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Some questons on a DIY system.

Hi,

I guess that I'll start with a brief introduction....

I'm a 43 year old Canadian (Wpg) who's been living in Germany for the past 5 years. I'm. As a young man I was very interested in electronics, had read a number of electronics textbooks and had built several of the usual projects - simple transistor radios, microphone amplifiers and the like.

Now that the kids are a little older and I have the time to invest in a hobby, I've developed a renewed interest in electronics (second childhood??).

I would like to build a vacuum tube amplifier and a pair of suitable speakers - my budget for this is 1000 Euros. The room in which I will listen to this system is 3 metres x 3.5 metres in size, and my listening position will be about 1.5 - 2 metres in front of the speakers.

Important for me is to "learn" and to develop a hobby - as this keeps the mind young - and because of this I would rather not buy a prebuilt system or a kit.

I've been lurking on this forum and on several similar forums for quite some time now, and have downloaded and read a large number of the online resources regarding vacuum tubes and valve amplifiers. I'm in the process of reading Morgan Jone's two excellent books.

In real life I'm a molecular biologist and work everyday with apparatus that use power supplies capable of delivering up to 8000 V dc, with electrodes immersed in buckets of conductive liquids - so I've learned to respect working with high voltages.

What I have and what I would like to do....

I have a Dual 704 turntable / Shure M97xE MM cartridge / GramAmp 2 phono-pre, and a Denon-685 CD player.

I've spent a lot of time looking over and reading about a large number of potential amplifier projects, and after all of this I'm tempted to build Claus Byrith's 8 Watt EL-34 SET amp, http://www.lundahl.se/claus_b_se.html, with which I am sure that most of you are familiar. Reading his paper on this amplifier a few dozen times over has been an excellent learning experience for me. Although I have not been able to find a great deal of "user feedback" on this particular circuit, what I have read about it suggests that the amplifier is capable of providing "good sound for a moderate investment". I've sourced parts and, depending largely on the types of parts (capacitors, in particular) I think that I could build this one for around 600 Euros using good quality, although perhaps not the most expensive of, parts.

I was thinking that perhaps I could partner this with Fostex FE207E (95 dB sensitivity) fullrange drivers in either MLTL or BR cabinets, which I could build for around 300 Euros.

So this setup should fit into my budget, and from what I've read should sound ok.

I've not mentioned a linestage - ideally, in my budget, I would like to pass on this option initially. So to this a couple of questions:

--- begin questions ---

The first stage of the this amplifier is configured as a cathode - follower. I understand that this stage acts as an impedance buffer between the preceeding and following stages.

Am I correct in assuming that I will be able to connect the outputs of my CD player (10kOhm) into the amp directly because of this?

The phono pre as well (1.6kOhm)?

I would then substitute 100kOhm log pots for the 100kOhm resistors across the inputs and leave the rest of the circuit as is?

Could I then also place a source selector switch into the circuit to switch between CDP / TT?

--- end questions (for now) ---

I'll probably start construction during the winter. The reasons for my starting to think about this and to ask some questions now are two fold, (A) I want to be sure of exactly what I am doing and why before I pick up a soldering iron and (B) it will give me some time to start ordering the parts "in a number of orders spaced out over time" - I think that this strategy will elicit a number of smaller roars from Mrs. Griz as opposed to one HUUUUGE roar (and the possibility of a swipe) if I bought all of the stuff in one go..... ;)

I'm sure that I'm going to have a lot more questions, and I'm looking forward to your comments and suggestions.

Thanks for listening!

Griz
 

SY

diyAudio Moderator Emeritus
2002-10-24 10:19 pm
Chicagoland
www.SYclotron.com
Molecular biology. Cool. I'm so ignorant of it that I believe that a replicon is a little green guy from Ireland.

Ahem. Even without the cathode follower, your CD player could have driven the circuit directly. A typical output impedance of a modern source is on the order of one or two hundred ohms, which will compare quite favorably to the output impedance of a CF. The 10K figure you cite is probably the rated load, not the source impedance.

You absolutely can incorporate source switching and volume control at the input of the CF and in fact, that's a better option for your planned system than a stand-alone line stage.
 
I'm sure that the circuit you have in mind will work well enough, but lots of other possibilities are open to you which would cost about the same and might sound nicer.
If you are designing the speakers with the fostex drivers you can expect them to be fairly efficient (more so if you use horn loading). This would widen the choice of amplifiers as you could go for something with very low power like a 2a3 amp. Something like this maybe? Nice simple direct coupled design with no negative feedback :)
 
SY said:
Molecular biology. Cool. I'm so ignorant of it that I believe that a replicon is a little green guy from Ireland.


I wouldn't worry. Until a short while ago I thought that "cathode followers" were members of some religious cult.

Now I know better. It's the "cathode follower followers" that are members....

Ahem. Even without the cathode follower, your CD player could have driven the circuit directly. A typical output impedance of a modern source is on the order of one or two hundred ohms, which will compare quite favorably to the output impedance of a CF. The 10K figure you cite is probably the rated load, not the source impedance.

Ok - thanks for clearing that up. So why would someone put a CF as the first stage of an amp? What type of source would have a high output impedance?

You absolutely can incorporate source switching and volume control at the input of the CF and in fact, that's a better option for your planned system than a stand-alone line stage.

That's cool - it will save me some bucks.

Thanks for listening!

Griz
 
martinab2 said:
I'm sure that the circuit you have in mind will work well enough, but lots of other possibilities are open to you which would cost about the same and might sound nicer.
If you are designing the speakers with the fostex drivers you can expect them to be fairly efficient (more so if you use horn loading). This would widen the choice of amplifiers as you could go for something with very low power like a 2a3 amp. Something like this maybe? Nice simple direct coupled design with no negative feedback :)

Hey, thanks for the tip.

There are indeed an amazing number of possibilites - I was positively surprised when I started to look around. Who would have thought?

I've looked at a lot of 2a3 circuits, including the Free Lunch. I'm sure that it's a great amp, and all of the "propaganda" I've read up till now support the notion that the 2a3 is indeed an excellent tube to us in a SET amp - but I have my mind pretty much set on the Byrith amp.

I kind of like the notion of using a moderate, adjustable amount of NFB - as a tool. Mr. Byrith makes a convincing argument in his paper, at least for me. And the LM3 - type of connection seems like a pretty cool idea.

I also suspect that horns are a little out of my league in terms of woodworking skills. A simple MLTL or BR cabinet will just have to do.

Thanks for listening!

Griz
 
rdf said:
If German ceilings share height dimensions with Winterpeg homes, put aside a few Euros for DIY room treatment. ~3 x 3 x 3.5 metres will make even bass response a challenge.

Hmm...

I'm not so sure what you mean by this.

The room is too large?

Too square?

Enlighten me please - I'm interested.

What I can tell you that German rooms are much different than Winterpeg homes - they are made of stone, brick walls and concrete-based floors. Even the ceilings are bricked. None of this wood and gyprock.

I'm sure that this makes a difference, too...

Thanks for listening!

Griz
 
SY said:


I suspect in this case that the CF was put in so that the feedback circuit would be driven by a known source impedance. The clue is the 22K resistor between the CF and the next stage.


Ok, thanks, I got it. Mr. Byrith actually explains this, but it took your rephrasing to make it "click".

"The 150kOhm resistor is the upper limb of a voltage divider where the lower limb consists of the 100kOhm resistance of the potentiometer in parallel with the 22kOhm resistor in series with the output resistance of the signal source. This output resistance is now playing a major role in the feedback circuit, and since I don't want that, I use the second half of the ECC83 as a cathode follower forming a buffer stage......If the amplifier is to be fed with a signal source with a low output resistance (preferably less than 1 / 10 of the 22kOhm resistor the cathode-follower may be omitted ad the signal applied directly to the 22kOhm resistor. If a potentiometer with a total resistance of 10kOhm is used in front of the amplifier, and this potentiometer is fed from a signal source of maximum 2kOhm, the output resistance from the wiper will be min....."

It all makes sense now. The cathode follower is needed if I plan to use a 100kOhm pot as a volume control.

Many thanks.

Griz
 

rdf

Member
2004-06-21 8:04 am
big smoke
Griz said:


Hmm...

I'm not so sure what you mean by this.

The room is too large?

Too square?

Griz

Bingo. All three opposing wall pairs reinforce bass at the approximately the same frequency, in the range of 100 Hz by quick mental calculation. You're also right materials make a huge difference. In this case you can expect much lower acoustic loss and more bass buildup than with typical North American construction. If the room is heavily furnished high frequencies will be damped and the room sound will strongly tend to the warm side. Depending on taste you might want to avoid equipment which follows suit.
 

wfmali

Member
2003-05-09 8:15 pm
Hmm...

I'm not so sure what you mean by this.

The room is too large?

Too square?

Griz,
you might try the following link. I gives you access to a program that calculates the acoustic behavior of your room. I tried it, and it really works pretty good. It is in german, but since you live there I guess you will figure out how to use it.

http://www.stereoplay.de/stp/raumakustikrechner#

By the way, when I left my brick house in Germany last year and moved into my nice US home, I had a hard time setting my equipment up for the different wall material here - it really makes a difference.
Marcus :)
 
wfmali said:


Griz,
you might try the following link. I gives you access to a program that calculates the acoustic behavior of your room. I tried it, and it really works pretty good. It is in german, but since you live there I guess you will figure out how to use it.

http://www.stereoplay.de/stp/raumakustikrechner#

By the way, when I left my brick house in Germany last year and moved into my nice US home, I had a hard time setting my equipment up for the different wall material here - it really makes a difference.
Marcus :)

Dankeschön for the link, quite a useful little program.

The room is going to be a compromise, anyways. It will also function as a study - so quite a large are of shelving is needed for books, and a computer desk is going in the room as well.

I'm thinking that the best approach here would be to put a large area of shelving against the wall behind the speakers, as opposed to on the sides of the room. The stereo would go in here plus all of the books etc. This should damp a lot of reflections off of the front wall.

The computer desk stuff goes along the opposite wall, in the corner. A table / chair in the opposite corner.

Tiled floor, no carpet.

Should be reasonable, or?

We're renovating the house, built in the 50's. I've renovated American homes before, and I had a lot to learn doing this here. Moving a wall made of wooden studs/drywall is much easier than moving a brick wall.... Taking out a floor made of plywood is much simpler than taking one out made of sand and concrete.... I'm starting to become intimately familiar with the workings of a jackhammer!

Thanks again for the link.

Griz
 
Griz,

Your problem, I think, will be not so much reflections, which can be treated away, as you suggest, but (multiple) standing waves (at the same frequencies).
I you encounter this problem, one trick you can try is to place the stereo diagonally in the room. This sometimes helps a bit in rooms that are too symmetrical, and thus become boomy.
(Sorry if this is slightly o. t. on the Tubes forum!)

Morgan L