Stereo Amp Project

[Topherdk]

Hello!

Project Link:
https://el34world.com/projects/StereoPowerAmp1.htm


Schematics:
https://el34world.com/projects/images/stereopowerampschematic.gif


This is my first ever amp build. I am building it for my record player.

Just have a few questions that would help me greatly.

1. What pre amp tubes should I get for the Y1, Y2, Y3?

2. I am working on a BOM so I can post it eventually, but if anyone has one already that would be great. Since I am new to this, not sure I would get it right.

3. Also I want the two channels going to one output. How do I do this?

[shooter]

the "Y" is actually a "V"  (Vacuum tube)


the biasing indicate probably used 12AX7's 
I prefer 12AU7's for audio amps, especially with 84's which require very little drive signal to reach "max-clean" output.

[Merlin]

3. Also I want the two channels going to one output.

What do you mean?

[Topherdk]

This is two channels, each going to their volume knob and own output. I would like them to each have their own volume knob but go to one output jack.

[Merlin]

You mean one speaker, like this?

[Willabe]

You mean one speaker, like this?

No, it's a stereo amp he want's to build for his record player. Look at his 1st post links.

[Williamblake]

As you appearently are still deciding on the details of your circuit i would suggest building one channel only and test with a line signal how it drives your speaker.

[Merlin]

No, it's a stereo amp he want's to build for his record player. Look at his 1st post links.

Then what does he mean by "I want the two channels going to one output"?

[shooter]

maybe just in the living room instead of bedroom and living room?   

[scstill]

The schematic in reply #1 shows two inputs each with their own amp (common PS)
but shouldn't stereo be a single input (like a turntable) into two amps?
Is this what is being asked for (one output was referred to maybe it should be one input)?

Also if the input is a turntable (is that what is referred to as a "record Player"?)
shouldn't linear non-distortion design be considered?

Although it would be cool to build a stereo guitar amp...

[shooter]

I see only 1 input per "side", each feeding a separate PI and PA
so left channel top, right channel bottom...stereo.


ya, it should be "designed" as a class A with "limits" so you can't push it into A/B (overdrive)


if he wants L/R in-preamp, a common PA as Merlin is asking about, then it's what we called "High fidelity" in the way back days.

[Willabe]

No, it's a stereo amp he want's to build for his record player. Look at his 1st post links.

Then what does he mean by "I want the two channels going to one output"?

I don't know. But the link shows a true stereo amp, 2 channels with 2 outputs. 

[Rontone]

Hi Topherdk,

I don't want to over-complicate things, but what kind of setup were you planning to use before the Stereo Power Amplifier?

Is it a moving coil or moving magnet cartridge on the player etc, or is the record player running into a Preamp/Phono stage or any other equipment you already have before it gets to the amplifier?

Or are you wanting to build a fully integrated amplifier to just plug the record player straight into?

[AlNewman]

Maybe you could run a load on both channels, with a line out, and mix the 2 channels into another preamp?
 

[Topherdk]

Hi All, thank you for the information! This is very educational.

Some information that has been requested:

Turntable: AudioTechnica AT-LP60
https://www.audio-technica.com/en-us/at-lp60

It has a built in switchable phono preamp

Integral Dual Magnet™ phono cartridge

My current set up is:
TV (with optical to RCA adapter into Stereo Receiver)
Turntable via RCA into Stereo Receiver
Stereo Receiver: Nikko NR-550
https://reverb.com/item/45278902-nikko-nr-550-am-fm-stereo-receiver-35wpc
Then I have two Bose speakers wired into the red and black clips on the A Speakers spot.

The stereo receiver is having some issues and I wanted to build a tube amp to replace it.

[Willabe]

If you want only 1 output, then you don't need a stereo amp.

What Merlin showed you in reply #4, a single amp but with 2 input channels sounds like it will work for what you want. 

[acheld]

My personal take on this is that Doug's stereo guitar amp will not be the most appropriate for hi-fi.  It will produce sound, but there will be a ton of distortion.

Second, this would be a very ambitious first build for someone with no experience.   High likelihood of multiple errors, heartache and a failed build.   Not impossible, but it will be painful for the builder.

IIRC, Bose speakers do require a fair amount of power (though he did not specify the model, or power requirement).  I guess 18W per channel would work, but this amp will be overdriving at much less power, I would think.

Having been down this rabbit hole myself, my suggestion to to find a more suitable design from the DIY-hifi world.   This guy has really great designs (https://www.analogethos.com/_files/ugd/c50b96_d62fa62cd5cc4e05a4f4a40f0503692d.pdf), but maybe not enough power for Bose.

I think the first step in this project is to define what power you need to drive your speakers, and go from there.

[shooter]

Fwiw;
this is my current setup, both home-brew Monoblocks, the "main" amp left, mixes L/R into a single-board chip amp I built, (splits the signal out for the 2nd mono).  Drives the 2 bookshelf Klipsch  ~~~~ 15W Audio.  The tube amp was a guitar amp re-worked for audio friendly use.  It drives the 4.5" Mid-bass, currently using 6K6 PP at ~~~ 5W audio.


the system won't win blow your face off, but plenty loud enough you won't be talking normal when it's cranked.

[scstill]

This guy has really great designs (https://www.analogethos.com/_files/ugd/c50b96_d62fa62cd5cc4e05a4f4a40f0503692d.pdf)

nice compact stereo design...
I have a few newbie HiFi design questions on the schematic in the link...

1) What is the purpose of the 180k resistor from the EL34 plate to the front of the .22uf coupling cap?

2) In HiFi is there any reason that the SE transformer has a separate screen tap rather than just taking it from the PS

3) Are there any tube rectifier HiFi amps out there, or is that frowned on do to the sag?

4) Do HiFi guys go PP when they want more power (AB concerns right) or do they just build a bigger SE?

5) Is there a distinct HiFi advantage to having a choke vs resistor in the PS? and why the 220k bleeder?

[bmccowan]

Agree with the others that a guitar amp circuit is not a good starting place for an audio mono or stereo amp. Also agree that you will be a lot happier with tube friendly (very efficient) speakers. Many good stereo tube amps use EL84s for power tubes, so you are not that far off.
Here are three good sources of info, including schematics and building advice. You will enjoy the research I think.
You also might be able to find good used equipment that needs help - but the days of finding cheap deals are about gone.
https://diyaudioprojects.com/Tubes/tubes.htm
https://www.cascadetubes.com/
http://www.pmillett.com/

[shooter]

2)  the OT tap is called UL (Ultra-linear)  typically tapped at 40%, it keeps G2 "in check" giving you a sorta hybrid between pentode and triode.


3) there are/were,  The cork-sniffers want ALL tube layouts, the PS is still "stiff"


4) the "purists" will say SE is the only option  PP, well designed works just fine for the other 97%  SE favors odd harmonics while PP favors even (I could have those backward)


back to the garden!

[Rontone]

3) Are there any tube rectifier HiFi amps out there, or is that frowned on do to the sag?

Leak Stereo 20 and Quad II are all tube, and both sound incredible,

A good phono stage into a Leak Stereo 20, into a pair of Heybrook HB-3 speakers [or Westlake Audio monitors if your in the US, its all about those Seas drivers, especially the mid driver] is a magical thing

[bmccowan]

I have rebuilt several 60s era tube stereo amps from Fisher, Dynaco, and Grommes. All are tube rectified and all sound great, with subtle differences. All were relatively easy to work on and schematics were easy to find. And the simpler the circuit the better the sound IMO. My current favorite is a pair of EL84 monoblocs from a Fisher console. I drive them with a simple all tube preamp. This is how I cut back on my tube guitar amp addiction

[mresistor]

Seas, Vifa   awesome drivers for sure.. Fostex ain't too bad either.    Madisound has a good selection of drivers.

[shooter]

current favorite is a pair of EL84 monoblocs

yep, my best Audiophile...HiFi build was a quad '84 mono-block driving a pair of Audio Nirvana's

[scstill]

Hey Shooter are you a painter?
Floor looks like artist studio

[shooter]

 
17 years I gave it a shot!
here's an old thread


https://el34world.com/Forum/index.php?topic=21390.0

[DummyLoad]

Build a Dynaco ST35 or ST70 clone? Some clone stuff made for either, transformers, chassis, etc. Edcor sells a transformer set for ST35, build into a PiMetal enclosure.

Transformers

Rackmount Chassis


--Pete

[scstill]

Interesting how Dynaco has the printed circuit board exposed on the top of the chassis.
https://www.getdynaco.com/tube-amplifiers/ready-to-ship/st-35-tube-amplifier
Do DIY clone builders use the PCB?

I prefer Hand Point to Point
Are any point to point wiring designs in HiFi? or do they always use a board?
Should the same layout practices as in guitar amps be followed in HiFi?

Dynaco SS Rectifier...
https://diyaudioprojects.com/Schematics/Dynaco-ST35-Tube-Amp-Schematic.htmDynaco option alot expensive components; is it gimmick or worth it?   
https://www.getdynaco.com/upgrades-options/st-35-options
They design the preamp with the tubes inside the chassis seems hot.
https://www.getdynaco.com/pas-tube-preamps/ready-to-ship

[bmccowan]

Interesting how Dynaco has the printed circuit board exposed on the top of the chassis.
https://www.getdynaco.com/tube-amplifiers/ready-to-ship/st-35-tube-amplifier
Do DIY clone builders use the PCB?

I prefer Hand Point to Point
Are any point to point wiring designs in HiFi? or do they always use a board?
Should the same layout practices as in guitar amps be followed in HiFi?

Dynaco SS Rectifier...
https://diyaudioprojects.com/Schematics/Dynaco-ST35-Tube-Amp-Schematic.htmDynaco option alot expensive components; is it gimmick or worth it?   
https://www.getdynaco.com/upgrades-options/st-35-options
They design the preamp with the tubes inside the chassis seems hot.
https://www.getdynaco.com/pas-tube-preamps/ready-to-ship

I think most Dynaco clone builders use the pcb board. I rebuilt a pair of MK-4s and thats what I did.
There are many point-to-point diy tube power amps and preamps out there. Explore the rabbit holes I linked to in post #19.
The layout practices in HiFi amps almost never follow the same practices as in guitar amps. Unless its a guitar amp builder building the HiFi amp, turret/eyelet boards are rare IME. Full point to point or tag strips are common. Many vintage HiFi amps are point to point rats nests that give vintage Gibson amps a run for their money.

[kagliostro]

HiFi Is not in my Know How, however, if you are looking for good PTP, very well documented projects, do a search among Mullard projects book, you'll find something of interesting for sure

https://www.worldradiohistory.com/BOOKSHELF-ARH/Circuits-For-Audio-Amplifiers-Mullard-1963%20.pdf

Here an example of what you can find

http://www.r-type.org/articles/art-003h.htm

Franco

[scstill]

compared to radio and guitar P2P wiring those Mullard HiFi layouts are really clean.
Great attention to detail. Does this attention result in operational benefit? or just nice to look at?

Mullard refers to "tagboard" for mounting their components.
I recently discovered something similar at Amplified Parts and am using on Supro clone and Prew42
Maybe on my first HiFi build too
https://www.amplifiedparts.com/products/turret-strip-24-lugs-two-rows-u-style-extra-dense

Would it still be considered "point to point" wiring when using a board like this? Or just hand wired?

[kagliostro]

A real PTP is without any kind of board, but very often we refer to PTP also if there is a mix of real PTP and Tag Strips

Later, if I find the link, I'll post one referring to different construction methods

EDIT: See here

https://mhuss.com/AmpInfo/

Franco

[shooter]

Does this attention result in operational benefit? or just nice to look at?

depends on your skool'n


a rats nest that sounds exceptional beats looks good every day.


"best practices", right angle bends, sensitive signals separate from dirty signals....Etal, serve's you well.


just guessing but most early designers came from "classical Engineers" where "clean layouts" is impetrative in the world of RF.  those jobs were all full, so the engineer got a gig in audio and used those "RF rules" in audio.
or
wound up working for Gibson, inhaled, got creative 

[kagliostro]

A well planned layout is mandatory to try to avoid problems of Humm, captured and amplified noise and oscillations

Franco

[scstill]

Have always been fascinated by the Arcturus blue tubes. Have a few in stash.
A few years ago I came across this design and have been considering it.
https://www.stonevintageradio.com/description.php?II=964&UID=
I love the look but worry about the vintage tubes delivering such low power.
The guy sent a better schematic than what is online; says it sounds really good. 
Worth the build effort? Would the pricey James OTs be worth it?

[shooter]

Worth the build effort? Would the pricey James OTs be worth it?

worth isn't quantifiable by anyone but you


what's "pricey"?  don't know what James gets, do know that all the audio, n most guitar builds I used EDCOR iron and was quite happy with my investment.  I choose audio OT's rated about 2X amps "max-power," so if that's a 4W(?) go with a 10-15W Class A OT


both my audio amps are in the <10W range, more than enough to hear the music anywhere in the house

[kagliostro]

As a non HiFi guy what I can say is that the top of that amp has a nice look

But inside ..... a very poor one (referred to the layout and look)

As Shooter say, with few W of power you can be comfortable or not, to me what I think important is the quality not the quantity, so a 3W to 5W may be comfortable if there is quality

One thing will be mandatory to me, don't privilegiate aestetic in place of substance

Franco

[scstill]

Only can find James transformers second hand. Maybe not in biz anymore??
EDCOR might be the way to go. Have some investigation to do.

I agree with the low wattage comments as most of my low wattage guitar amps sound great.
I'm not really a HiFi guy either, just play music on my phone through Sonos
But it seems like a nice and different project.
as well I'm running out of guitar amp space....

[acheld]

Edcor's are great, but so are Hammond if properly spec'd.   

Since this is your first foray into hi-fi, I'd strongly suggest building your power amp first -- you can always send line-in from your existing setup.  Then build your pre-amp. 

Simple but well known circuit attached, and photo of completed project.   Apologies for the dust!  Amp sounds great at 7 watts, though I am listening at 3 watts normally.  If you need more power, P-P is the way to go.

And yeah, those Arcturus blue tubes are the bling!

Edit:  Oops.  Pic now attached.  The Hammond PT is a 290Dx.   

I don't truly understand that 180k resistor and its connection to the grid.  (I'd better not guess. . .). It's Hi-Fi !

[scstill]

Simple but well known circuit attached, and photo of completed project.   Apologies for the dust!  Amp sounds great at 7 watts, though I am listening at 3 watts normally.  If you need more power, P-P is the way to go.

No Picture attached....
What is the purpose of the 180k between the plates?
is the OT a Hammond model?
Seems like the SS diodes could be relaced by a 6v tube rectifier.

[kagliostro]

On SE amps there is no advantage using a vacuum rectifier in place of Solid State rectifier

Franco

[shooter]

the purist tube audiophiles would disagree, not with science or observation, nope, it's the ear, it hears things sane people can't 


this is the PS I used in my best tube audio build, can't find the #'s but it was salient both with the ear but the scope did show milli's AC wander'n about.


the 2nd one I use  parts for SS audio

[kagliostro]

If you want to exceed use UF diodes instead of 1N diodes

UF4007 instead of 1N4007 (for higher power amps UF5408 instead of 1N5408)

Franco

[scstill]

this is the PS I used in my best tube audio build, can't find the #'s but it was salient both with the ear but the scope did show milli's AC wander'n about.

I like this design and such a clear hand draw almost better than my schematic drawing tool :-)
I hope you don't mind a few questions to help me understand this design (always learning)

Would you recommend keeping the SS rectifiers or flip for a 6v tube with reduced caps.
Are the diodes/resistor hanging off the ground of the Preamp HT Cap to reduce a ground loop?
You have two PT primaries is this to further isolate the filaments from the HT and are both 6v secondaries run off the same primary?
Do you have a 120v pilot light or is that a meter?
have you ever compared noise reduction of DC heater vs AC?

Did you go with Octal 6sn7 rather than a 9pin like a 12au7 for better audio performance
Why do you vary/alternate the cathode bypass on the power tubes?
Why didn't you connect the Power and Pre plates with a large resistor as I've seen on some other hifi's?
Says NFB not connected, what was your thinking and did it show any value in testing?

[shooter]

I like SS rectifiers because they are more "stable" than tube....sag, etal..SS does tend to throw transient spikes though, which is "solved" with caps across the diodes.


the diodes form a "ground lift", the idea as I understand it....make the "ground plane" referenced "above" any sneaky's lurking in the grass (chassis ground, or dirty ground).


the power indicator was a diode/resistor pack meant to replace neon


I might have gave up on DC filaments, (not always good at going back n cleaning up my revisions)  IIRC i messed around there awhile
sorta kinda stole the filament section from a VOX AC30C2


the PA section needs very little drive signal, so the 6sn7 has plenty of gain, the 2nd stage, I was trying to get the input signal "centered" to avoid asymmetry, like I said before, the components might have been changed, possibly even a CF as the 2nd stage if my drive AC was good. 
the point in an audio pre is to get the cleanest (Sig/noise), and "balanced" output signal that can be fed into the PA


don't recall why i didn't use NFB or the "logic" behind messing with caps.  I've since found anything much bigger than 50uF on a clean amp is wasted effort for the most part.
typically when I go bigger, i'm trying to "hide" a problem I can't find