NAD 3150
- Thread starter gpounce32768
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gpounce32768
Active Member
Replacing R676 with 740 ohms drops the protection relay voltage down to 22v with the amp on mains and no add-on resistor across the coil, the protection relay operates normally. Unfortunately it looks like the amp is working and not dead lol but I'll get into sampling the caps and sound testing.
eschenborn
Member
I have just received a 3150 yesterday, not opened the amp up yet, however.
the previous owner reported it to hang in protection. he had 4 ohm speakers connected to it, the switch obviously on the 8 ohm setting. it starts ok with the switch on 4 ohm (connected to 8 ohm speakers now), and keeps out of protection if switched to 8 ohm later (maybe an anecdotal finding though).
I am curious what I will find inside and report. I will do all the necessary replacements (thanks to the contributors in this thread for a new aspect) and replace-upgrade the caps. so there might be some opportunity to compare our results. great! I am not alone. I have read about some thermal problems in the power supply of elder units like the NAD 160 receiver and thus will be on the lookout for that.
it seems that everything in the machine is easily accessible, although I don't like the cheap all-on-one-board designs. at least you can screw off the bottom. the 3150 has two transformers but seems not true dual mono, both feeding into one power supply. the sound as-is is punchy and spacious, although with a certain veil and grain to it, a bit cardboardy. curious how this will be after a recap.
I will also replace the IC in the tone stage (NE5532) with a discrete op-amp or with a self-made buffer (some experimentation needs to be done here). in contrast to the 3020 this HAS opamps in the tone stage, as do 3155 and 3240PE. I don't know if the 3140 has them, too.
the pic shows the unit freshly arrived sitting on top of its elder siblings for a quick sound-check.
the previous owner reported it to hang in protection. he had 4 ohm speakers connected to it, the switch obviously on the 8 ohm setting. it starts ok with the switch on 4 ohm (connected to 8 ohm speakers now), and keeps out of protection if switched to 8 ohm later (maybe an anecdotal finding though).
I am curious what I will find inside and report. I will do all the necessary replacements (thanks to the contributors in this thread for a new aspect) and replace-upgrade the caps. so there might be some opportunity to compare our results. great! I am not alone. I have read about some thermal problems in the power supply of elder units like the NAD 160 receiver and thus will be on the lookout for that.
it seems that everything in the machine is easily accessible, although I don't like the cheap all-on-one-board designs. at least you can screw off the bottom. the 3150 has two transformers but seems not true dual mono, both feeding into one power supply. the sound as-is is punchy and spacious, although with a certain veil and grain to it, a bit cardboardy. curious how this will be after a recap.
I will also replace the IC in the tone stage (NE5532) with a discrete op-amp or with a self-made buffer (some experimentation needs to be done here). in contrast to the 3020 this HAS opamps in the tone stage, as do 3155 and 3240PE. I don't know if the 3140 has them, too.
the pic shows the unit freshly arrived sitting on top of its elder siblings for a quick sound-check.
gpounce32768
Active Member
I did a MOTL Yamaha last year that perked up considerably after a recap, would not be surprised if the sound changes a good deal. I've not listened to mine critically yet- its on my junky test speakers. My seller said it didn't work- turned out to be missing pre-out/main-in jumpers. Good to know about the tone opamp upgrade tho, I'll do that too.
eschenborn
Member
Nelson Pass suggested some discrete opamp designs here: https://www.passdiy.com/pdf/diyopamp.pdf
I will try to build one of them and test it in the place of the NE5532 in the NAD 3150.
I will try to build one of them and test it in the place of the NE5532 in the NAD 3150.
gpounce32768
Active Member
I did some sniffing around in the schematic on the 5532, I quite like the use of the opamp there. Not sure about a DIY opamp, but considering an AD8620 in its place.. but regardless I need to do the caps first.
eschenborn
Member
sure, caps first. what makes you like the use of the IC there? comparing the schematic to that of the 3140 without IC, it is interesting to see what the opamp replaces.
gpounce32768
Active Member
I like the tone controls in the op-amp negative feedback- perhaps a nice place compared to doing it in the power stage with the speakers involved...
I went for the LM4562, needed a minor mod to the power supply. Opened up the sound a fair bit, yeah I'd say a noticeable improvement.
Did quite a lot of work on the 2x3150's recapped twice, cree rectifier diodes, metal film resistors, blah blah... Only sounded OK. Hope
you have better luck.
eschenborn
Member
I understand. possible that the end result will only be mediocre. I am curious as how far I can get it. my experience with 80's + gear is that upgrading does not bring the sound out as easily as it does in older stuff, like from the late 60s or early 70's. I will be doing this as a test of how far it can go. the power amp seems simple and good, no differential, but the preamp... would be interesting to hear the 3140 which is fully discrete.
but we'll see how the 3150 will behave with new caps first and then w/o the ICs in the tone stage. the amp feels powerful and has a good resolution, but there is an artificial glare to the sound, at least to my ears, at least in the as-is state. I never heard a 3020. that would be needed to have a reference for my research concerning the NAD amp family from the 80s. part of my work will be to change the power amp input to the "lab" input the 3020 (and 3140) had, aka bypass the high pass filter that sits there in the 3150 before the first transistor stage (for reasons I can simply not imagine).
By no means an expert, I've refurb'd 2x3150, 1x3140 and 3?x3020, they only sound ok, think the problem I have is the lack of sound stage. I like the 3140
slightly better than the rest however this is probably placebo knowing it has a discrete preamp. Forgive my suggestions but if I was to do another 3150 I
would go for,
Nichicon KW main filters
Nichicon PW remaining power supply
Elna Silmic II on power rails and audio path with the exception of small values where MKS2 film caps would be used. I think @leesonic(?) is a strong advocate MKS2
over electrolytic. I can see the lower tan delta being appealing.
Use an opamp socket for rolling, the LM4562 was an improvement
I think it's great that you use the 3150 to learn.
slightly better than the rest however this is probably placebo knowing it has a discrete preamp. Forgive my suggestions but if I was to do another 3150 I
would go for,
Nichicon KW main filters
Nichicon PW remaining power supply
Elna Silmic II on power rails and audio path with the exception of small values where MKS2 film caps would be used. I think @leesonic(?) is a strong advocate MKS2
over electrolytic. I can see the lower tan delta being appealing.
Use an opamp socket for rolling, the LM4562 was an improvement
I think it's great that you use the 3150 to learn.
gpounce32768
Active Member
That front end circuit (I assume you mean in front of Q603/Q604). I have the impression its generally a ac coupled input with bias for the the transistor, and some hi frequency roll-off.
eschenborn
Member
interesting that you say that also about the 3020. I was always thinking about getting one to get the most of it and understand why so much was raved about it. I thought maybe it was si famous because then most amps came with ICs in the tone stage and this did not... yours is one of the first voices I hear not totally hyping the 3020. or the 3150, for that matter. anyway, I got the machine because I like it for its place in NAD'S history, for its very plain serious aesthetics, and in order to see what is truly behind it. so we'll see. I would also love to compare a brand new NAD, just for curiosity. but that would be more than toying around with cheap stuff.
thanks for your suggestions re the choice of caps. I will put in small WIMA MKS films wherever the values allow it (everything in the signal path), and for the remainder I'll probably use panasonic FCs as always. the main filters will be nichicons as that's the only fitting size I find. I'll look for the price of Elnas at mouser now, though, thanks for suggesting. I will also replace all the ceramics... loads of them in there... far too many... with either small WIMA films or silver micas.
and yes, absolutely, the opamp socket will be put in there for lots of fun. I would have built and tested a pre-amp circuit with only one input (minus the inverting one) but the tone stage, being in the feedback loop, is in the way. need to put some more thinking into that.
Maybe I'm being too tough on the 3150 but I gave it every chance, probably spent 200hours on it. Initial recap with cerafines to "tone it down" and then redone
with Silmic II's for the better, Nichicon in psu. Even purchased a second 3150 thinking it was a problem with the original unit, refurb'd, same result.
The 3020 is rated as one of the most influencial amps of that era. I would have to agree. It was a game changer. Prior to the 3020 the big boys
had the market stitched up and generally produced some ordinary entry level cr@p to fund their higher end stuff. The 3020 through some clever design
blew this entry level cr@p out of the water and significantly cheaper also. Use the 3150 as a learning experance and you can't go wrong. Despite the
birds nest of wires and haphazard layout, the nads are very easy to work on.
with Silmic II's for the better, Nichicon in psu. Even purchased a second 3150 thinking it was a problem with the original unit, refurb'd, same result.
The 3020 is rated as one of the most influencial amps of that era. I would have to agree. It was a game changer. Prior to the 3020 the big boys
had the market stitched up and generally produced some ordinary entry level cr@p to fund their higher end stuff. The 3020 through some clever design
blew this entry level cr@p out of the water and significantly cheaper also. Use the 3150 as a learning experance and you can't go wrong. Despite the
birds nest of wires and haphazard layout, the nads are very easy to work on.
gpounce32768
Active Member
I started sampling the electrolytics in my 3150, ESR has drifted quite a bit so I'm going to do a full recap of the signal caps, will do the supply caps too if they don't measure reasonably. I pulled IC501 and put in a socket for the op-amp rolling. I have a reasonable selection of film caps so will replace electrolytics in the signal path with them. I've generally replaced them with better spec electrolyitcs, not really buying the arguments in favor of film OTOH theres plenty of room on this board so I might as well try it.
NAD operated the NE5532 at about 18Vdc, this limits your options
unless you tweak the power to the IC (R554,5, 560ohms). Think
I went with 680 for the LM4562, that was like 7 years ago so there
are much better opamps available today.
Apart from the main filters, the low noise/leakage caps in the preamp
and phono stage (normally orange or pale green) deserve special
attention, either Nichicon UKL or MKS2 are the common choices.
Think there is one cap where you have to remove the bottom strut
(or was that the 3140?), need to remove/loosen front and back plates
apart from that it's reasonably easy.
unless you tweak the power to the IC (R554,5, 560ohms). Think
I went with 680 for the LM4562, that was like 7 years ago so there
are much better opamps available today.
Apart from the main filters, the low noise/leakage caps in the preamp
and phono stage (normally orange or pale green) deserve special
attention, either Nichicon UKL or MKS2 are the common choices.
Think there is one cap where you have to remove the bottom strut
(or was that the 3140?), need to remove/loosen front and back plates
apart from that it's reasonably easy.
gpounce32768
Active Member
I don't mind fooling around with the regulators, I'll pick up a couple different opamps in my next buy to play around with. I'm glad I'm doing the electrolytics, found one in the opamp feedback was way out- so far most have been the usual drifting about, new ones testing at more consistent values. The amp sounds good on my mid-range speakers though I'm only part-way thru the recap. I'm digital sources only, but will do the phono sections too.
gpounce32768
Active Member
Yep C539 is something of a pest to replace, nothing is hard to remove but a bunch of stuff is in the way. The brace obscuring the solder traces needs to be unscrewed from front & rear panels, 2 screws holding the heatsink assembly to the brace, and the front panel has to come off. With all that removed, the main board can slide off the hooks on the brace, exposing the traces.
gpounce32768
Active Member
On my system the cap C647 22uf right next to the hot R676 was cooked and open. If servicing one of these units but not doing a full recap definitely have a look into the protection circuit caps.
All the to-220 transistors run hot in this design- even the sinked devices. I installed larger heatsinks on those, re-used 3 of the stamped aluminum originals on the un-sinked devices.
All the to-220 transistors run hot in this design- even the sinked devices. I installed larger heatsinks on those, re-used 3 of the stamped aluminum originals on the un-sinked devices.
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