Hello. I was recently discussing my Altec 1593B with a local hi-fi dealer who commented that the frequency range on these amplifiers were limited by design (obviously voice range and its use as a commercial PA) and could easily be modified for full range by cutting out or replacing just a few capacitors. Does anyone know if this is true? If it is true, does anyone know of the mods to give this amplifier a full frequency range ability?
I have a schematic attached for reference if you are able to point out specific changes for such a mod.
Your thoughts would be most appreciated. Thank you.
I have a schematic attached for reference if you are able to point out specific changes for such a mod.
Your thoughts would be most appreciated. Thank you.
Attachments
The spec sheet shows a frequency response of 20Hz -20KHz but at rated power of 50 Watts the response is only 45Hz - 20KHz. The amplifier may be limited by the transformers. I don't think there's anything to replace or mod.
Craig
Craig
Last edited:
Gah! It is 1969 all over again again!!
There is the "filter" switch to cut all bass below 500Hz; the not-filter input cap C101 runs to 3Hz. C106 C107 is another 3Hz corner. So we have -6dB @ 3Hz, -2dB @ 6Hz, -1dB @ 12Hz. This is "nothing" compared to speaker bass errors. (If you have 12Hz speakers you need more than the 50 Watts.)
C108 C109 throw a slope at 150KHz. I doubt the amp runs that high, but near enough they had to control the phase shift.
C112 C113 cause a slight shelf near 30KHz, but this is inside a larger NFB loop so not much effect for your purposes.
There is a top-loss because the NFB is not taken from the speaker taps but a tertiary winding. If you obsessed over >50KHz response I would examine this closer... but frankly if you did you would be using a post-1980 amp with maybe too-much extension beyond the audible range.
C103 causes a very slight (<2dB) rise at 24KHz. I really suspect this trims-up the accumulated 20KHz losses in those old slow transistors and two transformers.
Yes, the 50 Watt bass bandwidth may be less than the 1 Watt bandwidth. That is usual on all but the largest over-size output transformers. Essentially full power at 45Hz is plenty.
There's much to say "We don't do it that way today!". I don't see anything *wrong*, or easily tweeked.
If you let the dealer take your money, get full documentation before/after. Preferably a form hard to cheat (though any test can be cheated). He *could* touch-up R116 for very lowest even-order distortion. But chasing after 2nd is not a high-gain past-time, 2nd does not offend the ear only the meter.
There is the "filter" switch to cut all bass below 500Hz; the not-filter input cap C101 runs to 3Hz. C106 C107 is another 3Hz corner. So we have -6dB @ 3Hz, -2dB @ 6Hz, -1dB @ 12Hz. This is "nothing" compared to speaker bass errors. (If you have 12Hz speakers you need more than the 50 Watts.)
C108 C109 throw a slope at 150KHz. I doubt the amp runs that high, but near enough they had to control the phase shift.
C112 C113 cause a slight shelf near 30KHz, but this is inside a larger NFB loop so not much effect for your purposes.
There is a top-loss because the NFB is not taken from the speaker taps but a tertiary winding. If you obsessed over >50KHz response I would examine this closer... but frankly if you did you would be using a post-1980 amp with maybe too-much extension beyond the audible range.
C103 causes a very slight (<2dB) rise at 24KHz. I really suspect this trims-up the accumulated 20KHz losses in those old slow transistors and two transformers.
Yes, the 50 Watt bass bandwidth may be less than the 1 Watt bandwidth. That is usual on all but the largest over-size output transformers. Essentially full power at 45Hz is plenty.
There's much to say "We don't do it that way today!". I don't see anything *wrong*, or easily tweeked.
If you let the dealer take your money, get full documentation before/after. Preferably a form hard to cheat (though any test can be cheated). He *could* touch-up R116 for very lowest even-order distortion. But chasing after 2nd is not a high-gain past-time, 2nd does not offend the ear only the meter.
Last edited:
- Status
- Not open for further replies.