| thomgun_lc |
;) 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:smash:
"Everything must be simple as possible , but not simpler":smash: :o |
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| Robski666 |
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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| thomgun_lc |
;) The purpose of this preamp is to give my chipamps a valve sound.So, i will get a smooth and warm sound from tube.:smash:
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. :angel:
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.:o
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).:angel:
Need ur sugestion to build a valve preamp.
Thx;)
regards
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TomZ |
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| Robski666 |
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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| RetroAudio |
| it's sort of funny how something simple always generates a series of posts that go on and on and on.....:D |
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| thomgun_lc |
;) 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?
:confused:
I need some preamp schematic using 12au7/12ax7 family.Because i can found this tube very easy.:angel:
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.:o
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?:smash:
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.:smash:
regards
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TomZ |
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| Robski666 |
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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| thomgun_lc |
;) 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.:angel: 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.:o
Thx
:smash: |
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| Jay |
Tom, I will send you a schematic using 12AX7. I know there are people who likes to add 2nd harmonic distortion to colour the sound. IMO, if you want to colour the sound you should find other ways instead of adding distortion. But the tube can indeed create sounstage (seems 2nd haromincs have something to do with soundstage :confused: )
CDP + GC --> Probably not enough gain to boost the details.
CDP + SRPP 6SN7 + GC --> Better dynamic, more detail, more soundstage, MORE distortion --> I prefer CDP + GC
CDP + CF 6SN7 --> No comment, I prefer the two above
CDP + Opamp pres + GC --> prefer CDP + GC
CDP + 3 BJT buffer + IGC --> suggested
But what is an amp!? Only class-A amps can properly "colour" the sound. With non-class-A amps, everything can be handled in the speaker section :D |
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| dave dove |
my first scratchbuild linestage was this:
http://www.users.globalnet.co.uk/~valveamp/
build whatever power supply you like
you can always improve it/change it later
ecc83/12ax7 has a lot of gain for a linestage
ecc82/12au7 sounds quite nice in this
and you could use just 1 valve
most of the valves in the list are easily available
and then by changing a couple resistors you can try something else
this is a really good introduction to valves
dave dove |
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| thomgun_lc |
Does anyone have a simple tube preamp schematic?like cathode follower?i will use 1 tube as a stereo channel.
:smash: |
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| thomgun_lc |
Hi guys,I have a question.If i use 1 tube as a stereo,is it ok?or it will produce some crosstalk?:smash:
Is it ok if i use only one stage like common cathode only? |
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| SY |
The inter-section capacitances are low enough that you'll only see crosstalk at very high frequecies, and even then, not that much. This will probably not be your limitation on separation.
If you're using the tube as a cathode follower, there's even less of an issue since both plates are at AC ground.
And if you use a tube from the ECC88 family, there's even a handy shield between the sections. |
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| Bandersnatch |
Hey-Hey!!!,
Look here:
http://audioroundtable.com/GroupBuild/Projects/
at Guinevere. Gain is only slightly behind a 12AU7. Output Z is less than 200R and it sounds brilliant. Simple L-C power supply. 250VAC to a choke and on to a good cap.
It can be done for less than $200 and it is simple enough for new builders. I penned it and several folks built it right off the 'net. Send a note to the folks who did and I think you'll hear nothing but good stuff.
cheers,
Douglas |
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| rickl |
I'm using Joel's 6sn7 based pre and think it is pretty nice. It was much better than my vintage tube preamp and better than my ss pre.
Since I had most of the parts around I didn't spend too much either.
I've been impressed with Hey Hey Douglas's designs and would look at it too. Just wish I could get only 4 fets and try a CCS. Mouser has a 50 minimum.
rick |
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| thomgun_lc |
Hi Bandersnatch!!:smash:
Thanks for ur attention.I have seen ur link and found that there is a simple preamp using some CCS.
But, i only have ecc82 tube family.Can i change 5687's tube with ecc82 family?confused:
What is the different between using VAC to heater and using VDC to the heater?Which is better?
To JC_Fardo;)
I have see ur link and i have build a PCB for that simple preamp.But,i don't use 5687 tube, i change with ecc82/3 family.So, i did some changes on R plate&R cathode value to set the correct bias for ECC82 family.But, i'm worried because it only have one ground for stereo ( i used 1 tube for stereo).How about if i add 10r from signal ground to power ground.Is it the way to avoid crosstalk?:confused:
And, i don't have a custom transformator, so i used back to back transformator.
To Joel Tunnah;)
I only have ECC82/3 tube family, can i substitute that 12az7 with 12ax/au7?Is it an unity gain?like a buffer?
I used back to back transformator, so i don't have center tap (the output pin only 0&220), can i used 6r4 as a rectifier?
Thx
regards
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TomZ |
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| Jay |
| Wow, that's what I want to build for a Gainclone. Thomgun, stop designing your own pre! :smash: :D |
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| thomgun_lc |
;) Hi Jay!
I really confused to decide which PCB should i design:D.
After see guinevere schematic, i really want to build for my gainclone,But i only have ecc82/83 tube.And my question is, could you get that MOSFET in our country? :smash: |
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| Bandersnatch |
Yo can indeed use a 12AU7. You will want to reduce idle current to 4-5 mA.
On AC v. DC heaters, it is easier to do AC, and since it is possible to get 12AU7 quiet with AC I suggest trying. AC has no risk of making noise from diodes, yes?
cheers,
Douglas |
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| Jay |
Hahaha Tomz, in which part of the country? ;) Yes, of course they are available. And I think your basetown has them too as it exports drivers to big companies, and produces many fake components too :D You just need to hang around with the right people :D
Well, I guess transistor is transistor, and ccs is ccs. They must be easily switchable with other MOSFETs. |
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| Bandersnatch |
you'll need depletion mode MOSFETS for that circuit. See Gary Pimm's pages for designing with enhancement mode devices. A BJT ccs will not do the same thing if implemented like the Bottlehead C4S. That one also requires 3 terminals, the third on the MOSFET one is the low impedance mu follower output, and is optional...you can connect right to the plate.
cheers,
Douglas |
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| thomgun_lc |
;) So, what must i change if i use 12au7 tube.What value of the Rp&Rc resistor should i change.:confused:
Can i substitute the mosfet with another type of MOSFET?
Last night, as a beginner project, i build this very simple preamp.It's based on "dave dove" recommended link (SJS electroacoustic's site).Would u mind to check this out?
regards
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TomZ:smash: |
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| dave dove |
tomZ
i've never used pcb
but all looks ok
except
R1 and R2 - gridstoppers need to be as close to pin2 and pin7 as possible to work
12au7 = ecc82
R5/6 = 20K
R3/4 150R
good luck
dave dove |
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| thomgun_lc |
;) Hi dave_dive thx for your suggestion.I try to rebuild this PCB using my favourite PCB software (eagle) and i have rewiring the path of stop grid resistor.I will upload the PCB picture again.
Should i have regulated DC for heater or using AC?I still don't know the different between using AC/DC for heater.What about the sound? :confused:
Mr.Dave_Dove, i used CRC filter,what is the minimum value for PSU's capacitor value?100uF?50uF?
I do some simulation for CRC filter in PSU buildeng using Duncan Amp's sofware, but i don't know the best capacitor value for the 12au7 preamp.Does it need high capacitance?
regards
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TomZ:smash: |
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| dave dove |
hi tomZ
i used AC heating with this linestage
never had any problems
as long as you twist heater wire tightly and keep it out of the way of the signal stuff as much as possible
i am not very technical
i used whatever capacitors i had
someone will be able to tell you better
i used LCLC
20H>470uf>20H>470uf
it was quiet enough for me
try get someone else to check your pcb
i never use them and don't know a good one from a bad one
good luck
dave dove |
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| thomgun_lc |
Hi there!!This is my new PCB layout for basic tube preamp using 12au7 based on sjs's websites.Please check it out.And i also attach the PSU for this tube preamp.Thx
regards
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Tomz
:smash: |
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| thomgun_lc |
| Here is the PSU for this tube preamp:smash: |
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| dave dove |
thomgun
looks ok
much better
what is R2 on psu?
dave dove |
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| thomgun_lc |
;) Because CLC is an expensive, i use CRC and using this configuration to get "pseudo choke";)
This picture will explain about it.:smash: |
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| dave dove |
R2 on psud represents the load that is the circuit
not a resistor
dave dove |
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| dave dove |
how's it going thomgun?
not far to go now.....
let me know how it goes...
dave dove |
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| dave dove |
how's it going thomgun?
sorry i was in a rush last post
you have not too far to go now.....
your HT voltage is way too high
you only want 280V
in psud
if you change the transformer to 240V
(i believe you are using back to back transformers)
change load section (R2) to constant current
than set that to 10mA which will be close enough
you'll see you have too much voltage
in your case
the best way to reduce that is with second RC filter
try less resistance than the first RC stage
till you get 260-280V
3*22uf caps should be fine
or you could try 220uf but watch how long the line takes to rise
the longer this takes the slower you amp will sound
there will be a good compromise
let me know how it goes...
dave dove |
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| thomgun_lc |
:smash: Hi Dave_dove thx for your concern in my thread.Actually, i still get stuck on PSU.I don't know what is a minimal value for this 12au7 preamp.:confused:
Is it 100uF+220uF?Or 22uF is sufficient for this preamp?:xeye:
Is 12au7 like high capasitance?
Yes,of course i use back to back transformator.My mains supply is 220v.
Mr.Dave_dove, i will use a bleeder resistor for the safety.How a bout if i use a "load" in psud as a bleeder resistor?So,a load resistor=bleeder resistor?
Need your suggest to build this PSU:bawling:
I got many option to build this PSU:
1.Using CRC filter
2.Using some MOSFET(IRF 840)/Transistor(Tip 50) as a stabilizer.
I want to build a fast PSU with a very small ripple.But i still get no idea, of course with a bleeder resistor.
Please need your assistance.
regards
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TomZ:smash: |
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| dave dove |
thomgun
if you can't afford a choke:
220uf > 100R > 22uf > 100R > 22uf
this should do...
i've never used transistors
so i can't comment
the above smoothing will be OK
dave dove |
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| thomgun_lc |
Ok,Mr. Dave dove.
It will use 2 level CRC filter. It will take a time to rebuild my PCB layout, because my computer is re-format and all of my eagle layout are gone:bawling:
Still don't know how to recover my files from formating harddrive:bawling: Could u help me in pm?
Mr.Dave_dove, what about the bleeder resistor?I think a bleeder resistor should be draw about 1mA to drain the capacitor and bleeder resistor will act like a"load"in psud, is it right?
regards
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TomZ:smash: |
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| thomgun_lc |
;) Hi there.I have tried to recover my computer system and save my pcb layout.:cool:
I still get a stuck on PSU building for this tube preamp.I need to measure a bleeder resistor value.Can anyone help me?
What is the best value for decoupling capasitor?:confused: |
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| dave dove |
thomgun
i did send e-mail
but you can't have received it
use 220uf for the first cap
the other two should be 22uf
100R for resistors
220K 1W should be fine for a bleeder R
dave dove |
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| thomgun_lc |
I have bought 2 transformator (each 2 A) i use mount pcb transformator.I use it for back to back system to get a best with minimum result. However,i'm eager to build using tube rectifier but i don't have CT in transformator (because i use back to back transformator the output of the trafo is 0-220 without centertap).If i use fullwave rectifier, i should build a "virtual ground".:confused:
So,i use bridge diode rectifier:bawling:
I will try to build the best PSU for this tube with a very small ripple.Maybe i will add some zener diode to smooth the ripple. And use some transistor to provide some current.
How about the heater supply?Is it worth if i use only AC without regulator?How about a DC for the heater?:smash:
In 12au7 i have some choice to decide which voltage of the heater should i use 6/12v?What is the different between that?;)
regards
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TomZ:smash: |
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| dave dove |
i'm going to say some stuff now
which others may disagree with:
AC heaters will be fine for THIS linestage
i have had no problems with 6.3V AC heaters
solid state rectification will be fine
use ultra fast recovery diodes
like uf4007 or whatever
you will still be pleased
and save some money
regulators and valve rectifiers sound different
whether better depends upon your preferences
dave dove |
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| thomgun_lc |
Hi,dave dove!This is my project report to build this simple preamp:
1.Finally i use this configuration for my PSU: 22uF-->100r-->100uF-->100r-->220uF+220k parallel as a bleeder.
I got a a very smooth ripple.My mains supply is 220v.I use back to back sytem using 2 transformator (each 2 ampere).I do some test and get only 207VAC after back to back.After through bridge rectifier,it should be 293VDC.
My question is, in the SJS's website this 12au7 preamp only need 280VDC not 293VDC,so,how to drop the voltage until 280VDC?Should i use voltage divider?
Or, use 293VDC as a supply but do some changes in Rplate's value?How to calculate this Rplate's value?
Need ur help please!
regards
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TomZ |
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| dave dove |
thomgun
the bleeder resistor does not go into psud
if you right click that
select change
select constant current
set to 20mA
you now have 280V
if you change C2 to 20uf watch the rise time/line
it will shift to the left
this indicates a faster psu
you still have enough smoothing
and it's cheaper too
when are you going to build it?
dave dove |
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| ivegotmono |
Hi,
I,m a newbie too!! 'vef got an Eico HF-12 Integrated amp and it has a12au7(it's the version1) preamp at Valve2. an au7 has an amplification factor of about 40. If you can accomplish the power supply with a few resistors and capacitors you might even be able to run it at tour house line of 220. Mine runs at 185vB+. The two sections are connected in series to get the gain so you would need two of them for 2 channel. If you use Mullards the sound is especially sweet. I've never heard this in combination with a solid state power amp though. If you need the tone controls look at the eico HF-81 schematic for the values. Actually the HF-81 would be the best place to look since it's 2 channel and has all the information in one spot. You should be able to find a free one at:
http://users.rcn.com/fiddler.interport/HF81.HTM
click on the schematic button
Remember you only need the valve 2, from the volume control to the place where the tape monitor jack connects for a preamp.
steve |
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| Rocky |
| How do you get an amplification factor of 40 from 12au7? it lays from 17 to 20 AFAIK.. |
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| thomgun_lc |
My progress report to build this tube line preamp:
I still do some changes on the PCB because i use a small chassis. I wouldn't put the transformator and the tube outside the chassis, that's why i try to reduce the size of the PCB.
Here is the PCB. Please take a look at my pcb:
Regards
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TomZ:smash:
Tube Preamp 12au7 board: |
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| thomgun_lc |
| This is the PSU board:;) |
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| thomgun_lc |
And this is the heater board.
Please give me a comment about my PCB board. |
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| ivegotmono |
Rockys right, I was thinking of at7. I'm palying around with all the 12a?7 tubes in my HF-12 right now and I made an error. The au7 amplification factor is about 20 not 40. The 12au7 sounds better than the at7 IMHO but not as much gain.
steve |
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| thomgun_lc |
;) That's why i use 12au7 tube, because it only have medium mu. If i use 12ax7,maybe my Gainclone become harsh because of too high mu/gain.
:smash:
Any comment for my PCB design?
thx |
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| thomgun_lc |
| ;) If CRC give a slow response for power supply and a choke give a fast enough but very expensive. How to afford a cheap choke? I heard some people using primary 1A EL's transformator to get 2.4H 60mA, but i still don't know how to do that.:smash: |
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| dave dove |
thomgun
your pcbs all look OK
but i have never used pcb
i cannot comment on your DC heaters
i've never bothered with them
a cheap choke will be worse than resistor
i have tried hammond 157g 30H 40mA
and they do work ok
i don't know if you can get them
but
your power supply looks fast enough to me
when are you going to build it? ;-)
dave dove |
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| thomgun_lc |
;) Hi Dave Dove.I will build this preamp maybe in this month and if i have a time to build.
Actually i'm still looking for the component.
How about u Mr. Dave dove?Do you have any other project? |
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