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DIY Tube Preamp - Click HERE for Original Thread

FBLEAGH

Hi guys,

I want o have a go at making a preamp as my first foray into tube DIY.

I found the SJS line preamp (http://www.users.globalnet.co.uk/~valveamp/ under read it, line preamp , and second design + powersupply ) and the design looks nice and simple and fairly easy.

i jsut wanted a bit of help with the power supply section.
a) would a toroidal transformer be a good choice ?
b) what specs should i be looking for in the transformer. i guess it would be 220V primaries and 2 6.5v secondarys. but what about VA etc ??
c) where cana i get tubes locally ? ie australia

I was gonna chat to http://ourworld.compuserve.com/homepages/harbuch/ and see what thier price would be on the xformer.

any other things i should be aaware of with this design ??

timc

This link has a list of valve suppliers in Australia - http://home.mira.net/~gnb/elec/valveaus.html
Even Jaycar is selling a limited range of valves.
I find it just as easy and cheaper to order them across the net from places like http://www.thetubestore.com
You can also try guitar/music shops.

For the transformer, I think toroidals are fine, but many people have different opinions/preferences. They are one of the easiest to mount.
I would be interested to see the costs of the harbuch transformers in small/custom runs...

Looking at the design, if your are going for easy, I would use a solid state power supply instead of the valve rectifier shown.

Regards,
Tim

halojoy

But I found this page with a good tutorial.
(searched Google, keywords: tube line amplifier beginner)

My First Tube Amplifier

Here is another "TUBE DIY Page"
http://tubesall.hihome.com/

This is a real good one. Well described projects:
http://www.glass-ware.com/tubecircu...it_Archive.html

:cheerful: let's tube it :cheerful:

Brett

Howdy,

I'll make this really brief as I'm madly trying to finish a project for tomorrow. I live in northern NSW and build tube gear (and have for years). I'll try to add more later or feel free to email.

a) Transformer: Torroids are too wide bandwidth and let in far too much junk that's a hassle to filter out later. An EI is a much, much better solution. An electrostatic shield between the primary and secondary is a good investment too, esp if you're having them custom made. Try www.tortech.com.au in Sydney (strathfield?) All custom transformers are expensive, esp as you will need a few different winding for B+ and heaters.

b) I took a look at the schematic and I like it.
Transformer specs;
Primary: 230V
Secondary 1: 330V - 0 - 330V at 100 mA for the B+
Secondary 2: 6.3V at 2A for the GZ80
Secondary 3: 8V at 1.5 A for the signal tubes

The first two secondaries are over-specified by a large margin. Most of the cost of a custom trans is on labour, so it's better to over spec it, because it sounds better, and because most people who play with tubes will build something else later and it's good to have the extra rating in case you want something with a lot more grunt, always handy in a line stage. Besides, over-speccing means parts run cooler and are more reliable.
Actual continuous current draw on the secondaries will be a max of about 15 - 30mA, 600mA and 600mA.

I also wouldn't bother with DC on the heaters as they're indirectly heated, and so would get a 3.15V - 0 - 3.15V heater for the signal tubes, and use a resistive divider from the B+ to bias them via the centre tap to 40V or so.

c) Best place in Oz for tubes is David Crittle at www.retrovox.com.au.
However, he may not have what you want.
I'll give you a pair of new 6N1Ps if you send me your address details. Nice tubes.
I hardly buy any tubes locally. Most of mine come from the US, HK, Italy, Lithuania or the UK and it is a zero hassle fast reliable deal. I can recommend reliable sellers I've dealt. Airmail is fast, reasonably cheap, and unless you buy expensive tubes, you'll seldom cop import duties or Govt Suck Tax (keep under $A499 landed incl postage). I will provide more details of parts and tube sources later (I don't have all the URLs from where I'm posting. Trust me, importing is a yawn.

The PSU chokes are a minor hassle, but they're small so postage should be cheap. These will probably have to be impoerted. I always use Lundahls, but they cost around $A160ea and take about 4 weeks to order through the Australian importer.

More manyana

Cheers
Brett

fdegrove

Hi,

Keep in mind Mr.Shiltons' warnings against either topology 2&3.

To my mind #2 is the better of the two,but you can't drive long interconnect cables with that due to high output impedance.

The PSU as proposed is pretty much universal so no quibbles there.

Depending on the tube of your choice you may have to burn off some excess voltage.

If that's the case,I would regulate it ,if you want to do that with tubes you will then have to provide the extra heater current unless you want to just put in some glowdischarge tubes or a string of zeners that are decoupled locally.
To my ears it well worth the extra outlay.

Happy building,;)

fdegrove

Hi,

Here's a nice little circuit that is up to the task.
It will be a lot better at driving cable capacitance and should mate well with the PSU.

Cheers,;)

Hi Fred,

What is the approximate output impedance of the circuit you posted? Would it drive a Zen V4 with an input impedance of 47K or so?

G

fdegrove

Hi Gavin,

Since I don't see anyone named Fred here I assume you mean the circuit with the 6SN7s' a bit higher up.

Zout should be around 2K and it should be able to drive a 47K Zin.

Cheers,;)

dhaen

Thanks for the clarification Fred.

Sorry Frank. I haven't had my gallon of coffee yet this morning.:xeye:

G

FBLEAGH

Ok thanks guys,

Now i've got something to start on :)

btw do you think this a good design to start with ?

Is this going to be easy to modify and pay with later ?

I was gonna build it using the tubebuilding PTP boards, good idea ?

also where can i find some good info on tube theory ? eg topologies, basic design ideas etc :)

oooo 1 more thing, how easy will it be to add a decent selector ciruit and possibly some tone controls later ( and where whould the tone controls fit i the circuit )

THanks agian
Fbleagh :)

fdegrove

Hi,

quote:

also where can i find some good info on tube theory ? eg topologies, basic design ideas etc

See here amongst others:

http://www.diyaudio.com/forums/show...=&threadid=7512

quote:

btw do you think this a good design to start with ?

Other then that you said it to be a preamp I don't know what circuit you picked.
Care to tell us some more?

quote:

Is this going to be easy to modify and pay with later ?

Depending on real estate,why not?

quote:

I was gonna build it using the tubebuilding PTP boards, good idea ?

You mean these phenolic boards with a row of solder lugs?
Those are easy and give better soundquality then PCB.

quote:

oooo 1 more thing, how easy will it be to add a decent selector ciruit and possibly some tone controls later ( and where whould the tone controls fit i the circuit )

Selector switch is no problem but tone controls never interested me.
Can be calculated though.They can be done within a feedbackloop or passively with specially tapered pots.
When passive they can go at the inputs.
Is this for a guitar preamp stage or similar application?

Let us know what you want to do and we'll take a look.

Cheers,;)

FBLEAGH

thanks for your response fdegrove

I am looking a the line preamp design 2
Looks nice and simple.

as for the application i am looking at, it will be used as a preamp for my solidstate power amp.
and i want to add a selector switch ( cd, pc, dvd, tv )
and an extra set of pre amping outputs to goto my headphone amp.

hmm you mentioned that this could be used as a guitar preamp :) hmm that could be cool, i ve started learning bass and need an for practicing at home :)

fdegrove

Hi,

The circuit on the picture above will work even better than #2
and can be arranged much the same way.

Where it says "stepped" on the picture you put the volume control.
It has a very good sonic reputation as a topology and the 6SN7 is one of the best sounding octal tubes around and still in production.

Moreover it can drive much longer interconnects than the anode follower as proposed in #2.

Gain will be more then ample for all known sources and you have all the required components values for it to work right here.
Might you have more questions,just ask.

At the end of the day it is your call,so I'm only ging advise here.

Cheers,:cool:

FBLEAGH

Ok so the above design uses both halves of a 6sn7gtb.
i s that right ?

and then i make another circuit the same for the left channel.

cool.

i understand ( basically ) what is going on in the bottom half but what is it doing in the top half , ie what is the second tube half doing ?

BTW thanks for all you help :)
just finshed reading http://www.eecs.umich.edu/~mmccorq/...troduction.html -- good intro to tubes, i know feel i ahve at least some understanding of whats going on :)

FBLEAGH

also what are good 6SN7GTB's to look for ?

RCA, GE, Raytheon ??

TubeHound

rca 5693 red base (6sn7) Arguably the best! $100-150 for NOS pairs.

DaveInVA

Or get some 12SX7's.....

Dave

fdegrove

Hi,

No need to shout it from the rooftops.
Seems to me someone is browsing a databook.

Indeed,a very good alternative.

No need to spend big bucks on tubes unless you want to build a very,very good preamp in the first place.
And you all know my recipe for that by now,don't you?

Worthy of consideration as well: *SU7.

There're bound to be others but I need to look them up.

As far as the diagram posted goes it is an SRPP (shunt regulated push-pull) in it simplest form and more than adequate for the task.

The top tube basically replaces the classic anode resistor and isolates the bottom half from the PSU.
Low output impedance and better dynamic range are the result but it is highly dependent on a well regulated PSU.

More about it later,:)

FBLEAGH

As I am fairly new to all of thiswhat would you guys suggest as a good tube to start with preferably easy to get hold of and reasonably cheap, but with some good tuberolling options later.

fdegrove wrote:

quote:

No need to spend big bucks on tubes unless you want to build a very,very good preamp in the first place.

would you be so kind as to point to where i can read about this recipe for preamps :)

Cheers guys, youve been a great help :)

To get your feet wet I would (personally) recommend that you get the Bottlehead Foreplay, build it, tweak it and then go for the "build it from scratch" preamp (or amp). The Bottlehead site can be found here:

http://www.bottlehead.com/

There is a forum with lots of experienced "Foreplay builders" as well as a plethora (did I say that?) of tried and true tweaks for the preamp. This will get you smelling solder fumes and get your feet wet and is a good design. Whichever path you choose, enjoy.

FBLEAGH

I just a response from harbuch on the transformer

$112.15 as EI or $77 as toroid.

add 10% for GST in Australia.

good price ??

As for G's post, i looked at the bottlehead foreplay and i know there is heaps of info out there on it , but i would rathe get right in there and build one from scratch. I've already learnt heaps just in researching this much :) I tend not to learn as much from kits as i dont have to nut it out to start with.

Cheers
Fbleagh

timc

Hi Fbleagh,

The transformer prices sound reasonable to me, better than
anything I have been able to find in Australia.

What was the spec? Was it similar to what Brett posted for your original project?
Primary: 230V
Secondary 1: 330V - 0 - 330V at 100 mA for the B+
Secondary 2: 6.3V at 2A for the GZ80
Secondary 3: 8V at 1.5 A for the signal tubes

Regards,
Tim

Joel

FBLEAGH,

Since you're new to tubes, please start off on the right foot and realize that there is no need to spend lots of money on tubes. Get a "used/tested good" pair of 6sn7's and be on your way. Also, two 6CG7, or even four 6J5's are options if you can't find cheap 6sn7's. Preamp tubes almost never go bad, and due to the number of people obsessed with "NOS", you can pick up used ones for very little cash. You will never know the difference (because there is none).
Just because RCA put a red colored base on a tube doesn't mean it "sounds" better, or works any better.

To answer your question, there is no difference in sound between brands either. Have fun.

Joel:umbrella:

FBLEAGH

timc, yeah it was the same spec as the one listed above

ie.
Primary: 230V
Secondary 1: 330V - 0 - 330V at 100 mA
Secondary 2: 6.3V at 2A
Secondary 3: 8V at 1.5 A

I am finding that there is much larger range of 12ax7's out there compared to the 6sn7's

are they a good tube ? I know there is a difference in pinouts etc but what sonic differnfce or different driving attributes do they have ?

fdegrove

Hi,

quote:

To answer your question, there is no difference in sound between brands either. Have fun.

You can just as well claim that half the population is deaf???

I'm not to claim one tube is better then the other,but saying there that there is difference?

Get real,please.:xeye:

Joel

There is a difference in gain. 6SN7 has an ideal voltage gain of 20, 12AX7's is 100. As far as "drive" - I assume you mean current capablity? - 12AX7's idle at under a milliamp, 6SN7's at 8 or 9.

Any old tube manual would be a good investment for you. They are cheap.

Joel

Joel

quote:

Originally posted by fdegrove
You can just as well claim that half the population is deaf???
I'm not to claim one tube is better then the other,but saying there that there is difference?

Frank, the phenomena is called a "mass delusion", and is quite well documented. It's like when 500 people see a UFO at the same time... :D

Get real? My thoughts exactly.

Cheers,
Joel

fdegrove

hi,

I agree,we are all deaf.:D

FBLEAGH

Ok i've been doing more thinking and research.

2 questions

1) instead of getting a custom xformer for this, is there a multi purpose tube transformer i can get ?? ie one i can use on later projects ?? i would imagine lots of secondaires that u can combine.

2) are there any other designs that are worth looking at ?? other topologies etc ?? I jsut want a nice sounding preamp, that i can tweak and modify later, but is a good starting point.

And the kit idea is pretty much out as i cna do this much much cheaper as DIY. I have my sources :)

Cheers
FBleagh

fdegrove

Hi,

1)I think it would best if some of the other members of the Sydney area would help you out on this.
Basically with a B+ of ~ 300VDC you can go a long way tweaking to your hearts' content.
Add a decent choke,some caps in the PSU and your halfway there to audio bliss.

2)There are probably a few hundred of those on the net already.
I'm not going to defend or dismiss one circuit over the other but what is needed for a linestage is:

A good PSU.

A good sounding medium mu tube.(mu is amplication factor,medium is all in the range of say 10 to 40)

If you want to stick to the 12**7 range the following tubes come to mind:
12AU7 12AY7 12BH7 and I'm sure there are some others that would fit the bill.

Low enough output impedance to drive a reasonable length of interconnect.

Ciao,;)

Joel

quote:

Originally posted by FBLEAGH
1) instead of getting a custom xformer for this, is there a multi purpose tube transformer i can get ?? ie one i can use on later projects??

First off, I agree with all that frank just mentioned. As far as the transformer - decide on the circuit, then pick a suitable one. There is no need whatsoever to go ordering custom transformers for a simple preamp project!
Something in the range of an 80-100mA rating will work for nearly any preamp circuit. But a preamp is a Class A amp, and a 40mA unit feeding 2 6SN7's will get hot.

quote:

2) are there any other designs that are worth looking at ?? other topologies etc ?? I jsut want a nice sounding preamp, that i can tweak and modify later, but is a good starting point.

There are plenty out there. I would think a 12AY7 driving a paralleled 6SN7 in each channel, capacitively coupled to the output, would be an excellent place to start. Doubles as a crystal clean headphone amp too. I just built one myself, and use it daily. I'm working up a drawing of the schematic to post on here maybe tomorrow.

Joel

Brett

quote:

Originally posted by Joel
First off, I agree with all that frank just mentioned. As far as the transformer - decide on the circuit, then pick a suitable one. There is no need whatsoever to go ordering custom transformers for a simple preamp project!

Joel,
Please point to a source of off the shelf tube transformer manufacturers in Australia.

miguel2

Hi there,

It depends on the gain that you need, but for a CDP input I think a very simple pre is the best choice here.

I have an EF86 pre, one stage in triode mode. It is simple, the tube is screened (but a bit microphonic) and the EF86 was made for audio applications. The PSU I use is by far more complicated than the amp section. I tried an 12AU7 approach but prefer the EF86.

The problem here can arise with output impedance. This circuit likes it over 200k but most power amps are around 47k. I am thinking on how to solve this without another stage.

As for the transformer it is custom made. If you have some factory near then its quite simple. Mine was cheaper then an Hammond.

Joel

quote:

Originally posted by Brett
Please point to a source of off the shelf tube transformer manufacturers in Australia.

Brett, please point to one in new york city!! haha. Have you heard of the internet?
Seriously, I can't buy any parts locally - I get everything through the mail, and I would assume you could do the same - even in Australia.

G'day mate.;)

fdegrove

Here is a source:

LANCROFT

I can't see anything on powerxformers but they should be able to build those as well.

There must be others but this is as close to Sydney I could get.

Took me 10 seconds to find,so what's the big deal?

Ciao,:D

Brett

quote:

Originally posted by Joel
Brett, please point to one in new york city!! haha. Have you heard of the internet?
Seriously, I can't buy any parts locally - I get everything through the mail, and I would assume you could do the same - even in Australia.

Considering the number of people who live in NY and surrounds is more than we have in a country with a land area about the same as the continental US, I'm surprised.

There is no one down here who has a stock product line like Hammond, so you just can't ring up Parts Express and have one here the next day like I could easily if I were in NYC. Sure you can get one from overseas via mail but airmail from the US is expensive, and surface takes forever (3 months) and transformers arent lightweight. Plus most of the transformers out of the US have a 100-120V primary which is of little use here. Hammond do make some universal primary models, but they cost a lot more.

Frank is correct, that Bob at Lancroft could make one, as could Harbuch, Tortech, Torema, Black Art, Turner and about a half dozen others I could think of. But no one has a stock line that I'm aware of so it will have to be made. So it's a custom.

See how There is no need whatsoever to go ordering custom transformers for a simple preamp project! makes no sense in an Australian context.

Joel

Ok Brett, I stand corrected.
No need to get so bitter.:(

miguel2

My custom 120 VA / 6 voltage outputs xformer costed around 30 euros. I think the shipment of one from the USA to Portugal would cost around that!

Joel

Try this out. It's been working good for me.

If you want to furthur simplify it, it will work nearly the same with only a single 6SN7. You're just raising the output impedance. I didn't notice much, if any, change in sound or performance. I use it with 63 ohm Sony headphones, and it can drive them to pain. It's also my only preamp.
12AY7 can be replaced in the schematic by almost anything - AT7, AX7, 5755, 5751, etc. I found 1/2 of another 6SN7 just didn't have enough gain though. My current version of it uses a 6C8-G.
Power supply consists of a 300V-0-300V secondary, rated at 100mA. Two filters of 500ohm resistor/100MF cap + 500/40MF. 5Y3GT rectifier. Filament line is center-tapped and grounded.:up:

Joel

Brett

Howdy FBLEAGH,

Things seem to have gotten a little off track, so I want to back up a bit and clarify some things. You said you wanted to make a line stage and use the project for the experience. No matter what project you choose you will gain valuable experience, but it is the part around the line stage spec that has me curious.

What do you plan to use the linestage with, ie, what sources do you have? What is the input impedance and sensitivity of the power amp you want to use?

My guess for the answers are, between a CDP (or other high level source) and a poweramp, >20kohm and about 1V. So you need a line stage with an output Z of less than 2k (lower the better) and a mA or two of drive at least. But what you DONT need is any gain. The Red Book standard for CDP outputs is 2Vrms, so you already have twice the voltage drive you need to send most power amps into clipping. So adding a stage with 20x gain just means you're going to have to waste all that gain away in the volume control. If you put a pot before the tube, you'll lose your signal to noise ratio, and one ofter the stage will give you a variable, but highish output impedance. A two stage line stage is idiocy. Even with a stage gain as low as 4 and a CDP as source, you will be able to overdrive EVERY amp I've ever seen, and some by over 20dB. I drive my poweramp with my CDP,DVD, VCR and tuner through a passive TVC, and am still 20dB or so from max even when it's exceptionally loud. At full gain I cannot bear to be in the room > 115dB SPL.

Almost every system has too much gain and too little headroom. Doing it DIY means you can optimise it for what you need, not trying to have a universal stage (like most manufacturers try to do) that does nothing at it's best in your system.

Any of the circuits like the basic anode follwers in the link you first posted, or the SRPP Frank suggested will work, but far from optimally. My suggestion would be to breadboard one of these on a simple chassis and listen for a while (the offer of the 6N1Ps still is there). Most of the passives can be reused as can the iron, so the experimental cost will only be a few dollars. Later try something like a CCS or choke loaded 12B4A or even a 6C19pi, both of which are cheap tubes and will give gains below 6, low output impedance and a huge amount of grunt to drive capacitive cables (if needed). Another option would be to use an output transformer. The CCS is the cheaper option, maybe $A150, and the choke loaded or transformer stage for about double that. All will easily exceed the performance of anything you can buy here for a lot more money.

Cheers

Joel

My mistake guys - I was in such a hurry to finish the drawing, I attached the ouput to the wrong point.
Here is the correct schematic. Any other mistakes?? :rolleyes:

Bas Horneman

Joel...

What do you use for drawing schematic..

I use the free program switchcad..serves me well...but i like the look of your schematics...

Cheers,
Bas

By the way..For the guy asking about the transformer...a decent price for something you saw would be around 50 US$.

Why don't you guys try to find a "ordinary" transformer shop..anyone can wind something like that in a jiffy really.

It's the output transformers that needs some practice.....

Joel

quote:

Originally posted by Brett
But what you DONT need is any gain. The Red Book standard for CDP outputs is 2Vrms, so you already have twice the voltage drive you need to send most power amps into clipping.

I actually agree with you for once. I don't think anyone who uses a cd player as source needs a preamp at all. But the guy asked for a preamp design - who am I to argue?

quote:

So adding a stage with 20x gain just means you're going to have to waste all that gain away in the volume control.

So? Better to throw away gain than to not have enough. And I found that when being used as a headphone amp, you DO need gain afterall. Even with a CD source.

quote:

A two stage line stage is idiocy.

Nice comment.

quote:

Any of the circuits like the basic anode follwers in the link you first posted, or the SRPP Frank suggested will work, but far from optimally.

"Far from optimally" in what sense? They are all proven designs.

Joel

quote:

Originally posted by Bas Horneman
What do you use for drawing schematic..

Hi Bas,

It's just a bunch of clipart files basically. The suite is called "TubePad", and I think you can find it here http://www.mines.uidaho.edu/~glowbugs/

You need to use microsoft Paint, in Windows, to put the drawings together though.

Bas Horneman

Thanks Joel..

Brett

But what you DONT need is any gain. The Red Book standard for CDP outputs is 2Vrms, so you already have twice the voltage drive you need to send most power amps into clipping.

I actually agree with you for once. I don't think anyone who uses a cd player as source needs a preamp at all. But the guy asked for a preamp design - who am I to argue?

Even a passive pre has to compromise between the impedances seen and driven adequately by the CDP output, the output impedance of the passive stage, the input Z of the power anp, and the assosciated capacitances in the betwork. Most CDP output stages harden considerably in sound as the loads get lower, often 20kohms is the minimum for most opamp output stages to drive (irrespective of what the datasheets might indicate), esp the 4558 and the 5534, the most common devices seen in commercial players.

So adding a stage with 20x gain just means you're going to have to waste all that gain away in the volume control.

So? Better to throw away gain than to not have enough. And I found that when being used as a headphone amp, you DO need gain afterall. Even with a CD source.

Why have all the gain thrown away? Why not have something better optimised to the gain requirements of the circuit? Most systems IME have way too much gain to start with, so few systems ever see full gain, even for those CDs etc that are mastered low. So, already with an excess, you throw it away in a pot before the stage, so your SNR is affected by maybe as much as 30dB.

What relevance does a headphone stage have to the original poster's question? You might also note you need the gain because you are losing some in the CF (< unity gain) and through the losses in the stage's output Z, esp driving a low impedance load.

Any of the circuits like the basic anode follwers in the link you first posted, or the SRPP Frank suggested will work, but far from optimally.

"Far from optimally" in what sense? They are all proven designs.

In all the circuits with a fair bit of gain, mainly noise as I've explained. Many of the anode followers have quite a high output Z.
The SRPP will vary it's distortion and sonic characteristics into different loads. A lowish output Z does not neccessarily equate to decent drive abilities.

Sure the circuits are proven, in the sense that they work. But a 1948 sidevalve V8 "works" and is reliable. But it hardly makes it a high performance design.

Joel

Brett,

I'm not quite sure why you are so opposed to the designs that Frank and I have offered him. This is supposed to be a simple, affordable project to get the guy started in DIY. You have now successfully clouded the entire discussion to the point where he and many others will now doubt that these are "good designs". Congratualtions.

Also,
1) I did not suggest that anyone use an input impedance of 20k. My schematic shows an input impedance of 100k - which is just peachy for a cd player to work into.
2) A "headphone amp" IS a preamp. I said you could use it as one.
3) I didn't mention that the CF loses gain because I assumed everyone knew that.
4) I hardly think the 20 or so gain of the 12AY7 is going to add 30db of noise! This is ludicrous.
4) If you have a better alternative for a newcomer to build, please offer it.

fdegrove

Hi Joel,

quote:

Here is the correct schematic. Any other mistakes??

Not a mistake but if you want to use this circuit as a linestage preamp wouldn't it be wise to add a second smaller value coupling cap and say a 100K shunt resistor.

You can then make both outputs switchable: headphone/preamp.

Loading down a lineoutput with a small value resistor is going to take down the input impedance of the amplifier offering a severe load.

Just my 2 eurothingies,;)

FBLEAGH

Thanks for the intersting discussion guys.

are hammond power xformers supposed to be really good of something ??

302AX 300-0-300 200mA 2.5v 2A, 5v 3A, 6.3v 6A
$250.50AUD + GST

why such a big difference between that and my custom one ?

fdegrove

Hi,

This what your Harbuch costs:

quote:

$112.15 as EI or $77 as toroid.

But has it the same specs as the Hammond one?

The more secondaries the more it is going to cost since the winding machine has to be stopped and so on.
That's labour and you end up paying for it.

The Hammond are fine but not exceptional IMO,the good thing is they have a range that is particularly suited for projects such as yours.

Ciao,;)

Brett

quote:

Originally posted by Joel
I'm not quite sure why you are so opposed to the designs that Frank and I have offered him. This is supposed to be a simple, affordable project to get the guy started in DIY. You have now successfully clouded the entire discussion to the point where he and many others will now doubt that these are "good designs". Congratualtions.

Joel, just like you, I'm entitled to my opinion, and I expressed it. I've also built and used many different topologies and know IME what works well. I find your comment to be very disingenuous: I said "My suggestion would be to breadboard one of these on a simple chassis and listen for a while (the offer of the 6N1Ps still is there). Most of the passives can be reused as can the iron, so the experimental cost will only be a few dollars. Later try something like ......". Maybe not everyone wants to stick with what you find appealling. Please also keep your sarcasm in check.

Also,
1) I did not suggest that anyone use an input impedance of 20k. My schematic shows an input impedance of 100k - which is just peachy for a cd player to work into.

I never suggested you did. My reference to 20k was in regards to questioning what sort of input Z his power amp might be. Many SS amps are less than this. Please ensure you take my comments in context in future, it makes you look less of a fool.

(2)A "headphone amp" IS a preamp. I said you could use it as one.

You used a mention of your headphone preamp as a justification for needing the increased gain in your previous reply to me. Hence my response. Also, as there is no requirement to drive an extremely low load for a line stage, ie a set of cans, why would you want to add a piece of sonic pig misery like a CF?

3) I didn't mention that the CF loses gain because I assumed everyone knew that.

Why would you assume that? The original poster is a newcomer, and neither you or I know what he knows. So I explained my reasoning for more than you.

4) I hardly think the 20 or so gain of the 12AY7 is going to add 30db of noise! This is ludicrous.

Comment in context please. With a stage gain of 20x or 26dB (none of which is needed), which you want to attenuate on the input to the stage, it can certainly increase the output SNR by a theoretical 26dB, possibly more depending on implementation and the setting of the volume control. The 30dB was a quick mental calculation and I was maybe off by a couple of dB. the 12AY7 isn't a particularly quiet tube IME.
I think I see though. Your reference to the 12AY7 indicates quite clearly that you are not upset that I choose something different to you, but that I am critiquing your design. I would not ordinarily suggest using a 12AY7 in preference to a 6SN7 which has better linearity. I couldn't care less what you listen to and like. But if I have tried it (numerous times) and found it wanting, I'm going to post it if I feel like it. There are much better sounding and measuring circuits out there than 2 stage CFs.

4) If you have a better alternative for a newcomer to build, please offer it.

I already have. No budget was mentioned, so I assumed it was modest, and suggested trying the SRPP and AF. Then try a CCS or choke loaded 12B4A. Neither of those are complex, the CL design being just as simple as an AF and has other advantages too. Kits are even available for the Bottlehead C4S (a type of CCS), and I could veroboard one in 15mins for about $A20 in parts.

I read the original poster's intent was to learn, as well as having a functional line stage. Just building an AF, or what you have and leaving it at that, will only have some educational value in construction and soldering. There are better circuits than an AF, SRPP and definitely a CF (though Kimmel suggests a pentode CF is excellent, and I can see why, I haven't tried it myself) for a linestage.

Brett

quote:

Originally posted by FBLEAGH
Thanks for the intersting discussion guys.

are hammond power xformers supposed to be really good of something ??

302AX 300-0-300 200mA 2.5v 2A, 5v 3A, 6.3v 6A
$250.50AUD + GST

why such a big difference between that and my custom one ?

The difference in price is due mainly to import duties, shipping and an Australian agent adding their markup. I have used Harbuch transformers many times in various industrial applications and found them of fine quality. Two of my vintage pieces run off a Harbuch step down trans. The only advantage to you purchasing the Hammond would be in having a lighter wallet to carry around, and the difference in cost between the two will pay for most of the passives and tubes probably.

Cheers

Joel

Brett, if you could refrain from openly calling me a "fool" in your posts in the future, I'd appreciate it. I'm sure I don't need to remind you about the forum rules.

You are certainly entitled to your opinion, and I think you already expressed that. Yet, once again, you offer no evidence to support any of your statements. The whole "cathode followers are bad" line is so old and tired. Where is the proof? Why exactly is building a kit of a CCS better for learning than any other circuit??

I'm not saying everyone should build an rc-coupled CF amp. But if you are going to offer criticism, please use facts so we can learn. If the circuit I posted is 3db down at 15kHz, I want to know! But, I suspect you are not capable of providing any real information to educate others - only vague, diffusing commentary on whatever's currently fashionable.:whazzat:

Joel

quote:

Originally posted by fdegrove
Not a mistake but if you want to use this circuit as a linestage preamp wouldn't it be wise to add a second smaller value coupling cap...

Hi Frank,
You mean across the ouput cap? I don't bypass electrolytics with film caps - it doesn't add anything I can measure, and it doesn't effect the sound, to my ears.

quote:

Loading down a lineoutput with a small value resistor is going to take down the input impedance of the amplifier offering a severe load.

I have to disagree. The input impedance of the power amp is fixed - at least in any amp I've seen. Changing any value in the preamp output will not change the fact that it must devlop it's voltage across the grid resistor in the amp's input.
The 2.7k is there to bleed off any stored charge in the big cap, as a protection.
If the follower is faced with developing its voltage across 3k or the impedence of the next tube's grid (500K? 1M?), which do you think it will chose? You can see how the small resistor becomes irrelevant.:nod:

Joel

fdegrove

Hi Joel,

quote:

You mean across the ouput cap? I don't bypass electrolytics with film caps - it doesn't add anything I can measure, and it doesn't effect the sound, to my ears.

No,that is not what I meant.
Having a second otput at the CF for specific use as a lineout using a smaller film or PIO cap in such a way that you do not have to couple through a large electrolytic.

If you consider the imput impedance of a tube at 100K a 5 micro F
cap should be adequate if you shunt that with a 100K.

Ciao,;)

Joel

Frank,
Yes, if you have no intention of driving phones, you can use a much smaller film cap at the output. If you think this makes an audible difference, you should do it.:up:
I just don't hear it.:hphones:

planet10

quote:

Originally posted by FBLEAGH
re hammond power xformers supposed to be really good of something ??

Think of Hammond as "Transformers R Us" -- they have a huge range and are relatively inexpensive in North America where they are made.

Anything heavy is best sourced locally.

dave

dice45

Peter,
not intending to interfere with you here, "... But I cannot be a judge here... " just stuffing you :)

Joel,

quote:

Originally posted by Joel
[B]... The whole "cathode followers are bad" line is so old and tired. Where is the proof? ...

my scanner is not yet up and running, otherwise i would post the page from the guru book:
Valley & Wallman, Vacuum Tube Amplifers,
Chapter 11: direct coupled amplifiers, p483, figure 11.21: Curve and circuits "Linearity of a cathode follower"
Bottom line: a CF ought to work into an infinite resisitance -- or atleast into one as high as possible. As the CF has to run on a certain quiescent current, you need either a huge load resistor to a huge negative supply voltage or a CCS.
The curves tell that clearly.
My practical experience: in most cases a CF with small load resistor sounds like ****. No urban legend but experience and worse, backupped by theory of the guru book.

DTopic: Joel, i tried to reach you twice today via email. Why do my emails bounce? I expect members to have valid email adresses. Not only during registration. Ok?

Gunderz

If you guys want to read end maybe learn more about buffer stages like the cathode follower etc I would recommend the October 1999 issue of Tube Cad.

http://www.tubecad.com/october99/

jh6you

Hi tube lovers

Years and years ago, much ill magazine info made me a bad habit to change different parts including capacitors for the good sound. Mostly I was disappointed with the results. I was beginning to feel that the changing them was a kind of changing my suits for department store owners. These days, for the good sound, I focus more on the basic circuit. One day, I might return back to the old habit. The probability is however considered very low.

JH

Ken L

On the topic of the thread

to Frank - the 6SN7 preamp circuit you posted seems simple and elegant. It is the best you know of?? And I don't wanna hear you repeat "you would never favor one circuit over another" You're enlightened now so you're gonna have make a statement - of some sort anyhow. ;)

By the way, you got a simple elegant PSU Circuit to go with it??Don't hand me the qualifications for a good power supply, give me a circuit - I'm serious. Being enlightened means you now have to do more such things - you have to do _more_ not less.:D

I have my "only half-kidding" hat on here.:rolleyes:

Anybody else? want to comment on those items? Please?

Mohan Varkey where are you?

thanks

Ken

I plan to use them to study and try to learn about circuitry:D

I bought a RCA Radiotron Designers Handbook and am trying to become technically more proficient.

planet10

1st let me state that i have not yet built a cathode follower...

But i have observed some "trillion" posts on the JoeList (where the guys eat tubes for breakfast with their possiage) on pros & cons of the device by guys that really know their stuff (we have a few of them here).

What i absorbed from this is that it is really hard to make a cathode follower sound good. But it is possible and a device that needs a low output impedance can indeed be better with one than without. But the key is to have active loads ... taken to extremes you get something like this Allen Wright follower (a fellow who believes in simple, but no simplier than is required to do the job) extracted from a schematic on his site.

dave

Brett

quote:

Originally posted by Ken L
to Frank - the 6SN7 preamp circuit you posted seems simple and elegant. It is the best you know of?? And I don't wanna hear you repeat "you would never favor one circuit over another" You're enlightened now so you're gonna have make a statement - of some sort anyhow. ;)

Hi Ken,
I'm not Frank, but I hope you won't mind my 2c.
The circuit is called an SRPP (Shunt Regulated Push Pull), or sometimes SEPP (Single Ended Push Pull). It can be very good into a purely resistive load of high impedance. Lots of capacitance in an interconnect, a low load impedance in the following stage or driving a power tube, and they can sound less than the best in my experience. Not make-you-run-back-to-SS-bad though.
For a great explanation of how this type of circuit works, take a look at <a href="http://www.tubecad.com/page4.html">Tubecad</a> and the article, SRPP Deconstructed.

quote:

By the way, you got a simple elegant PSU Circuit to go with it??Don't hand me the qualifications for a good power supply, give me a circuit - I'm serious.

For the B+, something like this is good.
<img src=http://www.users.globalnet.co.uk/~valveamp/images/CommoOE3.JPG>
For an SRPP, the heaters would need to be biased above ground because the max heater to cathode voltage is 200V. The top tube will have it's cathode at about 1/2 B+, or 150V in this example, which will probably be OK for a linestage. Biassing the heater for both halves to say 50V, will give an added margin of safety for the top tube, plus it also reduces noise and hum to a great extent.

I wouldn't bother with DC for a linestage unless the noise and hum were excessive, just use a power trans with a centre tapped filament, and using a resitive divider (bottom resistor capacitor bypassed) from the B+ to get the 50V, fed to the centre tap. Sorry, I'm not at home (babysitting), so I can't post a pic of the schematic I described.

Anyone who wants to experiment with tubes, would be advised to go to www.duncanamps.com and download copies of the <a href="http://213.123.250.245/cgi-bin/tdsl3.exe/">Tube Datasheet Locater </a> and the <a href="http://www.duncanamps.com/psud2/index.html">PSUD</a> power supply design simulator. Both are worth their weight in gold.

quote:

Anybody else? want to comment on those items? Please?

I'm not sure if you want something more specific, but I would also look at the standard common cathode circuits in the link FBLEAGH made in the first post, buy a whole lot of clipleads and experiment with some cheap tubes. I build my prototype amps on some old pieces of scrap plywood, and tack-solder components in place until I'm happy with it before putting it in a case and making it look pretty. If I bother at all.

quote:

I bought a RCA Radiotron Designers Handbook and am trying to become technically more proficient.

RDH, along with Valley and Wallman are the real reference works for tube audio. RDH can be a tough read though, like a textbook, so I would suggest going to Tubecad (link above) and starting with the earliest articles, read anything you might think interesting. Don't worry if you don't 'get it', just let it soak in, and come back and ask questions about anything you don't understand. John Broskie explains things very well IMO.

HTH
Cheers

Brett

dhaen

quote:

My point is: If Joel can�t hear the difference between capacitor x and capacitor y, he is right to say so

quote:

Cathode followers: Are a standard tool in the �electronic toolbox� for driving low impedances.

Only they don't (ref Valley and Wallman, Broskie etc). They have a low output impedance which doesn't mean they can drive a low impedance.

quote:

�Oh, what about SRPP (such as Franks nice circuit in this thread), or mu-follower� I hear people cry?
Well, they are implementations of Cathode Followers too! Are the designers (to many to mention), who use these circuits fools too?

Ultimately, this circuit comprises two grounded-cathode amplifiers, not the grounded-cathode amplifier and cathode follower that is commonly assumed. Both tubes provide voltage gain into the load and both tubes only offer their rp's in parallel as the main contributors to the output impedance. Broskie, Tubecad SRPP Deconstructed May 2002

quote:

You cannot look at Cathode followers in isolation: They are always fed by a stage, and feeding a stage.
The distortion of the feeding stage will be lower, because of the higher input impedance of the cathode follower.

Providing the ubiquitous grid resistor is not present in the CF's input.

quote:

The distortion of the stage being fed will be lower because of the low source impedance. Especially DHT�s.

A CF RC coupled to a DHT will have all the same issues as discussed before. DC coupled it will show an advantage once the DHT starts to flow grid current, as well as allowing the bias to be set for the power tube bt the CF. Most implementations of CFs into DHT power tubes are themselves quite a grunty tube.

Horses for courses, as the expression goes.

Re: The Moderators.
One of my criticisms of how the office was implemented from day one has been that there is no way to tell when one is on or off duty. I would like to see the wording under the individual moderator's name to vary from a standard title when off duty, to moderator, as well as the little policeman icon in the text, when on duty. If they want to post both audio and administrativa in the same thread, it should be in two seperate posts. I have seen the cooling affect of a moderators presence on a thread more than once where their presence as a member would not have. having to log in in two different ways would also allow a moment's reflection before continuing on a particular course of action.

Cheers

dhaen

Brett,

quote:

Absolutely, but if he is wrong in our opinion, we should still defend his right to express his own.

quote:

Only they don't (ref Valley and Wallman, Broskie etc). They have a low output impedance which doesn't mean they can drive a low impedance.

So are you saying that their use in such applications (mostly outside audio) is erroneous?
I've yet to see a video line (150ohm drive capability needed at DC to 6MHz) run from an anode. Surely this is a much more stringent application than any audio line driver.

SRPP:

quote:

Well I don't much want to start the "he said - she said" game, but I beleive Thorsten thought differently.
I think that ultimately we must look at the circuits ourselves and make the decision.

quote:

Providing the ubiquitous grid resistor is not present in the CF's input.

Interesting; I'll look into this one.

quote:

A CF RC coupled to a DHT will have all the same issues as discussed before.

I disagree. The CF will be useful at grounding the Miller capacitance at least.

quote:

Most implementations of CFs into DHT power tubes are themselves quite a grunty tube.

It all comes down to designing it right.
And of course the right horses on the right courses as you say.

Hey, this is getting good..;)

fdegrove

Hi Dave,

Thank you.
And yes,I deliberately shortened the quote line a bit.:angel:

quote:

You are enlightened! Missed that turn of events

Ken,

quote:

to Frank - the 6SN7 preamp circuit you posted seems simple and elegant. It is the best you know of?? And I don't wanna hear you repeat "you would never favor one circuit over another"

To answer the first part:

No it is not the best I know off,not at all.
OTH,that was not what the threadstarter asked anyway.
I pointed to that circuit as being an elegant solution avoiding both pitfalls of the circuits Simon Shilton shows at his website.
No more no less.
All that person wanted was a bit of hand holding with the PSU.
Funny how things can evolve,no?

To answer the second part:

All I can say is that I don't favour or dismiss anything as far as topologies go.
As Brett puts it correctly: "Horses for courses"

If you want my best preamp for use in your particular environment,make a WIKI of your requirements and off we go.

Brett,

Thanks for replying while I was :sleep:

Ciao,;)

Brett

dhaen

quote:

Where does that also give someone else the right to brand people as sufferring from a "mass delusion" , or just to dismiss their experience as impossible because they have an experience that is outside his?

Absolutely, but if he is wrong in our opinion, we should still defend his right to express his own.

I agree with your sentiment about freedom of speech.
However there is a difference between, "I think you are wrong, here's why...", or "My experience is different...." and shouting you are all deluded without being able to back it up. When you talk the talk, better be able to walk the walk. Now when someone like Thorsten makes a big claim, I stop and listen as he has enough 'runs on the board' with me to know he has looked at the topic under discussion and made a reasoned decision based upon analysis and experience. I don't often agree with Thorsten, but I almost invariably learn something from his posts.

quote:

Only they don't (ref Valley and Wallman, Broskie etc). They have a low output impedance which doesn't mean they can drive a low impedance.

So are you saying that their use in such applications (mostly outside audio) is erroneous?
I've yet to see a video line (150ohm drive capability needed at DC to 6MHz) run from an anode. Surely this is a much more stringent application than any audio line driver.

My emphasis was on can. I know what your saying, but it's been a long time since I looked at these from an RF perspective, and I don't have my references in front of me. I'll examine it again.

quote:

Ultimately, this circuit comprises two grounded-cathode amplifiers, not the grounded-cathode amplifier and cathode follower that is commonly assumed. Both tubes provide voltage gain into the load and both tubes only offer their rp's in parallel as the main contributors to the output impedance. Broskie, Tubecad SRPP Deconstructed May 2002

Well I don't much want to start the "he said - she said" game, but I beleive Thorsten thought differently.
I think that ultimately we must look at the circuits ourselves and make the decision.

Fairy snuff.
I haven't seen Thorsten's analysis, but I'd be interested in reading it. I like Broskies anaylses because I usually find them to be right on the money. Otherwise I agree we should analyse, listen and measure ourselves, because to my thinking audio is probably 50% art, 50% science.

quote:

A CF RC coupled to a DHT will have all the same issues as discussed before.

I disagree. The CF will be useful at grounding the Miller capacitance at least.

Point taken.

quote:

It all comes down to designing it right..

That is so true with everything.

quote:

Hey, this is getting good.

I agree. THIS is the sort of discussion I find most interesting and valuable.

Cheers

Brett

quote:

Originally posted by fdegrove
Brett,

Thanks for replying while I was :sleep:

Oh Great And Luminous Munificent One,
It was my pleasure

fdegrove

Hi,

quote:

Oh Great And Luminous Munificent One,

That fires up my glowdischarge tube.:D

Ta,

Peter Daniel

The out of context parts were moved to a new thread: http://www.diyaudio.com/forums/show...83008#post83008

dhaen

Thank you Peter, thats made it a lot better.

---------I'm gone!-------------

Cheers

Brett

you can't simply remove a section of something like that without removing it's meaning, because then it has no context. There were numerous posts before the exised section that were allowed to stand, that contain incorrect ot irrelevant information, yet they are still part of the original thread.

Very poor decision.

Peter Daniel

quote:

Originally posted by Brett
you can't simply remove a section of something like that without removing it's meaning, because then it has no context. There were numerous posts before the exised section that were allowed to stand, that contain incorrect ot irrelevant information, yet they are still part of the original thread.

Very poor decision.

Brett,

If you point out the posts that contain incorrect or irrelevant information I can further split this thread and make you happy as well.

I just removed all posts that IMHO didn't have anything to do with DIY Tube Preamp.;)
But I may have been wrong and I will truly appreciate your assistance.

Ken L

and for the link.

and for the explanations

helping me along the path

Thanks Frank for your input I will make a wiki for you to respond.

I also noticed your throwing water on the fires - see, this being Enlightened is good for you.

Later

Ken

FBLEAGH

great discussion guys :)

btw do i need matched tubes for this ?

fdegrove

Hi,

Not a necessity but it sure won't hurt either.
Always a good thing to have tubes matched.

BTW if there's anything else don't be afraid to ask...
I realize fully that when you post a question to a forum like this you end up with more QQ then answers.

I'd welcome info on your circuit of choice.

Thx,;)

FBLEAGH

Well i've decided im gonna try the schmeatic given earlier ( SRPP )

Looks interesting and should be fun to play with.

But jsut for interests sakewhat would you consider the best preamp design ?? i know it very much to a persons tastes but just wondering :) I figure the more i ask the more i learn :)

fdegrove

Hi,

Let's narrow it down:

SRPP preamp is fixed.
I'll present you the best accompanying PSU and guidance with the help of our co-members.

quote:

But jsut for interests sakewhat would you consider the best preamp design ?? i know it very much to a persons tastes but just wondering I figure the more i ask the more i learn

You will learn along the university of life.

Bear with me,we're going to design you a preamp that's pretty close to what you can possibly imagine as being the best.
If your on a budget you better set your posts now so we know where to cut corners.
After all cutting the right corners is where the ultimate engineering challenge lies.

Ken L:

Isn't this what you want?

It's a great opportunity to at least learn a bit a long the way.

I'll see tomorrow if such a project has been run before and if not we'll give it a go.

Cheers, ;)

Brett

quote:

Originally posted by FBLEAGH
great discussion guys :)

btw do i need matched tubes for this ?

No, you don't need matched tubes, but like Frank says, they certainly don't hurt.

However (you knew this was coming didn't you?) there's matching, and then there's matching. Most tubes you buy matched, are out on a simple tester, or test jig, and are "matched" if the anode current falls within a specified percentage, so if your circuit uses substantially different operating points to the tester's rig, they may not still be matched in your circuit. The better tube sellers use a curve tracer like a Sofia to trace the curves over a large varation of operating points and then computer match to a certain percentage over the whole range of the curves.

At <a href="http://www.diyhifisupply.com/tube_supplies/tube_supplies.html">diyhifisupply</a> there is a more detailed explanation of this with curves to show as examples. If it were me and I didn't have any 6SN7's, before I went playing pot luck with dealers or (gasp!) ebay, I'd look at the <a href="http://www.diyhifisupply.com/tube_supplies/china_nos_tubes.html">Chinese Military NOS 6N8P</a> they have there. By all accounts they are excellent at good prices. The owner of the store Brian posts here (bcherry) and is great to deal with. [no affiliation but satisfied customer]

Another great source is Gintaras at <a href="www.kwtubes.com">KW Tubes</a>. Again excellent to deal with, and fast delivery. Sells Russian tubes and passive parts.

Please post your findings about the circuit when completed.

Cheers

Brett

quote:

Originally posted by FBLEAGH
But jsut for interests sakewhat would you consider the best preamp design ?? i know it very much to a persons tastes but just wondering :)

My view on amplifier design is that it should be designed with it's compromises so that they are minimally disruptive to the music, and stable. Each stage should interact with the one on each side as little as possible, and be as linear as possibly both statically and dynamically, with a good margin of drive ability.

In all amplifiers/systems, use as little gain as is required, and have as much headroom in each stage as possible. Almost all systems are the other way around.

In a poweramp, the driverstage should have several dB of headroom, so that the output stage clips first, not the whole amp at once. Even heavy clipping will be less intrusive this way.

My current preamp is evolving into this (whether it's the ultimate or not I doubt it is, but it is excellent). All stages are differential balanced.

- Phono1 (MC): VSE 2SK170/6922 cascode, passive RIAA, CCS loaded 6H30 pi-DR running at 30mA (or VSE RTP5 linestage - undecided) then to selector incorporating absolute phase selection (AP is on all main inputs)
- Phono2 (Decca): 6h30pi-DR cascode, passive RIAA, CCS loaded 12B4A then to selector
- Phono3 (Strain gauge): Win Labs current source, Lundahl 1517 balancing transformer, then selector
- CD: Balanced in to selector
- Spare balanced line level in for reel to reels
- AV inputs have own selector then via 1517 transformer to main selector.

No real linestage, and this is all in one box, except for the PSU
After main selector, then via S&B TX1022 transformer volume controls to poweramps.

PSU is using FW damper diode tube rectification, LCLC filtering, CCS and shunt regulator on all stages. Phono stages are to be shuntregged, then current sourced for the filaments. Filaments have their own transformers (EI core same as B+), as do the damper diodes in the B+.

quote:

I figure the more i ask the more i learn :)

Highly recommended approach.

Also read all of Lynn Olson's <a href="http://www.aloha-audio.com/library/index.html">Library</a> (best place to start), www.tubecad.com, Allen Wright's Tube Preamp Cookbook and Morgan Jones's Tube Amplifiers.

When you can find them, also get copies of the Radiotron Designer's Handbook v4, Valley and Wallman Tube amplifiers and an ARRL handbook from the 50's.

That should keep you busy for a while. The learning curve is steep, but it will make sense eventually. Or so I've been told.
Cheers

FBLEAGH

quote:

If your on a budget you better set your posts now so we know where to cut corners.

While i dont want to spend $2000 on a preamp, i am more than happy to spend a reasonable amount on the project.
As this sis supposed to be a learning exercise at the same time I am not planning on rushing this project. I'm not in any great hurry and will take my time building it :)

Again thanks for all your help guys, you are definately helping a great deal :)

PS. on the other hand i cant wait to hear my Kyuss and QOTSA disc's through my new preamp :) :) :)

burnedfingers

I would just like to say hi and say that I have recently joined this merry group and have enjoyed all the posts that I've read. I have had a solid state background and have lately been bitten by the tube bug. I am a novice with tubes as all I can remember from childhood is they burnedfingers. The nickname burnedfingers. I am getting ready to gather parts for my first tube preamp and have come up with a thought about substituting a 5687 in place of the 12AX7 and retaining the 6SN7. Would this work and how would I have to modify the circuit to handle this change? I saw the circuit in one of the posts here. Any help or ideas would be appreciated. Thanks, Joe(burnedfingers)

Brett

Hi Joe, and welcome.

I'd strongly advise using the SRPP in preference to the two stage 12__7/6SN7. It's a better topology, and you don't need a fraction of the gain you'll get from using a 12ax7 as the driver, even accounting for the loss across the cathode follower. The 6SN7 is a much more linear tube than the 12__7 family too.
I think I have a 5687 SRPP design somewhere here too, and I'll try to find it and scan and post.

Power supplies have been discussed earlier in the thread, and I think Frank (fdegrove) is going to do more with the PSU design.

Cheers

burnedfingers

Brett

Thanks for the quick reply. I am always interested in looking at more designs. I will look forward to seeing your design. Tubes no doubt will be a new challenge and I just wish I hadn't steered away from them so long. I could also use some help in the power supply design end. Oh, a copy of Valve Amplifier is on its way to me.

Regards,
Joe

fdegrove

Hi,

Just an example:

PATS' ULTIMATE PREAMP

Cheers,;)

Brett

Frank,

I've seen that before. Looks good, but I'd remove the cathode bypass (or at least try it without) and change that humungous output cap to about 2u2 at a guess.

The circuit I was going to post is similar, but is one of Allen Wright's and is in the TPCB, not on the website, so I'd like to get permission before I post it.

If I can work out how to get my pix scanned, I'll do a PSU for it too.

fdegrove

Hi Brett,

Yes,it unusual to use a small cathode bypass and then an enormous coupling cap to regain bass.
At least that's what it looks like.

I think he wanted a compromise between a bit extra gain and good transient response.

quote:

If I can work out how to get my pix scanned, I'll do a PSU for it too.

If you don't mind doing that?
My docs on PSU regs aren't here yet but it comprised a EL86 as series pass,a ECC83 as a two stage error amp and a 5661A/85A2
voltage ref.
It makes all the difference on an SRPP.
If I can find something similar I'll post it.
Have you used similar circuitry already?

BTW.I've got some more SRPP's with an 5687 if you want to see them here I'll squeeze'em in.

Cheers,;)

planet10

quote:

Originally posted by fdegrove
PATS' ULTIMATE PREAMP

More Nanaimo talent!

dhean and i are talkin' Diana Krall on the spawn of this thread.

dave

fdegrove

Hi Dave,

You can always count on this guy to fit the bill.;)

Cherio,

fdegrove

Hi,

A plot of the 5687:

Cheers,;)

Joel

quote:

Originally posted by Brett
...I agree with your sentiment about freedom of speech.
However there is a difference between, "I think you are wrong, here's why...", or "My experience is different...." and shouting you are all deluded without being able to back it up.

Except when I talked about a "mass delusion", it was quite obviously in a joking manner. If you have no sense of humor, I feel sorry for you.

quote:

When you talk the talk, better be able to walk the walk. Now when someone like Thorsten makes a big claim, I stop and listen

What 'big claim' did I exactly make? It seems to me that you're the only one making sweeping generalizations. And yes, I have no doubt that when any fashionable "guru" speaks, you diligently listen.

quote:

because to my thinking audio is probably 50% art, 50% science.

And this is your whole problem. Art is painting a picture. Your painting is as valid as mine. Audio amplifiers are not art. They are machines. Either they work, or they don't. Everything they do can be measured, either now, or in the future with better tools. There is no mystery involved.
If you are truly serious about learning something on this forum, as you say you are - you will stop your childish posturing.

planet10

quote:

Originally posted by Joel
Everything they do can be measured, either now, or in the future with better tools. There is no mystery involved.

What can be measured only in the future, is a mystery now.

dave

fdegrove

Hi Joel,

Welcome back to the scene.

Hey Dave,

quote:

What can be measured only in the future, is a mystery now.

I'll have to ask my guru about that.:D

Cherio,:cool: