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Old 5th December 2002, 10:31 AM   #1
argo is offline argo  Estonia
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Default Time for low Zout preamp

Apologies first, if I am already repeating a topic covered in other threads.
I have suspended my Mini -A building project for a while because I couldn’t get it playing properly for some strange reasons and I still have couple of IRFP240 fets left. So I thought, that Andrea Ciuffoly’s Power Follower 99 could be an easy enough design to experiment with those devices. Being a fet follower it needs high gain and low output impedance voltage source. I have couple of Russian NOS 6N1P (close to 6DJ8/ECC88) and 6N2P (12AX7/ECC83 Russian version) laying around and tubes line stage becomes an attractive choice. I would prefer only one tube (that is two envelopes) per channel. But a question remains which configuration to build to meet the high gain /low Zout specs.
At first I thought about SRPP because of its simplicity but it looks like that with these mentioned tubes Zout will always be highish.
Another option could be Grounded Cathode followed with Cathode Follower, either using same type of tube or two different types for one channel. But I have read somewhere that cathode followers can sound not so good if designed sloppily. Having very little experience with tubes to design my own tube preamp, I have been looking and searching around for suitable circuit using these tubes but I haven’t found any.
Can anybody point out some or make related suggestions?

Argo
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Old 5th December 2002, 10:48 AM   #2
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Hello,

I am in the same situation, but with phillips e88cc tubes, and the amp is an Aleph 60.

This topic has been discussed in "Tube line-buffer for cd" thread.

I think that you can make a fairly low impedance SRPP with ecc88, (Zout ~ 800 ohm, gain ~ 25). The only problem with the SRPP is that you have to optimize it for the required load. (read at http://www.tubecad.com/articles_2002...ed/page28.html)

The another way should be the White Cathode-Follower.

So, we are expecting some info from tube-guru's

thanks and regards,
Miki.
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Old 5th December 2002, 11:28 AM   #3
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Easy, use an output transformer designed for preamp valves!
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Old 5th December 2002, 12:05 PM   #4
argo is offline argo  Estonia
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Quote:
Originally posted by jeff mai
Easy, use an output transformer designed for preamp valves!
Yes this could be an option but I'd like to keep it without transformator first cause I don’t have one and would preferably use components I already have now in my junkbox: those mentioned tubes, caps, resistors.

Miki
thanks for the link – I have read some articles about SRPP but have missed this one.

Any cathode follower designs?

Argo
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Old 5th December 2002, 01:49 PM   #5
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Hi, Argo.

A WCF schematic is what I am waiting for, too

Until then I will make an SRPP with e88cc (Phillips), i will use it in the front of an Aleph60 (~ 47k input impedance), and try to optimize for this load.

Once it's finished, I will post the results.

Bye,
Miki.
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Old 5th December 2002, 02:21 PM   #6
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Argo,

With the tubes you have, and no desire to use an output transformer (best option IMO), SRPP with the 6N1P is probably the best option. However, the 6N1P is <b>not</b> a near 6DJ8 substitute (6H23 is) and will give a higher output Z then the 6DJ8, by a factor of at least 2, probably 3. Anyway, it will still work better than a 12AX7 in this application.

Cheers
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Old 5th December 2002, 02:35 PM   #7
almarcy is offline almarcy  United States
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Default design process

design is not just solving riddles. it requires you to build and listen and think.

abandon hope, all ye who enter here

there is more to learn than we have time for. enjoy your visit to each circuit and keep awe as your friend.

happy ears!
al
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Old 5th December 2002, 02:41 PM   #8
argo is offline argo  Estonia
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Default Re: design process

Quote:
Originally posted by almarcy
design is not just solving riddles. it requires you to build and listen and think.

abandon hope, all ye who enter here

there is more to learn than we have time for. enjoy your visit to each circuit and keep awe as your friend.

happy ears!
al
and does your riddle have any answers?

Argo
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Old 5th December 2002, 02:44 PM   #9
miguel2 is offline miguel2  Portugal
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Hi,

Got the same problem with a Zen V4. I have an EF86 based pre (triode mode, 1 stage, no cathode caps) and when I connected it to the Zen the sound was nice but it was too low. With 25W the Zen should play quite loud (I have a Rotel with 25W so can compare). First I tough I had an earthing problem, but now I believe that it is needed some impedance matching. Maybe I had a second gain stage to that pre.
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Old 5th December 2002, 03:21 PM   #10
Joel is offline Joel  United States
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Here's your typical cathode follower design.

And you guys should really use the "Search" feature before you post. This topic has been covered ad nauseum over the last two months.
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