Long tail pair with a short tail

What people are working on at the moment
Post Reply
izzy wizzy
Old Hand
Posts: 461
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Long tail pair with a short tail

Post by izzy wizzy » Wed Jun 13, 2018 5:57 pm

I have a question about a long tailed pair with a short tail. Imagine your typical long tail phase splitter. To get decent balance on the anodes with resistor loads, the tail should be a big resistor which implies a negative supply or a constant current source. Now instead of resistive anode loads, there's a PP transformer like so
6n6lineaud1.JPG
And now make the tail short so it's just a regular biasing resistor to ground. So we end up with something like this with one input grounded and the other signal
6n6lineaud2.JPG
6n6lineaud2.JPG (22.81 KiB) Viewed 314 times
It will be unbalanced by 1dB or so accourding to the model and you can see a rise in 2nd harmonic distortion which is to be expected.

So my question is, with very small signals, phono stage levels, what would be the expected impact on the sound?

cheers,

Stephen

User avatar
Nick
Site Admin
Posts: 11264
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Long tail pair with a short tail

Post by Nick » Wed Jun 13, 2018 6:40 pm

I would expect as you say a little 2nd, but no other real problem. FYI, in that case I would be looking at a CCS using a DN2535N3-G instead of a 317, they are only 56p from Farnell.

I just found Farnell had them when I had to repair a ARC phono which used them all over the place in LTP tails.
Resistance isn't futile it's V / I.

izzy wizzy
Old Hand
Posts: 461
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Long tail pair with a short tail

Post by izzy wizzy » Wed Jun 13, 2018 7:05 pm

Thanks Nick. I had used the 317 in the line stage but soon got rid and used an input tx and small tail. I'll look up the Farnel part as Ihave an order for there soon. Will be interesting to see if it's audible.

I did some more in the sim and it looks like unbalanced there's about 0.3% 2nd harmonic and balanced about 0.03%. Is 0.3% at full level audible? I have no idea. I'm only doing this as I don't have an SE transformer but can use a PP transformer.

cheers,

Stephen

RhythMick
User
Posts: 166
Joined: Fri Jun 23, 2017 12:24 pm

Re: Long tail pair with a short tail

Post by RhythMick » Wed Jun 13, 2018 10:46 pm

I have some spare SE transformers if you'd like to try them. I can take to Owston if you want.

User avatar
IslandPink
No idea why I do this anymore
Posts: 6038
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

Re: Long tail pair with a short tail

Post by IslandPink » Thu Jun 14, 2018 8:29 am

izzy wizzy wrote:
Wed Jun 13, 2018 7:05 pm
I did some more in the sim and it looks like unbalanced there's about 0.3% 2nd harmonic and balanced about 0.03%. Is 0.3% at full level audible? I have no idea. I'm only doing this as I don't have an SE transformer but can use a PP transformer.
cheers,

Stephen
What's 0.3% in dB relative to the main signal ?
Is that -25dB or -50dB ?
Either way, that will be audible, when I was doing the jFet phono input , there was a significant difference in tone from what we calculated to be the difference between no distortion, and distortion giving 2nd-harmonic at -70dB . It was better with the small amount of 2nd. These were sims on Spice , not measured, but I expect the delta was more or less as calculated.
White flags of winter chimneys waving truce against the moon ( Mitchell )

User avatar
Nick
Site Admin
Posts: 11264
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

Re: Long tail pair with a short tail

Post by Nick » Thu Jun 14, 2018 8:36 am

the difference between no distortion, and distortion giving 2nd-harmonic at -70dB . It was better with the small amount of 2nd.
Thing is, the no distortion case wont be no distortion, there will still be higher harmonics down there, but the addition of the 2md will mask them. I found when messing with the monoblocks that distortion down below 0.0005% mattered without the masking of 2nd and 3rd.
Resistance isn't futile it's V / I.

User avatar
IslandPink
No idea why I do this anymore
Posts: 6038
Joined: Tue May 29, 2007 7:01 pm
Location: Denbigh, N.Wales

Re: Long tail pair with a short tail

Post by IslandPink » Thu Jun 14, 2018 9:51 am

Amazing, isn't it !
White flags of winter chimneys waving truce against the moon ( Mitchell )

izzy wizzy
Old Hand
Posts: 461
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Long tail pair with a short tail

Post by izzy wizzy » Thu Jun 14, 2018 7:43 pm

Interesting stuff.

I don't know if I'm doing this right but anyway I ran 3 circuits. One diff with a short tail, the other with a CCS inthe tail and a single ended version.

This is the FFT traces of all three
5687fft.JPG
The first and 3rd look almost the same with the CCS version having suppressed 2nd harmonic. Is that right?

cheers,

Stephen

izzy wizzy
Old Hand
Posts: 461
Joined: Fri Nov 02, 2007 7:02 pm
Location: Folkestone
Contact:

Re: Long tail pair with a short tail

Post by izzy wizzy » Thu Jun 14, 2018 7:44 pm

RhythMick wrote:
Wed Jun 13, 2018 10:46 pm
I have some spare SE transformers if you'd like to try them. I can take to Owston if you want.
Thanks for the offer but I won;t be at Owsters ... this time ;)

cheers,

Stephen

Post Reply

Who is online

Users browsing this forum: No registered users and 5 guests