Morgan Jones' E88CC Phono

[ECC33]

This phono appears in all of Morgan's books and utilises the E88CC.
Although his latest book substitutes the ECC82 with a 7N7.

I have searched extensively (honest!) and can find no mention of anyone having built one.
I was thinking of building one, but maybe using an E88CC per channel and maybe a D3A as an input valve. And subbing the 7N7 with another E88CC (or ECC88)

Why?
I've got D3As, E88CCs and ECC88s but no 7N7s.

Has anyone built one?
Thanks!

 

[GlidingDutchman]

My friend has built one... see here: http://vinylsa.co.za/forum/viewtopic.php?t=1116

D

 

[GlidingDutchman]

Also see here: http://vinylsa.co.za/forum/viewtopic.php?t=953

 

[SY]

That is pretty much how I have my phono stage set up. I've updated some things, used different operating points, and (I think) have the overall design pretty close to optimized. I'll have it up on my website in a few more weeks.

Here's a 1kHz spectrum, 3VRMS out:

 

[Eli Duttman]

I've got D3As, E88CCs and ECC88s but no 7N7s.

The 7N7 is electrically equivalent to the 6SN7. Do you have a 6SN7 or 6CG7/6FQ7? A 6GU7 might do too.

 

[SY]

I should mention that if your cartridge or transformer can bear the input capacitance, a triode-connected D3a is a superb input tube.

 

[Stephen R]

And if it can't take the capacitance, try it is a pentode, same load R. I think it's better like this.

cheers,

Stephen

 

[kevinkr]

I should mention that if your cartridge or transformer can bear the input capacitance, a triode-connected D3a is a superb input tube.

I'll strongly second SY on that one, I use it triode connected too. I expect pentode connection would result in significant partition noise, this might or might not be an issue depending on the source - as a triode the D3A is almost impossible to beat for noise performance at reasonable cost. (It's about as noisy as a 68 ohm resistor.)

 

[Stephen R]

Noise with the D3a in pentode mode with same load as you would use in triode mode is no issue at all. I use to use it as a triode before going to pentode.

cheers,

Stephen

 

[ECC33]

GlidingDutchman, SY, Eli Duttman, Stephen R, kevinkr; thankyou all for your replies.

I wanted to stick to Noval based valves; hence not opting for a 6SN7 (ECC33)
I also wanted to keep the channels seperate, using seperate valves for left and right channels (well......if you can...you should)
I've got some D3As here so wanted to put them to good use. I was thinking of triode strapping them, naturally, but my also try them as pentodes. They didn't cost me much either.
SY, I look forward to reading your article.
Any more comments most welcome.

Thanks again.

 

[Eli Duttman]

I wanted to stick to Noval based valves; hence not opting for a 6SN7

So, use a pair of 12BH7s wired asymmetrically. Use system 1 in a channel and system 2 in the 2nd channel. When the triodes wear out, exchange the tubes between channels. You'll go a LONG time before you need new 12BH7s.

The triode in the 12BH7 is "identical" to the triode in the 6GU7 and it's close enough, electrically, to the 6SN7 triode to work well.

 

[oldeurope]

ignore this post ...

Originally #8 posted by kevinkr


I'll strongly second SY on that one, I use it triode connected too. ...as a triode the D3A is almost impossible to beat for noise performance at reasonable cost. (It's about as noisy as a 68 ohm resistor.)

Hello,
the "problem" is that the pic up system has a resistance of say 2KΩ.
Noise is ∝ √R.
√2KΩ ≈ √ ( 2KΩ + 68Ω )

But don't care, the "audio fools" don't understand this,
and nobody cares about that there is a "needle scratching
on vinyl".

Kind regards,
Darius

 

[SY]

the "problem" is that the pic up system has a resistance of say 2KΩ.

For an MM, straight in, that's correct, and the D3a's low ENR is wasted, though not unappreciated. But that setup not very common in high end audio, at least over here. My MC transformer's secondary is about ten times lower than that. Direct in, my cartridge has a DCR of 15 ohms.

 

[oldeurope]

#13

For an MM, straight in, that's correct, ... My MC transformer's secondary is about ten times lower than that. Direct in, my cartridge has a DCR of 15 ohms.

Hi SY,
how much is the ratio of the MC transformer?
10 is common, thus the transformer transforms 15Ωat the primary
to 10 x 10 x 15Ω = 1500Ω at the secondary.
Losses added ≈ 2KΩ
Using an MC + transformer is equal to MM straight in.

Kind regards,
Darius

 

[ErikdeBest]

hm...maybe the text below, by SY, makes another reply redundant?!

That is exactly right. Let's see why that's true. One convenient way to specify a tube's noise is to compare it to the Johnson noise of an ideal resistor, multiplied by the tube's gain. In other words, a tube can be thought of as an ideal (noiseless) tube with a normally moisy resistor at its input. This spec is generally called "equivalent input noise resistance." One of the very quietest tubes in audio is the triode-connected D3a, just like Alexander used. Run balls-out, its equivalent input noise resistance is about 60 ohms, i.e., it acts as an ideal tube with a 60 ohm (room temperature) resistor at the input. Now, a typical MC cartridge will have an internal resistance of just a few ohms, plus another ohm or so for wiring. Call it 6 ohms in total. There is, of course, an intrinsic Johnson noise to the phono cartridge, which sets a noise floor that a preamp can't help. All the preamp can do is add noise. OK, so with a source impedance of 6 ohms and an equivalent noise resistance of 60 ohms, it can be seen that the tube (and this is a pretty darn quiet tube running at its limits) is adding 10dB of noise beyond that of an ideal preamp. For a more sane operating condition, the ENR will be more like 100 ohms or so. An ECC88 is worse. Best case, and this is rarely achieved in practice, the ENR is about 350 ohm. So there's almost 20dB more noise than an ideal preamp. Paralleling gives a 3dB improvement, not super helpful. What does a transformer do? If you use a 1:10 stepup (and for simplicity, I'll ignore the DCR), the cartridge now appears as a 600 ohm source. Suddenly, the ECC88 is only adding 2dB more noise than the theoretical minimum. Transformers are a bit tricky to optimize, but they present the best solution for tube designers of RIAA stages.

Audiophool Erik

 

[oldeurope]

OT noise

Hi Erik,
look at this link.

Kind regards,
Darius

 

[SY]

Using an MC + transformer is equal to MM straight in.

Fairly close, yes. That was the point of my older post that Erik dug up.

edit: For the case of more modern MCs, the numbers look more like 400-600R than the 1k5-2k of my present unit.

 

[oldeurope]

#17

Hi SY,
I don't care much about thermal noise,
there is a much more important noise source:

Originally #12 bposted by oldeurope

...
and nobody cares about that there is a "needle scratching
on vinyl".

Thus for MM and MC + transformer I don't see any advantage
in using the D3A.

Kind regards,
Darius

 

[Stephen R]

Hi oldeurope,

I've been following your posts but I have no idea what point you are trying to make?

- Stephen

 

[kevinkr]

Most current MM cartridges have a dcr of well under 2K, my current one is a Grado Reference Platinum which IIRC has a dcr of around 470 ohms and an inductance of 47mH. The low output (0.5mV) MM Statement series Grado cartridges have a dcr of just 2 ohms and an inductance of 2mH so I believe in this case that the D3A would actually be the dominant noise source. Most high output MC types also have extremely low dcr and inductance and would again be the dominant noise source.

The low noise is worthwhile because it makes the dominant noise source the cartridge itself in most applications, in addition the low rp allows you to downwards scale the components in passive EQ networks for lower noise as well, and the D3A has much higher mu than the ECC88 - another factor that can be traded off for quieter overall performance by reducing the gain in the second stage. (This can be worth a few additional dB.)

I have never much cared for the sound of typical 6DJ8/ECC88 available here, and the few good European NOS types that do sound good to my ear are pretty expensive. The D3A sounds good, is relatively inexpensive and long lived.

It would also appear that the D3A has lower 1/F noise than a lot of types if my experience is typical.