New amp and volume control

[Mulburg]

I went from a fairly low 8 watt ACA to a moderately powered 25 watt aleph j diy amp. The volume on the moreplay now jumps up quickly from low to a little too high for low level listening. And to get the balance more even, you have to go up a little higher.

The sound quality is still great, no other issues at all. Is this something that can be mitigated?

 

[Paul Birkeland]

Why not use the balance control to get the channel balance more even?

You've gone up in amplifier gain (power is completely independent from gain).  You can attenuate the inputs of your amplifier if things are too sensitive, or you could get similar results by padding down the pot a little bit.  The Moreplay has extremely low gain for a preamp, so I would tend to suggest getting some Harrison Labs attenuators and just plugging those into your amp.

(You could also get less sensitive speakers)

 

[Mucker]

What kind of sources do you run into your Moreplay?

 

[Mulburg]

iPhone and or ipad.

 

[btol]

You can attenuate the inputs of your amplifier if things are too sensitive, or you could get similar results by padding down the pot a little bit.

How do I go about padding the pot? I plan to start my build this week and will also be using an Aleph J with the Moreplay. I have 99 dB sensitive speakers and would love to have as much usable range on the volume pot as possible.

 

[Paul Birkeland]

See item #3 and the picture on the first post here:
https://forum.bottlehead.com/index.php?topic=4295.0

You'll want to use 7.5K and 3.3K for the resistor values.

 

[btol]

See item #3 and the picture on the first post here:
https://forum.bottlehead.com/index.php?topic=4295.0

You'll want to use 7.5K and 3.3K for the resistor values.

Thank you! I will take a look.

 

[Mulburg]

I went back through and measured everything and everything is right on. But the difference between the measurements of A5, A6 and B5, B6 are off by 5k. The As are 55 and the Bs are 49. Individually they are within spec, does the difference matter? I did measure the resistors on each and they are both 217.

 

[Paul Birkeland]

That difference is coming from the tolerance of the balance pot and isn't anything abnormal.  If you perfectly centered the balance pot, you could get those resistances to be perfect as well.

 

[Mulburg]

Thank you Paul.

That difference is coming from the tolerance of the balance pot and isn't anything abnormal.  If you perfectly centered the balance pot, you could get those resistances to be perfect as well.

 

[btol]

I'm going to try the Harrison labs attenuators before adding Resistors to the volume pot. Any thoughts on 12db vs 6db? Will be using 99db Altec 601c and 30w DIY Aleph J.

 

[Paul Birkeland]

The Aleph J has almost 20dB of gain and your speakers don't need more than about 2W or so to play exceptionally loud.  2W into 8 ohms is 4V, and your amp will make 4V with only about 400mV of input signal.  The weakest sources I have ever found put out 300mV of output, so most are going to be close to doing the job without any preamp gain. 

Having said all this, -12dB is probably not enough, but definitely a good place to start and then you could scale your potentiometer resistors accordingly based on what you learn.

 

[btol]

Thanks Paul. I decided to go with a pair of Rothwell 20db attenuators.

 

[Paul Joppa]

Thanks Paul. I decided to go with a pair of Rothwell 20db attenuators.

Good choice, IMHO.

When they come, I'd appreciate it if you would measure the input resistance. The Rothwell 10dB measures 30Kohms, but I have not been able to discover the resistance of their 20dB unit.  These are higher than the Harrison Labs (10K for the 12dB), and I was about to recommend the Rothwells as preferable for that reason. 10K is a difficult load for Moreplay - it will work, but gain and peak output are reduced.

 

[btol]

That's great to hear Paul. Happy to measure input resistance and share the info.

 

[Karl5150]

Paul, does the less than optimum input resistance of the Harrison Labs units apply to BH integrated amps as well?
Karl

 

[Paul Joppa]

All Bottlehead amps, integrated or not, have an input impedance of (I think) at least 30K and are compatible with all Bottlehead preamps. Of course  :^)

Any amp or preamp with an external attenuator (such as the Harrison or Rothwell devices) installed at the input will present the impedance of that attenuator to the driving preamp.

To be fair, I am currently using 12-dB Harrison Labs at the input of both my Foreplay III and my Paramounts, so both the Eros and the Foreplay are driving 10K impedances. It's not a huge problem, but I do intend to acquire some Rothwells soon. The parable of the cobbler's barefoot children does come to mind!

 

[Mmaxed]

Just got my Moreplay going today.  Replaced a Schit Saga.  Needed more gain than the Saga, but Moreplay is tooooo much.  What would anyone recommend for attenuation? 

 

[Paul Birkeland]

I would start by asking what issue is presenting itself with the gain of the Moreplay?  For an active preamp, the Moreplay has incredibly low gain, so anything beyond a -6dB attenuator will take you back below where you were with the Saga.

 

[Mmaxed]

Yep, I was debating between -3 or -6 db.  With the Saga on vinyl the pot was sometimes maxed out.  Yeah it was loud.  With the Moreplay I only have maybe 10-15 degrees of rotation between nothing and too loud.  Would like a little more range on the pot.