Requirements for a perfect speaker for my 2 speaker (FR + Sub) setup.
Possible Contenders
Thinking about OB and Full Range speakers. The most apparent critical aspect is the omission of the cross over in the critical frequency range that humans are most sensitive to. This kind of conclusion is widely postulated on the web by a range of different people. Whether this is true or not can only be determined by iterative testing by the listener and the speaker setup. If we take the assumption that around the 200 Hz to 10 kHz range is the most imperative for removing cross overs, then a three way design can be explored.
This new concept is centered around 3 drivers driving the 20-200 Hz, 200-10,000 Hz and 10-40 kHz range, fully covering music from 20 Hz to 40 kHz.
Lower Frequency 20 Hz to 200 Hz (approx.)
Eminence Alpha 15A in a U baffle with approximate internal dimensions of 40cm x 40cm with a 13.5cm depth side wall. This most likely will be actively crossover with a 2nd order Linkwitz-Riley at somewhere between 100 to 200 Hz.
Mid Range Frequency 200 Hz to 10 kHz (approx)
Visaton B200 in an open baffle size of around 40cm by 120cm high. Using either 1 or 2 drivers. By having the baffle this size, and the speakers offset, it appears from EDGE simulations that the baffle boost around 200 Hz to 1000 Hz would compensate for the lowered response of the B200. This could lead to a relatively flat response from 200 Hz to 10 Khz, of which the rising mids can be balanced on the lower frequency by the baffle step response. The natural falloff of the baffle would be boosted with either 1st order or 2nd order filter to match closely with the Alpha 15A.
High Frequency 10 kHz to 40 kHz (approx.)
Fostex FT17H or other super tweeter that is relatively flat up to 40 kHz. This should be filtered with an inline capacitor.
More to follow!
In the past few months, work has been quite hectic as well as the family side of things, and haven't had much of a chance to do anything audio. Primarily, still enjoying my music through the Zen amp with the Fostex 127e. On one note, I have begun to be sensitive to the beaming of these speakers. Going to have to investigate ways to reduce this beaming... The plot thickens.
Recently, I purchased a Dayton Audio Class T amp from Decibel Hifi. This was very cheap and came with an power supply as well. This will be an interesting test to see how it sounds as it compares to my Zen amp and the Chipamp. Over the course of time, I am sure I will dismantle the unit and upgrade components where I can. I see already that the speaker connections need work along with the input and volume control. I would also like to build a new case and potentially use SLA batteries to power this puppy.
Still haven't had the opportunity to build the Linestage yet, nor have I even had the time to order the components for the Aikido stage. Shame on me. However, I will get around to it eventually and that should finally give me the missing link in my audio chain.
Been looking around the net for information on Open Baffle speakers. From my cursory reading it appears that OB are quite popular and have a good reputation for being a revealing speaker design. The alternate design I am also looking into are compression drivers mated to horns. In either scenario, a LF driver and amp would probably need to be used below 100-300Hz. At this point, it is interesting to read all the various opinions and technical background on the two designs, and should form the basis of my next speaker project. To that end, an order was placed for a pair of Eminence Alpha 15A speakers from Essential Audio. For the low end, I am currently thinking of a 2nd order Linkwitz-Riley active crossover at 150 Hz, with the Alpha's in a U frame open baffle. The construction and use of this should also assist in my current Fostex MLTL. The U frame should be quick to build, and I will mate them with the chipamp initially, but maybe target a 200W LF amp in the future.
Hopefully have some more updates later and actually get some more stuff done next time.
The following table is updated to use the 100 K resistor to ground for the output RC part.
| Frequency | C | R | V-Cap Price |
| 1 Hz | 1.59 uF |
100 K | US$251.99 (300V) 1.5uF |
| 3.3 Hz | 0.48 uF | 100 K |
US$139.99 (600V) 0.47uF |
| 5 Hz | 0.32 uF | 100 K |
US$114.99 (600V) 0.33ufF |
| 10 Hz | 0.16 uF | 100 K |
US$72.99 (600V) 0.15uF |
| 150 Hz | 0.011 uF | 100 K |
US$34.99 (600V) 0.01uF |
| 180 Hz | 0.008 uF | 100 K |
n/a |
| 200 Hz | 0.008 uF | 100 K |
n/a |
With the revised output impedance of 100K, it makes the the cost equation a little more sensible. The table below shows if the R is changed to 1M.
| Frequency | C | R | V-Cap Price |
| 1 Hz | 0.16 uF |
1 M | US$72.99 (600V) 0.15uF |
| 3.3 Hz | 0.048 uF | 1 M |
US$44.99 (600V) 0.047uF |
| 5 Hz | 0.032 uF | 1 M |
US$41.99 (600V) 0.033uF |
| 10 Hz | 0.016 uF | 1 M |
US$36.99 (600V) 0.015uF |
After a slight lull due to work commitments, I have finally got around to sourcing the final components for my line-stage, starting to finish off the DRD45 and also getting stuff ready for my Fostex MLTL.
The Line Stage
At the heart of this line stage is the Aikido with 5687 as the output tubes, and as yet unknown input tubes. This will be proceeded by a 100K DACT attenuator, which will itself be proceeded by a DACT switch. The switch will switch both ground and signal of each RCA channel. This should make the potential move to balanced inputs easier.
The reason behind using the Aikido line-stage instead of a passive stage is because of outputs. It allows me to bi-amp, have a tap also for a headphone amp and finally have a tap for a FR output. It may potentially drive all four, but at a minimum, it will drive at least 2 outputs. By using an active line-stage the output signal should be good enough to feed the various power amps. The following are the expected outputs. Output 1 and 4 will be paralleled.
The Aikido requires a RC output, and thus naturally forms a HP filter. Thus, even with the two low 1 Hz options, a RC filter is still required. The following parts value (to limit the size of the cap, to allow for a more economical use of high quality capacitors.). The sub-woofer filter will be some form of OPAMP based 3rd/4th order active filter.
| Frequency | C | R | V-Cap Price |
| 1 Hz | 3.3 uF |
47 K |
US$489.99 (250V) |
| 3.3 Hz | 1.0 uF | 47 K | US$189.99 (300V) |
| 5 Hz | 0.67 uF | 47 K | US$160.99 (300V) |
| 10 Hz | 0.33 uF | 47 K | US$114.99 (600V) |
| 150 Hz | 0.022 uF | 47 K | US$39.99 (600V) |
| 180 Hz | 0.018 uF | 47 K | n/a |
| 200 Hz | 0.016 uF | 47 K | US$36.99 (600V) |
Looking at the table above, the 1 Hz point is not practical for premium capacitors, from a cost and voltage rating perspective. A better compromise would be 3.3Hz or 5 Hz. At present, the outstanding items for resolution prior to the ordering of the components are the input tube and the output RC parameters as mentioned above. Changing the R to 100K will effectively half the value of the capacitor, further reducing costs.
The candidates for the input tube are limited in that I want to have a low Rp tube. Leaving 6H30, 6DJ8 and 6N1P. Having a stack of 6N1P/6DJ8 from the Decware amp, that seems to make the most of sense. In particular the 6N1P with higher voltages show incredibly low Rp, 956R at 300V! But by far the most flexible is the 6H30 with average Rp of around 1200 over a range of operating points.
The 12BH7 also entered the equation as I have a Maple Tree Audio Design EAR headphone and line amp that uses the 12BH7 as the line output amp, that I am about to rebuild without the line stage.
The Aikido will be powered by the matching PS-1 Voltage regulator with both HV and LV regulator. This seems an ideal match and in discussion with John, appeared to be a better match for the 5687 with lower voltages and higher currents than the Janus, which he suggested was better for higher voltages and lower currents.
The Aikido kit arrived a few days ago, and I ordered with it, the PS-1 Voltage Regulator kit. All I can say from initial un-boxing, is that the quality of packing, instructions manual/booklet and components are first rate! I do look forward to further unravelling the kit, and expect more photos.
DRD45
The final missing part was the Ultrapath capacitor, in which I invested in a pair of Mundorf M-Tube Cap 100 uF/550VDC. Whether this will be bypassed with a lower value special quality (Teflon, Silver foil, etc) capacitor will remain a future question. I have finally laid out the two monoblocks and marked the cutting plan onto the MDF panels. However, with a recent thumb injury, the machining of this will have to place further down the track.
Fostex MLTL
A pair of Fostex FE-207e was purchased some time ago for a MLTL, that had the original intention of being upgraded later to a Lowther or AER alternative. However, I also wanted to maximise the performance of the 207e. I purchased a pair of Phase Plugs from Planet 10 Hi-Fi. These are unfinished, and I will apply of few coats of Shellac to seal them, which should match the intended enclosures. I also purchased a bottle of Dammar as per Sakuma's advice. However, I will not apply the product until the speakers have had at least 200 hours of burn-in.
At present, the intent is to have the 207e cover from low bass in the 30-40Hz region up to around 10 kHz and then have a ribbon tweeter take over from there to around 40 kHz. The first step is to build the enclosure and test it before the application of a super-tweeter.
After listening to this amp and the Fostex combination for around 50 or so hours, here are some additional thoughts. The setup has changed, and the amp is directly fed by my Macbook Pro using standard analogue output, the source material is Apple Lossless through iTunes. Eventually, a proper DAC will be made to feed, along with a proper volume control.
The speakers are dead quiet. No hum. The only hum is the mechanical hum on the power transformer, which can be heard from around 1m distance. Not too annoying, but will try to add some damping to the chassis to reduce this somewhat. The tubes do run hot. Being my first all tube power amp, I did not realise that it was such a case. One can easily feel the heat rising around the tubes, especially on the top. It appears that the orange glow of the heaters is confined to the heaters (I think). I will make some more enquiries and also some testing of the circuit condition to make sure its all okay. The top panel (black painted MDF) gets quite hot to touch after a few hours of playing. At this stage, I don't think it is too bad, especially with Winter coming, it might be well to have all that extra heat in the room!
The driver tube I have now changed to a Phillips PCC88. I was initially running with the recommended Russian tube, but changed to this one because of my concerns regarding the heater voltage. The 6.3V spec'd seems to be running a bit high, and I may use some dropper resistors to bring that down. From memory, the tested voltage was around 6.9V or higher. This may also explain the heat from the tube.
Finally, listening to various music in my collection has really revealed this setup as really easy on the ears, even at loud volumes. I would not say this amp combination extends to the very highs or very lows (due to the speaker combination), but the sound is something that I find very soothing. This is especially true on female vocals (e.g., Missy Higgins, Dido, etc). This combo seems to have no problems with the kinds of music that I play, but it definitely is not great to very hard rock with heavy bass lines and crazy drumming.
All in all, this combo is very good, and in the future, I plan to upgrade the speakers by the addition of a super tweeter, building of a decent DAC and Phono stage, minor circuit upgrades to parts and eliminating the transformer hum, and finally upgrading the coupling capacitor from the current Premium DIY Hifisupply Obbligato caps to V-cap Teflon or Audionote Silver foils. But the top priority at this stage is to remove transformer hum, check and change (if required) heater voltages and add super tweeter.
After powering it up and listening to it for around 2 hours on my dipole Fostex FE127E MLTL here are some initial thoughts.
This amp took around 3 months to complete. The first was in ordering and sourcing the upgraded components. Also, the chassis design was undertaken. I then took a few months off due to having no time, and on a long weekend, I had the time to complete the amp. The staining and painting of the chassis was around half a day's work, but it spanned a day due to the time waiting for various finishes to dry. Up close, there are defects in workmanship and definitely learning lessons for the next chassis, but from normal viewing distances it does look quite smart. It took the better part of a full day to complete the PCB, and fix and wire everything up in the chassis.
After some false starts with grounding and connection issues, it was finally operational. A few notes. It takes about 10 to 15 seconds from power on for music to come through the speakers. The tube rectifier to thank for that. After some time playing, the chassis area around the power tube got warm. Not hot, but warm. Around the rectifier wasn't too bad.
The range of music that I was initially listening to was light (Dido, Missy Higgins, Coldplay, etc) but the sound was superb. With the Fostex, the sound stage was large, but could've been larger. The vocals, as I said before, were amazing. The bass, if it was a simple bass line was also impressive. There was a lack of very high end sparkle, that I was used to with my Mark Audio J6T, but that may be improved with a super tweeter. Overall, I am very happy with this amp. Much of the reason for building this amp was to further test and hone my skills in making high voltage tube amps. This proved that I could wire it up correctly, and test and find faults. It also proved to me that I can take a schematic and PCB making some minor changes, but still keeping the whole thing working.
However, it also demonstrated that 2W with my current speakers are not loud enough. Therefore, if I'd like an extra 3dB of headroom, and play it at most another 3dB higher. I would either need the same speakers with an amp of 8W or need the same amp with speakers that are 100 dBW. Therefore, if I built a 300B amp running around 8W, this would give me the flexibility of using the same speakers or using higher efficiency speakers. Conversely, I could use the 300B with slightly less efficient speakers and have the same 'loudness'. Any which way, this is an excellent amp for smaller rooms with high efficiency speakers. They produce a lovely sound, that should only get better with time, and have a wide range of differing tubes to be rolled and tested. It is reasonably priced and is an easy to build kit.
Highly recommended!
Here are some of the progress photos.
