The Phonoclone and VSPS PCB Help Desk

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J

jermo

Member
Joined 2009
oh balls, thank you! I'm pretty sure I asked for a 5532, the writing on these things is really faint so I didn't bother looking until I posted. This is why I came to the forums I knew the answer was out there!
I'll go get the proper op amp today, put it in there and tell you how it goes.
 
F

fluffhead

Member
Joined 2009
Finally killed the hum and it sounds great! There was a ground loop, which seemed obvious to you all but took me a while to figure out where. It seems the layout of the circuit (specifically the order the components connect to the ground) is more important then I first thought. Thanks again for the help!
 
rjm

rjm

Member
Joined 2004
phonoclone.com
Paid Member
rambojj said:
After building the VSPS I am interested in building a Phonoclone.
The RIAA Caps are not the same as the caps from the VSPS. There I used 4 x 1nF per Channel and 732kOhm, 100kOhm + 4,99kOhm and 2,2kOhm for the RIAA. At the Phonoclone there are 2.90nF RIAA (2.2nF||0.68nF). Why?
Click to expand...

Sorry for the delay attending to this.

First, while it makes sense to use the Allen Wright fourth time constant in the VSPS, is does not make sense to use it in the Phonoclone, so its not even suggested as an option in the Phonoclone circuit documentation.

Second, the slight differences in resistance and capacitance are just tweaking the response for different tradeoffs in frequency balance and ease of construction.

Option 1. (VSPS parts) 732K 105K 1n 3n

result: slight treble upturn of 0.25 dB. May be audible in the phonoclone, which for reasons beyond the scope of this discussion has a tendency to peak the treble response anyway. I stopped using this version early on and substituted one of the two following alternatives:

Option 2. (Phonoclone "accurate" parts) 750K 110K 1n 2.9n

result: this is near-perfect, if you go to the trouble of measuring and hand selecting selecting the capacitors to 1%. In in a bag of 100 10% silver mica caps though, you may be unlikely to find any 1.00 nF capacitors, as a batch tends to be all low or all high, but within the marked tolerance: the good ones are removed at the factory to be sold to the military or marketed in other non-consumer channels. This has been my experience anyway. 1% mica caps are expensive and hard to find.

comment: a number of people still don't seem to realize that the RIAA accuracy depends on the most outlying value. Improving the resistor from 1% to 0.1% tolerance will make no useful difference if the capacitors are 5% off.

Option 3. (Phonoclone, practical parts) 768K 110K 1n 3n

Rather than messing around a a futile search for 1% 1.00 nF and 2.80 nF caps, this version gives up and just uses 1.0 nF caps throughout. They'll be some variation, and it's worth channel matching the caps, but it probably not worth fussing over it more than that.

P.S. attached zip file contains plots of the phonoclone simulated response for the different options above. The treble and bass cutoffs are also included (assuming 4.7uF C3, 10K load, OP27 and 30dB gain for both stages). It's a pretty accurate simulation of the real world frequency response.
 

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N

northernsky

Member
Joined 2008
It works! My VSPS stereo version is now working. I solved the troubles I had last week,
a stupid error of course: I inverted the V+ and V- connection coming from the PSU.

And the sound is very good to me. Just few minutes of listening and the vynil records sound better than by using the phono pre built in in my integrated amp (an expensive commercial YBA Integré).

Thank you to the people who helped me and in particular to rjm for his project. Now I only need to put the board in a case


thank you again

Renato
 
N

northernsky

Member
Joined 2008
Fuse blow

Me... again.

My stereo VSPS is working fine, but in a couple of days three fuses of the PSU blew at switch-on or off.
I use a 0.5A fuse as specified in the VSPS building guide but I don't know what type of fuse is: slow blow or fast blows (terms I read in this thread). The transformer is a toroidal 80VA 2x12VAC (230VAC primaries).
I suspect that it is a problem of inrush current at switch on, because once the PSU is on the VSPS is working fine. Moreover the fuses do not blow when I use the light bulb tester which I read also acts as a soft starter. You know I am a newbie, but if I apply the Ohm Law, at full power I get 0.35A current at IEC plug, so 0.5A could be a not sufficient margin at switch on.

Do you think I can increase the value of the fuse, could be more serious problems or do I need a soft starter to avoid damage of the VSPS circuit?

Thank you again for your patience


Renato
 
rjm

rjm

Member
Joined 2004
phonoclone.com
Paid Member
The fuse is connected on the 230V line right? Just checking the obvious first...

A 0.5 A fuse limits the power to 115 Watts. In my view if the VSPS is drawing more than 115 Watts it's time to shut things down, so I don't really recommend increasing the value.

You almost certainly are using a fast fuse. You need to use a slow-blow or SB type fuse that will not trip on the inrush transients.
 
A

AndrewT

R.I.P.
Joined 2004
Hi,
an 80VA 240Vac toroid will need a T1A mains fuse to start reliably without nuisance blowing. This is a guide figure, it may be that this particular transformer could use/need T800mA or T1.2A

If you want to close rate the mains fuse then consider a soft start.

BTW,
a T1A will pass 2Aac for quite a long time before it finally ruptures.
What damage to your household could that 480W of misused power be doing in the meantime?
 
N

northernsky

Member
Joined 2008
Fuse blow

The fuse in my VSPS PSU was F0.5A (fast blow).

I replaced it with with a T0.630A (slow blow); I switched on/off 10 times the PSU
without fuse blow.

Thanks to your help I learned how to recognize a fuse, how to get a guess of circuit current, how...


Thank you again, your help is unvaluable


Renato
 
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