I found the FETs introduced distortion. I don't believe FETs are very linear when used as a switch like this, in analogue audio.
They gave the sound a distinct 'softness' is the only way I can describe it.
If you think back to 1980's car radios - the early digital ones - those suffered a similar issue but far worse.
P.S. apologies for the late reply - I didn't receive an email notification about your reply.
Where in the Freestate do you live? I passed through Bloem several times over the years, and I worked in Vereeniging and Vanderbijlpark for a while.
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They gave the sound a distinct 'softness' is the only way I can describe it.
If you think back to 1980's car radios - the early digital ones - those suffered a similar issue but far worse.
P.S. apologies for the late reply - I didn't receive an email notification about your reply.
Where in the Freestate do you live? I passed through Bloem several times over the years, and I worked in Vereeniging and Vanderbijlpark for a while.
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Hello Tony, I would like to improve my NAD 1000 and looking on the net I found your post about the additional diode in the bias string. Can you please draw a scheme how exactly the diodes should be added ? I could not understand from the post how to do it. If you have any other ideas of improving NAD 1000 I will be very thankful if you share. Thank you in advance !
Old thread but: the NAD 1000 is a good example of a NAD device where all electrolytic caps need to be replaced. All caps in the circuit in post #188 have 25V ratings so using tantalums 6.3V won't end well after a certain number of power on/off sequences. Tantalum caps are excellent but specifically with tantalum caps one uses a twice times higher voltage rating than the highest DC voltage. Also normally one uses radial caps where radial caps are used. All in all this was not the best of choices and chances are that the tantalums will go kaputt. The fluid of the old caps must be removed and the PCB should be cleaned from the debri as it is corrosive.
* The diode should be in series with the others so inserted in the string. Then you'll have 3 diodes in series. So in practice you will have 2 diodes on a spot where now only 1 is. Easy.
** The JFETS as switches were also a poor choice, it helps to have a "shorting output to GND" muting relay. Micro low power version, only needs to switch 2 channels to GND.
* The diode should be in series with the others so inserted in the string. Then you'll have 3 diodes in series. So in practice you will have 2 diodes on a spot where now only 1 is. Easy.
** The JFETS as switches were also a poor choice, it helps to have a "shorting output to GND" muting relay. Micro low power version, only needs to switch 2 channels to GND.
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Hi Jean-Paul ! Thank you very much for your quick replay ! Thanks for the advises . I already replaced all the electrolytic caps with new ones ( all Nichikon). The sound has been improved a bit. I also added two 10 000 uf / 50 V in parallel to the 470 uf caps in the powers supply . Do you think it is a good idea ?
No that is a bad idea. Completely unnecessary. Just replace the 470 µF for either 1000 µF or 1200 µF 50 or 63V and make sure to pick low ESR types that fit physically. Flying lead wires are plain stupid, sorry.
Please note that extreme completely unnecesary capacitance leads to too high surge currents which may damage the rectifier diodes. Also there are regulators that regulate voltage so no problems with ripple voltage.
C301/302 can be upped to 220 nF. C315/316 and C321/322 can be bipolar caps like MUSE ES. Choose 50V types if these fit better physically. Avoid buying these from Ebay and the like but choose a distributor. Don't be tempted to use higher values but higher voltage ratings are no issue. Measure diameter, height and pitch of the old caps and choose the exactly fitting ES type. Never use lower voltage rated types!!!
Without the JFETs as series switches the device will sound better. When using a shorting output to GND type muting the switch is out of the signal path. These muting PCBs are perfect for the job if OP wishes to reply:
https://www.diyaudio.com/community/...-psu-mod-output-delay-ground-isolator.358951/
NB: the extra diode mod is recommended by audio_tony. I never did that.
Please note that extreme completely unnecesary capacitance leads to too high surge currents which may damage the rectifier diodes. Also there are regulators that regulate voltage so no problems with ripple voltage.
C301/302 can be upped to 220 nF. C315/316 and C321/322 can be bipolar caps like MUSE ES. Choose 50V types if these fit better physically. Avoid buying these from Ebay and the like but choose a distributor. Don't be tempted to use higher values but higher voltage ratings are no issue. Measure diameter, height and pitch of the old caps and choose the exactly fitting ES type. Never use lower voltage rated types!!!
Without the JFETs as series switches the device will sound better. When using a shorting output to GND type muting the switch is out of the signal path. These muting PCBs are perfect for the job if OP wishes to reply:
https://www.diyaudio.com/community/...-psu-mod-output-delay-ground-isolator.358951/
NB: the extra diode mod is recommended by audio_tony. I never did that.
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Thank you very much for the feedback ! I will remove the 10 000 uf. I will leave only the new replaced 470 uf Nichicon caps in the power supply.
I looked at the scheme where is the output, with the 2SK363 ( Q309 and Q363). If I understand right the idea is to be muted the output when you switch on headphones. Do you think it is possible to remove the Q 309 and Q 310 ( I will not use headphones) and shorten on the board S and D so the signal go straight to the output RCA connectors?
I looked at the scheme where is the output, with the 2SK363 ( Q309 and Q363). If I understand right the idea is to be muted the output when you switch on headphones. Do you think it is possible to remove the Q 309 and Q 310 ( I will not use headphones) and shorten on the board S and D so the signal go straight to the output RCA connectors?
No muting = severe power on/off plops. Woofers generally don't like it and many detest power on/off phenomena. Muting of outputs is done to avoid power on/off plops occurring at the line outputs. Those plops or DC pulses go to the power amplifier that will amplify anything that is sent to him at full volume 🙂 Muting is no luxury but necessary and it makes the device ergonomically better unless you like farting devices as some seem to do. The shorting to GND contacts should be parallel to the 22 kOhm resistors at the output.
You could up the filter caps a little as suggested as 470 µF is somewhat small and todays 1000 or 1200 µF 50/63V will more or less be equal in size. That is twice the value, no negative side effects and half the ripple voltage. Adequate so to say. Win-win.
Enough information, good luck with modding.
You could up the filter caps a little as suggested as 470 µF is somewhat small and todays 1000 or 1200 µF 50/63V will more or less be equal in size. That is twice the value, no negative side effects and half the ripple voltage. Adequate so to say. Win-win.
Enough information, good luck with modding.
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The diode mod increases the bias current in the final stage, which reduces distortion.
I got the idea after looking at the 1000'S' schematic, which is pretty much identical, but has the additional diode.
I have attached the relevant portion of the two schematics.
I got the idea after looking at the 1000'S' schematic, which is pretty much identical, but has the additional diode.
I have attached the relevant portion of the two schematics.
Hi Tony ! Thank you very much for your reply! I will do it these days and I will give a feedback. I will change the 470 uf caps with 1000 uf ( 100V Nichikon) in the powers supply and C301/302 will be upped to 220 nf like I was advised by Jean-Paul. I see in the scheme of NAD 1000S the input cap ( C303) is even 470 nf. What is your opinion about that ?
Before you ask: please don't be tempted to use parallel caps for coupling. Just 1 good cap really is optimal.
Yes, I will remove the original caps and I will put on their place the new ones. I am not going to make parallel assembly on the original caps. But thanks for the note !
I removed R305 (100k) and replaced both C301/303 with a single part (1uF)
Attached are the sims I did - you can see the phase and frequency are improved.
I have also attached the modified input stage (component designations are not matched to the NAD schematic but it's easy to see which parts are which)
R11/C3 are near the input sockets. My NAD 1000 is long gone now (sold on Ebay a few years back) - but looking at the schematic again - I can't help feeling that reducing C305 (220p) or removing it altogether would be beneficial, because there is a pot before it - and this means that as the pot is varied, so will the HF response (although this effect would be minimal here). Removing it might affect HF stability - but it could usefully be reduced to 100p I think.
Standard:
Modified:
My input stage ended up looking like this:
Attached are the sims I did - you can see the phase and frequency are improved.
I have also attached the modified input stage (component designations are not matched to the NAD schematic but it's easy to see which parts are which)
R11/C3 are near the input sockets. My NAD 1000 is long gone now (sold on Ebay a few years back) - but looking at the schematic again - I can't help feeling that reducing C305 (220p) or removing it altogether would be beneficial, because there is a pot before it - and this means that as the pot is varied, so will the HF response (although this effect would be minimal here). Removing it might affect HF stability - but it could usefully be reduced to 100p I think.
Standard:
Modified:
My input stage ended up looking like this:
Yes RC filters should before the potentiometer.
Would not remove it completely though and since it simply works OK without affecting the audio band maybe it is better not to change it. Good theory but maybe practice works out differently.
Would not remove it completely though and since it simply works OK without affecting the audio band maybe it is better not to change it. Good theory but maybe practice works out differently.
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I agree about removing it, which is why I added my caveat about HF stability. However I suspect that reducing it to 100p would be ok - but as it stands - the pot is 20k, so low enough in value to prevent any nasty changes to the HF response in the audio band.
Tony, after the mods what were the audible differences? Do you remember which mod what brought to the sound ?
I did those mods so long ago, and any opinions on the sound would be purely subjective anyway.
I do however vaguely recall that there was some slight improvement in very deep bass, and the top end was not as harsh sounding.
Yesterday I changed the caps in the power supply to 1000 uf/100V ( Nichikon, low ESR type) , they fitted very well on the board. Then I bypassed the FETS switches. Bypassing the FETS brought quite big improvement to the sound. I did not expect that. The sound became deeper and more detailed, very audible. I upped C301/302 caps to 220 nF but that made the sound worse, may be I did not put the right type or quality caps but anyway I returned the old ones. These days I am going to try the mode with the diodes and I will give an a feedback.
Remove R305 (100k) (it's not present in the 1000S model)
Replace C301/302 with a single cap. Use a poly cap, 1uF is good. Even a good electrolytic will be fine here - a Panasonic FC or MC series.