JLH Liniac Revisited

[wrenchone]

Here's the trailing edge.

[wrenchone]

As promised, I looked at the line amp square wave response with 6ft of cable terminated by a 10k resistor. The cable caused a small increase in output undershoot. I have some nice IMB 270 pF polystyrene wrap and fill caps at home, so I tried the equivalent amount of capacitance as compensation, and the response is nice and slightly overdamped, the way I like to see it.

Attached is a schematic representing the current state of affairs. For anyone trying to duplicate this circuit, Q2, Q4, Q14, Q17, and Q19 have source resistors selected for the proper value of drain current (10mA for Q2, Q14, and Q19, 1 mA for Q17, and 5mA for Q4. These values will need to be different depending on the FETs you have on hand. Q3 and Q20 were selected for Vgs > 5V at 2mA drain current. Q1 and Q18 were matched for Vgs at 10 mA draiin current. Q5 and Q6 were matched for Vgs at 2 mA drain current.

I'm installing the new compensation caps tomorrow, then I'll try loading it into my living room system for some listening tests.

[wrenchone]

I had a little extra time today, and simulated a bipolar cascode with the base circuit referenced to the summing node. THD is slightly better than with the PN4391 JFET cascode - 0.0041% vs 0.0044% or thereabouts. Distribution of harmonics is about the same, with the overall levels on each harmonic in the JFET cascode just a little bit higher. This says nice things about the PN4391. I may try the bipolar cascode down the road, but I will have to use a clean current or a heavily filtered split resistor to drive the base so that I'm not injecting any nasties directly into the summing node.

The completed lineamp board is currently sitting on a shelf in my living room waiting its turn to be installed. It'll probably be behind the mods I'm planning for my newish P-P tube amp - check my "Kingfisher" thread for details on that one.

[Joachim Gerhard]

i am really interested how your modern liniac sounds so please fire it up and tell us how it sounds. i have not seen such an interesting single ended circuit for a while. i usually do parrallel symmetric and i can remember quite firce discussions we had 25 years ago about the merrits of the two aproaches.

[wrenchone]

I finally got this line amp into a box with an RIAA preamp along side it, with the intention of bringing it to this year's Burning Amp. Fate intervened, and I'm still working on the preamp box. Here's the response curves for the "Liniac-Like" lineamp. Tonight I get to hear how it sounds (maybe).

[wrenchone]

This line amp, combined with a nice California Audio Labs Ikon MkII CD player, is letting me hear everything whether I like it or not, including rustling pages, violinists picking up their bows, and traffic outside the concert hall. The recording is Neville Marriner and The Academy of St. Martin in the Fields, performing Vivaldi's "Four Seasons". The Decca reissue of this recording on CD is pretty nicely done, and I just picked up what I hope is a fresher copy of the vinyl release, which originally came out on Argo.

[wrenchone]

My overall impressions of this circuit are still very positive. The extra 5X gain (replacing a follower line amp) helps to squeeze the utmost out of my components. Resolution of detail is exquisite. What also helped was subbing my old speakers back into my setup, which with the 1.5k crossover frequency imposed by my new jfet active crossover, are now very smooth and detailed at high volume. The speakers used a 5 kHz crossover frequency in the past, which did not sound anywhere near as good.

The Tri-Trix speakers I used in place of my old speakers for a while are very harsh (painful, really) in comparison. The old speakers are now going to get some loving detail and attention so that they look as good as they now sound. I'm scratching my head as to what to do to alleviate the harshness of the tri-trix speakers.

With these results as impetus, I'm going to try to adapt this approach to a vacuum-state line amp.

[gazzagazza]

My recollection of the Liniac is that it was a two device circuit, with shunt feedback. I remember building and testing one back in the 70s and it was awful. Terrible distortion figures.

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[wrenchone]

Well, this version simulates very nicely, if you check the thread, and sounds great. It's not a straight Liniac, as already pointed out by a pundit, but inspired by the original circuit. It's the first line discrete amp with gain I've built that I've liked. The first one I tried got ripped out after about an hour of listening. Gain of ~one is easy. Gain of 50 - not too hard. Gain of five - another story.

[Ian Finch]

Hi Wrenchone
A long time in the finishing but well worth it, I imagine.
This is relatively complex and unusual stuff for many of us. Would you care to note any special requirements of components selected, operation and perhaps some PCB details if you feel they are relevant to anyone wanting to emulate your good work. I think you might have Joachim in there, at least.