Hibryd amplifier with tube/valve ECC88 (PCC88) and chipamp LM1875 - diyAudio
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Old 30th January 2012, 06:26 AM   #1
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Thumbs up Hibryd amplifier with tube/valve ECC88 (PCC88) and chipamp LM1875

Hi all!
I need a schematic or project for hybrid amplifier with tube/valve ECC88 (PCC88) and chipamplifier LM1875 or LM3886.
Thanks for your help!
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Old 30th January 2012, 06:46 AM   #2
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there's this new thing out called google... Seems not to be catching on, but I think it works fine.

there are several threads here where similar builds have been discussed
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Old 11th July 2012, 05:59 AM   #3
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Quote:
Originally Posted by aardvarkash10 View Post
there's this new thing out called google... Seems not to be catching on, but I think it works fine.

there are several threads here where similar builds have been discussed
Please pointed out one topic.
thank you!
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Old 11th July 2012, 06:55 AM   #4
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The search term you need is "Gain clone".
Here is one.
Tube Gainclone for DIY Buffs

Several other search results will direct you right back to DIYAudio threads.

Ian
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Old 11th July 2012, 04:06 PM   #5
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Quote:
Originally Posted by gingertube View Post
The search term you need is "Gain clone".
Here is one.
Tube Gainclone for DIY Buffs

Several other search results will direct you right back to DIYAudio threads.

Ian
Ian, very interesting schematic (project)!
What changes to the schematic should I do instead to replace LM3875 with LM1875 or LM3886.
What tube/valve participate in this project.
Thanks for your help

Last edited by formula 22; 11th July 2012 at 04:19 PM.
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Old 11th July 2012, 04:14 PM   #6
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Typically a ECC88 / 6DJ8 /6922 tube is used.
Supply voltages for the LM1875 are lower. The gain will have to be altered too I think.
Why do you want to add the tube ? The LM1875 sounds very good by itself. The tube will degrade signal to noise ratio and add more harmonics to the sound most likely making it sound 'warmer'. But some prefer that route ! Everyone gets what they want !
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Old 11th July 2012, 04:45 PM   #7
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Quote:
Originally Posted by ashok View Post
Typically a ECC88 / 6DJ8 /6922 tube is used.
Supply voltages for the LM1875 are lower. The gain will have to be altered too I think.
Why do you want to add the tube ? The LM1875 sounds very good by itself. The tube will degrade signal to noise ratio and add more harmonics to the sound most likely making it sound 'warmer'. But some prefer that route ! Everyone gets what they want !
Then I replace LM3875 with LM3886?!
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Old 12th July 2012, 03:27 AM   #8
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My simple answer would be , maybe you should use the LM1875 as it is shown in the application note for the chip. It works very well and has good sound.
Simple uncomplicated and good sound !

http://www.ti.com/lit/ds/symlink/lm1875.pdf
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Old 12th July 2012, 04:00 AM   #9
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Quote:
Originally Posted by gingertube View Post
The search term you need is "Gain clone".
Here is one.
Tube Gainclone for DIY Buffs

Several other search results will direct you right back to DIYAudio threads.

Ian
Ian, Is can be tube/valve voltage increased to + /-45V (+ /-90V) and ate without any changes needed in the schematic (Tube Gainclone) hybrid amplifier with LM3875?
thank you
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Old 12th July 2012, 04:24 AM   #10
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Had to "duck off" and have a look at the LM3875 datasheet and the circuit on the The jLTi site.

The power amp chip data says voltage rails between +/- 20V and +/- 84 volts.

I would aim for say +/- 60V that won't bother the ECC88 at all.

That 10K cathode resistor means that the ECC88 current with +/-35V is going to be just a little less than 3.5mA.

Going up to +/-60V rails means that ECC88 current goes up to just less than 6mA. ECC88 are often run at that current and even higher. It will probably make it sound a little less "tubey" as the ECC88 is then on a more linear part of the curve.

You could increase that 10K to get back to the 3.5 mA'ish operating point.
15K would suit about +/-50V rails
18K would suit about +/-65V rails
22K would suit about +/- 80 V rails

Personally I would not go above around +/- 65 to 70 Volts. Thats just me being conservative, why? because of lots of bad experiences when I was young and stupid trying to squeeze the last watt out of circuits and usually squeezing out charcoal instead.

Cheers,
Ian
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