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July 03, 2020, 07:17:49 AM

Author Topic: Gain Question  (Read 698 times)

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Offline faskenite

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Gain Question
« on: February 07, 2018, 06:08:05 AM »
Right now I am running a fairly low output mc cart into Sowter SUT’s, a Wright Audio phono stage and the Quickie I just built.  (Sounds good!  Will be working on microphonics.). One thing I like about the Quickie is the healthy dose of gain - I have been using Slagleformers previously.  Anyway, if I put a Stereomour II in place of the Quickie, would there be a significant difference in gain?

Offline Paul Birkeland

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Re: Gain Question
« Reply #1 on: February 07, 2018, 06:13:22 AM »
This is certainly a worthwhile question to ask, but sadly I'll have to respond with more questions...

1.  What's the output voltage of your cart?
2.  What step-up ratio are you using on the Sowters (good choice BTW)?
3.  How much gain does the Wright phono stage have?
4.  What power amp are you using with the Quickie? (or how much gain does it have)
5.  What speakers are you using with this setup?

Since you're replacing a preamp and a power amp with an integrated amp, these become important considerations.  With answers to all these questions, we can quantify the change(s) in system gain.
Paul "PB" Birkeland

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Offline faskenite

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Re: Gain Question
« Reply #2 on: February 07, 2018, 07:48:30 AM »
This is certainly a worthwhile question to ask, but sadly I'll have to respond with more questions...

1.  What's the output voltage of your cart?
2.  What step-up ratio are you using on the Sowters (good choice BTW)?
3.  How much gain does the Wright phono stage have?
4.  What power amp are you using with the Quickie? (or how much gain does it have)
5.  What speakers are you using with this setup?

Since you're replacing a preamp and a power amp with an integrated amp, these become important considerations.  With answers to all these questions, we can quantify the change(s) in system gain.

Thanks for this.  I am running two carts:  a Lyra Helikon stereo (0.5 mV) and a Lyra Dorian mono (0.25 mV) on two different tables.  Sowter step-up ratio is 20:1.  I don't know the gain of the Wright, but the late great George provided variable gain controls for each channel, so it can be dialed in to taste.  The power amps are Manley 300B Neo-Classics, running in single ended mode.  Feedback is variable:  gain at 0dB FB is 30 dB, gain at 10dB FB is 20 dB (I am running it at about 2 or 3 dB FB these days, almost , never more than that).  Speakers are Lowther EX3 drivers in Medallion cabinets (so what, a genuine 96 dB/watt, if not more?)  I also use a REL Strata III powered sub (gotta have one with Lowthers) but I presume that doesn't matter.  Comments?

Offline Paul Birkeland

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Re: Gain Question
« Reply #3 on: February 07, 2018, 08:17:36 AM »
Gain sure shouldn't be a problem in your system!  I think the Wright phono pre had around 60dB of gain, which would get you 5V out of the phono pre with the Lyra and a 20:1 step-up.  This is a ton of signal!

A 300B amp with 30dB of gain will make 8W at the speaker terminals with 0.25V coming into the amp itself.  If use 10dB of feedback, then you need 0.8V at the input of the amp for 8W out.  In either case, this is significant attenuation of the signal coming out of your phono preamp.  Thankfully it has level controls!

Are you intending to replace the 300B amps and the Quickie with the Stereomour?

The Rel sub is actually an important piece of information to know about, as they generally have low-ish input impedances (10K or thereabouts) which become a factor if you're using a line level signal to drive them (as opposed to feeding them with speaker wire).  It looks like Rel actually provides a cable with the Strata III for this purpose, and I'd certainly suggest using it!

There is also the question of how well the phono preamp can driver autoformers, which isn't super easy to answer without running some complicated tests. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline faskenite

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Re: Gain Question
« Reply #4 on: February 07, 2018, 09:27:03 AM »
Gain sure shouldn't be a problem in your system!  I think the Wright phono pre had around 60dB of gain, which would get you 5V out of the phono pre with the Lyra and a 20:1 step-up.  This is a ton of signal!

A 300B amp with 30dB of gain will make 8W at the speaker terminals with 0.25V coming into the amp itself.  If use 10dB of feedback, then you need 0.8V at the input of the amp for 8W out.  In either case, this is significant attenuation of the signal coming out of your phono preamp.  Thankfully it has level controls!

Are you intending to replace the 300B amps and the Quickie with the Stereomour?

The Rel sub is actually an important piece of information to know about, as they generally have low-ish input impedances (10K or thereabouts) which become a factor if you're using a line level signal to drive them (as opposed to feeding them with speaker wire).  It looks like Rel actually provides a cable with the Strata III for this purpose, and I'd certainly suggest using it!

There is also the question of how well the phono preamp can driver autoformers, which isn't super easy to answer without running some complicated tests.

Thanks for this!  I actually keep the gain controls on the Wright very low.  The SUT and a non-AC linestage, whether the Slagleformers or the Quickie, together with turning down the Wright, means as little noise as possible.  Which I like, especially with Lowthers!  The REL is run off the speaker terminals.

I'm thinking about a Stereomour simply because (1) I have just started DIY building, and it is fun;  (2) I have always liked the sound of single ended 2A3 amps as a nice alternative to 300B's (although for me, 2A3's in push-pull have been ho-hum);  and (3) a Stereomour integrated might be a nice change in my living room system.  The speakers it would drive there are relatively insensitive (ProAc Response OneSC's) but the ProAcs are well known to be an easy load to drive in terms of their impedance curve and volume requirements in the living room are never high.   

Offline faskenite

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Re: Gain Question
« Reply #5 on: February 07, 2018, 09:28:17 AM »

There is also the question of how well the phono preamp can driver autoformers, which isn't super easy to answer without running some complicated tests.
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PS - The SUT/Wright combo drives the autoformers just fine!