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NAD 3020 amp upgrades?
NAD 3020 amp upgrades?
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Old 30th January 2007, 04:59 AM   #21
TDWesty is offline TDWesty  Canada
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My digi-key package arrived today :-)

First, I put my 3020 back in the system for a quick listen of a few well known tracks, including one where it falls apart badly. (just about anything on Robbie Robertson's 1st album)

Then, I upgraded the 3020 PSU caps from 2200uF to 5600uF, with very slightly larger diameter units from United Chemicon SMG series.

All went smoothly, and my solder job even looks better than original (which isn't saying much...).

Back to the living room, the 3020 sounds much more composed on Robbie Robertson, where previously the bass was out of control and flabby - now it is much better controlled, although still a little heavy handed and loose for my tastes.

Now I have most of the caps to replace on the 3020, but really wanted to try the PSU caps on my 3125, which has been my main amp for 20 years now. (And was just brought back to life a few weeks back, when I decided to bypass the infrasonic filter section in the pre-amp, which was slowly dying.)

I had ordered 10,000 uF Panaonic TS series, to replace the stock 4700uF units in the 3125. They were snap-ins, so install was quick and painless. The old units were ELNA, and looked ok, except for slight bulge in one.

Listening to the 3125 didn't reveal as much improvement - it already sounded much cleaner and more dynamic than the 3020, especially on complex tracks, when the 3020 seems to just lose its composure. There is a bit more punch on very dynamic tracks, but the lower bass on the 3125 is not nearly as heavy as the 3020, which still seems too boomy to me.

One more swap for tonight - before putting the 3125 cover back, I decided to replace the 1000uF reg PS caps, this time with same size Panasonic KY, which are much smaller diameter, but same height. I have heard the smaller caps should remain the same size, including on the reg PS. Here, I had a problem with one solder track on the board coming loose, but was able to bend the lead back over a secure section and make it work. More care next time...

On listening, there seemed more of a difference now than after replacing the big caps - detail in the mids and highs seemed better, although bass seems about the same.

I'm still a little puzzled about the dramatic differences in the bass between the two amps. Next I plan to replace most of the remaining small caps on the 3020, in hopes of bringing back some clarity and definition. Then maybe I'll try a chipamp with the 3020 as a pre-amp. :-)
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NAD 3125 & 3020 amps, 4125 tuner / Rotel RCD-965BX CD / B&O 2400 / Nakamichi BX-125 / PSB 70R speakers / BrianGT chipamp in progress...
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Old 3rd February 2007, 02:36 PM   #22
cpemma is offline cpemma  United Kingdom
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Quote:
Originally posted by es44
If it could be of any help for you, i have two different service manuals for it...
And circuit only for a third, the 3020i

Though this shows 2 x 4700uF caps on the PSU so not the OP's model with 4 x 2200uF.
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Old 3rd February 2007, 02:52 PM   #23
AndrewT is offline AndrewT  Scotland
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Hi,
the 3020 was designed for cheaper systems and these usually had fairly small speakers that had poor low end extension.

NAD may have engineered in a small amount of bass lift to augment the falling bass of the partnering speakers.
In those days, at least in the UK, there were a band of good audio retailers who compiled systems that made the best from matched components (from different manufacturers) that when swapped around may not perform as well.
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Old 3rd February 2007, 02:53 PM   #24
AndrewT is offline AndrewT  Scotland
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mexbro link doesn't.
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Old 3rd February 2007, 05:04 PM   #25
TDWesty is offline TDWesty  Canada
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Quote:
Originally posted by AndrewT
Hi,
the 3020 was designed for cheaper systems and these usually had fairly small speakers that had poor low end extension.

NAD may have engineered in a small amount of bass lift to augment the falling bass of the partnering speakers.
In those days, at least in the UK, there were a band of good audio retailers who compiled systems that made the best from matched components (from different manufacturers) that when swapped around may not perform as well.
Wouldn't this sort of thing show up on freq resp measurements? Or is it more of a dynamic issue with how the amp interacts with the speaker load?

I've now spent some time studying the mods listed here and plan to try removing the tone and balance controls next. I've never used them as I like a flat response, and my speakers are very flat also.

Perhaps cleaning up the circuit will affect the bass response; we'll see.

Right now I'm listening to my 3125 again after replacing a few more caps in the power amp section based on what I had on hand. (the largest feedback caps are still original). This seems to have cleared up the previously distant sounding treble and upper midrange, but there is a certain harshness in female vocals now that wasn't there before, especially as the volume increases above low levels.

The original caps in the 3125 are ELNA, and I'm not sure what the 3020 are - the symbol is a triangle with little squares at each corner. It would be interesting to measure the old ones as they come out to see how far off they are...

I'll report back after I do the tone control mods...
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NAD 3125 & 3020 amps, 4125 tuner / Rotel RCD-965BX CD / B&O 2400 / Nakamichi BX-125 / PSB 70R speakers / BrianGT chipamp in progress...
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Old 3rd February 2007, 06:17 PM   #26
cpemma is offline cpemma  United Kingdom
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Quote:
Originally posted by AndrewT
mexbro link doesn't.
Does now.
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Old 3rd February 2007, 09:25 PM   #27
AKN is offline AKN  Sweden
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Hi,

Nad 3020 does not have bassbost in form of some EQ.

The amp has many sources for resistance to be added from power transistors emitter junction to speaker output, note this is outside feedback loop.
Signal has to pass: polyswitch - thin cables to headphone jack - over the headphone jack bypass - trough thin cables again and finally to speaker output. This adds series resistance and I have measured it to approx 0.3Ohm, most of it over the polyswitch (beware).
Speakers will of course be more or less affected by this as Q will rise.
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Old 3rd February 2007, 11:37 PM   #28
TDWesty is offline TDWesty  Canada
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Quote:
Originally posted by TDWesty


I've now spent some time studying the mods listed here and plan to try removing the tone and balance controls next. I've never used them as I like a flat response, and my speakers are very flat also.

I'll report back after I do the tone control mods...
I did the step 1 mods (remove tone controls) at the peak audio site above, but only on the right channel so far. I still need to get some better resistors to do it properly. So far the amp stills works :-) but the gain reduction is evident. I'm not sure of the reason for reducing the preamp gain from 6 to 3. I did notice that there is a typo in this section - he refers to "F" connections on the PCB corresponding to circled B on the schematic for the right channel. On my amp, it is E for right channel (circled B) and F for left channel (circled A). I spent a lot of time tracing the board before deciding it must be this way.

I would be interested in knowing the reason for the preamp gain reduction though.

Now I'm going to try the other channel and give it a listen... :-)
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NAD 3125 & 3020 amps, 4125 tuner / Rotel RCD-965BX CD / B&O 2400 / Nakamichi BX-125 / PSB 70R speakers / BrianGT chipamp in progress...
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Old 4th February 2007, 05:37 AM   #29
PeAK is offline PeAK  Canada
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Quote:
Originally posted by TDWesty


...the gain reduction is evident. I'm not sure of the reason for reducing the preamp gain from 6 to 3. I did notice that there is a typo in this section ...

I would be interested in knowing the reason for the preamp gain reduction though.
Hi Shawn,
It's PeAK chiming in. Good to see you on your way. The Bass controls attenuate the amount of feedback. With "no" feedback, the preamp gain would be the open loop value and be vary high. When 1/6 [560/(560+3300] the open loop output is fed back, feedback theory dictates that the gain is "roughly" the inverse of the "amount of feedback" or 6.

When R540 is removed, essentially 100% of the output signal is fed back and the gain attenuates to 1/1=1. Unity Gain. The 6 to 3 change I mentioned was due to a different mod related to a cap divider coming into the preamp section.

Not sure about the typo (have not verified) but it should be self evident as you have found. Last, when you are doing piecemeal mods, I'm not sure what you will get as the mods were broken down into sections but meant to done "together" so that issues with DC offset and improper biasing do not exist. If you do want to try things out, peice meal, then the feedback requires that feedback be done so in an AC sense and C524 be kept in at all times.

I'll try to check in here from time to time but feel free to email me and cross post here with your info for others to try.


P.S. I'll get around to modifying the broken links and uploading a component placement diagram...and fixing those typos you point out...

regards %^Q
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Old 4th February 2007, 06:33 AM   #30
planet10 is offline planet10  Canada
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NAD 3020 amp upgrades?
Quote:
Originally posted by TDWesty
the reason for reducing the preamp gain from 6 to 3
I often found mysel fusing the 20 dB reduction switch on my NADs... a gain reduction in the pre-amp would be welcome.

dave
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