Greetings all-
I've been lurking for a while and haven't posted here. I have two early Amber stereo 70s (black with rack mount handles) that are great. I'd like to use them in mono configuration with my Acoustat Spectra 44s, but one only works in stereo. From what I've read it could be as simple a fix as using deoxit on the stereo/ mono switch, which I'll do. The Spectra 44s are a difficult load and I don't want to stress the amps.
So...I'm looking for good LM391-100 or 391-90 drivers and an actual manual (Hifi Engine show that there is one, but it's not actually there). The schematic seems to be available. Does anyone out there have experience with Chinese made 391s? I'm a bit dubious.
Run as stereo amps, I prefer the 70s to my Eagle 2 and my BEL 1001 and they're basically equal to my buddy's Stax DA-80. Not too shabby.
Thanks-
Harry Z
I've been lurking for a while and haven't posted here. I have two early Amber stereo 70s (black with rack mount handles) that are great. I'd like to use them in mono configuration with my Acoustat Spectra 44s, but one only works in stereo. From what I've read it could be as simple a fix as using deoxit on the stereo/ mono switch, which I'll do. The Spectra 44s are a difficult load and I don't want to stress the amps.
So...I'm looking for good LM391-100 or 391-90 drivers and an actual manual (Hifi Engine show that there is one, but it's not actually there). The schematic seems to be available. Does anyone out there have experience with Chinese made 391s? I'm a bit dubious.
Run as stereo amps, I prefer the 70s to my Eagle 2 and my BEL 1001 and they're basically equal to my buddy's Stax DA-80. Not too shabby.
Thanks-
Harry Z
Much on this lovely lovely little amplifier here; https://www.diyaudio.com/community/threads/amber-stereo-70.368808/
dave
dave
They are all just voltage grades. You might get lucky and have a -60 that will take 100 volts. Or not. The -90 was never offered by NS originally. Only 60 and 80 initially, and then later the 100. Any -90 would have been from some second source. Or a re-marked -80. NTE has never been trustworthy….
The circuit is relatively simple and can be duplicated with discretes. But to get close to original performance, several pairs need to be well matched. Monolithic dies do this for you, which is why these chips work so well.
The circuit is relatively simple and can be duplicated with discretes. But to get close to original performance, several pairs need to be well matched. Monolithic dies do this for you, which is why these chips work so well.
Thanks fellas. Much appreciated.
Since they have mono switches, I presume that this halves the load that the amp sees? I've read that they are stable in mono operation and can produce something like 400wpc into a 2 ohm load. But... I'm afraid that they may not be happy with the high impedances in the bass frequencies of the Spectra 44s...
Since they have mono switches, I presume that this halves the load that the amp sees? I've read that they are stable in mono operation and can produce something like 400wpc into a 2 ohm load. But... I'm afraid that they may not be happy with the high impedances in the bass frequencies of the Spectra 44s...
High impedances never hurt anything. Low ones do, and bridging is effectively a low impedance. The danger of low impedances is that output transistor failure can take part of the driver circuit with it. If that’s an LM391, you’re in a pickle.
Its opposite with tubes. Excessively high impedance can cause tube or output transformer failure, and low impedances produce a tolerable overload which can be sustained for some time.
Its opposite with tubes. Excessively high impedance can cause tube or output transformer failure, and low impedances produce a tolerable overload which can be sustained for some time.
Got both amps on a buddy's bench last night. They both look really clean from 20hz north of 20k and are putting out around 85+ wpc into 8ohms and over 140 into 4-
.
I've been a tube guy for years but with the Acoustat Spectra 44s and these things am enjoying LPs, tapes and digital more than ever... Found two more of the early black ones with silver handles yesterday at great prices and picked them up. Should be set for years.
Thanks all for your input, advice and suggestions.
HZ
. I've been a tube guy for years but with the Acoustat Spectra 44s and these things am enjoying LPs, tapes and digital more than ever... Found two more of the early black ones with silver handles yesterday at great prices and picked them up. Should be set for years.
Thanks all for your input, advice and suggestions.
HZ