Simplistic NJFET RIAA

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#6,762
Update - I found a cut track that had a tiny piece of copper left briding the hole :S

It's alive!!!!!

After a quick measure with my Dvmm and 1 kHz tone applied at 1mV, I get the following AC readings at the output:

4-5mv hum with no signal (both channels)
Left with 1mV in @ 1Khz: 1.45V
Right with 1mV in @ 1Khz: 1.34v

Top of C3 is now at 12.1V, vs. 11.8V on the other channel.

Are these OK? I'm a bit concerned that the channels are mis-matched with different gains in different sections. What is the best way of matching all the voltages up??

Are there any ways I can make imrovements here? All my RIAA caps are polystyrene, with 1% metal film resistors (apart from 1W which are 5%). Will chaning the 100nF for a better quality cap make much of a difference?

I currently use a Doug Self op-amp phono stage (with a few tweaks), first impressions are that the Salas is a decent step up, espescially in the treble region.

Tommorrow I will make a start on screening to see how I get on (I might screen the transformers on the left as well as a dedicated "box" for the phono stage)

PS - why has one of the caps been changed from 16nF to 15nF in the schematics? I just wondered but haven't found the post with the explanation.
 
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#6,763
If the collector voltage is not reflected on top of C3 before the 100nF cap, then something must be different between the good channel that does reflect and the bad channel that doesn't. If its not a connection, then its a wrong value or a bad component.

P.S. We cross posted, it was debris. So be it, best news is you found it at last.
 
#6,764
df_genius said:
4-5mv hum with no signal (both channels)
Left with 1mV in @ 1Khz: 1.45V
Right with 1mV in @ 1Khz: 1.34v

Top of C3 is now at 12.1V, vs. 11.8V on the other channel.

Are these OK? I'm a bit concerned that the channels are mis-matched with different gains in different sections. What is the best way of matching all the voltages up??
Click to expand...

I gave you instruction earlier, its to trim R6, use 100R trimmer to match gain. 1mV to go ~1.4V implies either 63dB gain (doubtful with your cct) or more than 1mV input. Be sure that generator does not waver and misleads you.
 
#6,765
df_genius said:
Are there any ways I can make imrovements here? All my RIAA caps are polystyrene, with 1% metal film resistors (apart from 1W which are 5%). Will chaning the 100nF for a better quality cap make much of a difference?

I currently use a Doug Self op-amp phono stage (with a few tweaks), first impressions are that the Salas is a decent step up, espescially in the treble region.

Tommorrow I will make a start on screening to see how I get on (I might screen the transformers on the left as well as a dedicated "box" for the phono stage)

PS - why has one of the caps been changed from 16nF to 15nF in the schematics? I just wondered but haven't found the post with the explanation.
Click to expand...

That value has been changed due to new better modeling since that CCT you chose was published. Can be trimmed in 100pF steps to taste.
To consider quality issues you should be able to listen without intruding hum for some time.
The 100nF is influential for subsonic response and SQ and it can be 47nF also if you got big speakers and susceptible turntable.
 
#6,767
I'm still having hum problems. I have tried using half-wave and full-wave rectification and three different transformers but still get the same level of hum. I have tried having the transformer up to 1m away with no difference and have also tried moving/rotating it. At the minute I only have the Phono transformer connected, everything else is not powered.

I can't use the quanghao boards with their default rectifier layouts (i.e. centre-tap on transformer -> two diodes -> 0V), I need the CT tied straight to 0V (the DC-B1 and my regs use this layout)

All my 0V points come back to a star point at the phono sockets so don't beleive I have ground loops. The shunts are connected to the star point at their outputs only, not the inputs.

DC voltage after rectification is 52V at the minute. I have tried the 35-0-35 150VA, a 100VA with 2 x 18v outputs wired in series and a 300VA 33.5-0-33.5 (but this puts out around 37V AC)
 
#6,769
Those are system experiments to battle hum that nobody can address from afar. Maybe you, by trying configuration tests can achieve something positive but as I have wrote when you showed the box housing toroids, DAC, preamp, and phono, it looks very difficult.
 
#6,770
The difficulty I have is that I removed power to all the other components, it was just the phono section running on its own, and I was listening to the output direct, not through the DC-B1. I have tried many configurations of grounding schemes and transformers/rectification, and these have resulted in no real difference to the hum level. At the minute I think it is either the regs or my board layout. I cut the tracks to their minimum length and this hasn't made much of a difference either. I am currently building a V1.2R reg to see if that makes a difference.

I know it's not an easy task I took on to get everything in the one case, but like most of us on this forum I enjoy a challenge 🙂
 
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#6,771
Its the AC field from transformer and primary/secondary wiring. 60dB gain is x1000. 1.2R don't attempt without a scope. It will oscillate with every half optimum layout detail. In MHz that will be. It will look steady on DVM but it will be radio.
 
#6,773
Salas, what do you think?

Imageshack - dscf2966g.jpg
Imageshack - dscf2969d.jpg
Imageshack - dscf2970l.jpg

Hum levels are now much lower than the hiss level (which is very quiet anyway). Here is a wav file of the phono. The level on the recording is low but my sound card clips easily:

Chain_Salas.wav

I need to measure and match the gain on each channel now. I have an old 15Mhz scope that I use to set up my tape recorders, where are the areas to watch out for with the 1.2R reg with regard to oscillation?
 
#6,775
df_genius said:
Salas, what do you think?
....
I need to measure and match the gain on each channel now. I have an old 15Mhz scope that I use to set up my tape recorders, where are the areas to watch out for with the 1.2R reg with regard to oscillation?
Click to expand...

Well, as far as the photos go, reminds a classic Japanese integrated from the 80's the way its wired inside, and the RCA row at the back reminds too. But the front face is very classic English. It took you much work to best arrange & wire all that stuff in there, no doubt. Was the chassis hosting a commercial integrated before?

As far as the .wav goes, I can't say anything about quality matters since its compressed enough and has an mp3 like feel as a transfer, but shows that the system surely works with no obvious anomaly. What soundcard was employed? You will tell us more on how it fairs in the real system at home.

Go to the simplistic low voltage psu's thread, see recently posted 1.2R layout suggestions by RCruz, and look for a flat thin line displayed with no AC waves or hash superimposed when probing across the output of the reg to ground and sweeping time base, with the vertical system set at smallest mV/div when AC input is selected on the scope.
 
#6,776
The case is nothing special, in its former life it was a Cambridge Audio A5. I made a new front panel for it.

My sound card is an old Soundblaster Audigy, shame I can't make a recording on my Nak or R2R and post it straight up on here.

I'll make some better clips when I get chance, that was a very rushed job....
 
#6,777
I cranked it up, and at least I can't hear anything obviously untoward in the background, and the channel balance (without knowing the record) sounded even enough. Is the bass fuller in that song in the actual system? Treble level it had OK.
 
#6,779
I built the DAC in my pre-amp to use with my PC as it has a SP/Dif output on the motherboard. I've made a couple more recordings with decent levels. This time using the on-board sound. I've yet to come across a PC sound card that sounds good. The Asus Xonars are good apparently.

Adele_Salas.wav
RockRoll_Salas.wav

Bass is very good indeed, the Fleetwood Mac track has never had much bass. I've got some Massive Attack on now and there is no shortage of bass.
 
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