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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 1:44 am 
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Pbpix wrote:
Flipperhome wrote:
Because the only thing I knew was you belatedly tacked an ISO onto the existing schematic 'for show' to get it past DIYaudio. That was the only thing I was "fully aware" of.

YEP... and you admited you KNEW the transformer was added ... so what was there to still criticize???

NOTHING.

so ... just apologize.
Tacking an ISO onto a schematic for show isn't 'adding' one.


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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 1:52 am 
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Flipperhome wrote:
Pbpix wrote:
Flipperhome wrote:
Because the only thing I knew was you belatedly tacked an ISO onto the existing schematic 'for show' to get it past DIYaudio. That was the only thing I was "fully aware" of.

YEP... and you admited you KNEW the transformer was added ... so what was there to still criticize???

NOTHING.

so ... just apologize.
Tacking an ISO onto a schematic for show isn't 'adding' one.

But you knew it was there.
Image

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 7:06 pm 
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Update:

Ok....
Last night (wee hours) I dug up the breadboard I was using last month or so for the 6SH7 - 6V6 version and got it back up running with my 250v bench supply.

Attachment:
6SH7 amp.jpg
6SH7 amp.jpg [ 52.74 KiB | Viewed 360 times ]


I wanted to first test with that very similar basic breadboard layout just to make sure all wires were still correct and to reacquaint myself myself with which circuit points are which again.
I also wanted to listen to it again to get a bit of a comparrison level in my mind as I try to see how the newer 6SL7 version will stack up.
And, of course, the 6SH7 works very nicely and sounds great.


Okay:
So then I removed the 6SH7 pentode from the circuit and started re-wiring for the 6SL7.

The "Lacewood amp", as published, was intended to take "line-level" input signals and as such, it uses a 6SN7 triode to drive the 6V6.
However, for MY version of this amp, I'm going to be feeding it from a lower level input signal derived from my Mp3 player (Sandisk clip-Jam Mp3), therefore I'll need more gain such as that provided by the 6SL7 which has a larger amplification factor of 70.


So I re-wired the breadboard for the 6SL7 triode according to the component changes from Flip ( Thanks for that effort Flip)

Note:
Unlike the 6SH7 print which employs global negative feed back, the "lacewood" amp author does not seem to elect to do this. Perhaps it has to do with the triode input or because we are using ultra-linear taps on the OT providing its own degree of FB?
Not sure... .... so .... I encourage some discussion here on that point.


Attachment:
lacewood 6SL7.jpg
lacewood 6SL7.jpg [ 82.95 KiB | Viewed 360 times ]


I have "fired it up" And so far... it sounds excellent... ( running only one channel)
The MP3 player has to be cranked up a few notches more though, ....to about 3/4 volume though compared to my other 6V6-PP amp using the op-275 opamp as a driver, which does fine at 1/3rd vol to 1/2vol.

Flip showed a 100k vol pot on the input ( something about "miller capaacitance") where the author used a 250k pot, but I had to crank it to max to get decent volume... so I just changed it to a 100k input to gnd resistor .

The bench supply, for my breadboard test, only goes up to a max of +250v so the cathode voltage reading on the 6V6 is only 14v @ 36ma with a 390 ohm cathode resistor.

Perhaps when I get the suggested B+ up at +300v the cathode bias will also be at the same 18v as the "Lacewood" schematic indicates 18.1v @ 46ma with a 392 ohm cathode resistor.

I don't know if the 18v bias point is in the center of class-A, but the author seems to have taken his steps to achieve "ideal" results using that 18.1v bias point w/+300v B+.

So far so good.

Later today or this evening I will try driving the 6V6 grid from an OP275 opamp as well as the OPA604 opamp.

From the text I read about the opa604 ( fully FET signal path) it will create more EVEN order harmonics.
-----------------
REF:
http://www.ti.com/lit/ds/symlink/opa604.pdf

"Many audio experts believe that the sound quality of a
high performance FET op amp is superior to that of
bipolar op amps. A possible reason for this is that
bipolar designs generate greater odd-order harmonics
than FETs. To the human ear, odd-order harmonics
have long been identified as sounding more unpleas-
ant than even-order harmonics. FETs, like vacuum
tubes, have a square-law I-V transfer function which is
more linear than the exponential transfer function of a
bipolar transistor. As a direct result of this square-law
characteristic, FETs produce predominantly even-or-
der harmonics. Figure 10 shows the transfer function of
a bipolar transistor and FET. Fourier transformation of
both transfer functions reveals the lower odd-order
harmonics of the FET amplifier stage
"

Attachment:
opa604 harmonics.png
opa604 harmonics.png [ 99.29 KiB | Viewed 360 times ]


---------------------------------------------------

I believe the 6SL7 triode as a driver also does this as compared with a pentode as a driver which can produce more odd order harmonics?.

(discussion welcome on this point)

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 9:36 pm 
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Peter, this little circuit Flip sent me works real nice. He says to increase R4 to get more gain. Build it with the op275, or opa604.
Attachment:
Opamp%20Preamp%20Bipolor%20Supply2[1].jpg
Opamp%20Preamp%20Bipolor%20Supply2[1].jpg [ 78.53 KiB | Viewed 354 times ]

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 9:52 pm 
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john8750 wrote:
Peter, this little circuit Flip sent me works real nice. He says to increase R4 to get more gain. Build it with the op275, or opa604....
I'm afraid you have that backwards. I said "gain can easily be increased by lowering the value of R4 (gain is set by 1+[R3/R4])."

Of course, gain can also be increased by raising the value of R3 but the OP275 likes low impedance values so it's better to lower R4, within reason.


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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 10:55 pm 
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Flipperhome wrote:
john8750 wrote:
Peter, this little circuit Flip sent me works real nice. He says to increase R4 to get more gain. Build it with the op275, or opa604....
I'm afraid you have that backwards. I said "gain can easily be increased by lowering the value of R4 (gain is set by 1+[R3/R4])."

Of course, gain can also be increased by raising the value of R3 but the OP275 likes low impedance values so it's better to lower R4, within reason.



That figures. Like I said, if I did something right, I made a mistake.
Sorry, but the circuit works very well. I like it. Thanks Flip.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Mon 08, 2018 11:55 pm 
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Pbpix wrote:
But you knew it was there.
Image
No I didn't and I'm sure you know the difference between adding something to a drawing for show, as you did for DIYaudio, vs actually wiring one up so, as far as I'm concerned, this discussion is finished.


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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Tue 09, 2018 12:35 am 
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Flipperhome wrote:
Pbpix wrote:
But you knew it was there.
Image
No I didn't and I'm sure you know the difference between adding something to a drawing for show, as you did for DIYaudio, vs actually wiring one up so, as far as I'm concerned, this discussion is finished.

Of course you know you were aware that the latest schematic shows a transformer... and what's the difference if I personally wired it in to MY device or not.
Electrically it works EXACTLY as drawn with the transformer shown and it will work properly and safely.
So don't be silly.
.... just admit it.
Why keep nipping and sniping? I don't get it.
This is supposed to be friendly helpful forum.

I thank you for helping me with any tech info... so leave it at that please.
It seems that in almost every thread you just continue to have to split hairs ad infinitum ... ad neausea

I appreciate all your technical help always (thank you)
... just please learn to stop all the silly negative sniping.

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Last edited by Pbpix on Jan Tue 09, 2018 12:40 am, edited 1 time in total.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Tue 09, 2018 12:39 am 
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Peter, as long as you are breadboarding. Why waste half a 6SL7?
I have this driving a 6v6.

Image


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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Tue 09, 2018 12:42 am 
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Mike Toon wrote:
Peter, as long as you are breadboarding. Why waste half a 6SL7?
I have this driving a 6v6.

Image

Oh... thanks Mike:
I'm not.... This is a stereo amp... and the other side is for the other channel.

If I don't feel i can get reasonable gain as it is with only one 6SL7 tube drive both output tubes... then I could always just ad the 2nd tube and use the circuit as you show it.

But as I look at the ckt further I see the 2nd half is a cathode follower ... right?

And a cathode folower is usually unity gain right?
So will it boost the signal beyond what i have now or just increase it's power ... lower impedance.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Wed 10, 2018 1:00 am 
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Today I tried using both the op275 to drive the 6V6 stage as well as the OPA604.

It's very hard to tell which may be "better"

Right now I'm listening to some piano tunes that for some reason sound very "tinny" w/the opa604.

I'll swap the op275 again and compare later..

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Wed 10, 2018 3:36 am 
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Pbpix wrote:
Today I tried using both the op275 to drive the 6V6 stage as well as the OPA604.

It's very hard to tell which may be "better"

Right now I'm listening to some piano tunes that for some reason sound very "tinny" w/the opa604.

I'll swap the op275 again and compare later..




Sounds like you need a tone control :wink:

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Wed 10, 2018 7:23 am 
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Pbpix wrote:
Today I tried using both the op275 to drive the 6V6 stage as well as the OPA604.

It's very hard to tell which may be "better"

Right now I'm listening to some piano tunes that for some reason sound very "tinny" w/the opa604.

I'll swap the op275 again and compare later..



Any test results yet Peter?

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Wed 10, 2018 9:47 am 
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i thought the opa604 sounded tinny on some music... so I put he op275 back in for a while... and all seemed good.
So I put the opa604 back to confirm the tinny sound on piano music ... but after returning the opa604 and listening to a whole range of music, I wasn't sure it was poor sounding anymore so the whole exercise just left me where I began.
So I can't determine with casual listening which preamp is best.
So... I have for the moment decided I'll probably just stick with the 6SL7 tube and leave it at that.
So now for the last hour I'm listening to all I can with 6SL7 back in place... and I certainly can't find any fault.

So I've started looking at a few wood boxes I have around here already to house this amp and plan the layout.

So... if I just keep it all tubes... it will just be simple and I'll be matching the Lacewood author's optimized design very closely too.
And so, as such, it will be a standard SE classic tube only design and easy-peazy to build I guess too.

The doubler power supply will be easy and fast. For the supply I just ordered up a cpl more of these nice, low-cost 820uf @400v filter caps for $3.00 each + shipping.
https://www.ebay.com/itm/820UF-400V-Cap ... SwzPBZoKvW

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Wed 10, 2018 10:01 am 
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john8750 wrote:
Pbpix wrote:
Today I tried using both the op275 to drive the 6V6 stage as well as the OPA604.

It's very hard to tell which may be "better"

Right now I'm listening to some piano tunes that for some reason sound very "tinny" w/the opa604.

I'll swap the op275 again and compare later..




Sounds like you need a tone control :wink:

Nah ... I'm trying to compare the 6SL7 to op275 and to the opa604 .... so I certainly wouldn't want any kind of a "tone control" in the mix while doing that.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 5:18 am 
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I'm still waiting to layout the chassis and looking at 2 small wood boxes which could work well.
So as soon as I decide which I'll stain and finish it.
Then I can drill holes and start mounting and building
As soon as I do that I'll have the final power supply for 300V built in that box.

So right now I'm still fiddling and experimenting with a few values and my bench supply which now can deliver only about 50ma max

So I temporarily have selected to use a 240 ohm cathode bias resistor. This results in 42ma idle current at 10v bias and limits my bench supply to deliver only B+ to 225v

So here is the way I'm lstening/testing
( just until I can get to the [Lacewood author's] suggested values of the B+ up to 300v and a bias of 18v using a 390 ohm cathode resistor)

I'm also only listening to ONE channel... yet I must admit it's really a treat. Sound stage is very realistic and all else seems full bodied rich sound. My music of choice is all the typical 50s American standard jazz vocals and cocktail lounge piano-trio type wonderful stuff which is fantastic on this amp ... albeit only one channel ... :-)

Attachment:
lacewood 6SL7-a.jpg
lacewood 6SL7-a.jpg [ 57.92 KiB | Viewed 236 times ]

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 7:45 am 
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Looks nice and simple Peter.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 7:54 am 
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john8750 wrote:
Looks nice and simple Peter.

Yes...
Sounds VERY nice John. Surprising how nice.
and the layout s/b simple too.

3 tubes and 2 output transformers on top.
power supply inside like my 6v6PP

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 6:15 pm 
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Pbpix wrote:
john8750 wrote:
Looks nice and simple Peter.

Yes...
Sounds VERY nice John. Surprising how nice.
and the layout s/b simple too.

3 tubes and 2 output transformers on top.
power supply inside like my 6v6PP




I love it when you talk amp stuff.

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 Post subject: Re: 6V6 SE HiFi amp (new project)
PostPosted: Jan Fri 12, 2018 6:35 pm 
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A straight through amp, no knobs to play with?
I found an interesting twist to a single knob tone control, the AMZ Presence circuit, I want to try this in an upcoming project.
http://www.muzique.com/lab/tone3.htm

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