Re-direction Part 3 - First Verification

This will be a long entry. Last weekend I was back home for a few days, and I took the opportunity to set up my speaker system. The main purpose of this was to verify two things - listening and volume and bi-pole speakers. The set-up was quite simple and there was no effort to optimise cabling, speaker position, etc. The amps were my previously completed LM3886 chip amp and the second was the Decware Zen kit. Both of these amps have been completed for over 3 years, but have had very little chance to run due to life circumstances. The speakers were a 'closed' bi-pole FE-127e towers.

A few notes about the amps. The Chipamp was made from the stock with no upgrades or modifications of any kind, had it was not a dual mono. The Zen was significantly upgraded from the kit. All resistors and most capacitors were changed. It has been modified to use a 5U4G rectifier and has a large 40uF ASC oil cap. The tubes used were all Russian 'EV' grade 6n1p and 6p15p.

The first arrangement was the Chipamp with the speakers set up as dipole. That is, both of them moving in the same direction (even though they are mounted back to back). This would be akin to an Open Baffle arrangement, as the dispersion pattern is a figure 8. Previously, I preferred this arrangement, and my starting point was from here. The source used was by QA350 running on battery power and with a range of CD ripped or HD Tracks converted WAV files.

First time, everything worked. Which was quite a relief. I will now talk about the Chipamp and Dipole in a whole. The sound field was strange, and with the nulling effect at 90 degrees of the speakers was quite prevalent. The sweet spot was indeed a spot, both vertically and horizontally. The speakers are mounted a little lower, around 800mm off the ground, and was lower than my ear level. I found that I had to be pretty level with the speakers and in the middle for the sound to be good. But when I was in the right spot the sound was pretty good. After listening to a few familiar tracks, I realised that this particular combination didn't sound right to my ears. So I decided to switch it to a bi-pole configuration.

In a bi-pole configuration, the speakers are wired so that they both move in the same direction relative to the speaker baffle face that they are mounted on. That is, they both move in to the speaker and out of the speaker at the same time. The net effect of this, was a dispersion pattern that is very omni-directional. This was quite obvious when standing 90 degrees to the speakers. Unlike the dipole, there was no reduction in volume.

Sitting back and listening, I found two things. Firstly, the sweet spot is much larger and more forgiving. I could imagine a few people being in that spot. Secondly, the sound stage and sound field was much larger and there was more immersion. After a little more listening, I quickly realised that this was the sound that I preferred.

After I got to this point with the speakers, I decided it was time to try the tube amp. I cranked it up with the Chipamp and did some casual measurement on my iPhone. The levels at the listening position was around the 80 dB marked, and hovered around there with peaks just shy of 90 dB. At this point, I realised that my goal of 100 dB plus at the listening position is not required for me. Therefore, I have to revised my design criteria, and it seems that I would like the amp and speaker combination to have total capacity to reach somewhere in the 90 dB range at the listening position. At this point, I am thinking specially between 96 and 96 dB. This would give some additional headroom, and would significantly open up the speaker and amp combinations.

The spec of the FE127e is 91 dB, and in a bi-pole configuration, it should be around 94 dB, which, in newly revised, should only need a 2-4W amp to reach the desired levels. I did notice that listening at loud levels, I did get a slight headache, and it was fatiguing. Hence my next move to change the amp.

Plugging in the Zen did not alter the sound dramatically. However, having only listened to these in the span of a few days, I imagine it'd be difficult to find all the differences. However there were two important differences that I noticed with the tubes. One is that it was not fatiguing at all at any levels. Second, the sound was more full, whereas the Chipamp was more sterile. So in this short sessions, I have decided that Chipamp (and solid state) was not the way for me moving forward.  Once I settled on this, I spent probably 6 to 8 hours in total listening to this setup. And it was really a delight.

Overall, the sonic presentation was natural, easy and spacious. The bass was not loud, but was present and without authority. This is one area that is becoming more and more important. That I need to really find a good speaker to supplement to provide the missing bass presence. With the Zen, two observations was made. The first, is that almost at full volume, the levels were around the very low 90 dB, maybe hitting 92 dB. This was probably as loud as I would want to listen to for a period of time (more than peaks or more than a track). Secondly, I found that classical music, which to to date, has been a little disappointing in my other setups, was very pleasurable. It didn't seem constrained and didn't feel like it was running out of steam.

So, the little effort that I made this trip provide to be very valuable. The following items have been confirmed.

1. Peak levels would be in the low 90 dB range, and thus total system response should be at least 96-98 dB at the listening position.
2. I prefer bi-poles to dipole. I didn't get to chance to wire it as a monopole - though I was thinking about, but I was just enjoying the sound so darn much.
3. I prefer the Zen to the Chipamp. And thus, I could make the extrapolation that I prefer tubes to solid state sound, or Class A to Class D. 

This has been both important and enjoyable, and now I have a few months to prepare my plan of attack before I am back at home permanently.

EL84 PP Idea

Well, I was on the train home and was thinking about the Beyma. I was considering have it passive crossover. Using copper foil inductors and Jantzen caps, it turned out to be around US$350. I was then thinking what if I just built two simple EL84 PP amps instead, and then I can experiment with a cheapie PA active crossover. This was, I can tune them and then once the sweet spot found, I can do a hardwired active crossover. Would that be cheaper?

Anyway, more incoherent thoughts later, see below. 2.6W in SE mode, and thus is Class A PP, it'd be 5.2W. 2nd harmonic should cancel out (mostly) and the 3rd harmonic should sum, but the predicted 3rd harmonic is pretty low. The PSU below using a choke input. It could be a simple, 'cheaper' build. But it could also be quite good. The output transformer is 8k in SE operation.

Oarta output transformer

It looks like the Lundahl LL1623 rated at 90mA would be the best choice for this amp. The amorphous core price is less than half of the Tamura, but more importantly, it is available. The interstage transformer would be the next choice. This would probably be the most important choice, given the different voltage swings that needs to be accommodated by the different tubes.

I think at this point, it would be important to at least try to limit the range of tubes to be used. This has to be correlated with my current stash of tubes. In this, I would say that there are four families that I would like to run:

1. 45, 145, 245 and 345. I have a number of pairs and have been universally hailed as an excellent audio tube.
2. F2a. I have three pairs of these long life tubes.
3. KT88/EL34 family. I have two quartets of the KT88 and EL 34.
4. 300B. I have one pair. 

Looking at the above, it would make most sense that I provide more effort towards the first three families given the volume of tubes on hand. With the 300B narrowed out, the voltage swings required are now limited to 30 Vpp to 60 Vpp, a little more sensible. This would mean that a tube with a gain of 20 would be plenty. At this point the 5687 and C3g seems the right direction. If I use a higher gain tube, I can use a step down interstage, which should be a good think overall. The other option, is to allow a different tap on the interstage to be used to connect to the grid of the output tube, which can select between say 1:1 and 2:1. But this may affect the performance and bandwidth of the interstage.

More questions... 

Oarta Output Transformer

It seems that the Tamura F5003 is in limited supply, and may not be available. So I may have to revert to another brand of amorphous core. Maybe Lundahl?

Oarta PSU

One interesting point is that if the PSU is cap loaded with a 10uF, at 200mA, it will give around 380V. But if I remove the cap, and have it choke loaded (using the LL1673), at at loads of around 100mA to 150mA, it will give voltages of 260-280V. Perfect for 2A3 and 45. So in this case, if I can provide switchable PSU filter, I can further extend the range of usable tubes, rather than using resistors to drop voltages.

Oarta - Some Design Images

PSU Design.

KT88. 400R cathode 

300B. 740R cathode

KT66. 300R cathode.

EL34. 400R cathode - can share the same plate as KT88.

6550. 400R cathode - can share the same plate as KT88.

The Oarta - One Amp to Rule Them All

It has certainly been a quite a long time since I have done ANY DIY audio stuff. I blame this due to my relocation to Hong Kong for the last 18 months and having young kids. There just ins't time. Well, with the imminence of return back home on the horizon, I have started to dream up what I will finish up. In this long time away, I have realised that I like variety. But I don't want to build too many amps. So, I have taken a few ideas, based around a SET and merged it into one amp. Which I call - Oarta, or One Amp to Rule Them All, not exactly creative.

The basic premise of this amp is that the PSU will allow the supply of around 390V at 200mA max, with heater windings two sets of heater windings, 2x 6.3V at 2A and 1 or 2 5.0V at 2. This should allow me to use a large range of tubes that I have on hand: F2a, 300B, KT88 and EL34. And also open up a whole range of other tubes that can run at those voltages.

The second part is a universal output transformer. I have chosen a 5k tap, but may move to a 3.5k for more power. For this amp, it will be no compromise, so a amorphous Tamura F5003 or F5002 will be on order. The driver stage will be a medium mu (think around 20) that is interstage connected to the output. To accommodate the wide range of output tubes, I will probably want a higher gain stage, so C3g triode connected may well be the final choice.

The trick here is to allow the switching of the output tube. To this, I am thinking of an adaptor plate that allows the socket and cathode resistor to the changed. The bypass resistor will then be mounted on the chassis. In this way, I can have a large film cap that isn't changed with each socket. On each adaptor plate will be 5 connections; grid, plate, cathode, heater + and heater -. I need to find safe and reliable connectors that allow me to change.

The final trick is have a 6.3v and 5.0v winding, and finding a method to accommodate a range of heater suppliers. For the indirectly heated 6.3v tubes, this is no issue, but with the DHT tubes, like the 300B, PX25, etc., this will need some more work. There may need to be an allowance for something like the Tentlabs filament supply, that can run from the 6.3v to power a 5.0v and run from the 5.0v to power a 4.0v tube.

If this can be made to work, I have an amp, Oarta, that will allow me to change tubes, without having to change anything else. This will allow me to not skimp on the rest of the components, knowing that it will be universally applicable. At the moment, my current thoughts for the design are:

PSU.
Amplimo 7N1474 Transformer (here - I may need to supplement with additional heater taps)
2x 6AU4GT diodes
Cap input 10uF ASC Blue line
Two LC stages with Lundahl LL1673 200mA (here) each with ASC 50uF.
I am thinking about a separate LC stage (15H with 40uf) for each channel and an additional LC stage for the driver.

The main issue with the PSU is finding space for all the ASC oil caps and the chokes.

This will give me around 386V of B+ at 190mA current draw (simulating with PSU Designer). At this B+, the following would be the power output with different tubes (from SE Amp CAD) using F5003 all running at 80mA per tube.

300B: 7.6W with 120 Vpp
KT88:  6.8W with 62 Vpp
EL34: 8.8W with 60 Vpp
KT66: 4.5W with 46 Vpp
F2A: 5.8 W with 32 Vpp (by hand)

And I would think that this would also work with tubes like GU50, PX25 and some of the other more rare European or exotic NOS tubes. And if I don't mind burning off voltage as heat, it could be used on 2A3, 45,  AD1, etc. - again, options. Beyond these, there are still a number of issues to work through, but in my mind, the concept already has been resolved. I am now thinking about cathode bias for the driver, and most likely will head down the LED route. Given the C3g triode seems to work well with around 2.0-2.5v bias. 170V at the plate, 2.5v bias 15mA. Nice and simple.

The main course of action now, is to determine how best to build the adaptor plate, this will make or break the design. It must be safe, easy and high quality to preserve the rest of the amp design. And the last question is how to deal with the different voltage swings required by the various tubes. Which differ by a factor of 4. I do not want to simply waste it by using an attenuator, and the first thought was to have taps on the interstage, which would allow me to choose the right ratio, 1:1, 2:1 or 4:1. This I think is possible with the Sowter 9525. But I probably want to avoid changing the IT ratios as that will change the frequency response characteristics.

Or I could just vary my source output - say between +0 dBV, +6 dBV and +12 dBV. (Which incidentally is possible with the Wadia 121 DAC that I am considering, see manual). Or, I could just accept it, and have to set the volume levels differently for each tube. This though, needs more thought and consideration.

C3g Headphone Amp Progress

  

Here are some photos of the progress build of the C3g Headphone amp. As you can see, the TubeCAD Regulator PSU unit is assembled, and the various major components laid out. The key components: Acoustic Dimension 41 step attenuator, Lundahl LL1689 Amorphous core output transformer, TubeCAD PS-1 heater and HV regulator, two Hammond mains transformers, and massive IEC Inlet with filter, fuse and switch. All of this in a 16x8x3 Hammond aluminium case.

There are some time restrictions as I will be leaving shortly, and need to complete this within a few days, otherwise it will have to go in the post. Note that I am missing still the Yamamoto Loctal teflon sockets. Still, a lot of chassis work to be done, as well as testing, etc. 

TU882 and the DT880

Again, I found an excuse in my packing to swap the headphones, from the Sennheiser HD650 to the Beyerdynamic DT880 (600 ohm version). The first thing I noticed was that there was no noise at all. No hum. Virtually silent. Very promising indeed. Listening to my standard favourite/test set of music, there were a number of differences between the Senns and the Beyers.

The bass is more present (i.e., louder) and rich with the Senns. The Beyer, they feel more articulate, but less in your face. Far more restrained on the Beyers, where on the Senns they feel like it has been let loose a little. The presentation of the Beyers was less warm than the Senns, and a little more clinical. The voices on the Beyer is more refined, but lack the lushness, similar as well with guitar strumming, the Beyers are precise, but lack that slight indulgence that makes it full and warm. Overall, the balance favours the mids and probably overall a little more balanced than the 650's, though probably a little shy in the bass region. I would regard the Beyers DT-880 as more precise, controlled and pristine. Whereas, I would describe the HD-650 as warm, natural and lush. Obviously very vague terms, which are highly subjective, not only to me, but between different sessions, moods, etc.

The above observations were made between two sessions, over two consecutive evenings at around the same time. The setup was identical except for the headphones, and it was the Elekit TU-882R with the Western Electric 396a (with around 20 hours on them thus far). The volume control was different by around 2 to 4 'hours' relative to each other.

C3g Headphone Idea

Here is something that I knocked up quickly as I was listening to the HD650 and Elekit headphone setup. This is in a similar vein to my D3a concept and shares many similar parts. I think this project would be very quick to knock up. This would make use of the TubeCAD Regulator PCB kit, making the build itself even more straight forward. The main reason for considering the C3g as well as the D3a tube are the various comments on the Internet regarding the consistency between various D3a samples. It appears that there may be a high sample variation between the tubes, and careful selection is required. The C3g, being a lower Gm tube, may have less sample variation. But time will tell, as I have to actually build the two amps first, to test the outcome. Again, this might work for other triodes as well.

More thoughts on the TU882R

Just having a lovely session with the TU882R and the HD650 right now. They WE396a tubes are in, and has been warmed up for over half an hour. Just a casual, easy listening session now, with Missy Higgins, Crowded House and Coldplay. A very nice way to end the day...

I am now trying the HD650 with the Medium impedance switch. The hum is now gone, and the amp is dead silent. According to the manual, this impedance setting is for 20 to 100 ohm headphones. However, I am trying to discern if there are any sonic differences between the two settings, apart from the hum. First impression is that the sound isn't as dynamic or lively. It is a little more laid back and somewhat 'lazy'. The bass isn't as well controlled or present either.

Well, after the recent experience with the WE tubes, I decided to order three more pairs of the 5670/396a from Brent at Audio Tubes. As usual, all my previous experiences with Brent has been excellent, and this time around, it was no different. He offered a good deal when I purchased three pairs; Western Electric 396a, WE made 396A for National and a British pair labelled 'National'. I have always had good experiences with British made tubes, the 12AE6A Brimars being a prime example, and thought that they could be a good counterpoint comparison with the others. Well, I hope to receive them in the next few weeks or so, and start to enjoy their different sonics.

As I am writing this, I am definitely preferring the high impedance tap, even though there is the hum in the background. It just mates so much better with the HD650. Well, more testing to come.

I have recently noticed that some of my music has very strong super stereo effect, where music is coming out of one side only. I do find this a little distracting at times, and started to look into placing a crossfeed. I installed with in my Mini Max Millett but never used it, cause it didn't sound right. On review of the setup, I think I might have wired it incorrectly. The next step is to remove it from the amp itself, and create myself a little stand alone box to house the crossfeed. This might make it easier to compare the effect and see whether it is right for me. Anyway, more to come later.

WE Strikes!

The thing was, as I was starting to pack up the stuff ready for the move, I was in the room with all my headphone gear, and decided that it was best to do all the packing with the headphones on. As such, I thought, why not try the Elekit for the next week. So, out with the Crack, and in with the TU882. And the first thing I noticed was that the hum was not as loud as before (or so I thought), but it was definitely lower than the Crack that I just unplugged. That is the good news. The bad news was, I was using a pair of Raytheon 2C51 and I just wasn't all that endearing, the sound that is. So, I thought, I might spend a few minutes to change out the Raytheon and put in a pair of WE396a that I had purchased. Firstly, it was very soft on the right ear, almost no sound. My heart sank.... 

Was it the amp, or the new tubes? No idea. But as the amp got warmed up, slowly, the volume on the right side picked up and now it settled in to match the left. A sigh of relief. But boy, only the first hour of music, and the sound is so much better! So much so, I am thinking I need to get me more of the Western Electric NOS. Another thing I noticed was that the hum levels was actually less than the Raytheon tubes (this is going by memory...). But, it is now very quiet. Not dead silent, but very quiet. Not as quiet as the Ear, but close. Regardless, the sound was so much improved, it makes me really want to keep listening to this setup. 

Anyway, a moment of revelation, and onto the shopping! 

Crack and Speedball Up and Running!

Finally put the replacement parts into the C4S board this morning. See the photos below. The rebuild itself was very quick, only 5 components to solder and 3 wires to reconnect. After doing a few visual checks to make sure everything was in order, I fired her up. And yes, it worked! No problems this time. Equal volume on both sides, and all LED lighting up as they should. Now this amp has been fixed, I now have four fully working headphone amps; the Crack, TU882R, Ear+ and the MiniMax Millet. I'd have to say that the sound stage is a lot more compressed then what I remembered last time I was listening to this amp. I am using the stock tubes supplied by Bottlehead, which is a Philips ECG 6080WC and (I think) a Sylvania 12AU7.

An initial observation about the floor noise of the Crack. There is a hum, but given it is AC filaments, it could be from that source, but it could also be from the B+, who knows. I would have to say that it is not as loud or obvious as the hum on the Elekit, but this is just anecdotal observation, as the last time I listened to the Elekit was a few weeks ago. Again, the Ear+ doesn't have this problem, but that is DC filaments. Could it be from the B+? The Crack has CRCRC filtering. The Ear has CRC for the output tube, and an additional RC stage for the driver tube. The Elekit has  cap input, followed by a FET, which I can only presume is acting as some kind of series regulator. 

Well, moving house very soon, and all of this needs to be packed up and transported. However, the beauty of the headphone amp and system, is that they are so portable, and can be one of the last things packed, and the first items unpacked. I think in the coming months, I'd have a good opportunity to start some comparisons between the three amps.

Repair of the Crack/Speedball

Finally got around to removing the board that was damaged due to my own fault. See the photos below. You can see a very small hole in the small blue resistor 237R. It measures over 4k now. One of the diodes also do not bias up at 1.4V. All parts removed and the through holes cleaned. I accidentally ordered the 2N2907 and 2N2222, rather than the "A" versions. Now, I have ordered the correct ones, and also a replacement 237R resistor. Should all arrive by next weekend, in time for re-installation. 

Confirmation from Sowter

Here is confirmation from Brian Sowter that their attenuators cannot be used as unbalanced to balanced convertors. The email snippet for your information.


From Brian:
"You cannot use one of our transformer attenuators as a phase splitter.  3575 could be used following the attenuator but our type 1125 has full geometric balance and would be more accurate than any non transformer method."


To my question:
"I am planning to build the Raven and was wanting to use the 9985 as both a phase splitter and an attenuator instead of the transformer phase splitter currently recommended (either a 3575 (which I have) or the LL1676).

Can you confirm that the 9985 is suitable as a phase splitter as well, and with excellent imbalance."

Elekit TU-882R Completed!

Today, I had the opportunity to revisit the parked Elekit headphone amp. I removed the aftermarket pot, with its, 'too long' wiring, and installed the stock standard Alps pot with the associated PCB. Fired it up, the problems experience were all but gone! I am not happily enjoying the amp. There is still residual hum, but its' level is now constant with the volume. Only the digital hash coming from my source is present, and that is proportional to the volume control level. I would like to run the amp in for about a hundred hours or so, over the next month, before I make further, more educated comments. Thanks to Victor to recommending the fix.

So far, the sound has been quite enjoyable. First impressions are that the bass is not as 'slamming' as the Crack, and more inline with the Ear++. The amp has much higher gain that the Ear++, as the volume from my computer is quite low, and a good listening level is around 40~50% on the volume control.

More F4 parts and update on TU882 Kit

Having looked around at the different suppliers and options for the source resistors for the F4, I think that the Mills MRA5 0R47 option would be the best. The Caddock MP915 requires a heat sink, and their other range of higher power resistors that do not require heat sinking, like the MV261 series are not easily found. Having made a personal note to avoid Parts Connexion, I have sourced Michael Percy for them, and will put together an order, along with the Nichicon KG that they stock.

Other information of note. The transformer selection for 2 channels of the F4 requires a minimum 300VA transformer, with two 18V secondaries. In my design, since each channel gets its own PSU, I will aim use a 250VA to 300VA transformer per channel. This should provide adequate headroom and maybe keep the load lighter, and thus the core cooler. From this, I can deduct 5A rated choke should be adequate, one for each of the positive and negative rails, instead of the parallel 0R47 resistors. The Hammond 159ZJ should do nicely. Now I need to get four of them. It also appears that amps with large farads of filtering capacitors may have a problem with the power on thump. So I will look into a soft start arrangement, and try to keep that to the primary side of the transformer.

I also contacted Victor about the hum and noise issue, and he suggested that I revert the amp back to the standard configuration, using the supplied pot and PCB to see if this problem can be removed. Smart idea. I will do that when I get the chance.

Completed the Elekit TU-882

Last night, I had the opportunity and time to fully assemble and complete the last steps of the Elekit TU-882R headphone amp. Firstly, I have to say that the quality of components and fit are top rate. The chassis work is extremely nice, though it may not be your taste, one cannot complain about the quality. I myself, like it, and will most likely leave the tube guard off, as I like to look at the tubes, and also do some tube rolling. More on that later.

Check out the progress build photos below. You will notice that I have put to use the stock 0.1uF polypropylene coupling caps to good use. I have used them as the PSU electrolytic shunting.

I had about one hour last night to listen to the amp before I had to retire for the night. Firstly, it worked! On first impression, the sound is quite relaxed, but what I noticed most was the bass control. A lot firmer than the Ear+. Anyway, more on that later, but I discovered an interesting problem.

There is sever noise or ground contamination. This is the situation. When the volume is all the way down, I can hear hum on both channels. Relatively loud, and doesn't go away when I connect or disconnect the source, or when I touch the chassis. When I turn the volume 2 clicks on, I can hear some strange buzzing on the left channel, with the hum still on in the background. As I turn the volume up, the buzzing doesn't get any louder. Until about the top two clicks, the buzzing disappears immediately, and is replaced with noise on both channels (the white random kind). I can still hear the buzzing at the top three clicks, but it is getting progressively softer. Meanwhile, the noise is also getting softer the further away from full volume, within the first 2 or 3 clicks, it is gone.

The strange buzzing is heard through the music, quite annoying. Now, I did not use the stock supplied PCB for the volume control, and this may be attributed to that, but I am sure it has something more to do with the ground scheme. Perhaps, I have to get the saw out earlier to get the IEC with a proper ground connection done sooner. Anyway, will be speaking with Victor about this, and see if he has come across this before, and find a solution.

Otherwise, this has spoilt a good and fun kit to build. And whilst the music is playing, but minus the buzz or hum, it is quite enjoyable and pleasant. More to come soon!

Progress on the TU882

After having received the resistors earlier today, I actually found some time to progress the build further. Check out the photos below. I found that it was best to pre-tin all the wires before installing them. I also note that there wasn't an Australian lead supplied, and it has no earth connection. This is something that does concern me, as I want to make sure the equipment is safe, with kids around. I might look into modifying the kit once complete to add a proper IEC three terminal connection to allow for a ground connection. Otherwise everything went very smoothly.

Modifications to Elekit

Recently had the chance to review the components and check that all the parts were present and accounted for. There was only one very minor issue, in that one of the screws was indicated in the manual as having 6  numbers, but shipped and only requires 5. A minor error, otherwise, all parts in excellent condition. On examination of the PCB, I noticed that the through holes were very small. Indeed, none of the after-market capacitors or resistors leads will fit through the holes. I emailed Victor and confirmed that I need to very carefully enlarge the holes. He recommended a hand drill for the process. So, off to the hardware store to find a small pencil drill bit and a matching small diameter drill bit. Hopefully I can begin the through hole enlarging process in the next few days. (HT58RCWVRAK9)