Repaired a Technics SU C2000 control amplifier, which is just a preamp. An LED displays that it is in this VBO mode. The SU C1000 has a battery back for this, but no battery pack in the C2000 unless it is somehow hidden in the faux (poids for your bucks) heavy metal sub frame. No monster caps either , so what is this all about ?
> Repaired a Technics SU C2000 control amplifier, which is just a preamp. An > LED displays that it is in this VBO mode. > The SU C1000 has a battery back for this, but no battery pack in the C2000 > unless it is somehow hidden in the faux (poids for your bucks) heavy metal > sub frame. No monster caps either , so what is this all about ?
> > Repaired a Technics SU C2000 control amplifier, which is just a preamp. An > > LED displays that it is in this VBO mode. > > The SU C1000 has a battery back for this, but no battery pack in the C2000 > > unless it is somehow hidden in the faux (poids for your bucks) heavy metal > > sub frame. No monster caps either , so what is this all about ?
> Just as a guess, flash memory?
> David.
From the C1000 repair and user manual you press a button to opt for battery operation for no mains hum/ fridge spikes etc presumably (if/after the battery is charged off the mains) or opt for mains power to the preamp. So I assumed the same with the C2000 but no battery or battery switch or anywhere obvious a missing battery could be/have been connected/located. If it was not for Technics make and going by the heavy lump of metal, for no functional purpose, I would have said it was a con.
> From the C1000 repair and user manual you press a button to opt for > battery > operation for no mains hum/ fridge spikes etc presumably
Shades of the 1920s and 30s, when battery operation was preferred by some "audiophiles" of the day (because "mains sets hum"). But I thought that attitude had died out decades ago, apparently not.
(if/after the
> battery is charged off > the mains) or opt for mains power to the preamp. So I assumed the same > with > the C2000 but no battery or battery switch or anywhere obvious a missing > battery could be/have been connected/located.
I had assumed before that the battery was to back-up settings, hence my comment about flash memory. If the VBO is intended to run the pre-amp, but there is no battery, and no mains supply, I can only guess that in VBO mode the pre-amp is entirely passive.
> If it was not for Technics make and going by the heavy lump of metal, for > no > functional purpose, I would have said it was a con.
I'm not sure that just because it has a well-known name on the front you can necessarily assume that it's not.
> N_Cook wrote: >> If it was not for Technics make and going by the heavy lump of metal, for >> no >> functional purpose, I would have said it was a con.
> It's a very clean power supply, virtually as good as a battery as regards > supply noise.
> Technics have this used all over the place, from pre-amplifiers to CD, DVD > and Blueray players.
> N_Cook wrote: > > If it was not for Technics make and going by the heavy lump of metal, for no > > functional purpose, I would have said it was a con.
> It's a very clean power supply, virtually as good as a battery as > regards supply noise.
> Technics have this used all over the place, from pre-amplifiers to CD, > DVD and Blueray players.
Looks like a regular linear ps to me except for the transformer being about 4 times the size necessary for a preamp and relays - more superfluous weight. Pair of 3300uF caps , 78M18,79M18, 5V reg , no chokes, no mu-metal or anything noticeably odd but, at least, no gold plating.
> Looks like a regular linear ps to me except for the transformer being about > 4 times the size necessary for a preamp and relays - more superfluous > weight. > Pair of 3300uF caps , 78M18,79M18, 5V reg , no chokes, no mu-metal or > anything noticeably odd but, at least, no gold plating.
I was wrong in calling it a "very clean power supply". I should have said "it has the effect of a very clean power supply"....
Have a look around the preamp section. As from the link I gave (from google), it's not a regulator but an "active filter".
Quote "tracks input voltage as changed by variations in line voltage and load, and takes out some AC. That may be useful under some special circumstances. In the tube days, this was done using a large choke, that's in a way what this circuit simulates."
> > Looks like a regular linear ps to me except for the transformer being about > > 4 times the size necessary for a preamp and relays - more superfluous > > weight. > > Pair of 3300uF caps , 78M18,79M18, 5V reg , no chokes, no mu-metal or > > anything noticeably odd but, at least, no gold plating.
> I was wrong in calling it a "very clean power supply". I should have > said "it has the effect of a very clean power supply"....
> Have a look around the preamp section. As from the link I gave (from > google), it's not a regulator but an "active filter".
> Quote "tracks input voltage as changed by variations in line voltage and > load, and takes out some AC. That may be useful under some special > circumstances. In the tube days, this was done using a large choke, > that's in a way what this circuit simulates."
> FWIW I tried a patent search. Got nothing.
> -- > Adrian C
There are 2SD2037 and 2SB1357 ,probably as pass transistors downstream of the 18V regulators, using some of the headroom to drop to +/- slightly lower rails and a load of little electros, which doesn't strike me as particularly groundbreaking, let alone simulating a battery.
>> Looks like a regular linear ps to me except for the transformer being >> about >> 4 times the size necessary for a preamp and relays - more superfluous >> weight. >> Pair of 3300uF caps , 78M18,79M18, 5V reg , no chokes, no mu-metal or >> anything noticeably odd but, at least, no gold plating.
Doesn't sound anything special. 78M18 and 79M18 are bog-standard regulator chips.
> I was wrong in calling it a "very clean power supply". I should have said > "it has the effect of a very clean power supply"....
> Have a look around the preamp section. As from the link I gave (from > google), it's not a regulator but an "active filter".
> Quote "tracks input voltage as changed by variations in line voltage and > load, and takes out some AC. That may be useful under some special > circumstances. In the tube days, this was done using a large choke, that's > in a way what this circuit simulates."
Active filters in power supplies are common when low ripple is required but voltage stabilisation is not required. At it's simplest it's just an emitter follower with the base fed from the input via a resistor and decoupled to ground by a large capacitor. If the current loading is high a compound transistor (darlington pair) might be used. Again nothing special there, they've been used for years (thermionic version were in use before the invention of the transistor).
