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Old 29th February 2004, 02:59 PM   #1
Morse is offline Morse  United States
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Default Observations requested: OPA vs LM vs TDA; LM1875 vs LM3875 - anyone compared them?

Hi everyone and thanks in advance for any info;

I'm rather new to this whole GC thing, with only my TDA2030A under my belt, and I was wondering if anyone has observations and comparisons on both chip families and individual chips - i.e. TDA family vs LM family vs OPA family chips, for example. A direct comparison of the LM1875 vs LM3875 would be of great interest.

The sort of information I'm looking for would be something like "chip 'a' tends to be more analytical in sound (even brittle) while chip 'b' has a warmer more valve-like sound; however, chip 'b' is more sensitive to highly reactive loads, and tends to lose dynamics with complex loading." Which chip has the "best" midrange - anyone found a chip that approximates well the sound of a 2A3? 300B? 6BQ5? Information on a chip's tonal qualities seems lacking online (certainly the app notes all like to pretend that their chips are tonally neutral - is this REALLY the case with all the common chips?).

Sorry if this topic is already hidden in the archives - I did a search, but couldn't find a treatment of the subject. If it's there, a link would be appreciated.

Thanks in advance for any information!
All the best,
Morse
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Old 2nd March 2004, 04:04 PM   #2
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Thjere was a lot of this stuff discussed in Peter's "Just Another GC" thread that first caused us to split this topic out from SS.

Personally and subjectively, I like inverted non-minimal OPA549s, and spit on everything else...
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Old 2nd March 2004, 07:09 PM   #3
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Default Re: Observations requested: OPA vs LM vs TDA; LM1875 vs LM3875 - anyone compared them?

Quote:
Originally posted by Morse


The sort of information I'm looking for would be something like "chip 'a' tends to be more analytical in sound (even brittle) while chip 'b' has a warmer more valve-like sound; however, chip 'b' is more sensitive to highly reactive loads, and tends to lose dynamics with complex loading." Which chip has the "best" midrange - anyone found a chip that approximates well the sound of a 2A3? 300B? 6BQ5? Information on a chip's tonal qualities seems lacking online (certainly the app notes all like to pretend that their chips are tonally neutral - is this REALLY the case with all the common chips?).

It never hurts to bring old topic back

I only tried 3 chips and some time ago posted my impressions. I forgot most of them by now, but it seemed to me like OPA549 was more analytical, with more "proper" presentation (and maybe a bit better bass), while LM3875 was more warmer and "eophoric" sounding. Probably LM chip is more tube like (than OPA). It is not my opinion, but other peoiple tried both LM 3886 and LM1875 (if I got the numbers right) and 3875 was a better overall performer. 3886 should have better bass and better drive into lower impedances (as it has souble current output), but the midrange and highs performance isn't seemingly as good as less current capable device (3875). As to 1875, I'm not sure, but somebody mentioned that it may sound a bit strained?

Now TDA7293 (or whatever the number) was a complete write off and I didn't like it at all. It seemed to show some sign of veiling and coloration that by comparison to LM and OPA chips didn't sound as crisp and natural to me. Bass was sort of boomy too.

Well, that's all I remember
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Old 2nd March 2004, 08:23 PM   #4
mikelm is offline mikelm  England
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Years ago I tried LM 1875 V TDA1514

At the time I thought that 1875 sounded more natural and smooth despite the 1514's better figures.

More recently I got a very nice result with TDA2050 using batteries. From memory this one was quite outstanding but from what I have heard here it does not fare so well with transformer, bridge etc i.e. it has poorer noise rejection than the LM3875 which many people seem to prefer.

have not tried texas ones

In summary I would try TDA2050 with batteries
and LM3875 If you prefer tranny and bridge.

however the next one I make will be biased into Class A for the first watt using casoded CCS's.

There is a diagram showing a balanced version in a thread here called "first watt....something..."

mike

here is the link

http://www.diyaudio.com/forums/showt...129#post327129
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Old 3rd March 2004, 02:21 AM   #5
Morse is offline Morse  United States
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Hi Pinkmouse;

Thanks for the tip. I'll look into a more specific search and see if I can find that post. If so, I'll put a link to it in this thread for anyone else who might be interested.

Hi Peter;

Thanks again for the great information! I was considering some TDA7293's but I'll put that on the back burner now. Very interesting comparisons of the 3875 vs 3886; it reminds me a lot of the 2A3/300B dilemma (albeit without the huge price difference on NOS and spares!) that I faced when I built my first SET. My preferences would run to the LM3875, in that I personally will always give up some bass 'grunt' to get a more musical midrange. Perhaps the LM1875 would be compared to something like the 6BQ5 - musical but a little strained when driven hard. God knows, the guitar guys love that one for it's tone in "overdrive" conditions.

Right now, my only chips to choose from are LM1875, LM4766, TDA2003, and TDA2030A (for power chips - I've got OPA134's, OPA2134's, OPA2228's, TL072's, and TL082's on hand for preamp use, and even a few LM308's, LM741's and LM386's in ye olde parts bin). Probably keep to the plan and build an LM1875 first with a better PS, chassis, and fittings than the TDA2030A and see how that goes. On the next Digikey order I'll tack 4 or 5 of the LM3875's so I have a small stock of 'em on hand for my next gen amps....

Hi Mikelm;

Thanks much for the info on the TDA1514 vs LM1875. I've felt like I'm missing out on something, but have been a bit too cash strapped to buy the TDA1514's (at $9.9USD ea., I can buy 4 LM1875's per TDA1514!). Hmmm, sounds like I'll have to scrounge up some affordable (read that as dirt cheap!) gel cells and a charger circuit for the TDA2030A's. The "DormAmp" I built 'round that really is an amazing little performer for the money, so if I can improve on things a bit with a battery pack....hmmm, maybe I could use that as an excuse to build a solar battery charger!

For the LM1875's, I'll go out to our lone electronics store tomorrow and see if they've any 36VCT trafos in stock. I've got 2 or 3 25VCT@2A trafos around the house, but I'd like to try something with a little more 'oomph' this time. Also considering trying out a DIY stepped attenuator around some 2 pole 12 throw make before break rotaries I found there (and maybe a silver contact DPDT wired to give say 10dB of cut so that it would be a 'rough adjust/fine adjust' system.

Thanks too for the link - very interesting ideas you're playing with there....not too dis-similar to some of my thoughts about using something like 12A*7's or 6922's for the input stage of a hybrid (mosfet output?). Got plenty of assorted small valves here, but OPT's and HT PS trafos are another thing entirely....

For everyone, thanks for the information and the ideas! Any more suggestions are much appreciated, too!

All the best,
Morse
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Old 3rd March 2004, 05:57 AM   #6
mikelm is offline mikelm  England
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The "DormAmp" I built 'round that really is an amazing little performer for the money, so if I can improve on things a bit with a battery pack....hmmm, maybe I could use that as an excuse to build a solar battery charger !

I've heard that at least one of the big japanese multinationals is putting a huge R&D resource into fuel cells. Different types for different gases.

So we could also think about:

GC powered by battery

battery charged from fuel cell

fuel cell power by gas ( of your choice )

i.e. Gas powered hifi, neat huh...

using efficient speakers the whole system could be what ? 85% efficient.

Now if you could cut out the batteries and charge the caps directly from the fuel cells...... that might be the the 'greenest' amp in the world ?
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Old 3rd March 2004, 07:10 AM   #7
Morse is offline Morse  United States
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Hi Mikelm;

>>>I've heard that at least one of the big japanese multinationals is putting a huge R&D resource into fuel cells...<<<

They're not the only ones - there's a lot of effort going on worldwide.

>>>...Different types for different gases...<<<

Right. What you'd probably be after is a sealed system with hydrogen, since my limited understanding is that most of the others are variations on "cogen" (co-generation; i.e. they produce both electricity and heat - desireable in northern climes but pretty undesireable in a Midwestern US summer!). Use the solar cell to dis-associate the hydrogen, then recombine it to yield electricity from the cell - essentially the cell IS a kind of battery, albeit not in a conventional sense (in one way it certainly is though - most of these fuel cells yield poor Vout per cell, so they use a series stack of cells, or a "battery" of cells). Problem is that it's not 'cost effective' at current when manufacturing costs are included (there's hope for the future though - it's a wide open field). Another potential issue is safety, since hydrogen is genuinely ugly stuff to deal with, unless it's stored on something like a platinum catalyst (and Pt is more $$ than Au...ouch). Similarly, Pt is often used in the cells themselves - finding a cost effective substitute is a major part of the research.

Oh well, it's a seriously cool idea - pity I can't afford to try it here! Sorry if I put anyone to sleep!
All the best,
Morse
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Old 4th March 2004, 04:24 PM   #8
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Ahh, a bit more time to reply properly now...

Peter has summed the discussion up quite well, so I will just add a couple of comments on the end of his...

LM1875, very,very sweet mids, lacking bass, and treble a little stinging. Turn on/off thump as well.

LM3886, needs lots of capacitance in the PSU, at least 6800uf per leg, otherwise it sounds flat and compressed.

OPA548, good, like a turned down 549, great for backgound music, (and that's a complement!). I still listen to mine a lot in my dining room system.
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Old 4th March 2004, 04:48 PM   #9
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I would say that the LM1875 is more difficult to construct compared to the LM3875 which is a lot easier because of the extra space between the pins.
I cannot give any definate hints on the sound of the LM1875 compared to the LM3875, because both my LM1875 are none inverting, where as my LM3875 is a Valve Buffered Inverting GC. Still for what its worth the bass on the LM3875 blows the LM1875 away.
Needless to say they all sound fantastic compared to any other amp I have heard.

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