John Curl's Blowtorch preamplifier part II

[john curl]

I might say something specific and important about the price and quality of preamplifier and amplifier cases. I am NOT a machinist, or a mechanical engineer, but I have made audio products that require custom cases for the last 35 years. In fact, the world has gone full circle, and the guy who designed the enclosure for the original Symmetry Crossover, 32 years ago, invited me to lunch, this week.
Now, in between, what have I learned? Well, talk is cheap, and quality control can make or break you.
The 'low bid' can well be the 'high bid' once the headaches start.
For example, when we started Vendetta Research over 25 years ago, I had hoped to use a pretty, pre-finished plastic box for the SCP1 pre-preamp. I used an internal conductive spray to create the electrostatic shield necessary. Talk about minimum thickness! Still, I had hoped to keep the prices down, and the rework to make the boxes useful, at a minimum.
Well, we outgrew the plastic box, when it was discovered by open listening test that we could hear the Tantalum electrolytic caps in the power supply bypass. Of course, some here would insist that I am imagining hearing any differences, yet some here also castigate me for using a circuit with such poor power supply rejection that the cap is essentially in the audio circuit, because that is why it was so easy to hear.
Well, it came to making a decent custom enclosure for the Vendetta Research phono stage.
One company, strongly recommended to us, was located in California, and they did audio enclosures for other audio manufacturers, already. Initially, we made some initial prototypes to try out the new package, and the initial prototypes came out almost perfectly. Then, we submitted the prototype chassis and paperwork to the highly recommended independent company to make in quantities of 50 or so, for each batch.
Now this is what happened: Sometimes the top and bottom plates were scratched, as if they had been handled in a 'dirty' environment. One time they forgot to BEND the sheet metal power supply box that makes it an enclosure, but they still finished and lettered the batch anyway, and sent them along to us.
Then, we started to have FIT problems. We had to hand match different lids to different cases, and you could see that drill holes were often offset from one side to the other. This was OUR fault, I was told, because the box that we designed, required a near perfect fit, i.e. no slop, to make it fit together. Just because we had made dozens of the same boxes previously that fit together easily and perfectly, was no reason that future cases needed to do so.
Later, with even other fabricators, I hired a mechanical engineer to make precise blueprints for submission, so at least I had a reference to argue over. Now 17 years, after Vendetta Research has ceased to need boxes, who do I meet at the RMAF, Oct 3? The son of the guy who was in charge of the company that we first used, where we first had problems, 25 years before. He is in charge now, and assures me that these sort of problems are not likely today. In fact, he still remembers the boxes that his father's company made for us. Once again. full circle. Do I trust him? Yes, but 'Trust and verify' in future ;-)
Now, can people begin to understand why one might stick to one, VERY GOOD vendor, even if they seem to have a slightly higher price, than the lowest bid, and how we might get suspicious of a VERY LOW bid?
I say all this, because 'loose talk' about subjects like this, cause confusion in others, who have not yet the experience with specifying cases, etc. First, they might think that I was intentionally ripped-off by our vendor, and that we stupidly went along, or that cheap case can be easily found without large volume production, and in-house expertise, and oversight, as to how to get the job done. Please keep these lessions in mind, everyone.

[Joshua_G]

Originally Posted by john curl

The 'low bid' can well be the 'high bid' once the headaches start.
…
Now, can people begin to understand why one might stick to one, VERY GOOD vendor, even if they seem to have a slightly higher price, than the lowest bid, and how we might get suspicious of a VERY LOW bid?

This is in accord with my own experience as purchasing manager for electronics manufacturing company.

[simon7000]

John,

Making sheet metal oncie's is easy, each piece is fit to match. In large quantities you can tune in the equipment to make all the pieces the same.

Small quantities are a B... When you bend sheet metal it gets longer by about 40% of the material thickness. It depends on the tensile strength and the absolute precise setting of the bending pressure or distance limits. The tensile strength in a roll of steel is not very uniform in the first few or last few feet, so you have to only use the middle. Aluminum is more often obtained in sheets so you do not know which part of the roll it came from. Changes in the mill making it have a big difference in strength. Then the thickness also varies. This is a double whammy.

As if the material difference is not enough, lets talk about tooling. I can buy precision forming tools or "standard." The precision is interchangeable. So if you order 50 today and 50 after my tooling has been changed.... Then my press brake is level within .005" at 8' in the morning, in the afternoon sun it is different by .015"

I have however seen absolutely beautiful sheet metal products where everything not only fits, but snap fits like the bud boxes do, only without bud's gaps.

Sheet metal work has been around a long time, computer controls and optical sensors make it better. Skill still is best.

As to audio cases, I have built heatsinks out of laminations, 198 of them to be exact. Gives me lots of radiating area and good control of fin to gap ratios. Cases can be built the same way, think of log homes. Of course that method was a military secret in WWII. It is how we built radar tubes at low cost in great quantity.

[SY]

simon7000, slightly OT, but an excellent article in the AX which arrived here yesterday. My compliments!

[john curl]

Simon7000, bending sheet metal was NOT our problem. NOT BENDING sheet metal was our problem in one case. It was MACHINED CASE precision that was the REAL problem.

[Juergen Knoop]

I remember when Norsk Hydro introduced their satellite dishes. Afair they had 90cm diameter and where milled out of solid aluminium blocks.
I haven't read any complaints then and I find all the moaning about prices in the blowtorch thread astonishing immature.
The blowtorch preamp is a luxury product and it costs what it costs.
Regards

[simon7000]

Originally Posted by john curl

Simon7000, bending sheet metal was NOT our problem. NOT BENDING sheet metal was our problem in one case. It was MACHINED CASE precision that was the REAL problem.

John,

The last product of your design I bought was an ML JC2 preamp. It was sheet metal as I recall. I read your post and from the hole mistakes and mention of unbent cases thought you were into more commodity sheet metal parts.

If you have an NC milling facility that cannot match pieces that is entirely a different issue. There is some thermal dimension changes from high speed milling. But not keeping holes to a reference is just bad work. Not taking back defective product and issuing a refund is quite telling.

With NC milling the first piece costs a bit more than the rest for programing time. There may be a setup charge for small runs, but otherwise the unit piece cost should be consistent.

Oh yeah my JC2 lasted about six months, went back for warranty repair, still not back yet.

[john curl]

Sorry about your JC-2. What went wrong? I could follow up, if you want. The tech (1) at Parasound, Tony, is overwhelmed at the moment, I'm sure. That might create a delay. Surely you mean a Parasound JC-2 don't you?

[simon7000]

Originally Posted by john curl

Sorry about your JC-2. What went wrong? I could follow up, if you want. The tech (1) at Parasound, Tony, is overwhelmed at the moment, I'm sure. That might create a delay.

It has been many years, I don't know if the stereo store had credit problems or if it got resold. That was 3 preamps ago. Thanks anyway.

[stinius]

Originally Posted by john curl

Sorry about your JC-2. What went wrong? I could follow up, if you want. The tech (1) at Parasound, Tony, is overwhelmed at the moment, I'm sure. That might create a delay. Surely you mean a Parasound JC-2 don't you?

John

It's ML JC2