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I hate to say it but I take issue with Kusiak's statement that ALL transistors with Mondial or Aragon printed on them are in fact Toshiba's. Most if not all of them are in fact RCA/Motorola transistors. I know what you're thinking, but he's Mike Kusiak from Mondial so certainly he knows better...

There is no Series 2 that I've ever seen. This looks like a feeble attempt at creating something that it's not. I also notice that the person that installed the sticker used a pen to put a roman numeral "II" on the serial # sticker. Upload a picture of one of the channel boards and I can tell...

Measure DC mV across any one of the eight vertical .5ohm 2W resistors located at the bottom of the channel boards. Do NOT try and reach in the powered up amp with a set of bare probes to do this. You need a set of minigrabbers. Power the amp off, hook up the minigrabber connectors to the...

I'm sure that Mondial's procedure is a "better safe than sorry" adjustment. Better to have customers check and adjust when hot than cold to allow for possible production differences.

Measure voltage drop from JFET source to drain on one jfet, then multiply X .00509. This is dissipation for one jfet. Then multiply that total X 2 to get total package dissipation for each JFET pair.

Overall gain of the L10 should be unaffected by changing the volume pot from 25k to a 20k ohm. Maybe there's something strange going on with your volume pot? What is the output voltage from the source component that your feeding the L10 with? Is it > 2V?

The small board and transformer supplies +12V to the protection/muting circuits on each channel board. It can be bypassed but to be safe the overheat switch has to be wired in differently to keep thermal protection active. It sounds to me like you should be getting the seller to reimburse you as...

Not really a mystery, do a search for Zobel network. There's one hanging on the output of your Acurus or Aragon amplifier, there's also one on the feedback side of the complimentary input on your Acurus amplifier. Increasing the capacitance lowers the frequency cutoff. The resistance dissipates...

Here's how you want to construct the CRC, just replace 291r with 25r. Your AC mains ripple will drop drastically across the resistor. I'd go with a larger secondary capacitor. Probably 1,000uF or larger.

You have something connected improperly. A CRC filter with a 291 ohm resistor in the current path should produce probably 8 to 9 volts drop across it in the Acurus pre. What was the DCV measured across the resistor in the filter? This is too much resistance for an RC filter in this pre. You're...

Well that busts my last theory of your last shorter amp being an early pre-production version. This amp is a mid-production serial #, so anything I come up with will just be speculation. Its hard to understand why they'd have two versions of case size coming off the line especially in this...

I'm confused, too many amps for my old brain. Is this also the amp pictured in Post #11?

I've heard good things about TKD but never tried one myself, so I'll be interested in what you think of them.

Lowering the value of R16/R17 will not affect the bias in the Acurus to any significant degree. You'd need to cut the trace between the gates of Q7/Q8 and put a variable resistor there using a very low value of 100ohms or so. However I do not recommend this. The jfet's will conduct with the gate...

I would say that the original McCormack DNA-1/ DNA-1 Deluxe has an above average failure rate due to the main board problems I mentioned. If you do not have the ability to have the unit repaired by a competent tech then you may want to pass up the DNA-1. I also see some things in your images...

Well yes & no. Originally they didn't use the leads as vias. The holes had ferrules in them, but the connection between the pads and ferrules seems weak, plus many of the leads are really tight going through the ferrules which limits the flow of solder from the back side through to the front...

The DNA-1 is an excellent sounding amplifier. Its one of the best sounding amps I've had in my system. It can have issues with the main board as others have pointed out and these issues will typically result in the red protection light remaining illuminated on the front panel. Some owners have...

That's good news, it sounds like you've probably put this problem to rest.

So something to keep in mind is that when you start turning the power up and the bulb gets bright your DC rails are dropping A LOT. You could be introducing issues with the DBT at this point. Do this test, take the amp off of the DBT and idle the R CH again (no signal) and then ramp up the...

Does the protection trip if you run the L Ch only up to >10W and leave the R Ch idling with no signal?

I'd move up to a 100w bulb in the DBT to get closer to normal DC rail voltages. Also remember that as you take the output stage bias up your DC rail voltages will sag with the DBT (especially 60W) in the main AC line and may lower the chance of the fault showing up. You may want to leave the L...

P1 & P2 are essentially sampling the output of the channel that they are tied to. When a voltage level becomes high enough in either the positive or negative direction it trips the protection circuit. Disconnecting the P1 or P2 connection takes this ability away. After thinking about it some...

Good to have an inside source of info. I picked up a defunct DA-1 last year to rebuild and play around with, hopefully at some point later this year I'll have the time to dig into it. In my opinion, the DA-1's seemed like an amp with good bones, but a somewhat weak circuit design. Thats why I...

This is actually what I was thinking may be going on as well. A possibly bad bias pot and a local issue on the protection pcb. You could put it back together and power it up then once it fails and the prot relay kicks out then disconnect the R channel input at the prot pcb to see if the...