bbaum1

1590 and PA-1 help

6 posts in this topic

I recently aquired a pair of ADS 1590 in relatively good condition and a PA-1. I believe the PA-1 I have was modified for the 1290 speakers. The enclosed ADS service paper shows how to modify the two sets of resistors to modify PA-1 for the 1590 

Couple of questions for the knowlwdgeble forum contributors.

1- I hooked up the PA-1 to bi-amp the 1590 without any other changes, which gave me decent mids and tweeters, but no bass. Removing the banana plugs to the low pass imputs made no difference in the sound, no sound is being passed to the woofers. The PA-1 appears to be in great shape, but am curious if  setting the resistors correctly for the 1590 will fix this, or there may be a problem with the PA-1 or the speaker crossovers

2- I removed the PA-1 cover to see if I was able to solder the resistors, but could not find the pair of resistors listed. Does someone have a schematic for the PA-1 or have an idea of where the resistors are located on the boards?

3- More general question, what does the resistor modification on the PA-1 boards change? The crossover frequency or something else?

 

I know these might be difficult questions for a thirty year old equipment, but there are probably a few ADS aficionados out there with the answers. Thank you in advance for the assistance

 

Mark

PA1 Mod

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I have a couple of pairs of PA-1's as well as L1290's and L1590's.  Hopefully I can help you get your system working.

1) Did you change the "biamp" switch in the back of the L1590s to the "biamp" position?  This is the lower switch in the back of the speaker behind the cover (and below the fuses if you have fuses).  The switch needs to be set to the left with the PA-1's.  You should get a full range of sound regardless of how the L1290/L1590 resistors are set internally to the amp.  FYI, the upper switch sets the tweeter level to -0dB (right) or -1.5dB (left).

2) There are at least two versions of the PA-1's.  One version needs to needs to change one resistor to configure for L1290/L1590 and the other need to change two resistors.  There should be a diagram on the back of the PA-1 cover that indicates which one you have.  The common resistor location is on the input board.  This in in the bottom of the amp.  The resistor is on the lower right-hand side of the board.  There will be two resistors soldered in a piggyback fashion (one lead may or may not be connected).  The second resistor (if you have that model) is on the main amp board.  This is also easy to find since it also has the piggybacked resistor.

3) I believe that the resistors just change the amps crossover frequency to match passive crossover in the speaker.  Depending on the mismatch, it either won't make any difference (the crossovers overlap) or you will have a small "hole" near the mid-woofer crossover frequency.

A schematic for the PA-1 can be downloaded for free here.  http://www.vintageshifi.com/repertoire-pdf/Braun.php The caveat is the manual is in German.  There is also a on-line website that the sells an English version of the manual.  I don't recall the name of the place but can look it up later if you would like.

Glitch

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For reference, here is a picture of the "piggybacked" resistor on the input board with one lead disconnected...

Piggyback.jpg

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Glitch,

Thank you for the response and help.

1- I did change the bi-amp switch

2-Mine lists two resistor changes on the inner sticker inside the cover plate.  I have late series 2, so no fuses, or cut-outs to fit the PA-1. The crossover on the 1590 is 350 vs, 500 on the 1290. Based on that,  not too much difference

3-Good to hear, less reason to make the change if there is little difference. Would you make the change or keep it as is?

I will get some help to tilt the speakers forward and move the bi-amo switch again, maybe a connection or switch issue. It's baffling no sound from the woofers with the PA-1.

I was using an old Onkyo receiver and get some bass with the 1590 wired directly to the receiver, instead of the Pa-1. Anything else you'd try?

Sincerely,

Mark

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Mark,

You can "test" your amps by hooking the outputs to a known working set of speakers.  Hook up one speaker to the mid/tweeter output of the amp and the the other speaker to the low output (i.e. one amp, two speakers).  You should get full range, mono sound out of this unconventional setup.

You could also test your speakers with a known good amp.  Set the switch to the bi-amp mode and hook the left channel to the lows and right channel to the mid/high input.  In the bi-amp mode, the low inputs are connected directly to the woofers.  The mid/tweeters are still protected by the crossovers from low frequencies.  Regardless of this, I would keep the amplifier volumes low to reduce the risk of burning out a driver.

The attached picture shows the location of the "second" piggyback resistor (upper right of photo).

I would recommend that you configure the resistors to match the speakers if you are comfortable with soldering.  This is a fairly easy modification to make since resistors are relatively tolerant of too much heat being applied.  I've run all four combinations of matched and mismatched setups.  None of them sound awful (but why have a suboptimal setup?).

Glitch

Piggyback2.jpg

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I forgot to add a few more things...

It would make sense that you would have no bass if the PA-1's were installed with the speaker switch in the full range position,  The low frequencies from the amp would be routed to the woofer terminals that are disconnected in that switch position.  The higher frequencies from the amp would be routed to the all of the drivers from the full-range terminals.  Between the active crossovers in the amps and the passive crossovers in the speakers, no low frequency sound would make it to the woofers.

I would get your setup working and let it run for a while before trying the resistor modifications.  This way, in the unlikely event that something dies early on, you won't be wondering if it was something that you did while making the mods.

Glitch

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