Amber Series 70

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planet10

planet10

frugal-phile™
Joined 2001
planet10-hifi.com
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Bill Fitzpatrick

Bill Fitzpatrick

Member
Joined 2001
History:
There were differences between the designer(s) and those with the money. This proved to be the downfall of the company. They closed shop somewhere around 1979 after only a few years of operation.

The amps came in several flavors. Some had heat sinks on the rear, some on the sides. There was a black panel rack version, a grey panel non-rack version with rack "wings" available.

There was also a pre-amp (in both black and natural) and a tuner. And, I believe, an integrated amp. I have 3 of the Stereo 70 amps and a pre-amp.
Click to expand...

Circuit:
BJT in Class AB. Unique to this amp is the LM391N-100 chip which is still available. If you're going to keep the amp I suggest you get a few chips just in case they become unavailable in the future. You may also want to seek out and download a data sheet on the chip. I have a couple of amp schematics but they lack notations as to which serial numbers they apply to. You're welcome to copies if you like. There are no protection circuits except the speaker fuses. There are not enough output devices and heat sinking is insufficient to bias these into class A. You may want to clean the contacts on the plug-in printed circuit card; after these many years they probably need it.
Click to expand...

Experience:
They are very nice sounding amps but you don't want to push them overly hard into 4 ohms. The 2N5686 and 2N5684 output devices are still available at a cost of about $8 each. When one amp died on me I had to replace the outputs and drivers. The LM391 survived.

I haven't used mine in many years but have been thinking about pressing them into service again. First thing I'll do is make new, black rack mounted front panels for them. 2 of my amps have the rack wings and they aren't pretty.
Click to expand...

Anecdotes:
I have seen a number of these on ebay and they are ocassionally misrepresented as class A amps.
Click to expand...
 
M

maqm

Member
Joined 2010
Bill Fitzpatrick said:
History:
<blockquote>
There were differences between the designer(s) and those with the money. This proved to be the downfall of the company. They closed shop somewhere around 1979 after only a few years of operation.

The amps came in several flavors. Some had heat sinks on the rear, some on the sides. There was a black panel rack version, a grey panel non-rack version with rack "wings" available.

There was also a pre-amp (in both black and natural) and a tuner. And, I believe, an integrated amp. I have 3 of the Stereo 70 amps and a pre-amp.
</blockquote>

Circuit:
<blockquote>
BJT in Class AB. Unique to this amp is the LM391N-100 chip which is still available. If you're going to keep the amp I suggest you get a few chips just in case they become unavailable in the future. You may also want to seek out and download a data sheet on the chip. I have a couple of amp schematics but they lack notations as to which serial numbers they apply to. You're welcome to copies if you like. There are no protection circuits except the speaker fuses. There are not enough output devices and heat sinking is insufficient to bias these into class A. You may want to clean the contacts on the plug-in printed circuit card; after these many years they probably need it.
</blockquote>

Experience:
<blockquote>
They are very nice sounding amps but you don't want to push them overly hard into 4 ohms. The 2N5686 and 2N5684 output devices are still available at a cost of about $8 each. When one amp died on me I had to replace the outputs and drivers. The LM391 survived.

I haven't used mine in many years but have been thinking about pressing them into service again. First thing I'll do is make new, black rack mounted front panels for them. 2 of my amps have the rack wings and they aren't pretty.
</blockquote>

Anecdotes:
<blockquote>
I have seen a number of these on ebay and they are ocassionally misrepresented as class A amps.
</blockquote>
Click to expand...

Hello:
:)
I don`t know of any amplifier that feels itself confortable and can survive after: "push them overly hard into 4 ohms" (to use your words) this is an abuse that even the Professional amplifieres can`t resist and an audiophile won`t do ever.
The Ambers with its unusual overdesigned configuration this is: 300w/50Amp. output devices and its 64.000uF energy storage can deliver 400w into 2 ohm in mono mode which is a lot but it doesn`t mean that can be abused so as any other amplifier. The Ambers are among the best amplifiers built within its category if we consider its enormous reserve for delivering only a 70w/ch into 8 ohms.
It has been built like a tank, :tons: but even the tanks can`t be abused.:rolleyes:
 
G

ginetto61

Member
Joined 2009
Hi sorry to resurrect this old thread. I searched but could not find a schematic. From what i understand most of the voltage amplification is done with an op-amp that then drive a power buffer ? and it sounds nice ?
Anyone is aware of similar designs ? op-amp followed by a power buffer ?
Thanks a lot, gino
 
G

ginetto61

Member
Joined 2009
planet10 said:
I can’t currently access my HD, which robably has the schematic. HiFi Engine has it (you will have to become a member).
Amber Series 70 - Manual - Stereo Power Amplifier - HiFi Engine
LM391
dave
Click to expand...

Hi Dave, sorry for the belated reply :eek: and thank you very much for the kind and helpful reply. As i badly said it is a very general curiosity. From what i understand from this thread the old Amber Series 70 has a good sound and a very basic design (an op-amp buffered by a single output pair).
I will try to download the circuit as a first step.
Thanks a lot again. Kind regards, gino :)
P.S. maybe the LM391 could be replaced by something more recent like this one (it's also dual)
https://www.analog.com/media/en/technical-documentation/data-sheets/AD815.pdf
 
G

ginetto61

Member
Joined 2009
just to add that i have downloaded the schematic. I am surprised by the complexity.
I have seen somewhere in a datasheet of an opamp i do not remember a simple current booster made with a single bjts pair. But it was just a simplified schematic with no values
Thanks again, gino
 
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