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Adding series resistor for ribbon?

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Posted on February 16, 2015 at 12:00:30
AkuAnkka
Audiophile

Posts: 167
Joined: February 3, 2013
 Since most tubed SET amps are only good for 4/8 ohm's load, and Maggies ribbon is only 2-3 ohms, they cannot drive them very well. Since the ribbon is mostly (or fully?) resistive, would it be possible to just add a 1-2 ohm resistor in series with the ribbon, and run it with SET's 4ohm output? Or would it need some kind of a transformer?

If the resistor would work, could it have any negative effect on the sound quality?

 

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RE: Adding series resistor for ribbon?, posted on February 16, 2015 at 14:49:25
andyr
Manufacturer

Posts: 12551
Location: Melbourne
Joined: September 2, 2000
 Yes, it is perfectly possible to add a series resistor just next to the ribbon.

Unfortunately, even if you stump up for the expense of Duelund graphite resistors, it will still degrade the sound slightly - compared to not having a resistor. :-((

Also, adding a res will reduce the output of the ribbon - so adding a 2 ohm res will reduce it more than adding just a 1 ohm res. Which is not generally a problem with an active XO, as you can adjust output level for each frequency band.

I have been running a 1 ohm Duelund in series with my 2 ohm IIIa/T-IVa ribbons for about 6 years, as the ss amp driving my ribbons could not handle a 2 ohm load. However, I am about to upgrade to a new amp which the designer has come out with - which can cope with a 2 ohm load. So I look forward to being able to do away with the Duelund. :-))

You can also use a Spelz autoformer to increase load which the ribbon provides, to 8 ohms. But these also degrade the sound - compared to not having one ... albeit only slightly (so I am told).

Given the minimum desirable 4 ohm load ... do you have to use a SET for your ribbons? I suggest a 50w-into-2-ohms ss amp would be a better solution.


Regards,

Andy

 

RE: Adding series resistor for ribbon?, posted on February 17, 2015 at 01:50:27
AkuAnkka
Audiophile

Posts: 167
Joined: February 3, 2013
 Well surely I don't have to use SET, but I just think that it would be a good choice from sound quality point of view.

I don't know if there are any reasonably priced SET tube amps woth 2ohms output..?

 

Why do you think that a SET is a perfect choice for a ribbon? ..., posted on February 17, 2015 at 02:06:30
andyr
Manufacturer

Posts: 12551
Location: Melbourne
Joined: September 2, 2000
 Yes, I know the mystique about SETs. And that's one of the reasons why people choose tube amps to drive Maggies. However, I have read posts here which say that tube amps (not sure whether they're SETs or P-P) don't control ribbons as well as ss amps.

So maybe you need to research ss amps which can drive a 2ohm load? As I said, Hugh Dean's NAKSA 80 (down-rated slightly by having a lower DC rail - so it produces, say, 60w into 8 ohms and not 80w) can drive a 2 ohm load well. I'm sure there must be others.


Regards,

Andy

 

RE: Why do you think that a SET is a perfect choice for a ribbon? ..., posted on February 17, 2015 at 02:18:41
AkuAnkka
Audiophile

Posts: 167
Joined: February 3, 2013
 Unfortunately I could not find any distributor for NAKSA here in Europe, I don't know if there are any..? I would not want to order electronics all the way from Australia, due the high delivery funds, taxes, customs, difficult warranty arrangements etc. etc.

But surely if I don't find any good way to use tube SET for ribbons (and maybe for mids also), I will look for some nice A-class SS amp or such.

 

RE: Why do you think that a SET is a perfect choice for a ribbon? ..., posted on February 17, 2015 at 02:46:14
andyr
Manufacturer

Posts: 12551
Location: Melbourne
Joined: September 2, 2000
 There are no 'distributors' for Hugh Dean's amps - he supplies direct. But I suspect this is not your way of doing things. I know he has a customer in Copenhagen ... he may well have one in your country too (so you can hear it).

Regards,

Andy

 

RE: Why do you think that a SET is a perfect choice for a ribbon? ..., posted on February 17, 2015 at 07:13:01
Roger Gustavsson
Audiophile

Posts: 2058
Location: Huskvarna
Joined: February 12, 2010
 Andy, have you done any blind testing on this? It is very difficult to run tests like that without having exactly matched levels.
We are having a discussion on the sound of capacitors in a swedish forum right now, it is very similar. Not many have ran blind tests. In a controlled blind test things often show up differently...

 

RE: Adding series resistor for ribbon?, posted on February 17, 2015 at 08:24:13
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 SETs are not the best choice for driving the tweeter unless you get one with a pricey high nickel transformer and had taken into account the drooping top octave response with EQ or (much more expensively) with silver wiring. SETs that actually do the top octave well are very expensive because of this.

a PP triode amp is likely a better choice for the tweeter - something like a Border Patrol or Audion. You still have to pay up for good transformers but the circuit is not that weak on top octave FR.

I don't like having transformers in the path for the top octave so while I am a happy camper with triodes and even SETs for mids, I think a SS class A SE amp will do a better job, particularly if feedback is minimal/non feedback at all. We had a short discussion of a few amp options in the category recently.

 

RE: Adding series resistor for ribbon?, posted on February 17, 2015 at 09:45:30
AkuAnkka
Audiophile

Posts: 167
Joined: February 3, 2013
 That's very good information, thanks again Satie! The reason I'm interested on SET is that I have heard a few *very good* setups with them, but actually none of them was tri-amped, so SET was driving either full range or both highs & mids. And because of this, they did not have any problems with low impedances either.

Maybe I was just distracted by the great mids they had, so I did not even notice any problems with the highs ;=)

But actually your proposal of using SET only for mids would make things much easier for me. Since I'm going to use line of NEO-8's for mids, they could easily be driven by some lower power (=lower price) SET. And then using some good A-class SS for highs would solve the problem with low impedance. BUT; could such a setup cause some problems with the continuity of the sound, due the bit different character?

 

The sound of capacitors, eh! :-)) ..., posted on February 17, 2015 at 11:25:27
andyr
Manufacturer

Posts: 12551
Location: Melbourne
Joined: September 2, 2000
 Hope you have your flame-proof undies on. :-)) I have no idea which larger-value caps sound the best (that you use in passive XOs) but for coupling caps (1uF - 2uF) that I use in my 'Muse' phono stage, customer's input has shown:
* the best (that I have used) are Duelund RS400v Copper. Possibly a more expensive Duelund sounds better?
* then - in spite of being more expensive - Sonicap Platinum
* a long way behind ... AmpOhm PF-XAL-AL Paper-in-Oil Aluminium Foil.


Regards,

Andy

 

RE: Adding series resistor for ribbon?, posted on February 17, 2015 at 13:31:55
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 It is a risk to have different type amps as far as coherence is concerned. Some people are more sensitive to it than others. When running the midrange without a low pass, the tweeter can be set to 10-12 khz XO and there is little room for coherence issues as there is broad overlap at the top octave.

If you run 1st order with the likely 5-6khz XO then overlap is again going to "save" you from the coherence problem unless you are particularly sensitive to it.

 

RE: The sound of capacitors, eh! :-)) ..., posted on February 18, 2015 at 12:04:16
Satie
Audiophile

Posts: 5426
Joined: July 6, 2002
 The new Jupiter Cu wax cas have captured the heart of my modster friend and have displaced the Sonicap Platinums. For value I can't find better than the Dayton tin foil caps from parts express.

 

RE: The sound of capacitors, eh! :-)) ..., posted on February 18, 2015 at 14:20:03
andyr
Manufacturer

Posts: 12551
Location: Melbourne
Joined: September 2, 2000
 Haven't tried the Jupiter Cu, Satie, but those Duelund ones I mentioned sound better than Sonicap Platinums, too. And they're cheaper!


Andy

 

RE: Adding series resistor for ribbon?, posted on February 20, 2015 at 14:34:57
A.Wayne
Audiophile

Posts: 2527
Location: Front row center
Joined: November 30, 2011
 The biggest issue will be the lost sensitivity, but it can be done ....

 

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