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Heathkit AP-1800 preamp out problem?

V

V00d00

New Member
Hello guys and girls,

I have recently obtained a Heathkit AP-1800 preamplifier and a Heathkit AA-1600 power amplifier. When I connect preamp out 1 from the AP-1800 to the input of the AA-1600, only the high frequencies come through. When I connect preamp out 2, only the low frequencies come through.

Connecting to tape out 1, for example, gives the entire spectrum but that is obviously not the solution because it bypasses the entire control section.

Since I do not have a manual I'm at a loss. I was already wrong in assuming the speaker connectors on the AP-1800 where real amplified speaker output connectors until I found a thread here which stated they are only a loopback feature to switch externally driven speakers. I don't want to screw anything up before I know what this is about.

Is this behaviour by design or is there something wrong with the circuitry? Or should I connect them in a totally different way?

Of course I have already searched the internet for a manual but what I have found costs a ridiculous amount of money (even only the costs of shipment to Europe). So if anyone knows where to obtain them for a reasonable price (or help me out in some other way), please let me know.

Thanks for any help you can provide.
 
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I have that pre and I believe an extra copy of the manual. It is really hard to track problems in kits sometimes. People create some ingenious problems. I had to buy the crossover for that set separately and yours is built in. :) Let me check on that manual for you.
 
V00d00 I have three of those pre's and I have never had that problem! I have the entire system from the pre to both aa1600's and aa1800;s. I do have a copy of the assembly manual if mpholland can't find his extra. I could copy a schematic and send it too you via email. I guess I could try to copy the entire manual but that would take some time! Let me know.

Steve AKA boxoboom
 
Thank you both mpholland and boxoboom. Your help is greatly appreciated.

It's very possible that the previous owner decided to do some engineering on his own and integrated the filters himself. Although I don't see the point in that when using only these two amps together. (Of course I could combine the outputs using a simple resistor circuit but that would be a little weird. First splitting the signal and then putting it back together again.)

Mpholland: Is that crossfader an optional module for the amp? As in that there is reserved space in the amp to install it?
Do you mean that you can send me the copy if you can find it? (sorry, I'm not an English native speaker so the meaning of a sentence is not always clear to me) :)

Boxoboom: The schematic alone would be a great help but the entire manual would be fantastic. I have no idea how many pages it is but if you are willing to copy the entire manual then I'll be the happiest man on earth!

By the way: What do you guys think of the quality of these amps? I have used a Graetz Profi 306 (on JBL XL1000 speakers) before the Heathkits and I thought it was quite good but the Heathkits kick the Graetz's, erhh, behind. :D Both in quality and power.
 
mpholland said:
I have that pre and I believe an extra copy of the manual. It is really hard to track problems in kits sometimes. People create some ingenious problems. I had to buy the crossover for that set separately and yours is built in. :) Let me check on that manual for you.
Click to expand...

boxoboom said:
V00d00 I have three of those pre's and I have never had that problem! I have the entire system from the pre to both aa1600's and aa1800;s. I do have a copy of the assembly manual if mpholland can't find his extra. I could copy a schematic and send it too you via email. I guess I could try to copy the entire manual but that would take some time! Let me know.

Steve AKA boxoboom
Click to expand...

LOL, +1 for having 3 of those AP-1800's, and a complete stack with the 1600 and 1800. If you guys can't find the schematics, I also have a build manual.

@V00d00, Man, you emailed me yesterday via youtube and I tried to reply but it came back as permanently undeliverable. Glad you came here! :thmbsp:

The Heathkit Pro-Series gear is really quite good. I think you'll enjoy it once you get it sorted out.
 
mpholland: That is one nice setup you have. It makes mine look a little more humble ;)
So if I understand correctly there is a separate 19" rack mountable crossover unit available for the system? Or was the AP-1800 available in different editions? Do you also have a picture of that crossover unit?

Now for the part of stepping on toes. What will be the solution? Are you willing to send me your extra copy? And if so, what would it cost me and what means of payment do you wish? It has to be sent to The Netherlands ( or Holland if you will, what a coincidence :D )

I have to admit that I'm slightly in doubt at this point. A real manual would be great (b.t.w. is it an original or a copy?) but a digital copy would eliminate the shipment cost. Choices, choices ...

Rob41: That is strange. I have checked the settings and I should be able to receive e-mail. Thanks for trying anyway. As I said before: I don't want to step on anyone's toes by bypassing their offer but if you could send me a copy that would be great.
I'm enjoying the set right now and I'm very pleased with it. But as said before it is through the tape out. So I cannot use any of the controls. Right now I only have the computer connected and use the volume control there.

Thank you all for your help and offers so far.
 
Voodoo, I have the schematic in printed form only and it is a large one as Heath always did provide a table sized schiz for the kit builders. I bought mine back in 80 and have the complete set with the exception of the power meters. Been looking but I haven't seen one on eBay I could afford! But if you are willing to wait until next week sometime I can try to copy the entire manual for you and send it to you if no one has an extra manual! From looking at the schematic he must have taken it off of the tone controls some wheres as the outputs come out of the mode selector which is a part of the Delay turn on portion of the main circuit board. I would look inside and see where the outputs are wired to if it were me. they should be wired differently, like off of the bass turnover switches or something like that.

Let me know what you would like me to try to do.
 
Boxoboom, I would be more than happy to wait. I'm already grateful that you are willing to put all the effort into copying the manual. :thmbsp:
Of course I'll wait for the others to reply before making the final decision.

Both bass and treble controls affect the sound of preamp out 1 (high pass). Only the bass control seems to affect preamp out 2 (low pass). Does this mean anything to you? If I have some spare time the upcoming days I'll have a look inside again.
 
Anyone still there? :)

I haven't had the time yet to look inside but I probably will have the time somewhere next week.

Boxoboom, have you tried copying it yet?
 
Hi all

With the priceless/unaffordable help of mr. boxoboom I have been able to figure out the problem (which in fact wasn't really there).

It turns out that pre-amp out 1 from the mode switch board is wired to a crossfader pcb which is "glued" to the side. From there two pairs are wired to the pre-amp out 1 and pre-amp out 2 connectors on the back panel.
The pre-amp out 2 from the mode switch board is actually wired to the adapter out connector on the back panel.
Also three wires are soldered on the backside from connector P205 to power the "cross fader pcb".
So the only thing I had to do was to connect adapter out to the AA-1600 and it is working like a charm! :D :D :D

If one person on this world should win the lottery it should be mr. boxoboom. He is simply too kind for this world.

Many thanks for your help!
 
Hello to all.

I don't mean to hijack this thread, but, once again I have run into an electronic problem. This is the only thread that has a mention of the aa1800 manual
I picked up a non functioning AA-1800 amp. One side blows fuses, burns the 22ohm resistors, and fries the power amps. All the small transistors test OK, and I am running out of ideas.
This thing is hard to start with a variac. It does nothing until about 60vac, then clicks over the first relay. Then at about 85vac the second relay kicks in. That's when the fun starts with smoke and sparks...

Does anyone have a copy of the manual, either printed or digital? I would gladly send remunerations.
Thanks in advance.
Desperately, Andrew Chang
 
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