This link is provided by Shoog:
http://www.vacuumstate.com/fileupload/dpa300B_brochure_lo_rez.pdf
Anyone try the differential push pull power amp shown in page 2 where the two power tubes are wired as LTP with CCS at the bottom?
http://www.vacuumstate.com/fileupload/dpa300B_brochure_lo_rez.pdf
Anyone try the differential push pull power amp shown in page 2 where the two power tubes are wired as LTP with CCS at the bottom?
Yes. Clearly better. Although I was told by someone who knows enough that it should represent the highest distortion of all PP topologies, but there was also some mention of rectification due to Ip through a common Rk//Ck tail and that all went over my head. I built it instead.. and it was better.
My experiments/builds were with SE drive stage (low mu, low Rp high current triode).. so not like Mr. Wright.. but apples for apples, my output stage comparison holds. In other words, his differential high mu triode RC coupled to OP stage might yield different results overall compared with the same Class A or AB1 OP stage (but why would you).
My experiments/builds were with SE drive stage (low mu, low Rp high current triode).. so not like Mr. Wright.. but apples for apples, my output stage comparison holds. In other words, his differential high mu triode RC coupled to OP stage might yield different results overall compared with the same Class A or AB1 OP stage (but why would you).
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One often sees claims like this one being made, but it seems to be completely without foundation. Apart from anything else, in its path from the microphones in the recording studio to output from the home CD player, the audio signal will have been through lots of stages where it has been subjected to huge amounts of negative feedback. Does Mr Vaughn therefore claim that the audio signal delivered by the CD player has had "the space and air between the instruments" thoroughly killed before it is fed into the home stereo amplifier? Does he then imagine that it is all resurrected again by the miracle of passing the signal through an SET amplifier? His claim seems to make no sense at all.
Chris
I just want to confirm you are referring to the LTP power tubes stage in this article:
http://www.vacuumstate.com/fileupload/dpa300B_brochure_lo_rez.pdf
Those are a part of it.
The most important thing is to design so that you have so low distortion open loop, that there's no need to have feedback to reduce distortion.
Output impedance can be dealt with other ways, like you stated. Drive the OT with source followers.
When not constrained by mass production cost issues, why not design this way? Make each single stage as low distortion as is possible, and the sum total is distortion so low there's no need for feedback.
Take care of each small problem, and the big problem disappears.
You mean like the mu-follower push pull circuit you showed before. That is low output impedance and horizontal load line. But the gain is high though.
Source followers operate in 100% local feedback. They are completely transparent and very low output impedance.
No, it's not true.
While all this talk about hysteresis is intellectually interesting, I must repeat: it will not be in the top 5 of distortion sources. It is not a real concern.
Come back with talk of hysteresis after your output tube loadline is horizontal. If you think that ANY process (within specs) in the OT produces even 10% of the distortion the output tube produces with a slanted load line...
Put in 2A3's with a µ of 3 or whatever it is, and see what the gain is. 4P1L has a µ of about 8.
More often than not it's a case of "how do I get enough gain to drive the amp to full power?"
Put a 6SN7 LTP in front of a 4P1L LTP; is this circuit high gain?
All my PP amps work on this principle - though implemented in a slightly different way. I think that Allens design principles offer the best possible chance of getting a PP which will better any SE.
Shoog
I have the JM Lab 714s for home cinema and although I would bet they are a bit easier to drive than yours I have driven these with a 2W SE amp without a problem. The only real limit in normal room is the SPL with highly dynamic music program like classical o jazz music featuring big groups and orchestras. I don't know your speaker in detail but mine is a nominal 8R impedance speaker with about 4.5 R minimum impedance. It's a 2-1/2 ways with one woofer cut around 700 Hz and the other crossing-over with the tweeter. The minimum impedance happens around the frequency range where one of the woofers is cut out, so it's between 500-1000Hz, but is not very reactive. For the rest it's not a difficult load. It not so difficult to drive.
In your case I guess they are a bit more difficult to drive but a PP amp won't have to much trouble if you consider them 4R rather 8R. The DF won't get so much worse if the primary-to-secondary ratio will be higher. That's an advantage in comparison to OTL amps, both tube and SS! You might only get a bit less power where impedance is 8R but your speakers are quite sensitive.
For example, if you want to use the EL 34 in triode mode without fb I think you could get away with a 10K/6R transformer (i.e. 40:1 ratio). It will work fine into 4R provied it's not highly reactive, basically and practically still a 15W class A amplifier....
I can't comment on the transformer iron arguments for favouring SE, although I suspect they are nonsense.
In all other respects, PP beats SE. It must do, because for a given design effort or monetary outlay you get all the behaviour of SE plus some cancellation of even-order distortion. Unless you think that even-order distortion is a good thing in itself, or is needed to mask unavoidable odd-order distortion. Some people claim the latter, but I suspect their ears/brains actually prefer the former.
Carefully applied NFB will always improve a good amp. It cannot improve a bad amp. For this reason NFB is easier to apply to PP than SE, as the inherent distortion of PP is lower so it better satisfies the general rule: make it good, then apply feedback.
(a) pure nonsense,
or
(b) an admission that the listener prefers to hear some distortion with his music but chooses to deny this (either through ignorance or pride),
or
(c) an admission that the designer is unable to properly design NFB.
In all other respects, PP beats SE. It must do, because for a given design effort or monetary outlay you get all the behaviour of SE plus some cancellation of even-order distortion. Unless you think that even-order distortion is a good thing in itself, or is needed to mask unavoidable odd-order distortion. Some people claim the latter, but I suspect their ears/brains actually prefer the former.
Carefully applied NFB will always improve a good amp. It cannot improve a bad amp. For this reason NFB is easier to apply to PP than SE, as the inherent distortion of PP is lower so it better satisfies the general rule: make it good, then apply feedback.
This is eitherAlan0354 said:
(a) pure nonsense,
or
(b) an admission that the listener prefers to hear some distortion with his music but chooses to deny this (either through ignorance or pride),
or
(c) an admission that the designer is unable to properly design NFB.
I agree with azazello. Speakers are usually crucial when it comes to SE.
I have a 300B PP and 300B SE. Both are my, I love them and they designed about 15 years ago. They sound fine, I do not intend to change something.
With ScanSpeak/Dynaudio combo speakers, I like PP more. But with full range driver (without XO), SE beats in every respect.
Attachments
While I've not built Allen's amplifier it was at his prodding that I added the CCS to the output stage of the 47 P-P amplifier. Have never looked back.
Since then all my amplifiers, both tube and solid state have been fully differential with CCS loading in the tail of both the input and output stages.
Thanks.
No preamp separate.
Driver tube for SE was C3g (18040 now).
For PP driver is E182CC + IT
A very interesting thread, many thanks for all contributions! Alan0354 knows how to post the questions in the right way to extract most out of peoples knowledge 
Hi Alan0354. You can buy Lundahl from K & K Audio - Lundahl Transformers, audio DIY kits and more in the USA. The prices are, I think, quite similar to the European prices.
Hi Alan0354. You can buy Lundahl from K & K Audio - Lundahl Transformers, audio DIY kits and more in the USA. The prices are, I think, quite similar to the European prices.
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