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Old 27th November 2008, 02:14 PM   #1
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Default Th. Lösch Phono Amp: Question about IC used & ECC808 to ECC83

Hi everyone,
I'm a pretty new member in the tube-infected community. I'm 20 years young, a student of clinical medicine and willing to proove my lack of technical knowledge provided by my school(TM) by trying to build Thorsten Löschs Version of the EAR834P as seen here:
http://www.jogis-roehrenbude.de/Lese...l-Phonoamp.htm
My father is helping, but he is more into general electric and doesnt even like tubes.

Most things in the scheme are clear to me, other than one or two, which I want to ask you.
Firstoff: SCHEME

1. An IC of the type "LT1084CP" is used to regulate the voltage as I understand. There are several types of that IC to buy on the market, which am I to buy? The 12V-version?

2. The bridge rectifier circuit has a specification for capacitiy, what does that mean? Is that a component specific information or am i to put condensors in it? Is the rectifier thought as an IC in the end?

3. As I understand it, I am to double the scheme to the left where it says "<- rechter Kanal", put everything exactly the same way and interconnect the other channel to the other half of the tubes, since there are double-triods. What is it whith the Alp Poti? Does it control the volume of both channels?

4. As found on the Internet, I could replace the very expensive ECC808, which is only available as NOS, with the ECC83 with a diffenerent socket configuration. How much better is the ECC808 with its infamous partition grid? Is it worth the money (I am willing to spend btw.!)

Thanks a lot so far,
Herr Grau
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Old 27th November 2008, 03:38 PM   #2
SY is offline SY  United States
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The 1084 is an adjustable regulator, so there's only one "version." Its output voltage is set by the 215R and 845R.

Each rectifier is bypassed by a cap. Presumably, this is to reduce switching noise as the rectifiers transition from conducting to nonconducting.

HTH
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Old 27th November 2008, 03:40 PM   #3
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Hi Herr Grau

Point 1: The LT1084CP used in that schema is the adjustable version, so it has no specific voltage output (the voltage output is set by the resistors 215R and 845R). There are versions for 3, 5 and 7,5A: 3A is more than enough for your application.

Point 2: The capacitors mentioned at the bridge refers to four capacitors that should be connected in parallel to the four diodes (each diode gets one capacitor).

Point 3: yes! double everything to the left of 'rechter kanal'. The alps potentiometer should be a stereo version, with one half for left and the other for right. How will the rest of the system look like? If you are going to use this RIAA stage with an integrated amplifier you may as well leave the pot out and use a simple 100k resistor from the capacitor end to ground. Also, the 1,1uF output capacitor may be a bit low in value if you plan to feed this signal into a low impedance input (say the 47k of a typical SS amp).

Point 4: I have about 4 pieces of the ECC808 which look to be new but which I have not tested yet. We can negotiate!
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Old 27th November 2008, 04:49 PM   #4
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Ach, noch ein Mediziner!

Mr. Gray,

You can save yourself considerable cash by using the ECC83/12AX7, instead of the expensive 6KX8/ECC808. Dedicate a twin triode to each channel's circuitry. Don't share 'X7 sections between channels. The current production Sovtek 12AX7LPS is clean, quiet, and affordable.

Another place that expenditures can be reduced, without compromising performance, is in the DC heater supply. Full wave rectify 25.2 VCT using a MBR20100CT common cathode twin Schottky diode (switching noise free), filter with a 25 WVDC/4700 μF. electrolytic capacitor, and regulate with a 7812 fixed 3 terminal IC. Place a Panasonic ECQ-V multi-layer film capacitor directly across the regulator's I/P terminals. Doing that snubs noise and improves regulator action.

BTW, a highly satisfactory alternative to the costly NOS Valvo ECC82/12AU7 is available, should you be interested.
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Old 27th November 2008, 05:10 PM   #5
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regarding the IC: Alright, I got it.

regarding the rectifier: Got that too

regarding the potentiometer: I already wondered why one would need such a thing, but since i dont know jack i leave the schemes alone. 100k putted in like this?

Click the image to open in full size.

New Question: 5. What are the other two potentiometres for by the way?


@ErikdeBest: Four ECC808? Sounds good so far. What brand are they? Since my tube-stash is one single Mullard ECC81, I guess I'll have to give you Money in exchange
How much did you think? (Say a little more, so i can haggle you down to the price you actualy wanted )

I also wrote to Klimo about the ECC808 since they use it in their Merlin, but I don't think they'll sell to an unimportant person like me.
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Old 27th November 2008, 11:20 PM   #6
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Hi,

Quote:
I also wrote to Klimo about the ECC808 since they use it in their Merlin, but I don't think they'll sell to an unimportant person like me.
Even over twenty years these ECC808 were hard to come by and expensive.
Just like the even better E283CC but that one has an even funnier pinout.

....Wie der andere Mediziner suggerierte, am einfachsten war ein Parchen 12AX7 von Sovtek so gibt's bestimmt keine Interefenz zwischen beide Kanale.
So, damit hat der Alte auch mal wieder den grauen Bard geschaut, na?

Not to rain down on anyone's parade but that schematic is a bit passe to say the least, RIAA in the NFB loop and to low a HT rail for the only so-so 12AX7 to shine, plus a 12AU7A as a CF.
Boring sound with very dull dynamics but you may like that....
Much like the preamp from Dr. Klimo which I'd prefer if I had to choose between the two.

Anyway, don't let me stop you...

Cheers,
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Old 28th November 2008, 01:20 AM   #7
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Quote:
Originally posted by fdegrove
Hi,



Even over twenty years these ECC808 were hard to come by and expensive.
Just like the even better E283CC but that one has an even funnier pinout.

....Wie der andere Mediziner suggerierte, am einfachsten war ein Parchen 12AX7 von Sovtek so gibt's bestimmt keine Interefenz zwischen beide Kanale.
So, damit hat der Alte auch mal wieder den grauen Bard geschaut, na?

Not to rain down on anyone's parade but that schematic is a bit passe to say the least, RIAA in the NFB loop and to low a HT rail for the only so-so 12AX7 to shine, plus a 12AU7A as a CF.
Boring sound with very dull dynamics but you may like that....
Much like the preamp from Dr. Klimo which I'd prefer if I had to choose between the two.

Anyway, don't let me stop you...

Cheers,

Frank,

To clear the air, let's understand that I'm not a Physician. I was educated as a Chemist (Chemiker) and I program computers for my living. The apparently failed to alert my attempt at humor adequately. BTW, I am a "geezer" and my beard is mostly white.

If NFB style RIAA EQ meets with your disfavor, perhaps a variation on RCA's "classic" passive EQ design could pass muster. I'd like to think that Jeff Yourison is nicely polishing off the last little bit of roughness and that the only remaining flaw is high Miller capacitance/phono cartridge interaction. Eliminating that requires changing the triode type in the 1st gain block and (naturally) reworking the RIAA network parts values. Look here.
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Old 28th November 2008, 02:02 PM   #8
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Well, of course you could replace the actualy used double triod with two ECC83 working on one channel, but that would mean working out a whole new scheme. Which I can't do, as I pointed out. I think when it comes to the pure manufactoring of the amp, I'm going to do pretty well, but I'm not yet very fit in the theoretics, because my studying kills much much time.

Plus, not to offend anyone, the whole thing is a "Lösch-Idea" which means that it can't be too bad, I think. If there is anything as well or better, to build with less afford and featuring an as detailed plan, I'm very openminded

Hoorah, Uni again....
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Old 28th November 2008, 06:02 PM   #9
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I can't see that you would need a new circuit, if that's what you mean by scheme, as the ECC808 is supposed to have the same characteristics as the ECC83 except for the pin-out. Its advantages are supposed to be lower self-noise and hum.
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Old 28th November 2008, 06:09 PM   #10
MartinR is offline MartinR  Germany
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Hello Herr Grau,

Quote:
regarding the potentiometer: I already wondered why one would need such a thing,
Quite simple, I needed it to regulate the volume. The phono preamp directly drove my monos.

If you´re interested I can send you a new version of the schematic which I´ve updated recently.

You might also take a look at this thread.

Kind regards,
Martin
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