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Old 17th October 2005, 05:50 AM   #1
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Talking Newbie want to build simple tube preamp&psu!need help!

Hi, i'm a newbie in tube. Actually, i want to build a preamp to accompany my gainclone chipamps.

I need to build a very simple preamp (beginner).I found many schematic, and i'm difficul to choose the best simple preamp.

I have a question:
1.Which is the best;srpp or single ended preamp?what is different between them?

2.Can anyone give me an information about how to build a good power supply for tube preamp?
Actually, i want to use 2 transformator using back to back design(not custom transformator).So,it will produce about 240Vac.But,I'm difficult to find the combination of the CRC filter(CLC filter is expensive for me,especially the price of the choke). I have tried using CRC filter and using 220r&50uF (C-R-C-R-C-R-C-R-C), it's a ver long filter to get a smooth ripple, so it will act like using choke.Can anyone give me another option to build the power supply?:smash(of course with a small ripple & not using choke)

3.Does anybody have a simple preamp schematic?I will build a tube preamp using 12Au7/12Ax7 family.

4.I need to build a preamp which provide a single gain or a gain less than 10.Which design should i build?grounded grid?grounded cathode?cathode follower?

please need ur help to build this simple tube preamp.

regards
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TomZ

"Everything must be simple as possible , but not simpler"
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Old 17th October 2005, 06:18 AM   #2
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Hi TomZ,

What is the purpose of the pre-amp as I don't understand the requirement of unity gain or less then 10??

unity voltage gain would be a cathode follower

grounded grid is not realy an option for an audio pre-amp

I presume this pre-amp will drive a power amp of some sort?

as for psu I'm not so sure you will need all that filtering C>R>C
should be fine.

back to back transformers work ok, or there are dc to dc converters which for low power units such as pre amps would work fine and due to the higher opreation frequency don't require as much filtering and as a bonus if you source one that runs from 12volts your filament supply is already available.

Robert
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Old 17th October 2005, 06:30 AM   #3
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Hi TomZ

check this thread you may find this helpful

Simple tube preamp...[/URL]
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Old 17th October 2005, 09:01 AM   #4
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The purpose of this preamp is to give my chipamps a valve sound.So, i will get a smooth and warm sound from tube.
No, not unity gain. I don't want to build a buffer(unity gain) because it doesn't provide a sufficient gain to make make my chipamps become more dynamic sound.And, my chipamp is non inverted version so i think i don't need to add a buffer.
Yes, i want to use this preamp to drive my Gainclone amplifier.
Do you know the combination of CRC filter?I use 220r and 50uF.
I want to minimize the ripple.
I want to use high voltage tube like 12au7/12ax7 in 150v-250v B+.
I don't need to use a high voltage if i use low voltage tube like 6922/6dj8.But, i want to use 150v B+ as a preamp.
Do u have DC-DC converter schematic?i have tried to use quadupler voltage from 40VAC but the result is very bad ripple.
If i use a switching power supply, there is a high ripple and not continous voltage( because a switching psu is a PWM).
Need ur sugestion to build a valve preamp.

Thx
regards
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TomZ
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Old 18th October 2005, 01:18 AM   #5
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High TomZ


switch modes designed properly should be fairly clean. any way at high frequence it is easier to filter and make clean in a good design.

Ok on power your filter need to know what you are going to use for preamp stage, likely current draw 10ma or so.

Also I see there is a thread on gg preamp, but there is enough discussion on that subject interresting reading. and some circuits are available. but with gg you will need something to buffer the input from the low input z of a gg stage hence the reason i thought gg wouldn't be usable.

As for psu filter you need to compromise assuming 10ma current draw you issues here is how much voltage can you afford to loose in the filter? at 10ma you will get 1 volt drop per 100ohms of series resistance in the series r. I think this needs to be maybe be 2k2r to 4k7 improve ripple.

if you like there is a link for psu design which is very helpful?
and suitable switch mode kit is available locally for about $30AUD.

check out some of the links and threads many schematics, the dificult question is which one. for me as I hadn't done any thing with valves in a long time I bought a kit from a local supplier jaycar electronics maybe not the best but it got me interrested.

Robert
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Old 18th October 2005, 01:21 AM   #6
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it's sort of funny how something simple always generates a series of posts that go on and on and on.....
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Old 18th October 2005, 01:29 AM   #7
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Hi Thomgun_lc,

Tag along here and you'll pick up on some things:

Grounded Grid Preamp Project And Possible Group PCB Buy

Enjoy
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Old 18th October 2005, 04:33 AM   #8
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I'm sory for a newbie question about this tube preamp. But, i really confused to decided which schematic should i used.
I found many schematic but still don't know which preamp should i build.
When i read an article about single ended preamp (using 1 tube for 2 channel), they said that a very simple design could make some tube noise which can decrease the detail of chipamp.Is it true?

I need some preamp schematic using 12au7/12ax7 family.Because i can found this tube very easy.
If i use 2 tube for 2 channel, i need to match both tube, is it true?
I only can find used tube, because the price are very low.
i try to build a swicth mode power supply from 12vdc-250vdc, but i have a problem with a step-up transformator.I must wind the transformator.The SMPS works in 33khz, is it ok?
The other option is to use back to back transformator which very simple and cheap but i still do some trial&error to find the best CRC filter combination.
I really need to build this simple preamp to give a total gain (preamp+gainclone) over 100x.With this total gain, i will get a "punchy"sound but warm&smooth.
I have tried to combine my gainclone chipamps with my friend's tube preamp and the sound was great,more dynamic but smooth & have a good imaging with a natural distortion.

regards
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TomZ
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Old 18th October 2005, 06:56 AM   #9
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Hi TomZ,

don't worry we were all newbe's at some time, i'm still a newbe.

simple well too simple could have poor performance and cause distortions you don't want, if you think about it you want to colour the sound but you don't want to make it bad.

do you have a circuit for your friends pre amp? if you like that sound it would be a good starting point.

33khz is fine it will need to provide 10 to 20ma current and 250vdc is fine for 12ax7

what is your local supply volts/frequency?? 120vac or 240vac 50 or 60hz?

If transformer is cheap maybe seconday 12.6vac (can use for 12ax7 filaments) at 0.5amp and a smaller rated 240 to 18v. If you feed 12.6vac into 18volt winding you should get 160vac if you bridge rectify that you end up with about 225vdc in the same way a 15v primary fed with 12.6vac should yeild 270vdc. no load!

given you want to use C>R>C filter maybe
secondary 12.6 into 15 to 240 for HT supply!

Really you need to decide on a circuit before you get into psu design, shouldn't need matched tubes, same type/make should be fine, if second hand thats different need to have similar attributes.

Robert
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Old 18th October 2005, 08:45 AM   #10
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Ok,Thx for ur help.
My mains local supply is 220v/60hz.So if i use back to back transformator, i will get 300vdc unload. So,i don't need voltage doubler
Do you have any recommendation to build simple preamp?using 12ax7/12au7?I need a simple schematic although it has some distortion.
Thx
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