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List of capacitor coupled solid state receivers and integrated amplifiers

EviesDad said:
I own a baby Marantz 2015 receiver (1973) which I had understood to be cap coupled, perhaps someone in the know could confirm? The smaller output 2010 may also be cap coupled.
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I believe you are correct. They have one large filter cap with two smaller coupling caps. Direct Coupled designs have two identical large filter caps.
 
The only SS Sherwood I am aware of with transformer in amp circuit is the S-7100 but its interstage transformer coupled, not connected to speakers.

After checking again, Steven Tate is correct, the STA-8010 isn't cap coupled but does have interstage transformer.
 
Out of curiosity, would simply inserting a cap of the proper value between the speaker outputs and the speaker itself make an amp 'capacitor coupled', or is there more to it? I understand why it's done - to keep DC out of the amps's output - but it seems to have an affect on the sound that many like. I wonder if one could get the same effect by installing a cap inline with the speakers.
 
David_NC said:
Out of curiosity, would simply inserting a cap of the proper value between the speaker outputs and the speaker itself make an amp 'capacitor coupled', or is there more to it? I understand why it's done - to keep DC out of the amps's output - but it seems to have an affect on the sound that many like. I wonder if one could get the same effect by installing a cap inline with the speakers.
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I am not an engineer, and don't completely understand the design rationale of cap coupled and direct coupled amps. But one difference that is usually discussed is that cap coupled designs tend to have one power rail referenced to ground. Direct coupled amps tend to have two power rails, plus and minus, referenced to 0V DC. That's why cap couple designs usually have one large filter cap and direct coupled designs have two - one for the positive rail and one for the negative rail. So, it is much more than just a cap between output and speakers.
 
Steven Tate said:
I am not an engineer, and don't completely understand the design rationale of cap coupled and direct coupled amps. But one difference that is usually discussed is that cap coupled designs tend to have one power rail referenced to ground. Direct coupled amps tend to have two power rails, plus and minus, referenced to 0V DC. That's why cap couple designs usually have one large filter cap and direct coupled designs have two - one for the positive rail and one for the negative rail. So, it is much more than just a cap between output and speakers.
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Cap coupled / single power rail amps are a simpler design, from what I understand and do need the cap to keep DC from the outputs. That part is clear to me. I also understand filter caps. However, my question is if one simply places an appropriate cap in the speaker outs of an amp, will one have an amp that 'sounds' capacitor coupled.
 
David_NC said:
Cap coupled / single power rail amps are a simpler design, from what I understand and do need the cap to keep DC from the outputs. That part is clear to me. I also understand filter caps. However, my question is if one simply places an appropriate cap in the speaker outs of an amp, will one have an amp that 'sounds' capacitor coupled.
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The answer to that is above my pay grade. I wish I knew more about amp design, but probably too old to go down that road. I’ll have to be satisfied with repairing and restoring these old units.
 
Steven Tate said:
Nope. Everything over 30 wpc, as well as a few under we’re direct coupled - 2245, 2270, 2275, 2325 just to name a few of the more popular ones. The DC moniker was used on a few models very late in the 70’s.
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EviesDad said:
I own a baby Marantz 2015 receiver (1973) which I had understood to be cap coupled, perhaps someone in the know could confirm? The smaller output 2010 may also be cap coupled.
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The cap-coupled Marantz units already on the list, are these:

Receivers

Marantz 2210 (10)
Marantz 2215 (15)
Marantz 2220 (20)
Marantz 2230 (30)
Marantz 26 (14)

Integrated Amps

Marantz 1030 (15)
Marantz 1060 (30)

The latest version of the list is in post #30. I'll update again soon.
 
Steven Tate said:
I am not an engineer, and don't completely understand the design rationale of cap coupled and direct coupled amps. But one difference that is usually discussed is that cap coupled designs tend to have one power rail referenced to ground. Direct coupled amps tend to have two power rails, plus and minus, referenced to 0V DC. That's why cap couple designs usually have one large filter cap and direct coupled designs have two - one for the positive rail and one for the negative rail. So, it is much more than just a cap between output and speakers.
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Here's a picture of the inside of a Marantz 1060 integrated showing what you described - just one large filter capacitor for the power supply (by the transformer), and two coupling capacitors. Typically, an odd number of big capacitors (like 3) means cap coupled and an even number (like 4) means direct coupled.

Capacitor coupled amps are not always as easy to identify as the 1060, however, by just looking at a picture. Some units have capacitors on both sides of the main board, some have been recapped with capacitors much smaller than the originals, and so on and so forth. That's why it's so useful to hear from those with service manuals and experience.


Marantz_1060_Insides.jpg
 
Does anyone know of any receivers or integrated amps from these manufacturers that were capacitor coupled?

Onkyo
Panasonic/Technics
Philips
Luxman
Yamaha

All were active during the cap coupled era, but I am not aware of any cap coupled models that they produced, other than the Yamaha CR-200. There must be some others.

Denon is another make missing from the list, but I don't think they were very active in the amplifier market back then.
 
I continue to get input from various sources about capacitor coupled amps, and about 10 more units have been added to the list. The total is now up to 149 receivers and 68 integrated amplifiers, far more units that I originally thought existed.

I'm sure many receivers and integrateds are still missing from the list. Continued input is welcome, particularly about the brands listed in post #49 above (Onkyo, Technics, Philips, and Luxman), who have no units listed, and Yamaha (where only one is listed).
 

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If the list is correct, my Kenwood KR-3200 (13.5 wpc @ 20 to 20k Hz, both channels driven, IIRC) is direct coupled. Most of the list is low powered receivers, and one wonders why this Kenwood (1972) was not designed as cap- coupled...
 
Sax & Guitar said:
If the list is correct, my Kenwood KR-3200 (13.5 wpc @ 20 to 20k Hz, both channels driven, IIRC) is direct coupled. Most of the list is low powered receivers, and one wonders why this Kenwood (1972) was not designed as cap- coupled...
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Looking at the schematic, I think it is cap coupled. There is a 1000uF 35V cap between the outputs and speakers on both channels. Hopefully, someone can verify.
 
To recreate output cap in the split supply amps, capacitor must have dc voltage bias, like in real output cap amplifiers.
Something like that was made by JBL speakers if I remember good.
 
GyroTuner said:
Not true. The higher powered gear was usually direct coupled even in the same product line (i. e. Marantz, Sansui, Pioneer), and some makes for the most part stayed away from capacitor coupling (i. e. Sony) even in the early 70s. There was also some transformer coupled gear, Sherwood, for example.

As for the reason for making a list, none really, other than that I'm interested in the topic. Solid state only as noted above. If you have corrections, deletions, or additions, it would be much appreciated. Thanks.
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I had a Realistic STA-65C and an STA-65D. One was transformer coupled. I got them around the same time and although they looked identical I could feel one was heavier. I opened it up and saw the transformers. That was the first and only transformer coupled SS receiver I have personally seen/owned.
 
Steven Tate said:
Looking at the schematic, I think it is cap coupled. There is a 1000uF 35V cap between the outputs and speakers on both channels. Hopefully, someone can verify.
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Thank you - the KR-3200 has been added to the list.

Here is an updated list, now containing 151 receivers and 71 integrated amplifiers. Additions and corrections to the list are always welcome.
 

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Add Heathkit AR-15 receiver and AA-15 amplifier. Also, almost ALL Fisher solid state, except 600-T, TX-300, 500-TX and 800-T are direct coupled.
 
fred soop said:
Add Heathkit AR-15 receiver and AA-15 amplifier. Also, almost ALL Fisher solid state, except 600-T, TX-300, 500-TX and 800-T are direct coupled.
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The two Heathkits that you mention are already on the list.

Regarding the Fisher amps, can you clarify your statement? Are you saying the four amps you listed are cap coupled and everything else is not? I don't think that is the case, but if you can be more specific, that would be great, as I want the list to be as accurate as possible.

Thank you.
 
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