RoHo

I used XSim crossover simulator recently when I re-designed the XO of my custom built speakers. Not only are these type of programs a great tool but also provide an excellent learning environment - "what happens if I do this and this and this". I chose XSim mainly cos I could get it to work on my Mac using Wine. And it's free. What's not to like?

Just listened to the latest episode on DIY speakers. Really enjoyed it and keep it coming. The mix of experience, humour and logical questioning is spot on, for me anyway 🙂

With a perfect amplifier power output will double into a halved impedance. So looking at the specs above if the amp was super-duper it would deliver 150 W into an 8 ohm load. I think that this amp, like a lot of receivers, is a lot less than super-duper in the power supply and so won't get near to doubling power into 4 ohms. Quoting this spec will broadcast this fact to the world at large. So they leave it out. It doesn't mean you can't use 4 ohm speakers, and Marantz apparently do allow this as explained above. But you would expect that known low impedance speakers my just pull the

I have also bought SE output transformers from NP Acoustics in Vietnam. Very happy with the product. There is some info on DIYAudio about them. Shipping from Vietnam should be cheaper than from the US.

All else being equal I would agree that the KT88s are being biased a lot lower than usual - 17W plate dissipation vs the max of 42W. I notice the main HV secondary of the power transformer is rated at 280 mA. This is marginal for a stereo KT88 amp and you would have to say sub-optimal. Increasing the plate current above 40 mA may well cause the total secondary current to exceed the safe limit. They are probably using the same power transformer from one of their cheaper models to save costs. But you have to wonder why use KT88s if you can't make use of the extra power they can provide?

The tube audio range were distributed locally by Golden Age Audio until Duc, the owner, sadly passed away. Not sure who handles them now.

Lundahl are quite reasonable value for money here in Oz. A step up from Hammond and Edcor, I would think.

The power amp uses 6cb5a, cheap TV tubes. I found out about them from Thomas Mayer’s Vinyl Savor blog. He wired them as triodes, traced the curves and reckoned they were as linear as a 300B. At 10 bucks each....shut up and take my money!! The input stage is another Allen Wright design, from his PP2C power amp and uses 6H30 tubes

It’s a Pre-amp, Allen Wright’s FVP5A circuit. Valves are Russian 6n6p. The transformer is a James from Taiwan. Sadly they closed down a few years ago. Good quality and much more affordable than the classy Japanese trafos like Tango and Tamara

Yep, the Toslink output is coming in very handy.

New miniDSP 2x4 HD with DIY valves. I like it both ways. 😀

It has worked previously but, yes, I should confirm it is functional Yep, made sure it was on

I have just replaced my old, original MiniDSP 2x4 crossover/processor with the newer 2x4 HD model. On of the main reasons is the new model has digital inputs, via Toslink optical or USB. My plan was to use the optical output on my elderly Rotel RCD991 CD player into the MiniDSP optical input. I've had the player since new, about 20 years, and never used the Toslink output. So I plugged it all in, started a CD playing and.....no input signal shown on the MiniDSP. I replaced the Rotel with my nearly as old Pioneer DVD player, which also has optical out, and it worked fine, so I figur

Both diagrams are effectively the same and will work, you're just taking the sub input from either end of the speaker cable. It is probably most convenient to take the sub input from the amp end of the cables. I can't see a change in DAC making a big improvement. Look at speakers first and whether the amp is optimal for them

I've had an RCD991 from new and it's still fine. IMO what holds it back is the analog output stage which is basically taken straight from the example on the PCM63 DAC data sheet. I changed it to passive I/V with a tube gain stage which was better and then replaced that with the stacked AD844 design of "LightSpeed" George which was detailed here and on DIY Audio. This took the player to a whole new level. Your right about the balanced output - complete waste of space. Have you experimented with upgrading the clock of the players you fix? I've often wondered if this is a worthw