More Decware SE84 Information

Just wondering if I wanted to change the rectifier in my SE84 kit from the N4007 to a 5U4G the wiring would be as shown in your manual "ZSmanual.pdf", in which the following wiring is shown:

• Two Red from the secondary is connected to the anode of the 5U4G (pin 4 and 6)
• Red/Yellow to ground
• Two Yellow from the secondary is connected to pin 2 and 8 of the 5U4
• Yellow/Black connected to the input capacitor.

Question is, on the "ZSmanual" schematic, the first RC filter resistor is rated at 50W, whilst on the SE84 kit it is a 6W. Do I need to change it to a 50W dale, or similar?

[Steve/Decware] You are correct about being able to wire the tube rectification as per the SE84ZS schematic. The 50W Dale used in the SE84ZS is not required. We chose that particular resistor because it is a 1% tollerence and like the way it sounds. The 6 watt dale will be absolutely fine.

Speaker Design Website

Another very useful site for information on U and H frame sub-woofer design (amongst other speaker related articles.

Decware SE83

After looking around for simply HV tube kits, I came across Decware. They make the Zen SE83 tube amp in a range of configurations. As you may know (and can find out more from the site itself), the base model is around a 1.5W to 2W Class A design using a Triode connected pentode as the output tube. The arrangement is clever in that it can appear to bridge two amps together to form a higher power 6W or so SET amp. The claim is that the sonics are not reduced. However, of interest to me specifically, is that they offer a almost all parts (minus power switch/socket, chassis, etc) kit for the same amp design for a reasonable price. The kit comes with output transformers, power transformers (with international windings of 240V, a great move unlike some other kit manufacturers who refuse to sell and/or option the power transformer for anything but 110/120V). So like all good things one comes across, I ordered the kit and started to think about upgrading the kit already!

The question was why did I abandon the Uniamp and the DRD45 project for this? Firstly, the power transformers for the Uniamp are playing up, and may have been shorted or wound only for 110VAC. Which is annoying. Secondly, I am still somewhat hesitant in doing a point to point job on the DRD45 with 500VDC without first working on something somewhat safer (that was the point of the Uniamp). Since the Uniamp hasn't got around to working yet, but I am still keen on a tube amp, this seemed to be a good alternative.

Looking at the schematics, the circuit looks to be a fairly typical SET with a PI (CRC) PSU filter, AC heater windings, grounded cathode input stage with a capacitor coupled to the power stage, all of which seemed fairly typical. However, on closer examination it appears that the output stage is somewhat unconventional. The output transformer is not connected to the ground! The two output terminals are connected direct to the speaker. Thus, no connection to the ground at all. On the input side, one is connected to B+ (specified at 346V DC) whilst the other is to the anode of the output tube (6BQ5, etc). This feature, is, according to Decware, what allows two amps to be connected as a bridged amplifier. I would love to investigate this further. A true SE amp of 1.5W ish, can be instantly converted to a 6W SE amp! Sounds tempting.

After ordering and reading through some of the information on the site, I sent Steve of Decware some questions, here are his responses. (Reproduced with his permission)

1. Can I substitute the SS diodes in the kit for a Tube rectifier? Like a 5U4G or similar. Looking at the schematic of the kit it appears that there is a secondary winding on the power transformer that is unused, I assume it is a 5V designed for the rectifier?

[Steve/Decware] Yes, the power transformer has the windings for a tube rectifier.

2. To connect in series bridged mono mode, what is the process for series connection? Would it be a series connection between the two output transformers; connecting - of transformer 1 to + of transformer 2 and then the speaker to + of transformer 1 and - of transformer 2. And at the input end, both inputs would be connected to the same signal.

[Steve/Decware] Yes.

3. As a later date upgrade, could I replace the AC heaters with a DC regulated supply or similar.

[Steve/Decware] Possibly, but it’s debatable if it would actually be an upgrade. You best bet for future upgrades is to focus on trying different coupling caps. The board has been designed to accommodate both the small stock cap as well as large after market caps.

4. Does the point-point wiring have audible differences to the PCB?

[Steve/Decware] Yes, but this board is quality designed so the difference is minimal. The tube rectification would make a much more noticable change than point to point.

5. In the future, am I able to order just the transformers from you, where I can source my own parts elsewhere?

[Steve/Decware] Yes, I plan to make it possible to order just the transformers or board next time I edit the web site.

6. The 0.1uF coupling cap that forms a R-C filter, can I up the value to lower the f-3dB point?

[Steve/Decware] You can, but I wouldn’t recommend it. The bass is perfect as is, and the phase response is exactly where I want it.

7. Do I need a preamp? I would like to run this direct after a phono stage (with say 40 dB of gain)?

[Steve/Decware] No preamp needed, no. Your input sensitivity will be 2 volts. You can achieve close to that with a 5mv cartridge like the Grado and a stage with 42dB.

8. Can I replace the 1K/6W PSU resistor with a choke (I have a few Hammond 159P 10H/125mA/155DCR)

[Steve/Decware] You can, but the fundamental signature of the amplifier will change as will the clipping characteristics. Right now the amp clips gracefully. If your goal is to get the best sound possible you might try it both ways and see which you like better.

9. Can a cathode bypass capacitor be added to the 6922 tube as well? Perhaps something in the range of 220uF to 1000 uF to assist with reducing any chance of NFB.

[Steve/Decware] Again, it can obviously, but you’ll want to listen to it both ways on a variety of tubes and determine which you like best.

10. Will the board fit larger (more exotic) coupling caps? 0.1uF? Can I say put a Mundorf Silver/Oil or a Audionote/Jensen copper in oil, etc?

[Steve/Decware] Yes, the coupling cap area of the board was made with two different hole patterns so you can use either small or large caps.

11. There should be no issues replacing the PSU caps (33uF/450V) with a few 30uF ASC oil caps I have?

[Steve/Decware] Probably not, other than a small change in the power supply ripple.

Tube Substitutes for the SE84

Currently investigating the Decware SE84 kit. The tubes used are some fairly commonly available tubes with a number of interesting equivalents. I like the tube complement because you can get a huge range of NOS, current production and Russian/Chinese equivalents. Great opportunity for tube rolling!

Input: 6DJ8, 6922, 6N1P, E88CC, E88CC/01, ECC88, CV2493,CV2492, E188CC, 7308, E288CC, CCa, 6N23P or 6H23, 6N11, 7DJ8 (different 7V heater).

Refer to this link for more info.

Output: EL84, 6BQ5, SV83, 7189, 7189A, CV10321, CV2975, CV8069, N709, 6P15, 6P14P.

Refer to this link for more info.

Speaker Design Website

Another two interesting and useful sites AJ Design Software and the WinISD online version with really useful software to doing preliminary speaker design.

RIAA EQ

After some more reading, and some more research, passive EQ seems for me the ideal option. With this decided, the choices then boil down to either a one stage RIAA equalisation or a split EQ. Having read some information regarding the Tango EQ-600 LCR RIAA equalisation 'unit', I become interested. This was short lived as I discovered they are no longer produced. However, upon further seraching, I have discovered two current manufacturer/supplier of a LCR RIAA EQ unit. One from Silk (which can be found from DIY Hifi Supply (bottom of page)) and the other from Acoustic Dimension. Both are reasonably costly (in the US$470, and Euro 420, respectively). More to follow.

Turntable

After some debate, and conversations with a few different hifi store vendors, the conclusion was reached, a Rega P3 with an Ortofon 2m Black cartridge. My original turntable choice, was a Project RPM5, but given the cost of that, with an Ortofon 2M Red was already AU$1100, the P3 with Black at AU$1500 was not too much of a stretch. The unit should be fully set up and arriving with a week or so. This is quite exciting.

Meanwhile, I have begun shopping at local Salvation Army, etc stores looking for old LP. Gound a great range of classical music in very good condition. Found one or two 'modern' LP, the rest of the usual Irish Greatish Hits, Scores from Scotland, Nana Mouskouri, Barry Croker, etc. Prices were typically $1 per LP, but I found one store that was selling them at $0.50 per LP, with a much larger selection then most.

Time to start purchasing the cleaning kits, replacement inner sleeves, etc. Fun times ahead!

Markaudio 2" Speaker Projects

Currently for my surround setup, I am using the older Mark Audio J6T. These are still available from the Australian distributor, Decibel Hifi. They also sell some very compact 1 litre enclosures for these speakers, of which I purchased and have installed the drivers into. They are superb! The sound is crystal clear, articulate and refined. Quite different to my Fostex 127, but not necessarily better or worse. In fact, they do go down quite low. From design, the f-3dB is around 150 Hz, but in some music records it does reach quite low in the normal musical octaves. Not great for LFE in movies, but when talking about music, voice, etc (rather then effects), it is very pleasurable. I enjoy them so much that I am considering upgrading to the new Alpair 5 speakers, which is an improvement/refinement of the 6T. In doing so, I also want to move up to using Tasmanian Oak (or commonly called KDHW). The following are two designs for a 1l and 2l cabinet using standard stock KDHW readily available in Australia. The f-3dB should be around 150 Hz and 130 Hz respectively. (All dimensions in mm, and uses 135mm wide and 110mm wide boards.) 1 Litre. Internal: 97(w) x 110(d) x 97(h) = 1.035 l Externa: 135(w) x 135(h) x 148(d) BoQ (all 19mm thick, with butt joints (no rebates,etc)): 2x 135x135mm, 2x 110x135mm and 2x 110x97mm. 2 Litre. Internal: 97(w) x 110(d) x 232(h) = 2.475 l Externa: 135(w) x 1270(h) x 148(d) BoQ (all 19mm thick, with butt joints (no rebates,etc)): 2x 135x270mm, 2x 110x135mm and 2x 110x232mm.

Tube Information

Great site (most will probably already know it) that contains some basic information on various popular, and not so popular, tubes.

PCB Prototyping

Found a few more PCB proto-typing manufacturers who do low volume PCB. This is going to come in handy for some future and current projects. 4PCB PCB Express Express PCB

Phono Preamps

Excellent link and description of a tube phono preamplifier. This design is quite well documented and has been through some 20 iterations by the designer/author since 2000. This appears to be someone who is not just designing by paper, but also iteratively refining the designer after auditions and contemplation. The design uses a lot of irons and uses D3a and 5687 tubes. Another interesting design is coming by Andrea Ciuffoli. He seems to be updating his site with regards to vinyl stuff quite recently. His' Phono 2 design makes use of all D3a tubes, and appears to be a relatively straight-forward design with a passive EQ. It appears from many of the sites that I have read, is that the power supply quality is very important. Above and beyond these designs, I have ordered a simple Bugle PCB from Hagtech. This is a battery powered OPAMP phono stage that is simple and cheap to implement. Should provide a good 'sanity check' reference to the more exotic (and expensive) options. Continuing to explore.

Turntable Decisions

From not wanting to use vinyl, to wanting to switch to vinyl has been a quick and steep learning curve. Having read up on the Internet as much as I could fine relating to vinyl, it appears that there is a wide range of choices and opinions regarding turntables. The Project RMP5 and Rega P3 seems to be a consistent theme when discussion relates to starter turntables of a decent quality. Over the weekend, I visited a local audio shop and had a look at the RPM5. It looks to be a decent unit, and well made. However, the salespeople were unwilling to hook with the demo unit and play some music through it. Apparently they said that "it would sound different". Obviously. Not great service. The intention is to purchase a decent unit, with a decent resale or trade-in value so that if this vinyl experiement works out, it can be upgraded to a higher quality unit. Regarding the type of cartridge, it seems universally accepted that MC cartridges will offer a better quality sound, at the cost of a lower output signal (less than 1 mV). However, it also appears that they cost more and the stylus cannot be easily (if at all) replaced. Which then leads to the phono preamp. A transformer step up from MC to MM seems to be best way to ensure that both MC and MM cartridges can be accommodated. Therefore, the two distinct questions in the phono preamp is then: 1) Active or Passive RIAA equilisation; and 2) Tube, Solid-state or hybrid amplification stages. More comments to follow, but for me, it appears that a hybrid amplication using passive equalisation may be the direction I want to head in...

Since the last post....

A few things have happened since the last posting, all of which has kept me from updating this blog as much as I'd like to.

1. Completed timber chassis for the Uniamp. With one amp fully wire and connected, had problems with the fuse being blown every time. I suspect this may be due to the powre transformer not being rated for 240V, even though I specifically requested a 240V primary. Had not had the chance to fully ascertian the reasons yet. Will wire up the other one and see if the same problem occurs.
2. Almost purchased all componets for the DRD45. Some circuit design changes. But filled out with ASC X386S in the PSU, Caddock MK132 in the signal, Mundorf TubeCap for the Ultrapath, Electra-print irons.
3. Starting out with Vinyl. Contemplating Project RPM5 turntable. Beginning to investigate DIY phono preamps.

Hopefully more updates to follow, along with some photos.