HQMC Phono Stage and Simple PSU Help Desk

HypnoToad said:
You can use an R-core or center tapped transformer with the SPS board, only using one secondary or by having the secondary's in series or parallel depending on the voltage. But IMO it's a waste to have an R-Core setup in this way.

I see you have the OPS board and can use any center tapped transformer with it, just do like everyone else and have the PSU in a separate case for best results.
Click to expand...

Hi HypnoToad,

Thanks for that, yes I have got the OPS board so am going ahead with an R-core transformer and the PSU will be in a separate case.

I have ordered a fused power socket with switch for the the PSU, what fuse size should I use? I don't think the OPS will draw much current when only powering the HQMC so I was thinking fairly low rating such as 2 amp but not sure about the switch on surge. Any advice appreciated

Kind Regards

Steve
 
Steve.
With the OPS, I went first for the toroidal transformer (made in UK), with the transformer and OPS in the same case as the rest of the preamp, but I had a lot of noise related to where and even how the transformer was positioned, so after loosing this battle for a long time I've decided to use R-core (from china) and....no real difference.
I personally don't see a point in using r-core, especially in separate box.

Regards
Rafal
 
Hi Rafel,
I have no noise with my OPS.I am using R core transformer. You should not get any noise from OPS. Most of us using OPS or SPS power supply and none of them reported noise related problem even with EI core.

Regards
Sachin
 
Well.
I guess I'm unlucky and both of the transformers are bad quality or ...I just don't know...in best case it was pretty quiet , never dead quiet but it was enough to move the transformer from its best position just few mm and the noise would be twice as loud or worst.
 
earthsounds said:
Well.
I guess I'm unlucky and both of the transformers are bad quality or ...I just don't know...in best case it was pretty quiet , never dead quiet but it was enough to move the transformer from its best position just few mm and the noise would be twice as loud or worst.
Click to expand...

It also depends on the gain of the phono stage, if you are using a MM stage like the CNC you have far less gain than the MC stage like the HQMCPS.

You have to have the transformer and any wiring that contains AC as far as possible from the inputs or input wiring of the phono stage. This is why a separate case is recommended.

Can you post a picture of the internals of your setup?
 
earthsounds said:
Steve.
With the OPS, I went first for the toroidal transformer (made in UK), with the transformer and OPS in the same case as the rest of the preamp, but I had a lot of noise related to where and even how the transformer was positioned, so after loosing this battle for a long time I've decided to use R-core (from china) and....no real difference.
I personally don't see a point in using r-core, especially in separate box.

Regards
Rafal
Click to expand...

Hi Rafal,

Thanks for your input and sorry you've had problems with the power supply. I have bought the same cases as Vincei who posted a picture of his completed psu and phono stage on the previous page. So I guess mine will look similar when it's completed. If I get anywhere close to the quality of work Vince has done on his project I'll be happy, especially if it turns out to be better than my Trichord Dino.

I have to admit I am a little wary about buying the transformer from China as I have found some people complaining about mechanical noise coming from them. However they are pretty scarce in the UK, but everything I have read suggests that they should be quieter than toroids or EI versions. I'll keep looking and see if I can find a recommendation from someone.

I do agree with Sachin that, due to the high gain in the HQMC phono stage, if possible it really should be in a separate case to the PSU.

Kind Regards

Steve
 
Hi All,

I've come (finally) to put my order in for the parts to build the HQMCPS and it turns out Mouser are out of stock on the following part.

Pulse Film Capacitors 63V 4700pF 2.5% - 505-FKP24700/63/2.5

I note that these are 2.5% tolerance. They won't have any in until the end of June. They do have some that are 10% tolerance but I am wondering if this is not tight enough for the circuit. Perhaps one of you Guru's can tell me if this would be ok or not.

Kind Regards

Steve
 
You can always go up in voltage but keep to 2.5%.

The lower tolerance the better, these are RIAA caps, the correct capacitance is needed to keep the right RIAA equalization curve.
 
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Oddly enough (to me at least) the quality of the capacitor makes a difference in a passive RIAA EQ circuit. Of course tolerances are most important.
 
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HQMC Phono Stage and OPS PSU

Hi Sachin,

I'm finally beginning the build of the HQMCPS and am starting with the OPS.

A quick question.

On the BOM you sent over for the OPS you gave me the part number for some electrolytics of:-

5 X http://search.digikey.com/us/en/prod...5558-ND/245157 (4700uf 35 v caps)

However in the OPS manual it specifies 4700uf @ 50v

So could you tell me which one is correct and if it is the 50v ones then can I use the 35v ones instead or do I need to re-order

If you could let me know that would be great

Kind Regards

Steve
 
Hi Steve you can safely use 35v or 50v caps. Please remember lead spacing should be 7.5mm else caps won't fit on PCB.

Regards
Sachin
 
I just built out a new board running off of batteries - I've noticed some hum / noise on the left channel at high volumes. All my voltages are OK and the gain / impedance match between channels, but there is still some hum. I've gone as far as mounting the board (with standoffs) on a blank copper-plated circuit board, drilling holes for the (shielded) cables to pass through from the bottom and running the (shielded) power from the top so that there is minimal EMI.

Any suggestions?

-D
 
derekva said:
I just built out a new board running off of batteries - I've noticed some hum / noise on the left channel at high volumes. All my voltages are OK and the gain / impedance match between channels, but there is still some hum. I've gone as far as mounting the board (with standoffs) on a blank copper-plated circuit board, drilling holes for the (shielded) cables to pass through from the bottom and running the (shielded) power from the top so that there is minimal EMI.

Any suggestions?

-D
Click to expand...

Swap the inputs then try it, and then the outputs and see if it changes channels.
 
Guys, I have a question. How is a HOMC phono stage different than a MM phono stage? I'm using an SAE HOMC with my Bottlehead Eros. It seems to work very well.
 
MM carts have a magnet at then end of the cantilever that moves around between coils, the MC has a coil of wire that moves around between magnets.

HOMC carts are the same as LOMC carts but they either put more windings of wire to give the higher output, have stronger magnets or both.

MC carts have very low inductance so their phono stages can have much lower shunt impedance without it affecting the frequency response, whereas you need over 20k for a MM cart or it will roll off the top end.

So you can use a HOMC cart with a MM stage with a stock 47k impedance but not a MM cart with a MC stage with the usual less than 1k impedance.
 
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