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 Post subject: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 4:34 am 
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I have been experimenting lately with SE 6V6 using a simple 6SH7 preamp.
It is a very nice easy to build amp:
( viewtopic.php?f=12&t=329087 )

Because I found SE a bit intriguing, I decided to do a little research and I came across this 6V6 SE amp : The 6V6 Lacewood Amp
http://www.cascadetubes.com/the-6v6-lacewood-amp/

Image

I decided to try to build this because it's a simple layout and looks like a rewarding project.
I like the Ultra Linear idea too.

So I decided to order the Edcor OTs tonight.
Shipping is 6 weeks so I should have lots of time to plan the layout and to seek some comments and feed back from any of you guys here who might feel so inclined to offer thoughts or help.

I have mixed feelings about the 6sn7 triode preamp because I'm considering maybe driving it with either an OP-275 op amp or possibly the OPA604 opamp.

Flip.. if you read this plse give me your thoughts.

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 6:40 am 
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SE isn't my cup of tea but if it floats your boat then go for it.

Just some random thoughts, I'd up the coupling cap to .22 uf for a little better bass response. That circuit is really designed for 'normal' live levels and doesn't have enough gain for your MP3 players.


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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 6:48 am 
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Flipperhome wrote:
SE isn't my cup of tea but if it floats your boat then go for it.

Just some random thoughts, I'd up the coupling cap to .22 uf for a little better bass response. That circuit is really designed for 'normal' live levels and doesn't have enough gain for your MP3 players.

Thnks.. looking at the triode inputs made me think that too.
So another triode stage in front of it? ... or change to pentode preamp?
...or just go for the op amp?
Of course I'm leaning to opamp for simplicity.

I'm driving my bench-test 6V6 tube (from the 6sh7 test) here now with lots of ummph with the op275 .

Maybe time to try those opa604?

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 7:08 am 
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Pbpix wrote:
Flipperhome wrote:
SE isn't my cup of tea but if it floats your boat then go for it.

Just some random thoughts, I'd up the coupling cap to .22 uf for a little better bass response. That circuit is really designed for 'normal' live levels and doesn't have enough gain for your MP3 players.

Thnks.. looking at the triode inputs made me think that too.
So another triode stage in front of it? ... or change to pentode preamp?
...or just go for the op amp?
Of course I'm leaning to opamp for simplicity.

I'm driving my bench-test 6V6 tube (from the 6sh7 test) here now with lots of ummph with the op275 .

Maybe time to try those opa604?
Since you're not using negative feedback a single 12AT7/6DT8/6SL7 would have enough gain.


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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 7:14 am 
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Flipperhome wrote:
Pbpix wrote:
Flipperhome wrote:
SE isn't my cup of tea but if it floats your boat then go for it.

Just some random thoughts, I'd up the coupling cap to .22 uf for a little better bass response. That circuit is really designed for 'normal' live levels and doesn't have enough gain for your MP3 players.

Thnks.. looking at the triode inputs made me think that too.
So another triode stage in front of it? ... or change to pentode preamp?
...or just go for the op amp?
Of course I'm leaning to opamp for simplicity.

I'm driving my bench-test 6V6 tube (from the 6sh7 test) here now with lots of ummph with the op275 .

Maybe time to try those opa604?
Since you're not using negative feedback a single 12AT7/6DT8/6SL7 would have enough gain.

I see the 6sl7 gain is 80 and the 6sn7 is only 20.

Is that going to be the thing to do it?

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 7:21 am 
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BTW flip:
As far as opamps go.
I'm experimenting with the single ended 6V6 and the op275.. but I have a TL082 in there now using the dual 20v PS.

The spec for it is +/- 15v with max of +/-18 ... but it seems to be operating nicely on +/-20v.
I was testing it and see that I can feed it 1khz and drive it to 32vPP before flat topping.

Wonder why the 20v seems to be ok?
Specs must be liberal?

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 7:34 am 
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Pbpix wrote:
Flipperhome wrote:
Since you're not using negative feedback a single 12AT7/6DT8/6SL7 would have enough gain.

I see the 6sl7 gain is 80 and the 6sn7 is only 20.

Is that going to be the thing to do it?
I presume you mean "Amplification Factor" and it's 70 for the 6SL7 (60 for the others) but you never get the full "Amplification Factor" realized as gain. And then there's the circuit itself and, in particular, an unbypassed cathode results in degenerative feedback, lowering the gain while also reducing distortion.

The 6SN7 gain in that circuit is around 9.5x. Divided into the cathode bias (12.5 V) that means it takes about 1.3 V to drive the whole shebang to the edge of clipping. You only need around 2.5x more gain to bring that down to half a volt and a 6SL7 should be able to do that, no sweat.


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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 7:47 am 
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Pbpix wrote:
BTW flip:
As far as opamps go.
I'm experimenting with the single ended 6V6 and the op275.. but I have a TL082 in there now using the dual 20v PS.

The spec for it is +/- 15v with max of +/-18 ... but it seems to be operating nicely on +/-20v.
I was testing it and see that I can feed it 1khz and drive it to 32vPP before flat topping.

Wonder why the 20v seems to be ok?
Specs must be liberal?

32Vpp is +- 16 Volt (peak), or 4 volts less than Vcc. There's nothing particular 'wrong' with that but it's nothing to write home about either.

ICs don't 'poof' the instant you go .00001 V past max Vcc. All manufacturing processes have tolerances, which is why cautious engineers build in safety margins. The upshot of all that is it might work at a higher voltage, or it might not. Or it might fail prematurely, or work forever. You can't know because it isn't characterized at that high a voltage. "All bets are off."


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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 8:06 am 
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Flipperhome wrote:
Pbpix wrote:
BTW flip:
As far as opamps go.
I'm experimenting with the single ended 6V6 and the op275.. but I have a TL082 in there now using the dual 20v PS.

The spec for it is +/- 15v with max of +/-18 ... but it seems to be operating nicely on +/-20v.
I was testing it and see that I can feed it 1khz and drive it to 32vPP before flat topping.

Wonder why the 20v seems to be ok?
Specs must be liberal?

32Vpp is +- 16 Volt (peak), or 4 volts less than Vcc. There's nothing particular 'wrong' with that but it's nothing to write home about either.

ICs don't 'poof' the instant you go .00001 V past max Vcc. All manufacturing processes have tolerances, which is why cautious engineers build in safety margins. The upshot of all that is it might work at a higher voltage, or it might not. Or it might fail prematurely, or work forever. You can't know because it isn't characterized at that high a voltage. "All bets are off."

Well with the +/-20v ... it seems 32vpp is the max I can get out of the op275 too.
Right at that point the peaks start flattening.

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 8:35 am 
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Pbpix wrote:
Well with the +/-20v ... it seems 32vpp is the max I can get out of the op275 too.
Right at that point the peaks start flattening.
That wasn't what you said when the 5902 bias was 21 V.


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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 8:59 am 
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Flipperhome wrote:
Pbpix wrote:
Well with the +/-20v ... it seems 32vpp is the max I can get out of the op275 too.
Right at that point the peaks start flattening.
That wasn't what you said when the 5902 bias was 21 V.

I don't remember now... but i was thinking I thought it was 37v ... and I think you said that was reasonable that it could almost approach the rails.
IIRC
So.. at 32v... I am wondering where I came up with 37v previously???
Maybe I'm not measuring it the same way now?

Just have scope on output

Could I have counted 5v blocks on the scope wrong and 6 blocks @ 5v instead I counted 7?

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Fri 27, 2017 9:25 am 
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Ahhh I found it.
On my bench I have been using my HP dual supply with an exact +/-20v
So as a test I raised it to +/-22v.
Then YES.. I get exactly 37vPP max out of the chip.

So all I can guess is that my 40v divided in two as a supply has not been exactly 40 volts.
Must float higher and I didn't notice it or something.... and/or the two 1 watt 20v Zeners I use in series aren't exact too?
That's the only thing I can figure... right?

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Tue 31, 2017 4:33 am 
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Hi Peter
I have looked at the Lacewood and like it. If I wasn't so busy with another project, I would build one with you.

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Tue 31, 2017 4:36 am 
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How about a CCS Peter.
Of course if I built it, it would be called the Red Oak, for the smell.

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Tue 31, 2017 5:49 am 
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john8750 wrote:
Hi Peter
I have looked at the Lacewood and like it. If I wasn't so busy with another project, I would build one with you.

I want to see if it sounds as nice as the Author claims.. and basing it on the 1-tube single channel 6V6 SE I have on the bench... it does sound nice.
So.. I want to try it using the ultra linear OTs.

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Tue 31, 2017 5:51 am 
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john8750 wrote:
How about a CCS Peter.
Of course if I built it, it would be called the Red Oak, for the smell.

Yes .. probably will use CCS.
And maybe use 6SL7 instead of 6SN7.
Or... maybe Opamp.... op275 ot OPA604 ... we'll see

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 Post subject: Re: 6v6 SE stereo (Lacewood amp)
PostPosted: Oct Tue 31, 2017 7:19 am 
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Pbpix wrote:
john8750 wrote:
How about a CCS Peter.
Of course if I built it, it would be called the Red Oak, for the smell.

Yes .. probably will use CCS.
And maybe use 6SL7 instead of 6SN7.
Or... maybe Opamp.... op275 ot OPA604 ... we'll see




Interesting to see that Peter, and your custom power supply.

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If I did something right, I made a mistake.


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