Hello people,
I just bought a couple of Elektor designed mono-blocks off ebay and would like to know more about them if I can..
They were a mystery, gamble buy as the guy wasn't even sure if they were amps but I took a chance. Here they are:
Searching on here, they appear to be either :
okt 91 - LFA-50-OA class A amp with 2SA1216/2SC2922 or
feb 94 - ulti-amp with 2SC2922/2SA1216 (better poweramp)
due to them using 2 x Sanken 2SC2922/2SA1216s. Circuit boards are EPS 880092-1, 2, 3 & 4 and is that a mains filter in the last pic?
Does anyone know anything about these designs, specs, what the pretection lights mean? Should they be good amps? Sensitivity would be good to know.
As of writing this I have yet to turn them on, do anything with them - I'm a bit of a scaredy cat when it comes to plugging in new amps with heart stopping pops, crackles, smoke etc or even my cat stepping on bit of bubble wrap.. - but may do so soon into some £10 Gale speakers.
They look fantastically well made and with extra large power supply caps.
The fuse next to the grey transformer is empty - no blown wires inside, just empty - anyone know what this protects against?
Any info would be much appreciated!
I just bought a couple of Elektor designed mono-blocks off ebay and would like to know more about them if I can..
They were a mystery, gamble buy as the guy wasn't even sure if they were amps but I took a chance. Here they are:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Searching on here, they appear to be either :
okt 91 - LFA-50-OA class A amp with 2SA1216/2SC2922 or
feb 94 - ulti-amp with 2SC2922/2SA1216 (better poweramp)
due to them using 2 x Sanken 2SC2922/2SA1216s. Circuit boards are EPS 880092-1, 2, 3 & 4 and is that a mains filter in the last pic?
Does anyone know anything about these designs, specs, what the pretection lights mean? Should they be good amps? Sensitivity would be good to know.
As of writing this I have yet to turn them on, do anything with them - I'm a bit of a scaredy cat when it comes to plugging in new amps with heart stopping pops, crackles, smoke etc or even my cat stepping on bit of bubble wrap.. - but may do so soon into some £10 Gale speakers.
They look fantastically well made and with extra large power supply caps.
The fuse next to the grey transformer is empty - no blown wires inside, just empty - anyone know what this protects against?
Any info would be much appreciated!
LFA-50.
Here's a builder's page, plenty more if you goggle : www.jls-info.com/julien/audio/lfa.jpg
Well made duo, looks like the assembler spent serious cash.
It's basically the LFA-150 with lowered rail voltages to accommodate high biasing.
Here's a builder's page, plenty more if you goggle : www.jls-info.com/julien/audio/lfa.jpg
Well made duo, looks like the assembler spent serious cash.
It's basically the LFA-150 with lowered rail voltages to accommodate high biasing.
Hi,
Short the input with a zero ohm RCA plug and don't connect the speakers.
Start them up with a light bulb tester.
If the light stays start measuring to find out what's happening.
If it goes off then probably OK. Check the supply rail voltages, four of them.
Check output offset and output bias current.
Warm it up and check those again.
Connect speakers and check that offset again and listen for unusual noises.
Switch off and remove the input short and connect a known source.
Disconnect the speakers. Switch on and recheck the output offset with the source connected but switched off and then switched on.
Reconnect the speakers and enjoy.
Short the input with a zero ohm RCA plug and don't connect the speakers.
Start them up with a light bulb tester.
If the light stays start measuring to find out what's happening.
If it goes off then probably OK. Check the supply rail voltages, four of them.
Check output offset and output bias current.
Warm it up and check those again.
Connect speakers and check that offset again and listen for unusual noises.
Switch off and remove the input short and connect a known source.
Disconnect the speakers. Switch on and recheck the output offset with the source connected but switched off and then switched on.
Reconnect the speakers and enjoy.
Thanks for that - when you know what you are looking for it's a lot easier!
Here is the best link I found:
http://pagesperso-orange.fr/francis.audio2/LFA50.doc
a word doc of scans from a magazine?, in French, explaining it all. I can at least get the specs from this.
It says 29V rails on this, mine are marked 59V... possibly a 100W version?
Anyway, I will see if I can OCR the scans and translate parts that look interesting..
They certainly went to a lot of effort if not expense and the cases are a perfect fit fot it all too.
AndrewT, what do you mean by starting it up with a light bulb tester? And a zero ohm RCA would be a plug shorted out? They actually used BNCs for this which shows the extra effort they went to.
They smell ok which is always a good sign and look very clean inside. I've also seen matched Sankens on ebay recently too should anything go wrong.
Here is the best link I found:
http://pagesperso-orange.fr/francis.audio2/LFA50.doc
a word doc of scans from a magazine?, in French, explaining it all. I can at least get the specs from this.
It says 29V rails on this, mine are marked 59V... possibly a 100W version?
Anyway, I will see if I can OCR the scans and translate parts that look interesting..
They certainly went to a lot of effort if not expense and the cases are a perfect fit fot it all too.
AndrewT, what do you mean by starting it up with a light bulb tester? And a zero ohm RCA would be a plug shorted out? They actually used BNCs for this which shows the extra effort they went to.
They smell ok which is always a good sign and look very clean inside. I've also seen matched Sankens on ebay recently too should anything go wrong.
It looks very neat.
The wires are all tightly bundled together which is not good from a crosstalk point of view. Its OK to bundle PSU wires together.
But bundling signal wires can result in positive feedback.
There seems to be a lot of cctry for a power amp.
I prefer the simpler designs as there is less to go wrong.
The heatsinks do look a little on the small side as I cant see a fan.
I do gigs for upto 6 hours of playing loud and know that over time heat can build up and sometimes become a problem.
So, I tend to use PC cases and have a large heatsinbk and a fan sucking in air and another one at the opposite corner blowing it out.
The wires are all tightly bundled together which is not good from a crosstalk point of view. Its OK to bundle PSU wires together.
But bundling signal wires can result in positive feedback.
There seems to be a lot of cctry for a power amp.
I prefer the simpler designs as there is less to go wrong.
The heatsinks do look a little on the small side as I cant see a fan.
I do gigs for upto 6 hours of playing loud and know that over time heat can build up and sometimes become a problem.
So, I tend to use PC cases and have a large heatsinbk and a fan sucking in air and another one at the opposite corner blowing it out.
I'm going to be a bit busy/going away as of now so won't get to test them for a week or so..
Something I read while researching said that the LFA 50-oa is based on the LFA 150 but uses lower rails for, err something to do with better biasing - it is time I confessed, I really don't know much about amp design..
Anyway, that could account for the printed boards saying 59V but this design actually using 29V rails. The LFA 150 doesn't use these Sankens whereas the LFA 50-oa does.
The top board of the stack is the protection circuit. I'm going to open up my in-need-of-repair Burmester 828 MkIIs which also uses these Sankens and compare the layout just to see if there are similarities - next week though.
I would agree with the wiring and cross talk in general but with these, it looks as though the input and output wires are only a few centimetres in length to the connectors. It would depend if the power and earthing wires bundled will produce much cross-talk. Those at the top are for the protection circuit it looks like.
The heatsink is firstly a thick aluminium bar that the Sankens are directly attached to and then this bar looks as though it is fixed to the heatsink with thermal paste. As a monoblock, hopefully the 25W of class A heat (how much is that?) per side of the chassis (npn transistors on one side, pnp on the other) is disipated enough. We shall see!
I'd be interested to hear more about how these should sound Scanspeakman. I was hoping that they might even be an answer to what I should use to power my Kef 107s (when I get around to refoaming them) - I don't listen at high levels but have heard that the Kefs need a lot of well controlled current for the bass to perform well.
Something I read while researching said that the LFA 50-oa is based on the LFA 150 but uses lower rails for, err something to do with better biasing - it is time I confessed, I really don't know much about amp design..
Anyway, that could account for the printed boards saying 59V but this design actually using 29V rails. The LFA 150 doesn't use these Sankens whereas the LFA 50-oa does.
The top board of the stack is the protection circuit. I'm going to open up my in-need-of-repair Burmester 828 MkIIs which also uses these Sankens and compare the layout just to see if there are similarities - next week though.
I would agree with the wiring and cross talk in general but with these, it looks as though the input and output wires are only a few centimetres in length to the connectors. It would depend if the power and earthing wires bundled will produce much cross-talk. Those at the top are for the protection circuit it looks like.
The heatsink is firstly a thick aluminium bar that the Sankens are directly attached to and then this bar looks as though it is fixed to the heatsink with thermal paste. As a monoblock, hopefully the 25W of class A heat (how much is that?) per side of the chassis (npn transistors on one side, pnp on the other) is disipated enough. We shall see!
I'd be interested to hear more about how these should sound Scanspeakman. I was hoping that they might even be an answer to what I should use to power my Kef 107s (when I get around to refoaming them) - I don't listen at high levels but have heard that the Kefs need a lot of well controlled current for the bass to perform well.
I will take a look in the original article when I am home tonight what the secundary psu is for.
The sound is hard to discribe. I always feel the need to laugh loudly when I read reviews descibing the sound as "with a lot of air" of "very black". I was able to compare it head-to-head to a NAD S300 amp and the lfa50 (in combination with the elektor The Pre-Amp) sounded better. In comparison to the Marantz PM7001 the Marantz gets blown away. The lfa50 sound natural is al I can say.
The lfa50 is able to deliver quite a lot of power (current). The impedance of my Scanspeak Reference Plus dips to 2 ohm at certain (low) freqs and this is no problem with this amp. It keeps good control on the speakers.
Scanspeakman
The sound is hard to discribe. I always feel the need to laugh loudly when I read reviews descibing the sound as "with a lot of air" of "very black". I was able to compare it head-to-head to a NAD S300 amp and the lfa50 (in combination with the elektor The Pre-Amp) sounded better. In comparison to the Marantz PM7001 the Marantz gets blown away. The lfa50 sound natural is al I can say.
The lfa50 is able to deliver quite a lot of power (current). The impedance of my Scanspeak Reference Plus dips to 2 ohm at certain (low) freqs and this is no problem with this amp. It keeps good control on the speakers.
Scanspeakman
Slip of the fingertip, my bad.
The heatsinks used are either Fisher SK56 or Seifert KL146 types.
A single 12"x4"x1.6" size is good for 0.45C/W : a pair of those heatsinks have a combined thermal factor of 0.225C/W.
The one who assembled these LFA50s set them up to fully bias the amps to 50W in 8 Ohm, not 25.
(= 200mV across the 0.22 Ohm emitter resistors instead of the Elektor prescribed 138mV.)
Biased to 50W should still keep the temperature of the heatsinks below 50C in a room with 25C temperature.)
The difference in output devices between the LFA50 and LFA150 only had to do with logistics, the Toshiba ringemitters used in the LFA150 became unavailable around 1990.
Your 828MKII has both Sanken as Toshiba MahJong bricks : 6 Sanken output devices and a pair of Toshiba drivers (2SA1094/2SC2564 IIRC)
BTW : the LFA50 and LFA150 have a large open loop bandwidth, >10KHz, an important factor for them to sound rather good.
Both amps also have a Sziklai output stage, also known as compound output, aka complementary feedback pair output stage (CFP).
A Sziklai output has less distortion, can deliver more clean power, but is inherently less stable.
The Threshold power amps have/had compound output stages, but the Stasis operation and bulk of those amps make them rock solid.
The LFA50 is not that stable, it swings if you use it with tricky electrostats.
The heatsinks used are either Fisher SK56 or Seifert KL146 types.
A single 12"x4"x1.6" size is good for 0.45C/W : a pair of those heatsinks have a combined thermal factor of 0.225C/W.
The one who assembled these LFA50s set them up to fully bias the amps to 50W in 8 Ohm, not 25.
(= 200mV across the 0.22 Ohm emitter resistors instead of the Elektor prescribed 138mV.)
Biased to 50W should still keep the temperature of the heatsinks below 50C in a room with 25C temperature.)
The difference in output devices between the LFA50 and LFA150 only had to do with logistics, the Toshiba ringemitters used in the LFA150 became unavailable around 1990.
Your 828MKII has both Sanken as Toshiba MahJong bricks : 6 Sanken output devices and a pair of Toshiba drivers (2SA1094/2SC2564 IIRC)
BTW : the LFA50 and LFA150 have a large open loop bandwidth, >10KHz, an important factor for them to sound rather good.
Both amps also have a Sziklai output stage, also known as compound output, aka complementary feedback pair output stage (CFP).
A Sziklai output has less distortion, can deliver more clean power, but is inherently less stable.
The Threshold power amps have/had compound output stages, but the Stasis operation and bulk of those amps make them rock solid.
The LFA50 is not that stable, it swings if you use it with tricky electrostats.
Haven't had any trouble with my "not-so-easy-to-drive" speakers.
The design runs quite hot, especially during hot summer days. I have build both mono-amps in a single casing from monacor. I have never measures the temp but I am nog able to hold my hand on the heatsinks for more that 2-3 seconds. But it doesn't seem to affect the relaibility.
Anyway nat.d.berg, I hope you have the same fun with this amp as I have got during the last 12 years. Let me hear your comments!
Scanspeakman
The design runs quite hot, especially during hot summer days. I have build both mono-amps in a single casing from monacor. I have never measures the temp but I am nog able to hold my hand on the heatsinks for more that 2-3 seconds. But it doesn't seem to affect the relaibility.
Anyway nat.d.berg, I hope you have the same fun with this amp as I have got during the last 12 years. Let me hear your comments!
Scanspeakman
I'm ashamed to say that they'e sat on a shelf since 2008..
Plugged them in for the first time err a couple of months ago! Unfortunately one is silent so in need of some repair.. It's on my list but lower down than a nice big beefy 80's Bartolomeo Aloia D100 Referenza that burned out some kind of bias resistor on first turn on.
Plugged them in for the first time err a couple of months ago! Unfortunately one is silent so in need of some repair.. It's on my list but lower down than a nice big beefy 80's Bartolomeo Aloia D100 Referenza that burned out some kind of bias resistor on first turn on.
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