects of gainclone while hopefully not losing out on others (immediacy, microdynamics).



cheers

peter
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Old 10th April 2003, 05:29 PM   #6
miguel2 is offline miguel2  Portugal
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I guess the transformer we are talking about here would have to be something very well made, which means expensive. Wouldn't a nice pair of opamps costing 1euro or such do the same trick, feeding one in the + input and the other on the - input? I guess the feedback is different and would have to be adjusted.
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Old 10th April 2003, 05:47 PM   #7
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jeff rowland is using transformers in the concentra but NOT in the poweramps......
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Old 10th April 2003, 06:02 PM   #8
mlloyd1 is offline mlloyd1  United States
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Transformers:
1. provide galvanic isolation,
2. are immune to some nasties that active devices are not (thanks to the laws of physics),
3. do not generate some nasties that active devices do (again, thanks to the laws of physics).

Jeff Rowland does indeed use Jensen transformers. And yes, they are expensive, but this IS high end, right?

However, active devices can sound good in this role.

mlloyd1

Quote:
Originally posted by miguel2
transformer ... would have to be ... expensive. Wouldn't ... opamps ... do the same trick...
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Old 10th April 2003, 06:07 PM   #9
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there are no transformers in the new poweramps.......
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Old 10th April 2003, 06:20 PM   #10
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Default The other side of the moon...

Quote:
Transformers:
Quote:
1. provide galvanic isolation,
Quote:
2. are immune to some nasties that active devices are not (thanks to the laws of physics),
Quote:
3. do not generate some nasties that active devices do (again, thanks to the laws of physics).
4. are sensible to magnetic fields..

5.suffer from histerisys of the magnetic material...

6.are sensivel to core saturation if they have a small DC across it...

7. are bandwith limited...
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