RMI-FC100, a single stage audio power amplifier - Page 53 - diyAudio
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Old 29th December 2008, 02:54 AM   #521
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Quote:
Originally posted by andy_c

"Follow the shoe!"

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Old 29th December 2008, 07:45 AM   #522
AndrewT is offline AndrewT  Scotland
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Default ClassA power prediction

Vre=20mV.
Ire =0.02/Re
Re=0r1 Ire=200mA
Re=0r15 Ire=133mA
Re=0r22 Ire=91mA
Three output devices in parallel pass three times the quiescent current.
Maximum ClassA current ~twice the quiescent current.
Max IclassA; 1.2Apk for 0r1, 0.8Apk for 0r15, 0.54Apk for 0r22

The Max ClassA power is I^2*Rload/2
5.7W into 8r0, 0r1
2.5W into 8r0, 0r15
1.1W into 8r0, 0r22.
These Max ClassA powers are halved when driving 4r0.

If you set up with Vre=17mV then the Max ClassA is reduced appropriately (~72%).
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Old 29th December 2008, 07:58 AM   #523
AndrewT is offline AndrewT  Scotland
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I use 600mW 1% metal film resistors and they fit 0.3inch (7.62mm) pitch.
They seem to be a standard size here in Europe. Body size varies 6.0 to 6.5mm long and 2.3 to 2.6mm diameter depending on manufacturer.
Available from Truohm, BC components and Philips in the Rapid catalogue.
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Old 29th December 2008, 11:55 AM   #524
AndrewT is offline AndrewT  Scotland
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Default regulated PSU heatsink grounding

The four pads at the heatsink locations need to be connected to Gnd.
These pads will short to Gnd if screws are used to locate the heatsinks.

But if heatsink pegs/dowels are used then ensure that each peg does connect through the anodising of the heatsink.

I might be tempted to hardwire the four component connections back to the Gnd.
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Old 29th December 2008, 01:10 PM   #525
roender is offline roender  Romania
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The heatsinks must connect two lateral groundplanes with the central groundplain.
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Old 29th December 2008, 02:00 PM   #526
pooge is offline pooge  United States
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Quote:
Originally posted by AndrewT
I use 600mW 1% metal film resistors and they fit 0.3inch (7.62mm) pitch.
They seem to be a standard size here in Europe. Body size varies 6.0 to 6.5mm long and 2.3 to 2.6mm diameter depending on manufacturer.
Available from Truohm, BC components and Philips in the Rapid catalogue.

Wow. Most of the 1/4 watt resistors I see are that size. I guess I'll be standing all the resistors up.
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Old 29th December 2008, 02:11 PM   #527
roender is offline roender  Romania
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Quote:
Originally posted by pooge



Wow. Most of the 1/4 watt resistors I see are that size. I guess I'll be standing all the resistors up.
Hi Pooge,

E-mail me your address and I will send you in an envelope all necessary resistors.

M
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Old 31st December 2008, 02:07 PM   #528
pooge is offline pooge  United States
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Thanks for the offer. Appreciate it, but I can get them OK. You've done enough to provide this amp for us.

For anyone in North America looking for a transformer for the input stage, I am making inquiries for R-core transformers. Unfortunately, suppliers are closed for the holidays, and can't be contacted. I have no idea what they will cost, but perhaps a group purchase would make it doable. But the only other supplier of stock transformers I found for the input stage PS so far is a Plitron toroid, and they aren't cheap either.
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Old 31st December 2008, 02:59 PM   #529
Sheldon is offline Sheldon  United States
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Interested in what you find, Pooge. BTW, this is not a budget amp. Just ordered the bulk of parts for two stereo amps, mostly from Digikey. Came to over $350.

Sheldon
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Old 31st December 2008, 03:17 PM   #530
roender is offline roender  Romania
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Guys,

This is not a cheap amp ... nor the sound
My grand total for this amplifier is over 1500 Eur, including the DAC (integrated in the same enclosure), but i must admit that I used a lot of butique parts and two big R-core transformers and a small one for the DAC.
This price doesn't contain R&D costs

Happy New Year!
Mihai
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