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.

PPA Amp Completed! (sort of...)

After a few years from starting the PPA v1 board, I finally had the time to finish off the board and give it a run through. Having forgotten what I was going to do with it, it was hard again, to figure out where I was at, and what I would need to complete it. The photos show the final setup, a real mess. But it works!

Initially I tested it with a TL072 amp, but it didn't work. There was no noise. My mistake is that the TL072 is a dual OPAMP and the board is for single OPAMP. Stupid me... Anyway, plugged a OPA227 in, and she was working like a charm.

Some initial thoughts. The setup is far from ideal, but the music was sourced from iTunes, using lossless AAC. All connectors were temporary, read poor quality connection and cabling. The headphones I used were my Sennheiser HD650.

With the bass boost on, as I put it in by default, the bass is too much for me. Maybe they would be well suited to smaller headphones, but that needs to be confirmed. With the bass boost off, the sound was well balanced, and has a certain 'fullness' and precision/clarity that was missing from my standard Maple Tree Audio EAR+HD tube amp. Mind you, having only used this amp for less then an hour, these comments are by no means definitive. So far, the sound has been very good with the 227, and I hope to test it with OPA627 and AD8610 and may even others. Which I think is the great beauty of the design. Find a single OPAMP and can give it a go.

On the side of noise, there was a low level of floor noise audible. But this could be due to a large number of reasons; dodgy wiring, use of a cheap regulated wall wart, lack of ground of the Alps control (as suggested by Tangentsoft) or maybe just bad wiring. I guess there will be more resolution on this, once everything is correctly wired.

I intend to use this also with my Shure SE210 IEM, and the pending Etymotic ER-4S. But right now, finishing off the case is the highest priority, as well as deciding on the power supply method. At present, using battery power seems to be the option (given I have the battery supply board), but determining a suitable voltage and charging method, that will be another decision in itself. Finally, PPA 2.0C arrived in the mail recently, and given I just soldered PPA1, it might be fine time to put together PPA2 with the diamond buffers.

PSU for the DRD45

The above is the schematic design for the DRD45 power supply. This was done using PSU Designer II. The above shows a residual 'noise' of around 6 mV, which with a 510 V gives a noise dB of around -98dB. This of course ignores the higher harmonics generated, but makes a good starting point. The design calls for a 50uF ASC oil cap, followed by Electra-Print's 20H choke, and then a dual combo of 100uF Solen aluminium can and a 47uF Solen PPE capacitor. There is scope to change the last 47uF to a 50uF ASC Oil. Wanted to avoid electrolytics not just for the rumoured acoustic difference, but also for reliability. The power supply transformer is 410-0-410V, which is an odd rating, but I am sure that Jack (Electra-Print) is able to wind one that is suitable.

dB Calculator

Here is another nifty webpage to assist with voltage noise and gain calculations.

LC Filter Calculator

Here is another nifty calculator for determining the frequency response of a LC filter circuit. This could also be useful for PSU design calculations. I used this to aid in the understanding of the determination of the 'Ultrapath' capacitor. Using an example Plitron PAT-3035-SE, with a primary inductance of 28H and an Ultrapath cap of 51uF, the frequency cutoff (not sute if it is f-3dB) is 4.2 Hz. My understanding from this, is that any audio signals above 4.2 Hz will be returned back to the cathode to ground, rather then through the PSU capacitors to ground. Doubling the capacitance to 100uF, results in a frequency cut-off of 3 Hz.

From 300B to 45

After some weeks of research, dialogue and thinking, the 300B amp has been put on hold for the moment, to make way for a 45 DRD monoblocks. The main reasons behind this change is; lower operating B+ voltage and availability of quality new and NOS tubes (there are no NOS 300B easily available). To this effect, I have ordered the chokes and reactors from Electra-Print, and they arrived within a few weeks. In addition, I have started to place the other components on order. In the signal section, I am using Caddock MK132 resistors, Mills high wattage resistors, Ohmite adjustable rheostats, Blackgate NH driver cathode bypass, and Solen PPE Ultrapath. Tube sockets will be teflon type. In the PSU section, I will basically using the same design as Electra-print design. The diodes will be changed to hyper-fast diodes, the filter caps will change in value. At this moment, I am considering filter values in the range of 500uF to 1100uF. Apart from some minor changes in component specification, it is very similar to the schematic as provided by Electra-print. The irons will all be Electra-Print, except for the Power transformer, which may be sourced from another supplier. Though the change from a 300B to 45 reduces power significantly, from around 8W to 1.5W, I believe that tandem with a 95dB+ speaker, and given my listening room is a small room, I shouldn't be too concerned. Full schematic, photos and progress will be available shortly. About half the components have already arrived, so looking forward to completing all parts, ready for construction and audition!

High Pass Filter Calculator

Here is a great link with a Java app that determines the frequency response of a RC high pass filter. Very useful for determining capacitor coupling values.