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6J1 China preamp thoughts
6J1 China preamp thoughts
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Old 14th May 2019, 04:13 AM   #141
avtech23 is offline avtech23  Australia
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6J1 China preamp thoughts
I'll chuck a circuit together on some breadboard when I get a chance and see whether the voltage multiplier is stable at higher values.

I'll probably have a look at alternatives for the transistors in my box of spares. I think there are some BD139/140 in there that might suit.
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Old 15th May 2019, 04:25 PM   #142
Angiolino is offline Angiolino  Italy
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Ho costruito il pre 6j1 facendo alcune modifiche che si trovano sul web: Sostituito Condensatore C13 con 2200uF 16v su alimentazione filamenti, ho cambiato tutti i condensatori da 35v con 50v più un condensatore da 470uF 50v con negativo alla giunzione delle resistenze R8-R9 e positivo a GND. Ho tagliato le tracce che portano all'interruttore di accenzione ed ho ponticellato per spostare l'interruttore a monte. Ho aggiunto un diodo alla resistenza da 2.2ohm per abbassare la tensione dei filamenti da 13.15v a 12.45v. Ho messo due resistenze da 47K tra ingresso uscita e massa per togliere il potenziometro del volume. Dopo aver collegato un lettore mp3 all'ingresso del pre e collegato l'uscita all'ingresso di un t-amp, già prima di dare il segnale si sente ad intervalli regolari un "Bump" che fa muovere i woofer delle casse e cosi' anche con la musica, anche se si sente bene. Non ho alzato troppo il volume per non danneggiare i woofer. Non riesco a spiegarmi da che dipende, qualcuno ha idea da che può dipendere, dove ho sbagliato? Grazie a chi riesce a darmi una spiegazione.
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Old 15th May 2019, 04:31 PM   #143
pinkmouse is offline pinkmouse  Europe
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6J1 China preamp thoughts


English please Angiolino.
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Old 15th May 2019, 05:18 PM   #144
Angiolino is offline Angiolino  Italy
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I'm sorry, here is the translation.

I built the pre 6j1 making some changes found on the web: I replaced C13 Capacitor with 2200uF 16v on filament power supply, I changed all 35v capacitors with 50v plus a 470uF 50v capacitor with negative at the junction of the R8-R9 resistances and positive to GND. I cut the tracks that lead to the switch and I jumped to move the switch upstream. I added a 2.2ohm resistor diode to lower the filament voltage from 13.15v to 12.45v. I put two 47K resistors between input, output and the ground, in order to remove the volume potentiometer. After connecting an mp3 player to the input of the pre and connecting the output to the input of a t-amp, even before giving the signal, one can hear a "Bump" at regular intervals that makes the speakers woofer move and so even with music, therefore the sound is good. I didn't turn up the volume too much to avoid damaging the woofers. I don't understand what the "Bump" depends on, where did I go wrong? Does someone have any idea? Thanks to those who can help or give me an explanation.

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Maybe I solved it, I realized looking at the other card to mount that the 4 fet are not equal but they are two pairs, I went to check the card that is not good and I realized that I reversed 2 fet. B647 was to be set on TR3 and I placed D667. D667 had to be set on TR1 and I put B647, tomorrow with great care I will reverse them and I think the pre will sound good. Greetings

Everything okay! I reversed the two fets with great difficulty and great patience, it sounds great. Between one song and another there is a very slight background noise, it may be the old recording, I will try more recent recordings (in fact with a recent recording no noise, no breath) that's okay. Greetings
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Old 17th May 2019, 10:58 PM   #145
Hofmann is offline Hofmann  Netherlands
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I was looking for a first tube preamp project, as well as a first pcb-kit project. After reading all of this I must say I am pretty excited. It seems like a great low cost project.

I think I will get this kit from Aiyima. I've had modules from this brand before and even though they are the same as the many unbranded ones, I have little to complain about their products. AIYIMA Tube Amplifiers Audio board Amplificador Pre Amp Audio Mixer 6J1 Valve Preamp Bile Buffer Diy Kits -in Amplifier from Consumer Electronics on Aliexpress.com | Alibaba Group

The acryllic case saves a lot of hassle with fabricating an enclosure, and for the price I will definetly pick one up too. Acrylic Box Shell Case 6J1 Valve Preamp Pre amp Tube PreAmplifier Board Headphone Amplifier Buffer Transparent-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

I plan on making the modifications shown in this thread before.

My only question remains the power supply. There is a 12v AC power adapter with EU plug available on Aliexpress, link below. AC 12V 1A power supply EU plug for 6J1 tube preamp amplifier board Pre amp Headphone amp 6J1 valve preamp-in Chargers from Consumer Electronics on Aliexpress.com | Alibaba Group

I also stubled across this 30VA 15v toroidal transformer. 1pc 115V/230V 30W Audio R Core Transformer high quality 12V+12V for preamp -in Transformers from Home Improvement on Aliexpress.com | Alibaba Group

Logically I would assume this transformer will be the better option for a preamp. But I do not know what is inside of the plug-in power adapter. And it would require my to make a bigger case for it.

I would really like to hear opinions on the power supply options.

EDIT: Even cheaper transformer: 30W double 15V power transformer Input:220V 50Hz / output:double15V-in Transformers from Home Improvement on Aliexpress.com | Alibaba Group

Last edited by Hofmann; 17th May 2019 at 11:04 PM.
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Old 19th May 2019, 05:02 PM   #146
Hofmann is offline Hofmann  Netherlands
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Could someone please recommend me a suitable power supply for this preamp kit?
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Old 19th May 2019, 10:30 PM   #147
avtech23 is offline avtech23  Australia
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6J1 China preamp thoughts
Just a single 12VAC plus pack like the first one should be fine.

All you need is something above 10w.

As a first project, stay away from mains electricity and go for the plug in option to begin with. Much safer and means an easier chassis build.
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