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About MarcAL

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  1. Bunnings have various leg options in steel and timber and may be able to be modified to suit your needs. You could also make a plinth out of plywood perhaps.
  2. DIY audio: what are you building? Well, to me that means post whatever DIY audio projects that you are building and share this knowledge and experiences with other like minded individuals whether it is built and finished or still in the building / designing phase. At times it may look like Frankenstein has been here to some but that can be entertaining as well. Anyhow I like horror movies. After all the journey can be just as satisfying than the end result. To all fellow DIY audio engineers, have a go and keep up the good work.
  3. From memory I think that I used the transformer shown above the chassis for the B+ for the 6AS7G with a supply voltage of 122VDC @250mA with an extensive PI filtering network. The other B+ was from a small reverse connected 6V - 240V potted transformer (mounted internally) for the 6SL7GT with a supply voltage of 250VDC @4.6mA with a simple PI filter. The B+ rectifier diodes were all 1000V fast recovery types with snubber capacitors. The heater rectifier diodes were Schotky types also with snubber capacitors. There were separate heater power supplies used for each tube as the current for each was different and easier to control when separated. The total outcome was very quiet and clean with no audible hum and less wasted heat. It was a project that involved more power supply design than amplifier design in the end but well worth it. Feel free to PM me for more details. Regards, MarcAl.
  4. I built a headphone amp similar to yours some time ago using the 6AS7G as an output valve and the 6SL7GT as the input valve but opted for solid state rectifiers and pi filtering for all DC supplies in the end. I attempted to use a valve power supply built on a recycled chassis at first but could not source a large enough choke and it was generating too much heat at the time. Also a delay timer was implemented for the two HT supplies and an infrared motorized volume control on the input. Output coupling capacitors were around the 100uF mark and bypassed with a 10uF Solen which I would like to upgrade some day. However it works extremely well on high impedance headphones such as the Sennheiser HD-650's and sounds magnificent without any hum. I highly recommend this as a worthy OTL project. Keep up the good work, it will pay off. Still going strong after more than ten years. Below, the power supplies and amplifier module.
  5. Thanks Mark, Capital idea. Hope to catch up for a comparison soon. Marcus.
  6. Finally finished a complete custom LDR upgrade on my main valve preamp. The new boards installed are for LDR output with muting relay, LDR control with power supply and muting relay control with delay on and two x three relay input select boards. I was going to make a six input board using LDR's however that is going to be in the next major LDR passive attenuator project coming soon... or in the pipe line. Everything is custom made except for the Altronics volume control module kit replaced with a 100K//100K = 50K motorised Alps pot for controlling the LDR's. LDR's have been fine tuned using a total of six multi-turn pots to get an extremely matched 50 ohm to 24K ohm range. This was a bit tedious at first but worth the effort in the end. Valves have been removed for now as the current input devices have adequate gain to drive my power amp. How does it sound?... you may ask. Well, I no longer have any hiss, hum, cross-talk, colouration or noise of any sort including the dreaded wiper noise. Just clean, undistorted sound which has to be heard and experienced. If you have a good LDR setup you will know what I mean. Now I am indulging in music and listening to almost everything again as it seems that I have been missing so much in the past. This is the strongest link in my sound system for now and a long well awaited device. I can always plug the valves back in and flick the left and right input switches for a tube treat but I am more than satisfied at the moment. So the main board in the middle with the two valve sockets is not even used right now. Bit of a pity but is still a valid option in the future. Two x three input relay boards, LDR volume output module with mute relay and LDR adjustment trimpots. Motorised volume control, infrared remote volume control board, input selection switch, LDR power supply and mute relay control with delay on board. Back to listening.
  7. I have had this problem plenty of times with vintage drivers in cabinets especially with DIY'ers past projects. In one instance the previous owner had fitted the drivers in before the paint has had sufficient time to dry and hence they were glued in. However my solution for stubborn drivers is to use a non serrated butter knife and apply pressure to the rim and try to pry it loose. Work your way under a bit of a time all round and do not force the driver in one place as you may distort the basket permanently and possibly damage the cabinet. If you have a piece of very thin flat metal place that under the knife as well as to not scratch or mark the cabinet. It can take a long time and you may end up using every curse word ever known to man but if you are patient it should work. Be extra careful with drivers that have been rear mounted as the gasket is very fragile and can get destroyed. Avoid using any chemicals or over heat as it will ruin the cabinet the driver or both! Good luck.
  8. Item: Altec Lansing 416-8A Low-Frequency Loudspeaker Pair. Location: Sydney South. Price: $1000 Item Condition: Recently reconed/refurbished, see pictures. Reason for selling: Spring clean out. Payment Method: Pickup - Cash, Paypal Only Extra Info: 15" die cast aluminium frames, 8 ohm impedance, Alnico magnet structure, Low-Frequency Loudspeakers as used in VOTT and other professional quality speaker applications. These drivers have been recently reconed using GPA parts, tested and work flawlessly. Fs is 19Hz each. Data Sheet: http://www.yesterdays-tech.com/Altec/416-8A.pdf Weight: Approximately 17kg boxed. Shipment: Will send interstate via courier at purchasers expense. Approximately $40, shipped as one consignment. Photos:
  9. Perhaps you could try using an LDR attenuator circuit instead of a pot or stepped attenuators. No moving parts that would produce crackling and in some cases certain coupling capacitors may be not required either. There are a lot of circuits out there already or you can design your own using the Silonex NSL-32SR2 or Silonex NSL-32SR3 available from element14. I am in the process of doing an upgrade to my existing valve preamp but still using the Alps pot for control of the LDR's. Worth looking into anyway.
  10. The sound stage and imaging is definitely there and so is the venue. The difference that I have found with these horns is that it is big. Real big and is just there even for other listeners sitting in the same room. No harsh direction issues as I have found with narrow horns and not shouty either. Definitely different to Multicells and other Cellular horns. I still like them don't get me wrong but these MR94B's are my personal preference. The other bonus is that it just fills the entire house and not just the listening room. No stage boundaries exist when played moderately loud. So far the neighbours have not dared to complain so it must be acceptable.
  11. Ditto. (Well it has been 6 months but years in the making) Ditto. (45+ years but who is counting) Ditto. (However I am not planing on dying any time soon)
  12. Can't put my ears on it however it is the best DIY sound that I have had so far under my roof. Altec MR94B Mantaray constant directivity horns with 288C compression drivers and Altec 413-8 bass drivers in Onken designed cabinets re-tuned to 33Hz. Passive two way Hiraga crossovers suited for 24 ohm compression drivers and 8 ohm bass drivers as above. Overall very smooth, detailed and gets down to 25Hz with no effort. No sub required most of the time.
  13. Not sure what GFRC is so I googled it and up came Georges River Football Club.😏 However I am curious as to what you propose to cover the GRFC with and to perhaps give it a decent WAF? Never the less please post some pictures, time permitting, of the cabinets including the amplifier line up you plan to use to get 9 or 10 channels with. I like to see what I may be missing out on. I had tried active crossovers at first with my 2 way line up with okay results but for now the Hiraga passive crossover network works a treat. Yes, I know, the finished article again, looks the same but now it's sounding even better, it must be the Russian PIO that seems to be getting better with age perhaps. No more mess on the floor of the tribal listening room and totally out of sight behind the Onkens.😎 Note: the timber panel on the crossover board is a foot so it can stand upright with the terminals at the top for easier wiring access.
  14. You can just parallel outputs if you want.
  15. I used decent quality solid copper banana posts as seen in the pictures previously so the crossover networks are modular and field replaceable. I avoid crossover networks in cabinets when external horns are used.
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