Dennis Had Inspire Amps

[cgn-dt-n]

Analog Addict

Nice report on the creation of the PSE

For me as someone who has no idea about the technology / electronics, it is always fascinating to see how the device is created piece by piece.

Modifications to construction on the fly? I thought the circuit diagram was fixed before the construction and the chassis was accordingly equipped with the appropriate holes etc. specially made for the project.

[Isaacc7]

Originally Posted by cgn-dt-n

Analog Addict

Nice report on the creation of the PSE

For me as someone who has no idea about the technology / electronics, it is always fascinating to see how the device is created piece by piece.

Modifications to construction on the fly? I thought the circuit diagram was fixed before the construction and the chassis was accordingly equipped with the appropriate holes etc. specially made for the project.

There are lots of different ways to build the same circuit. In theory any of them should work. Reality sets in once you start putting stuff in the box. How do you get that wire to the other place? Oh wait, I can’t get to the other thing now because that wire is in the way. Why is the amp humming? Lol. Building a single example of an amp requires a lot of adjustments on the fly. By the time you build the fifth one all the kinks have been worked out. Or, as he said, if you are Dennis and have been building for 50 years you can avoid a lot of fumbling lol.

[cgn-dt-n]

If I understand correctly, it is not a departure from the original circuit diagram but a changed layout due to the space available, size of the components and possible electrical interference. Basically the same amplifier, only the way the cables are routed and the components are placed is different.

[Analog Addict]

Well, here’s the rub. I don’t know how many connections and terminal strips I’m gonna need to build an amp. Dennis is obviously in a much better position in this respect with his decades of experience. Once a design is worked out and finalized, then this can be done by rote.

Also, once I had this chassis painted, I am loathe to drill new holes if I don’t have to, as to avoid chipping the paint. Powder coat would have been much easier to work with, but because there was JB Weld filler around some of the corner welds, powder coating was out of the question.

So that leaves me with trying to work with the holes that are already drilled for other connection points plus a best guess how many holes need to be specifically placed just for terminal strips, and where to put them in order to get the most efficient use out of them. Then the question of wiring layout comes into play.

One may notice that I built my grounding scheme first. I do this on purpose because it allows to to start to visualize where I want to route different wire sets.
For example, in this design, all the filament supplies are AC, so I need to not only twist them all, but also try to run them 90° perpendicular to any signal wiring to try and minimize any AC noise bleeding into the signal. And so on and so on.
Dennis does all this his without consciously thinking about it, but as is pointedly obvious, I’m no Dennis…

This is all part of the process that most people don’t realize is going during the prototyping of an amp, or the building of a one off design. I’m posting these building updates to try and give people an appreciation how much thought and how much work really is behind all these beautiful Inspire creations you all know and love…

PS: I’m out of town till next weekend, but will be available via PM for everyone’s Inspire needs…

[cgn-dt-n]

Thanks for the info
this helps me, as a technically inexperienced person, to understand a little bit of the immense effort behind the products. In addition, if the end product is functional, there is also the fine-tuning of the sound. a lot of work goes into the prototype until a series product is created.

[cgn-dt-n]

has anyone heard the new LP 396 pre amplifier???
where are the differences in sound to the CJ5 or 2030

[Analog Addict]

So I finally made it to the shop after being either busy or out of town. Brought along my PSE GK6'er to get the filament transformers in phase and add the plate caps/holes for the 816 rectifiers. Power supply was mostly done, and needed a few parts for the bias circuit.

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Dennis and I drilled the plate cap holes and added a couple of grommets. He then showed me how to phase the 2 filament transformers, a process actually very similar to using an extra filament tap as a bucking transformer. Hear are the rectifiers after installation of the plate caps.

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Got to the point where Dennis said "let's fire up the power supply..." and this is what happened...(Click on image for video)

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After a bunch of head scratching, circuit re examination and a lot of burnt fuses, we finally determined that one of the original rectifiers was shorted and causing the light show...Just happened to have a spare 816 on me and lo and behold, the PS circuit works! Tubes are not glowing much because there is no load to draw current, but you get the idea I hope.

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Meanwhile on the non foolin' around bench we have this....

The upgraded KT-88 Firebottle...

Dennis has upgraded the power transformer which now supplies a higher potential plate voltage and more current on all taps.

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While the summer doldrums are in effect, Dennis had some time to redo the tube charts for the Universal series of amps, including an Ammeter to measure plate current.

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And here's the end result...

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He didn't list any 5V4s, but told me that they can be used in the same slots as the 5AR4, but with a little less resultant power output.

Lastly, as for the 396A pre amp. I have not heard it yet. The current one and only doesn't seem capable of leaving Dennis' home system. What does that tell you?

Apparently Straitwire is finishing up chassis #2 soon, so one way or another, I am hoping to hear it soon...

[Analog Addict]

Went to the shop on Monday to work on my PSE GK6'er, and found that Dennis had two, count 'em two, PH-1 Phono pre amp's on hand. At least one of these is for sale, and you get to pick Black or Red.

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Cost is $2250 with the PH-1 using a 5AR4 rectifier, a pair of 6SL7s, and a 12AX7.

Meanwhile, in the back, here I am sharing a bench with a true master of the art.

How lucky am I?!?

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[Masterlu]

[cgn-dt-n]

Hello AnalogAddict

did Dennis change the circuit on the phono stage?
5AR4 and 6SN7?

mine came with 5Y3 and 6SL7.

Dennis said the circuit would only be designed for the 5Y3.
Can I try the other tubes as well?