Aa-1800
Sithlord,
When I turn the amp on the protection light comes on immediately. The speaker relay never closes. Removing the left amp molex plug from the protection board it then works normally and the speaker relay closes. Plugging the right amp molex plug into the left amp socket on the protection board while leaving the left unplugged, it works as advertised. I believe that pretty much rules out the protection board and power supply. Leaving it turned on with both amps hooked up the right side gets warm but the left side stays stone cold. The chassis is remarkably clean and I have not found corrosion/oxidation anywhere. Anybody have a schematic .pdf?
Sithlord,
When I turn the amp on the protection light comes on immediately. The speaker relay never closes. Removing the left amp molex plug from the protection board it then works normally and the speaker relay closes. Plugging the right amp molex plug into the left amp socket on the protection board while leaving the left unplugged, it works as advertised. I believe that pretty much rules out the protection board and power supply. Leaving it turned on with both amps hooked up the right side gets warm but the left side stays stone cold. The chassis is remarkably clean and I have not found corrosion/oxidation anywhere. Anybody have a schematic .pdf?
Found my AA-1800 manual (copy of original); the power transformer I calculate to be 140 to 150 volt center tapped to supply 100VDC(!) rails. There's another center tapped low voltage winding at 32 - 36 volts for a 24VDC supply; this could be a separate small transformer mounted elsewhere.
toodleoo:
You'll need to check the fuses on the left channel. There are a pair of 5 amp fuses for the output stage rails and two more .062 amp fuses for the input stage; the latter may be difficult to determine condition without an ohmmeter. All four fuses appear to be mounted on the circuit board.
toodleoo:
You'll need to check the fuses on the left channel. There are a pair of 5 amp fuses for the output stage rails and two more .062 amp fuses for the input stage; the latter may be difficult to determine condition without an ohmmeter. All four fuses appear to be mounted on the circuit board.
Aa-1800
I own two of the AA-1800 amsp. One I built and the other I bought a few years ago thru Ebay, originally for parts if the one I built couldn't be repaired.
The one I built died from a power spike. Nothing glamerous about that, but we did discover something interesting and possibly note worthy in the process. I was talked into replacing the coax that that runs from the RCA connectors to each amplifier board as an "upgrade". To our utter amazement, this upgrade made a massive improvement, but not because of the reasons one so often reads about regarding wire.
The old coax in this amp had turned black, it was horribly oxidized. I've no good explanation why it oxidized, I just know it did. After seeing this, I decided I didn't trust the rest of the wiring and proceeded to replace the rest of the internal wiring and molex connectors. I discovered this was over kill as the rest of the copper wiring was in excellent condition.
So, word to the wise. There might be others out there with degraded coax.
Oh, the other amp is now in working order. Oddly, each amp has a slightly different sound.
I own two of the AA-1800 amsp. One I built and the other I bought a few years ago thru Ebay, originally for parts if the one I built couldn't be repaired.
The one I built died from a power spike. Nothing glamerous about that, but we did discover something interesting and possibly note worthy in the process. I was talked into replacing the coax that that runs from the RCA connectors to each amplifier board as an "upgrade". To our utter amazement, this upgrade made a massive improvement, but not because of the reasons one so often reads about regarding wire.
The old coax in this amp had turned black, it was horribly oxidized. I've no good explanation why it oxidized, I just know it did. After seeing this, I decided I didn't trust the rest of the wiring and proceeded to replace the rest of the internal wiring and molex connectors. I discovered this was over kill as the rest of the copper wiring was in excellent condition.
So, word to the wise. There might be others out there with degraded coax.
Oh, the other amp is now in working order. Oddly, each amp has a slightly different sound.
"Coax" ... are you referring to the "phono cable" that goes from the inputs and has an RCA jack on the other end that pugs directly into the Amplifier Board on each side?
I did not think about upgrading this, but since I am recapping all three that I own, this should not be a too expensive upgrade and worth considering.
Thanks!
I did not think about upgrading this, but since I am recapping all three that I own, this should not be a too expensive upgrade and worth considering.
Thanks!
Member
Joined 2009
Paid Member
Black Gate is one of those special things that has attracted cult status. I've also heard of many problems with them. They have been out of production for years and attract silly prices (in my view). Although people with much more experience than me swear by them I'd recommend steering clear.
Probably just going to go the route of Nichicon for the Axial. As for the radials, everything I come across on Parts Express, Newark, Mouser, and Digikey are too large for the amp board except for Panasonic. Where the radials are located, diameter and height is a major factor. All the high-end radials are about 16mm in diameter and will not fit (220uf). Some of the heights on the better sized ones are over 50mm in an area allowing for only 24mm or so. Blackgate seems too much of an issue to find what I need and are pricey.
Fot the left channel amp in this thread ...
I was going to also suggest fuses left channel as well ALTHOUGH I have blown some fuses before and the protection light never stayed on as described.
I can get you a pdf of the schematic but it won't be until Friday evening. I am away for the next 2 days.
Fot the left channel amp in this thread ...
I was going to also suggest fuses left channel as well ALTHOUGH I have blown some fuses before and the protection light never stayed on as described.
I can get you a pdf of the schematic but it won't be until Friday evening. I am away for the next 2 days.
Hi Gareth,
Completely agree. Nicely out as well.
Hi rrcrain,
Anyway, the stuff you had in one amp was corroded (or rotten if you'd rather), and so it had no hope of working properly.
Now, before people start diving in and replacing capacitors left, right and center, don't you think some testing and checking might be in order first? The main filter capacitors are often just fine. Check these using an oscilloscope with the amplifier running with no signal. Then, apply a signal if you want. A single tone might be easier to decipher. The other capacitors can be replaced, but make sure you use the correct type for the job it's doing. There is no one "best" capacitor, and I'll bet that the audio rated capacitors are simply down rated (for voltage) capacitors. If you are going to go that far, clean and redo the thermal compound, checking the transistors as you go. Watch for leakage (C-E and C-B) and beta. The signal transistors should be matched in beta and tested for leakage. Make sure the differential pair is in thermal contact and stuck together. I use thermal compound and heat shrink tubing. Do not use "computer grease" as some are conductive. Plan on replacing the mica insulators.
I figure if you are going to this much trouble and are concerned with improving the sound quality, you may as well do the entire job properly. Many things I have suggested will improve the sound quality and also the measured specifications.
Hi Sithlord2007,
Semiconductor Mounting Considerations
There are documents at On Semi's web site that tells you the proper way to mount power semiconductors. It also tells you how much pressure to apply. Since most people over-tighten these screws, I'd highly recommend everyone read these. I just looked and found that two application notes are new, and the one I was thinking about has been re-issued under a different number. So, here are the links. It may be worthwhile for some of you to print the first one out. I have not read any of these yet, but I am about to print them all out myself. We older guys don't like reading from monitor screens. So, here they are :
AN1040-D Mounting Considerations for Power Semiconductors
AND8220-D How To Use Thermal Data Found in Data Sheets
AND8215-D Semiconductor Package Thermal Characterization
Think of application notes as free education. The quality is as high as any text book on the subject, and they are generally accurate (as opposed to reading posts like mine).
-Chris
Completely agree. Nicely out as well.
Hi rrcrain,
The characteristic impedance doesn't matter at all at audio frequencies, so a 52 ohm would have been fine, or twisted pair in a shield. That might actually work better at audio frequencies. You get a good return wire plus a shield in that deal. Then you could use mic cable found in most music shops.
Anyway, the stuff you had in one amp was corroded (or rotten if you'd rather), and so it had no hope of working properly.
Now, before people start diving in and replacing capacitors left, right and center, don't you think some testing and checking might be in order first? The main filter capacitors are often just fine. Check these using an oscilloscope with the amplifier running with no signal. Then, apply a signal if you want. A single tone might be easier to decipher. The other capacitors can be replaced, but make sure you use the correct type for the job it's doing. There is no one "best" capacitor, and I'll bet that the audio rated capacitors are simply down rated (for voltage) capacitors. If you are going to go that far, clean and redo the thermal compound, checking the transistors as you go. Watch for leakage (C-E and C-B) and beta. The signal transistors should be matched in beta and tested for leakage. Make sure the differential pair is in thermal contact and stuck together. I use thermal compound and heat shrink tubing. Do not use "computer grease" as some are conductive. Plan on replacing the mica insulators.
I figure if you are going to this much trouble and are concerned with improving the sound quality, you may as well do the entire job properly. Many things I have suggested will improve the sound quality and also the measured specifications.
Hi Sithlord2007,
You could call it either, but really the term you are looking for is "RCA patch cord". Phono cable often comes as a pair with a ground lead molded in as well. In this application, the quality of the shield, or "screen" is a more critical attribute than fancy ends or anything like that. Also make sure you use a thinner and more flexible replacement cable if this is needed. There isn't much wrong with the original stuff unless it's degraded.
Semiconductor Mounting Considerations
There are documents at On Semi's web site that tells you the proper way to mount power semiconductors. It also tells you how much pressure to apply. Since most people over-tighten these screws, I'd highly recommend everyone read these. I just looked and found that two application notes are new, and the one I was thinking about has been re-issued under a different number. So, here are the links. It may be worthwhile for some of you to print the first one out. I have not read any of these yet, but I am about to print them all out myself. We older guys don't like reading from monitor screens. So, here they are :
AN1040-D Mounting Considerations for Power Semiconductors
AND8220-D How To Use Thermal Data Found in Data Sheets
AND8215-D Semiconductor Package Thermal Characterization
Think of application notes as free education. The quality is as high as any text book on the subject, and they are generally accurate (as opposed to reading posts like mine).
-Chris
Sithlord:
Found this Hafler DH500 transformer on Ebay; it supports 90 volt rails and sounds about as hefty as the AA-1800's. Similar form factor, but doesn't have the low voltage 24 volt supply winding. You might want to ask about the spacing of the mounting lugs.
Power Transformer New for Hafler XL-600, DH-500 or amp - eBay (item 190337211013 end time Feb-20-10 11:11:47 PST)
A further study of the schematic shows that the AA-1800 and Leach's current version of his Superamp are only somewhat generally similar in design, there being interesting differences in the driver and VAS stages that I don't especially understand. So I wouldn't quite call it a Leach 'clone'.
Found this Hafler DH500 transformer on Ebay; it supports 90 volt rails and sounds about as hefty as the AA-1800's. Similar form factor, but doesn't have the low voltage 24 volt supply winding. You might want to ask about the spacing of the mounting lugs.
Power Transformer New for Hafler XL-600, DH-500 or amp - eBay (item 190337211013 end time Feb-20-10 11:11:47 PST)
A further study of the schematic shows that the AA-1800 and Leach's current version of his Superamp are only somewhat generally similar in design, there being interesting differences in the driver and VAS stages that I don't especially understand. So I wouldn't quite call it a Leach 'clone'.
Anatech ... Thanks for the advice!
Damon Hill ... Thanks for the heads up!
Also, I have a schematic for the Heathkit aa-1800. It is a PDF and can printed out on 8-1/2 x 11. It is three sheets and you will need to trim it and tape it togehter. Sorry, but I only have a small flatbed scammer. If there is something you can't read, let me know and I will help but it should be clear.
I am not sure how to post a file on here, so email me and I will send it over.
Floortoms1977@yahoo.com
Thanks!
Ed
Damon Hill ... Thanks for the heads up!
Also, I have a schematic for the Heathkit aa-1800. It is a PDF and can printed out on 8-1/2 x 11. It is three sheets and you will need to trim it and tape it togehter. Sorry, but I only have a small flatbed scammer. If there is something you can't read, let me know and I will help but it should be clear.
I am not sure how to post a file on here, so email me and I will send it over.
Floortoms1977@yahoo.com
Thanks!
Ed
Anatech ... Thanks for the advice!
Damon Hill ... Thanks for the heads up!
Toodleoo ... I have a schematic available (pdf) but do not know how to post it on here. Email me if you still need it. Same goes for anyone else.
Floortoms1977@yahoo.com
Thanks!
Ed
Damon Hill ... Thanks for the heads up!
Toodleoo ... I have a schematic available (pdf) but do not know how to post it on here. Email me if you still need it. Same goes for anyone else.
Floortoms1977@yahoo.com
Thanks!
Ed
OK ... here is another one for you!
We have bneen talking a lot about recapping the amplifier, but how about the preamplifier?
I have an AP-1800 Preamplifier that is also around 30 years old. Even though the components don't see as much voltage and heat as the amplifier, should I do a major recapping job on it as well? Just wondering because the preamplifier is a critical component in the signal path.
Thanks!
Ed
We have bneen talking a lot about recapping the amplifier, but how about the preamplifier?
I have an AP-1800 Preamplifier that is also around 30 years old. Even though the components don't see as much voltage and heat as the amplifier, should I do a major recapping job on it as well? Just wondering because the preamplifier is a critical component in the signal path.
Thanks!
Ed
As a rule-of-thumb I'd replace all electrolytic coupling caps with plastic film; even mylar caps are an improvement. If Heathkit's practice was to use a 10 uF series capacitor, use a 4.7 uF or larger, whatever reasonably fits in the available space.
After that, just replace all small electrolytics with the same value of new units; that will eliminate any marginal ones, depending on the quality of the parts originally used.
Further, replace all carbon film resistors with metal film, at least 100 ppm 1% and better quality if you can afford it.
I might have more specific recommendations, but I'd have to see a schematic for the values and the actual unit to see what kinds of parts were used. There may be some small value capacitors that could be replaced with better quality polypropylene or polystyrene parts.
Clean all switch contacts with De0xit or similar, and consider replacing the typical cheesy RCA connectors with gold-plated--some ingenuity may be required to do a neat job. These usually get a heavy layer of corrosion, unless the original parts were better quality than Heath typically used.
The rest is testing and listening to see if s/n and distortion specs are reasonably met. It's always nice to know the unit is meeting objective specifications as well as audibly sounding good.
After that, just replace all small electrolytics with the same value of new units; that will eliminate any marginal ones, depending on the quality of the parts originally used.
Further, replace all carbon film resistors with metal film, at least 100 ppm 1% and better quality if you can afford it.
I might have more specific recommendations, but I'd have to see a schematic for the values and the actual unit to see what kinds of parts were used. There may be some small value capacitors that could be replaced with better quality polypropylene or polystyrene parts.
Clean all switch contacts with De0xit or similar, and consider replacing the typical cheesy RCA connectors with gold-plated--some ingenuity may be required to do a neat job. These usually get a heavy layer of corrosion, unless the original parts were better quality than Heath typically used.
The rest is testing and listening to see if s/n and distortion specs are reasonably met. It's always nice to know the unit is meeting objective specifications as well as audibly sounding good.
Hi Sithlord2007,
Those are excellent preamplifiers.
I would replace the capacitors, but in no way would I replace all the resistors with metal film types. There are only a few resistor locations that would benefit from a metal film type. The gain setting feedback resistors are one set of locations. Resistors in the signal path of high gain, low signal level areas. The larger resistors should be replaced with metal oxide and the rest should only be replaced if they are off value or damaged.
I've seen more equipment damaged after a complete component change was attempted, most of the resistors replaced were not necessary.
Also, don't forget that there are other limiting factors in your rebuild. The noise and distortion of the amplifier and also possible ambient noise where you live. Look at the schematic first, locate those resistor locations that matter. Make a list and replace those parts only.
-Chris
Those are excellent preamplifiers.
I would replace the capacitors, but in no way would I replace all the resistors with metal film types. There are only a few resistor locations that would benefit from a metal film type. The gain setting feedback resistors are one set of locations. Resistors in the signal path of high gain, low signal level areas. The larger resistors should be replaced with metal oxide and the rest should only be replaced if they are off value or damaged.
I've seen more equipment damaged after a complete component change was attempted, most of the resistors replaced were not necessary.
Also, don't forget that there are other limiting factors in your rebuild. The noise and distortion of the amplifier and also possible ambient noise where you live. Look at the schematic first, locate those resistor locations that matter. Make a list and replace those parts only.
-Chris
aa1800
I have 2 heath aa1800's as far I remember they have + and - 100 volt supplies and the power is designed to provide 1 kilowatt of dc. if that helps. I also have an aa1640 which runs + and - 90 volt supplies and an
aa1506 60 watts per ch. that goes back to 1974 all 4 amps are dead quiet with no input that my mind says the main caps are still good. thats my take.
I have 2 heath aa1800's as far I remember they have + and - 100 volt supplies and the power is designed to provide 1 kilowatt of dc. if that helps. I also have an aa1640 which runs + and - 90 volt supplies and an
aa1506 60 watts per ch. that goes back to 1974 all 4 amps are dead quiet with no input that my mind says the main caps are still good. thats my take.
Hi. New to this forum. Just finished reading this thread and wanted to know how your restoration project of the AA-1800 turned out. Is it complete? Major issues encountered. I'd like to get my hands on an original AA-1800. I have a AA-1515 that still sounds darn good. I wonder if there are some things I can do to keep it sounding so - or improve it?
redjr...
I finished recapping my two AA-1800s about two months ago. (replaced all of the electrolytics except the 2 in the power supply) One out of necessity, the other as a preventative measure. I did replace all of the 20% carbon resistors with 5% film while I was at it. Low cost and easy thing to do. One of my amps was purchased years ago off eBay and I had a lot of trace repair to do as well.
I did not expect an improvement in sound. My singular goal was to restore one amp to serviceability. What happened was a very noticeable improvement in literally ever aspect you can think of. Simple things I noticed, bias and offset were now very stable, no drift.
As for bridging, I have to ask, WHY? This amp is very conservatively rated at 250W per channel.
I did not expect an improvement in sound. My singular goal was to restore one amp to serviceability. What happened was a very noticeable improvement in literally ever aspect you can think of. Simple things I noticed, bias and offset were now very stable, no drift.
As for bridging, I have to ask, WHY? This amp is very conservatively rated at 250W per channel.