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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Electrocompaniet Preampliwire 1A Schematic
Electrocompaniet Preampliwire 1A Schematic
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Old 28th January 2010, 05:08 AM   #1
ke9oa is offline ke9oa  United States
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Default Electrocompaniet Preampliwire 1A Schematic

I hope that somebody can help me. I have already contacted Per Abramsen about his unit. He said that the preamplifier had to have a model number such as an EC1. I sent him a JPEG of this unit, and haven't heard from him since.
I have contacted Electrocompaniet, with no results.
I purchased this item on eBay last month, and it had two problems. The first problem was an intermittent connection in the regulator section of the main board. I did repair that problem, but there is another problem. On the RIAA input (no MC board installed), the left channel is behaving as an unloaded input. If I try to inject an audio signal right at the motherboard, there is no amplification of the signal. All I hear is white noise, characteristic of an unloaded/unterminated input.
Without a schematic of this unit, I am stuck. Is there anybody that can help me?
Thanks in advance, for any help that anybody can provide.

Pete Gianakopoulos
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Old 30th January 2010, 02:40 AM   #2
ke9oa is offline ke9oa  United States
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Default Electrocompaniet Preampliwire 1A, repaired!

The problem with the phone stage turned out to be a shorted 47uF bypass cap, on the 45V rail. Why the designer of this unit chose to use 40V electrolytics on a 45V line escapes me. A 63V component should have been used.
I replaced the four 1000uF 63V caps in the power supply, but they do tend to get warm to the touch. Measuring the input of the plus and minus 45V regulators, I see 90VDC. Could be that somebody replaced the power transformer in the outboard unit. 45 volts drop across the regulator is not acceptable. Add the fact that 1/2 ounce / sq ft copper is used on the boards, and it makes me wonder why this is sold as a "high end" product.
Once I get this unit finished, it goes out the door.
I spoke to Pedar Beckman today, and he informed me that the company does not release schematics to the public, because this is a proprietary design. If proprietary means using 40V caps on a 45VDC power supply rail, I can understand why they don't want to release this kind of information. I would be embarassed to let anybody know about the "cost cutting" measures that were used. Hopefully, Electrocompaniet is doing better electrical design work nowadays.
I have been an RF engineer for the past 15 years...........if I did this kind of slipshod design, I would have been out of a job years ago.
Best thing to do when picking up one of these units is to replace all of the electrolytic capacitors, dereating them properly. Another thing I noticed........there are TO-92 transistors that are using heatsinks. This style device typically can dissipate about 250mW of power. If these things need a heatsink, this is pretty scary. At least, Electrocompaniet does warn you about the unit running pretty warm. High level Class A designs are fine, but if they are designed properly they don't have to run hot to the touch. I measured the heatsink temperatures of the voltage regulators at 160 degrees F.
This is way too hot! Never again, with an Electrocompaniet product!
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Old 31st January 2010, 12:11 PM   #3
ke9oa is offline ke9oa  United States
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Join Date: Jan 2010
Default Preampliwire 1A schematic

Upon further analysis, the 47uF caps are used as interstage coupling caps. Still, a direct coupled approach could have been used, eliminating these caps.
The reason that 90VDC was appearing across the 45V regulators was because the center tap connection from the toroidal power transformer had broken loose at the XLR type of power connector on the connection cable.
The unloaded output of this power transformer is 105VAC, center tapped. When the transformer is connected to the unit, this voltage drops to approximately 80VAC, center tapped.
After filtering this voltage, it is integrated up to plus and minus 60VDC. This gives a 15V drop across each of the regulator transistors.
Instead of using a 2200uF cap in the power supply for each rail, the designer used a pair of 1000uF caps in parallel for each rail. I would presume that this was to improve the transient response of the power supply, by cutting the inductance in half.
I decided to use a single 2200uF cap for each rail.............to negate the effects of the inductance, I took the newer approach, bypassing each capacitor with a .1uF film capacitor, also using a 1000pF fim capacitor with these other two.
Still, because of the poor attitude of Electrocompaniet I don't think I would ever buy a new Electrocompaniet product.
They should take a hint from companies like PS Audio, Hafler, Audionics, Parasound, and Mackie. These companies have no problem e-mailing PDFs of the schematics.
Years ago, I had a Belles Research DCA tuner. There was a problem with regeneration in the detector stage. Eventually, the company folded up and I gave the tuner to a friend of mine.
Years later, I did speak to Mr. David Belles, and he turned out to be a nice enough fellow. This tuner used an OEM version of the Magnum Dynalab FT-101 board. Eventually, MD was nice enough to send me a schematic of this board. Good thing for me, because I picked up a PS Audio tuner that used this board. The biggest difference between the original board and the OEM board besides the metering circuitry is the fact that an LM358 is used on the OEM board whereas a 5532 is used on the original board. Since I needed to replace a cracked ceramic filter on the PS Audio tuner, I upgraded the LM358 to a better sounding device.
The whole point is that the highbrow attitude of many of the "high end" equipment manufacturers can put their customers at a disadvantage, especially when the unit breaks (and they do break!) and the customer has no service information. Oh, you could send the equipment to one of the service centers, at only 90 dollars an hour, but this isn't for me, especially when only a few dollars worth of parts are required to repair the unit.
I am just glad that it didn't turn out to be anything that was too complicated. I hope I never have to pull that daughterboard off, with the time delay circuit. It wouldn't be too bad of a job itself, but with that 1/2 ounce copper foil that is used it could represent a problem when you try to clear out the solder holes for the connecting pins.
Years ago, when I worked as a printed circuit board designer, the interviewer told me "you have the power to make life miserable for a lot of people, so you need to be very careful when you do the board layout". What he was referring to was design for manufacturability. Lets take that to the next step........design for serviceability.

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