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Posted
  On 01/10/2024 at 4:09 PM, ex turpi hifi said:

Why did you connect both cables to the right-most (or left most if looking from back) set of posts in each grouping?

 

I'm guessing it doesn't matter but I'm wondering also about how to connect a sub to an amp like this.

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I can’t remember why as it was a friend’s amp. I think you are correct in that it doesn’t matter

Posted (edited)

Just chiming into this thread quite late. The internal metal bridges/straps/links are adjustable and configurable for using either 4, 8 or 16 ohm OPT taps. The external speaker terminal groupings are just another set of binding posts. Whether you use the right or left black or red it's the same for both black and red dual groupings. They're wired/bridged internally for each colour grouping. My guess is that the grouping of 4 offers "biwire mode" to be used at the speaker end, if the feature is available, using 2 separate runs of speaker cables - 1 run going to the tops and 1 run going to the bottoms.

Edited by xlr8or
  • Like 2
Posted
  On 02/10/2024 at 10:57 AM, xlr8or said:

Just chiming into this thread quite late. The internal metal bridges/straps/links are adjustable and configurable for using either 4, 8 or 16 ohm OPT taps. The external speaker terminal groupings are just another set of binding posts. Whether you use the right or left black or red it's the same for both black and red dual groupings. They're wired/bridged internally for each colour grouping. My guess is that the grouping of 4 offers "biwire mode" to be used at the speaker end, if the feature is available, using 2 separate runs of speaker cables - 1 run going to the tops and 1 run going to the bottoms.

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Yes that's correct. Mine says in the manual that it was factory set for between 4-6ohms, for example, and can be changed by a technician to 8-10 or 16ohms.

 

As an aside, and maybe you know - does this setting really matter? Can using mismatching speakers cause damage? How does the setting affect the sound?

 

I've looked everywhere and there seems to be no real consensus and varying guidelines. For instance I'm using vintage Rogers LS5/9 which are nominal 8ohm and the amp is set to 4-6ohm. Could this cause damage, or would the 8-10ohm setting be better?

Posted (edited)
  On 02/10/2024 at 3:48 PM, ex turpi hifi said:

As an aside, and maybe you know - does this setting really matter? Can using mismatching speakers cause damage? How does the setting affect the sound?

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Yes, it does matter as it impacts the primary load side of the OPT going back into the power tube. It doesn't run optimally. The signal going to the speaker is AC and therefore does matter.

 

As a general rule of thumb the OPT tap should match the nominal impedance load of the speaker. In this case the vintage Rogers/BBC LS5/9 is rated at nominal 8 ohm load. The tap should be changed to 8 ohm. Normally one would review the impedance and phase angle shift curve the speaker exhibits across the frequency band. Any dips in impedance and significant shifts in phase angle at these regions may require a lower tap value to be used. In the case of the LS5/9 graph below, a minimal dip of 6 ohm and a phase angle shift close to 0° for that region is apparent. I'd suggest in this case to change the taps from 4 to 8 ohm and re-evaluate the tonal characteristics. You may be pleasantly surprised with any element of 'leanness' removed from the listening experience.

 

BBCLS59IMPEDANCE.png.d1896426933eb8920cc3ccd0b273f938.png

Edited by xlr8or
  • Like 4
Posted

I think the amp I had was set at 8 ohms. I borrowed it from @AuDrewwho might remember. It’s a very impressive amp. The only downside is the weight and the amount of heat that it generated. 

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Posted
  On 02/10/2024 at 10:43 PM, PKay said:

I think the amp I had was set at 8 ohms. I borrowed it from @AuDrewwho might remember. It’s a very impressive amp. The only downside is the weight and the amount of heat that it generated. 

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Correct - actually, it's factory pre-set for 4-8 ohm speakers.

 

For speakers with higher impedance, e.g. a 15 ohm Rogers LS3/5a, it can be internally adjusted accordingly.

Posted
  On 02/10/2024 at 3:48 PM, ex turpi hifi said:

Yes that's correct. Mine says in the manual that it was factory set for between 4-6ohms, for example, and can be changed by a technician to 8-10 or 16ohms.

 

As an aside, and maybe you know - does this setting really matter? Can using mismatching speakers cause damage? How does the setting affect the sound?

 

I've looked everywhere and there seems to be no real consensus and varying guidelines. For instance I'm using vintage Rogers LS5/9 which are nominal 8ohm and the amp is set to 4-6ohm. Could this cause damage, or would the 8-10ohm setting be better?

Expand  

If you have the DA88, there should be no need to make any adjustments to the factory settings for your 8 ohm speakers.

Posted
  On 02/10/2024 at 9:04 PM, xlr8or said:

 

Yes, it does matter as it impacts the primary load side of the OPT going back into the power tube. It doesn't run optimally. The signal going to the speaker is AC and therefore does matter.

 

As a general rule of thumb the OPT tap should match the nominal impedance load of the speaker. In this case the vintage Rogers/BBC LS5/9 is rated at nominal 8 ohm load. The tap should be changed to 8 ohm. Normally one would review the impedance and phase angle shift curve the speaker exhibits across the frequency band. Any dips in impedance and significant shifts in phase angle at these regions may require a lower tap value to be used. In the case of the LS5/9 graph below, a minimal dip of 6 ohm and a phase angle shift close to 0° for that region is apparent. I'd suggest in this case to change the taps from 4 to 8 ohm and re-evaluate the tonal characteristics. You may be pleasantly surprised with any element of 'leanness' removed from the listening experience.

 

BBCLS59IMPEDANCE.png.d1896426933eb8920cc3ccd0b273f938.png

Expand  

Thanks for this - very interesting. I'm currently running the 4-6ohm tap as far as I'm aware. The amp was second hand and I haven't opened it so just going by what the default says in the manual (seller didn't know for sure). Do you think a fairly flat 16ohm speaker would push this too hard?

 

Many people seem to say one should experiment with the taps and just see which sounds best, hence my prior questions. The LS5/9 sounds great on the 4-6ohm tap, maybe due to the occasional dips. But then again it looks like it occassionally pushes upwards of 10ohms so maybe the 8-10ohm will sound better? I've heard the 4ohm taps are often preferred to the 8 for 8ohm speakers due to more control. Could there be a technical explanation for this?

 

Sorry for all the questions, I'm still getting up to speed on the intricacies of valve amps. I am tempted to get the impedance changed, but it also would involve getting a technician in so not sure it would be worth the hassle.

Posted
  On 03/10/2024 at 4:22 AM, AuDrew said:

If you have the DA88, there should be no need to make any adjustments to the factory settings for your 8 ohm speakers.

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Mine is actually an I35, for which the manual quotes 4-6ohms as standard, then 8-10ohms and finally 16ohm settings.

Posted (edited)
  On 03/10/2024 at 11:45 AM, ex turpi hifi said:

Thanks for this - very interesting. I'm currently running the 4-6ohm tap as far as I'm aware. The amp was second hand and I haven't opened it so just going by what the default says in the manual (seller didn't know for sure). Do you think a fairly flat 16ohm speaker would push this too hard?

 

Many people seem to say one should experiment with the taps and just see which sounds best, hence my prior questions. The LS5/9 sounds great on the 4-6ohm tap, maybe due to the occasional dips. But then again it looks like it occassionally pushes upwards of 10ohms so maybe the 8-10ohm will sound better? I've heard the 4ohm taps are often preferred to the 8 for 8ohm speakers due to more control. Could there be a technical explanation for this?

 

Sorry for all the questions, I'm still getting up to speed on the intricacies of valve amps. I am tempted to get the impedance changed, but it also would involve getting a technician in so not sure it would be worth the hassle.

Expand  

 

With valve amps the higher the tap the less current for the same power output - i. e., the power output is fixed and does not behave like a SS amp when the resistance is halved or doubled. The reason 4 ohm is often preferred is due to modern speaker design demanding current over voltage for power output. Valve amps flourish at much higher tap settings due to less current demand. Back track to 65+ years ago, before SS transistors made their introduction, and you'll find many speaker designs utilised 8, 16 and even 32 ohm nominal loads to run valve gear. UK speaker manufacturers of the time such as Rogers were manufacturing 16 and 8 ohm nominal load speakers. 8 ohm speakers became very popular in the 1960's. I'd be inclined to get it changed to 8 ohm. The listening experience at 8 ohm often sounds more encapsulating and warm. Before doing that though open up the unit and share some photos of the strap configuration inside to determine where it's currently set at.

Edited by xlr8or
  • Like 3

Posted
  On 03/10/2024 at 12:12 PM, xlr8or said:

 

With valve amps the higher the tap the less current for the same power output - i. e., the power output is fixed and does not behave like a SS amp when the resistance is halved or doubled. The reason 4 ohm is often preferred is due to modern speaker design demanding current over voltage for power output. Valve amps flourish at much higher tap settings due to less current demand. Back track to 65+ years ago, before SS transistors made their introduction, and you'll find many speaker designs utilised 8, 16 and even 32 ohm nominal loads to run valve gear. UK speaker manufacturers of the time such as Rogers were manufacturing 16 and 8 ohm nominal load speakers. 8 ohm speakers became very popular in the 1960's. I'd be inclined to get it changed to 8 ohm. The listening experience at 8 ohm often sounds more encapsulating and warm. Before doing that though open up the unit and share some photos of the strap configuration inside to determine where it's currently set at.

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Yes the technological trends in design are definitely of interest as well! I'm not sure I want to risk opening it up myself, so have emailed Jadis to see if they have a record of how it left the factory. Failing that I may consider getting it properly looked at, though I have to say that in a relatively nearfield setup with the Rogers I don't need massive amounts of power and it sounds fantastic. One does wonder what optimal configuration would do to the tone however... Given the weight of the unit etc, it may also be simpler to just pick up a pair of ~6ohm speakers...

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