Bottlehead Forum
Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: richp4003 on March 14, 2018, 09:59:18 AM
-
Just started the quest for something different (have some luxman 3045 monoblocks right now, KT88 running in triode)..
When the Kaijus are wired as monoblocks, is it a PSE setup or a push-pull? Im kind of new to this, but as a mono block, is there any concerns about running 2 OPTs vs one larger one as other 300B setups might have?
-
It's a slightly special arrangement, closest to PSE (parallel single-ended) in terms of how it sounds. We usually call it "bridged" which is not precise but helps make it clear this is not the usual PSE connection. You could think of it as tubes in parallel but transformers in series.
The problem with simply paralleling triodes is that the tube internal resistance is much smaller than the load resistance. So any difference between the tubes causes difference-signal current through the other tube. Sometimes this is called "current hogging." We, and many others, have noticed some degradation of sound quality with PSE amps.
My solution is to run the individual amps with the same input (so they are in phase with each other), but wire the secondaries of the transformers in series. This greatly reduces the interaction between the tubes, while leaving intact the single-ended harmonic structure. It doubles the design speaker impedance, so I designed the output transformers in Kaiju to have an additional tap at 2 ohms so that the series connection can be made for a 4 ohm load. The usual 4-8-16 ohm taps can be used to handle 8, 16 or 32 ohm loads in this bridged mode.
For some years, the large and complex Bottlehead reference system used four 300B amps per channel wired this way to drive the midrange speakers, which gave us a good deal of experience with this connection.
Incidentally, this is not an issue when paralleling pentodes, which have high internal resistance. I have designed, and we have built, an experimental pair of SE parallel pentode monoblocks with 6550s, making over 50 watts each. These amps us a single plate choke and output transformer each.
-
I hate to be a troublemaker (not really) but this arrangement could very easily be converted to single ended push pull as in the Marcel and Clovis amps by Phil Seig of the old Valve magazine days. All you would need is an interstage transformer to split the phase and a few changes to the circuit. Ever since I saw the article on this amp I have wanted to hear one.
Michael
-
It won't sound as good, at least not to me. That's why we strap SE amps when we want more power.
-
For those who haven't series bridged a (Bottlehead) single ended amp, you should try it. I have series bridged Stereomour IIs. There is no loss of transparency, no degradation of image, simply a doubling of power with no sonic penalty.
Jamie
-
All you would need is an interstage transformer to split the phase and a few changes to the circuit.
You don't even need that. A paraphrase phase inverter could be made from what's there already without too much fussing.
The series single ended approach is indeed quite superior though.
-
Hahah, he said paraphrase!
-
How many spells could a spell-check check, if a spell-check could check spells?
I am of course paraphrasing my grandfather, who was very fond of tongue-twisters. :^)
-
Wow! VERY interesting response. I kind of just started the investigation into whether I want to try 300B.. then I thought PSE was the way to go for a bit more power.. THEN upon posting on Audiokarma a few guys chimed in talking about the sound degrading that can take place with PSE, the same as you mentioned Paul. (which, given how "pure" we are trying to keep 300b, sort of defeats the purpose)
I really need to find someone with a 300B SET amp so I can borrow it for an afternoon.. I've yet to hear one (and hoping I don't fall in love because I am a big fan of my luxmans)
-
What part of the world do you live in? There might be someone close by...
-
I live in Fairfield, CT, USA.
-
So.. I was fortunate enough to have a DIY/builder come over with one of his 300B SET amplifiers (C3G drivers, elecrtraprint OPT)...
SET literally rocked my world. My luxman KT88 push-pull set up is by no means a weak link.. but 300B SET was something else! Detail, air, etc. Gone was that bit of harshness that makes itself apparent on the Zu Druid speakers.
Now I am on the hunt again for SET. Had a few more questions/ asking for opinions:
- Is there any quality degradation running these as monoblocks?
- What are the sonic difference?
- Is this a better path than going to a transmitter based SET (211, 845, etc)
I do listen to a lot of new wave, rock, modern indie (sort of all over the map) I miss the drive/punch/bass of the push pull, but as it stands I would take the 300B SET. However, if I can get more of what I like in the p-p in the SET setup.. then I would be golden.
-
- Is there any quality degradation running these as monoblocks?
We do not believe so with the method that we use to bridge the amps.
- What are the sonic difference?
More power!
- Is this a better path than going to a transmitter based SET (211, 845, etc)
This is a bit of a complicated answer. I build a lot of random amps with transmitting tubes, and I own a Kaiju, so I can give some commentary from experience. When you go a higher power single ended amp like a 211 or 845, the output transformer grows significantly. On a 60W amp I'm working on, the transformers alone were $1500. If you're looking at a 211 or 845 amp that's $2000-ish new, the quality of the output transformers will be a concern. With many transmitter tubes, there is a design choice to be made about how much feedback you use. If you use no feedback, the output transformer has to be a very high impedance step-down device, and these rarely have sufficient inductance to provide a satisfying bottom end. If feedback is used, the transformer requirements relax a little bit but then you have a different harmonic distortion profile that may not be as pleasing.
-
The 845 and 211 sound different than the 300B. Those amps tend to be more neutral sounding, while the 300B has more body in the lower mids that fleshes out the music a little better. That is one of the main attractions of the 300B. So if you heard a 300B amp and liked it, get a 300B amp. If you heard a 45 amp and liked it but wanted more power, get an 845 amp.
I used an 845 preamp for an extended period in place of my usual 300B preamp. These were running strapped Kaijus. Both sounded great, but I eventually went back to the 300B. It just sounds more relaxed and natural to me.
-
We do not believe so with the method that we use to bridge the amps.
More power!
This is a bit of a complicated answer...
Thank you and to Doc B.. Yes, I did like the sound. The issue I had with it was I felt it could use a bit more drive/punch/quickness? to it. The amplifier was all interstage transformer coupled, and using a basic EH tube. Would the additional power alone in a Kaiju monoblock solve some of this drive and quickness? (I know this is hard to say as there are MANY variables at play here)
Another question: Are the OPTs on Kaiju "special" beyond the 2 ohm tap for bridging.. or could they be replaced/upgraded down the road like something off the shelf from Tango? (realizing it would need 4/8 ohm taps to then make 8/16)
-
Thank you and to Doc B.. Yes, I did like the sound. The issue I had with it was I felt it could use a bit more drive/punch/quickness? to it. The amplifier was all interstage transformer coupled, and using a basic EH tube. Would the additional power alone in a Kaiju monoblock solve some of this drive and quickness? (I know this is hard to say as there are MANY variables at play here)
Another question: Are the OPTs on Kaiju "special" beyond the 2 ohm tap for bridging.. or could they be replaced/upgraded down the road like something off the shelf from Tango? (realizing it would need 4/8 ohm taps to then make 8/16)
I would conjecture that the active loads, shunt regulation and parallel feed output would contribute to increased drive and punch as much as the extra power would. And yes, the output transformers and plate chokes are special, designed in house by Paul Joppa specifically for this application. My experience with boutique transformers in place of the stock transformers was to go back to stock. I don't know if Tango even make a parallel feed output transformer or plate choke. Very seldom does an off the shelf product outperform a purpose built one.
-
So nice to get such quick and thorough answers! This SET endeavor is very difficult given the stuff isnt just readily available to try, and there are many different paths one can take.
So..another question as I narrow this all down: I came across a Kaiju build thread and it was mentioned the ELROG being a choice tube for this, and reviews of the ELROG (saw one on 6mooms) make it seem like a 45 tube with more power.. with greater immediacy, etc.
Given the cost of the ELROG being more than 50% of another Kaiju.. is the better choice one Kaiju with some ELROGs (or emission labs XLS?) or two Kaijus with "lesser" tubes (EH, Gold lion, etc)? In terms of getting a bit more of that drive/punch/immediacy of push-pull. (and yes, the "answer" is 2 Kaijus with kick@ss tubes)
-
Kaiju is a parallel feed amp, so there are relatively few appropriate upgrade transformers/plate chokes, fewer that will fit mechanically, and even fewer whose magnetic orientation is suitable. There is one set from Magnequest that would work - I allowed for that particular possibility. That would be the TFA-2004 output transformer (4-8-16 ohms) and EXO-003 plate choke.
For what it's worth, I designed the stock units to have roughly the same performance as those parts; differences are thus somewhat subtle.
-
Thank you and to Doc B.. Yes, I did like the sound. The issue I had with it was I felt it could use a bit more drive/punch/quickness? to it. The amplifier was all interstage transformer coupled, and using a basic EH tube. Would the additional power alone in a Kaiju monoblock solve some of this drive and quickness?
There are way too many variables to tell.
Another question: Are the OPTs on Kaiju "special" beyond the 2 ohm tap for bridging.. or could they be replaced/upgraded down the road like something off the shelf from Tango? (realizing it would need 4/8 ohm taps to then make 8/16)
There is no transformer from Tango that is an improvement over what comes in the Kaiju in my opinion. A big part of the reason for this is the parallel feed topology that we use which splits the role of the traditional gapped output transformer into two different individual pieces. The Tango FC-40-3.5S (at about $1200/pair) is pretty close as far as gapped transformers go, though it has slightly less inductance than the stock Kaiju setup. They are also too large for the chassis (another advantage of parallel feed).
Sowter could probably wind you a pair of 75H/70mA chokes, but it's hard to say if they would fit the chassis or not. They also have some transformers with a mix of GOS and mumetal lams that could be adjusted for the application (right between the 8983 and 8985). None of these parts fit the holes provided in the Kaiju, but they are smaller than the Tango parts and may fit without too many headaches. This is still $1000+ that may or may not be worth the expenditure.
-
What probably matters more than boutique parts is whether the speaker you have chosen is a good match. There is only one way to tell and that is try them together. Zu have a somewhat different design philosophy than we do, so I can't really offer a very educated guess on how they will match up. My general impression of Zus when I have heard them is that they can sometimes use a little help on the bottom end. I can't say if that is due to their sensitivity to setup as they describe in their ad copy, or a general house sound. We designed our speaker to take advantage of the relatively low damping factor of zero global feedback SE amps and consequently the bass is good with an SE amp. I do not know if the Zu speakers are designed with low amp damping factor as a consideration or not.
You might get some of the sound changes you are looking for with the existing amps just by experimenting with speaker placement. It's free to try.
-
More great info here.. honestly, I don't know *too* much about the Kaiju (seems like the other products offered have more "coverage" online) but it seems from what I have read here that its going to take a BIG jump in OPT to make any positive effect, if at all.
As to the Zu: They definitely tend towards lean on the bottom end, and at least with the Druids, that air gap on the bottom has a big effect on the response. I can tell from my Luxman experience vs. the 300B test, that the latter is more suiting the speaker. The Druid is very light on its feet and can really make use of the micro texture and air that 300B provides, and to the detriment of what I do have, it does accentuate that little bit of harshness that push-pull can have. Just for reference, Zu's recommended amps for tubes were both 300B: Audion Silver Night and Melody 300B. From speaking with some other guys that have owned a lot of Zu speakers and many combinations of amplifiers with them, their consensus was that they do will well with 300B power, but seem to do best with the power level of PSET 300B. 45 and 2AC didn't offer enough headroom.
Of course, PSET brings its own issues to the table.. which is why I am very interested in the Kaiju!
I will ask, from an academic perspective and for others who may come across this thread.. how do some of the top tier amplifiers deal with the limitations of PSET? I'm thinking Audionote Japan, for example. These are amplifiers that are basically cost-is-no-object.. so Im a bit curious why they would lean on PSET if it has an Achilles heel.
-
It would be inappropriate for us to pontificate about someone else's design rationale. What I can share is that we have found paralleling two complete SE amps at the inputs and series wiring the output secondaries seems to give twice the power without the potential headaches like current hogging that can happen with parallel tubes before the output transformers. We have done PSE amps too, with PJ keeping the potential problems in mind when making design decisions. The strapped Kaiju circuit sounded better to me.
-
I miss the drive/punch/bass of the push pull, but as it stands I would take the 300B SET.
This is an old thread, but it may still be of interest to would-be purchasers. I was looking for the same additional umph and punch from my Stereomour II and I got it by adding a Beepre preamp in front. It's a helluva preamp.
cheers,
Derek