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Moondog/DRD post on Welborne Forum

Erik Mandaville

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I have gotten several emails recently concerning the generally perceieved differences between the the Moondogs (available only used, now) and the current inventory of DRD amps. Ron W. has responded to this if anyone is interested.

I am becoming more and more interested in building the 2A3 version of the DRD for myself. In effect, I had already done this when I used the (Eliano-termed) Ultrapath connection on my Moondogs, but there are still some differences...all of this has already been documented here. I can probably afford the use of choke loading on the 2A3 grid, which I have come to really like on the version of the Horus I built over the summer. Grid chokes for the Moondog 2A3 are planned for the not-too distant future.

Ron basically indicates that he finds the DRD a bit more resolving than the Moondogs. Of course any company will sing praises over its products, but there are technical reasons for why his impression of the DRD as a fast and accurate amp could be justified. We have and continue to respect Leo's take on things, and he tried the Ultrapath connection immediately after me -- and said that he was never going back Those were on his Moondogs, by the way...

The other issue regarding the use of SS rectifiers has some specific points of interest related to the DRD output stage. Sonic characteristics aside for a moment, SS rectifiers have very swift inrush voltages that can be taxing on subsequent vacuum tube components. However, there is a major distinction that needs to be noted between the DRD and other single-ended amps: B+ inrush voltages are 'softened' as the tubes warm during charging of the cathode return capacitor (Which Ron W. calls the Ultrapath capacitor)-- sort of a very nice soft-start-side-benefit of the design. There is truly a great sense of unity and integrity in this circuit. Doubtless this must have much to do with the evident very good performance that owners have reported. Thus, the power supply related issues that may be a consideration with more conventional designs are less important with the DRD/Ultrapath amplifiers. Although I have enjoyed vacuum tube rectifiers on both my Moondogs (now much rejuvinated) and Horus rendition, I can see the possibility for outstanding performance achieved by way of SS diodes. Transient performance at both frequency extremes -- as well as midrange clarity -- could be awesome. I would just not want to be so dogmatic about either technology as far as how the amp turns AC into DC that I might miss out on superior performance.

I can say with some confidence that the DRD is probably very, very close to the Horus in terms of performance -- at least the permalloy OPT version I made. Those of you who were able to afford the cobalt output transformers are surely luckly, and I SO wish that I had been in the position to do the same.

The cathode resistor on the input stage is also capacitor-bypassed. In doing some rebuilding of my Moondogs, that famous C5 cap is back in position with a good quality electrolytic, and there it will stay. I'm putting one on each input stage of my JFL Horus amps this weekend.

In the end, I think any of you interested in SETs would be hard-pressed to find anything near the DRDs at their price-point. All the recent personality issues nothwithstanding, Welborne Labs is a small company working extremely hard to provide a top shelf amplifier for a great price. If you are able to build it for yourself, the value is of course better, still.


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I thoroughly enjoyed LoneStarBlues Ultimate Moondogs when they were here. My own are now once again dedicated to the Lowthers and have been once again wired for the higher impedance speaker load. Although maybe not as fleet-footed as the Horus parallel feed, they have a relaxed and rich liquidity that makes listening to them really rewarding a enjoyable.

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I agree that the Welborn Labs DRD kits look very good. I think that any stock amplifier is a starting point. If that point is acceptable then fine. If not, the amps are a great platform for modification to the owners' tastes.

The DRD amps will certainly bring out the best in Klipsch speakers.


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Hi, Leo:

I wholeheartedly agree, and I mentioned in some thread elsewhere that it would be a great amplifier to relatively easily change to a parallel feed design. This approach you certainly took to some length on your Moondogs.

I remember reading (at least I think I do!) Ron W. saying -- in written form, of course -- on his website that in looking for another amplifier to fill the Moondog's shoes, he had listened to and considered parafeed outputs, only to return to the Direct Reactance Drive design by Jack Eliano. I am not comfortable saying that this was the 'right' or 'wrong' thing to do, and Ron W. knows more about all of this by far than I. The DRD suited him well, and I personally think he chose a very capable and worthy successor to the Moondog.


...that the DRD is also available in tube or SS rectified versions should also be a comfort to those who roll out their sleeping bags in either of the two camps...

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Hi Leo/Erik:

I bought a pair of DRD300B "Ultimates" about a month ago. I posted my initial impressions on the Forum which were quite favorable.

After a long discussion with Ron, I went with the s-s rectified version. Besides, my DAC and pre-amp are tube rectified so I got 'enuf rectificashun' :-)

For under $2K, you cannot come close to these in terms of performance. They are "ridiculously inexpensive". Mine has Black Gates which, IME, take a long time to fully break-in. Once I get some more hours on the DRDs, I'll post follow-up impressions.

Sonically, they are extremely close to the Art Audio PX25 ($6000), which I used to sell when I had my audio shop. The PX25 is, IMO, the best sounding Art Audio amp. The DRDs have 98% of the transparency of the PX25 and maybe once they fully break in, may go neck-in-neck with them. For sure, the DRDs are dead quiet allowing for better low-level resolution.



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GMAFB! You've been on this Forum long enough to know that the current technology and methods of measuring components are not sufficient to "quantify" sonic attributes, therefore we have to use some other method to report similarities. In this case, subjective estimation.

Read carefully. I used expressions like IMO (in my opinion), IME (in my experience), etc., to qualify my remarks.

So, I'm sticking with 98%, not 97%.

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That sound great, Mike.

Thanks for reporting on this, and I don't doubt the SS rectifiers might do an excellent job given the nature of this design.


...as Leo points out, the DRDs are perfectly set up for possible modifications down the road. A parefeed output might be very nice, and would not be hard at all to incorporate. I'm curious, Mike: Does Welborne Labs offer the option of silver secondary windings on the output transformer? I'm actually more familiar with the original version of the DRD, which does.

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