quad 34 MM revision?

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25-Dec-2019 11:57 PM

Nost

Nost

Posts: 27

Hi all been a while..

I've recently upgraded my TT and have still felt overwhelmed by the sound I'm getting through my 34/306 dada upgraded setup.. cd input and fm4 are all very sparking and bright, full of presence etc, but I'm still not getting that with the phono stage.

for a giggle just to see, I plugged my TT into the CD input and crancked up the pot.. all of a sudden (albeit bass light) I had the prescence from the TT I've been looking for for the last several years!

What is going on in the MM module that is making the setup sound so muted and flat? the bass is nice, but the upper mid hf is muted beyond the ability of the tilt controls to manage.

Now I know the system is capable of delivering the sound I've been looking for, I NEED to find out how to unlock it... I've done all the mods from the dada manual which has improved the bass, but what do I need to do to get the clarity and sparkle?

Thanks in advance for your time.

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27-Dec-2019 10:22 AM

Nost

Nost

Posts: 27

*by overwhelmed I meant underwhelmed*

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27-Dec-2019 04:04 PM

Stefaan

Stefaan

Posts: 628


A MM Disc stylus does nog offer the same dynamics an MC stylus or a CD player does...

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27-Dec-2019 04:39 PM

FBatista

FBatista

Posts: 131

How is that possible? A TT itself doesn't have enough gain to be used in CD input, even FM input.

Based on your statement regarding good/pleasant bass perfomance I'd say, check C1b and C2b values on the MM board. If the original 220pF is present, lower that value. 

Together, phono board capacitance (C1b L channel, C2b R channel), IC lead and tonearm capacitances should sum up a value around the cartridge requirement. If too much, it will sound the way you describe.

For instance in my 34 I use 47pF.

Also consider Stefaan's post, which I totaly agree with.

Best regards,

Fbatista


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28-Dec-2019 11:53 AM

Nost

Nost

Posts: 27

.. By turning up the gain 'a lot'. It was quiet but loud enough to hear a sparkling, clear upper/mid, highs.

N.B.Considering the riaa specs in the mm module have already been found to be aggressive in the bass, could the same be said for HF? What caps/resistors govern the HF in the module? I've already lowered the capacitance down to 47pf and changed caps to extend the bass..

I believe it was a query of mine in this forum some time ago that led to the adjustments you suggested in the mm module to be included in the Dada manual (not my suggestion, just my query re dull sounding phono input after the upgrades.) all suggested tweaks have already been done. I'm not a perfectionist, I'd simply like the music to be 'alive', all other sources have this but for the phono stage.

Thanks for your replies, I'd love unleash more potential and i don't believe the cart or stylus are the cause..

for reference: quad 34,306,fm4. goldring lenco gl75 with linn basik LVX tonearm, sure m55 mm cart with jico stylus, dali suite 2.8 speakers.

Kind regards and happy new year

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30-Dec-2019 05:01 AM

EJP

EJP

Posts: 1690

There's something seripusly wrong here. Any Shure MM cartridge should work perfectly into a 34 MM input as-is, with the 180pF of shunt capacitance. Into a CD input it will be at least 40dB down, i.e. inaudible, and if you can hear anything it will be both bass-light, and treble-heavy because of the lack of RIAA equalization. There must be something wrong with your MM module.

EJP

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30-Dec-2019 09:00 AM

Nost

Nost

Posts: 27

Indeed, it was bass light, treble heavy and although the spl was very low (with high gain), the quality of the sound could be heard through the line-in.

I'm not displeased with the sound, there nothing 'wrong' with the module but the high frequencies seem muted, the sound stage is not open as I can hear from other systems...

I only wish to open up the higher frequencies. Is this possible at the component level with the mm module?
TIA for your reply
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31-Dec-2019 05:45 AM

EJP

EJP

Posts: 1690

Well I don't know what 'open up' means, but you should use the shunt capacitance recommended by Shure for the M55, which is zero. So you should remove the shunt capacitor altogether.

However the Vinyl Engine says 400-500pF for this model, which I can't find mentioned in the Shure owner's manual. If that is somehow correct, you were going in the wrong direction with 47pF, and you should increase it to 390pF or 470pF, whichever you can find.

EJP

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01-Jan-2020 05:24 AM

EJP

EJP

Posts: 1690

However modelling suggests that they are both wrong, and that Quad's original value which I now find to be 220pF is better than either 4-500pF or 0pF. 180pF seems to be the optimum, which gives a -3dB point at about 15kHz. I would use 150pF if you can find it, to take account of strays. Both increasing and decreasing it from this point reduce the treble response: for example, your current 47pF and 400pF are both -3dB at 12KHz.

EJP

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01-Jan-2020 01:47 PM

Nost

Nost

Posts: 27

Thank you for your time, EJP.


I've measured the capacitance of the tt leads from cart to rca plugs and they come in less than 30pf, so your suggestion of 150pf would be perfect to get close to the value you've modelled.

I've found some suitable silver mica caps so will have a play around.

do i need to alter the resistance in any part of the phono circuit?

Thanks again for your time


James
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02-Jan-2020 07:34 AM

EJP

EJP

Posts: 1690

You can play with increasing the 47K resistor to 56/68/74/82/91/100K. Each increase causes a little lift around 10KHz and extends the treble rolloff a little further. At 100K ohms it is about +3dB at 10KHz and -3dB around 19KHz. This is strictly a matter of what you like. Leave everything else alone.

EJP

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04-Jan-2020 11:12 PM

FBatista

FBatista

Posts: 131

The last few posts from EJP alone, are worth a 2 page article in the context of QUAD preamps and DADA's effort: moving owners and vinyl users to update/restore their units to the best possible condition.

I vey much appreciated it. Thanks EJP!

How's the 34, Nost?


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05-Jan-2020 11:33 PM

Nost

Nost

Posts: 27

All sorted!

Fitted some 150pf caps and the openness and 'air' I've been looking for has magically appeared. 47pf was definitely too low for my setup, glad I measured the capacitance of my cables and adjusted the capacitance  accordingly.

Massive thanks EJP, your time in simulating the circuit has given me just what I needed. Outstanding 🙂

Big smiles when listening now!

As a side note EJP, perhaps, given the modelling you've done on the circuit, it may be worth an entry in the upgrade manual for those who wish to tweak the phono input for best results. This preamp after all is designed primarily for TT users.

How to measure capacitance of their cables, finding info on their carts and selecting the correct value of capacitors... 

Seriously, I'm over the moon, this change is similar to the initial 'unveiling' I heard when I originally restored my setup.

Thank you again!

James

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06-Jan-2020 12:09 AM

EJP

EJP

Posts: 1690

That would be completely impractical. The component values I've suggested here apply specifically to the Shure M55 cartridge. There are thousands of MM cartridges out there and every one would require its own set of values.

Glad you got a result. Curious that both Shure and Vinyl Engine were wrong about this.

EJP

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