# Managing volume with speaker count and impedance changes?



## Greg Ellis (Oct 1, 2007)

I've recently acquired a Blackface Fender Deluxe (no reverb) from 1965. It's a push-pull 6V6 amp, roughly 23 watts I think. The original output transformer is long gone, and replaced with a Hammond 1760H that's got 4, 8 and 16 ohm taps.

I'm currently driving a 2 x 10 open back cab with a couple of different Emminence 8 ohm speakers wired in series for a 16 ohm load.

The rig sounds WONDERFUL, but currently it's too loud to reach the sweet spot on the amp without causing a disturbance.

I'm wondering if there are some easy ways I can manage the volume downward by changing up the speaker config.

For example, 

If I run a single 10" at 8 ohms instead of a pair of 10s at 16 ohms, will the reduced surface area mean less air moving and therefore lower volume?

I've read before that the best way to run an output transformer is to use ALL of it, i.e. if the OT supports 4, 8 and 16 ohms, then the 16 ohm tap is best, as that is the whole secondary winding, whereas the 8 ohm tap is only half and the 4 ohm tap is only a quarter. I'm not exactly sure what 'best' means in this context - power transfer, frequency response, or what - but it kinda makes sense to me that using all of the winding ought to produce a better result than half or a quarter.

Would using a smaller portion of that secondary winding result in a volume drop? e.g. if I wire up the same two 8 ohm speakers in parallel, for a 4 ohm load, would you expect that to produce a lower volume than the current series arrangement (at 16 ohms)? What other losses might I expect? Frequency response?

As another option, I have one of those Weber 8 ohm attenuators (the speaker motor type) that I could run in parallel with one of the 10" speakers. That would be a 4 ohm situation as well, with only one of the 'speakers' actually producing any sound. I've already tried the attenuator in a more traditional hookup, and it seems to steal away too much of the character of the amp. Might be different in a parallel situation?

One last question - can I reduce volume by deliberately creating an impedance mismatch? Which way would I want go with that? e.g. 16 ohm tap into an 8 ohm load, or the other way around, say 4 ohm tap into an 8 ohm load? Which sort of mismatch direction is dangerous to the amp?

Thanks for any thoughts.


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## WCGill (Mar 27, 2009)

Mismatching impedances will result in less power from the amp and frequency response changes. The only way to find out is to try it. Usually a 100% mismatch won't harm an amp and it's usually better to run a smaller load from a larger tap. As far as using the full winding for better performance, there is no basis in fact for it. Using an inefficient speaker to make the amp work harder will also achieve what you are looking for.


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## Greg Ellis (Oct 1, 2007)

Thanks Bill. I tried a few things yesterday afternoon.

Reducing the speaker count from two to one didn't seem to reduce the volume very much at all. Maybe a little bit but not enough to matter.

Running an attenuator in place of one of the speakers (ie. as a load box in parallel with the remaining speaker) didn't change things much either. 

I might have been losing a few decibels in both these cases, but it wasn't enough of a cut to change things up in a significant way.

Creating an impedance mismatch certainly DID reduce the volume quite a lot, but not in a very pleasant way. It changed the character of the sound quite a lot and made it feel very dead. I tried a few different setups with this and they all worked, they just didn't sound very good.

Using the attenuator in the tradition way was the most effective and configurable way to cut volume, but again it seemed to make the sound rather lifeless and dull if I was shaving off more than a handful of db.

I think I'll have to resign myself to the fact that this cabinet isn't going to play well at basement volumes. Oversize dimensions and high efficiency speakers (Emminence Ramrod @ 100.2db sensitivity + Copperhead @ 98.85) seems to sound great at stage volumes, but it's going to be way too much for regular practice sessions in the house.

One thing I haven't tried yet is reducing the cabinet size. I think I have an old 1 x 10 cab in the garage that's quite small. That might get me somewhere, probably at the expense of bass response.

And a less efficient speaker ought to help too. I think I have an old Marsland buried somewhere. I don't expect it to sound very good, but it might give me a good idea of how much volume reduction can be achieved on that route.


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## StevieMac (Mar 4, 2006)

The "inefficient speaker" approach _might_ get you close to where you'd like to be Greg. Case in point: I have a '63 Gibson Falcon that I've tried every conceivable 12" speaker with. Without exception, the aftermarket speakers made the amp considerably louder BUT none sounded as sweet as the _uber-inefficient_ Jensen P12S the amp came with. Perfect for recording/micing at gigs/practice at home but that's the limit of it's application. 

Sounds like all the other methods you tried sound were "tone suckers" as well...


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## WCGill (Mar 27, 2009)

Yup, I also have a Falcon, POS Jensen in it, probably the same as yours Steve and I tried every speaker in it too, and I have a *lot* of speakers. The Jensen is the one and only for that amp. Weber makes a "DT" series which are inefficient for this exact application, haven't had any though.


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## Greg Ellis (Oct 1, 2007)

I cranked up the amp today to where it belongs, around 7 on the volume dial.

I can't do that very often while anyone else is home, but I needed to see what it was like.

The amp sounds amazing like that, just the sort of thing I was hoping for when I bought it; BETTER that I thought it would be, actually.

BUT... that experience made it clear to me that if I want to practice at home with the amp opened up, it's not a BIT of volume I need to lose, it's a TON.

I'm pretty sure speaker swaps and impedance mismatches aren't going to cut it. Attenuation isn't going to work either, not without stealing away all the tone.

I'm going to have to go some other route. Speaker isolation maybe. Or soundproofing. Or both, lol.

Back to the modeler for now I guess.


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## WCGill (Mar 27, 2009)

There's no free lunch. Somewhere you're going to have to lose something to get something else. A good master volume works on most of my builds but on your Deluxe, VVR might be better.


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## Greg Ellis (Oct 1, 2007)

Yeah, I've thought about VVR before. 

I think it's going to be a while before I really feel ok about modding this particular amp tho. I don't really know it well enough yet to understand what I'd like to do.

I picked this one because I figured it could get up over drums and bass, and from the limited high volume time I've spent with it, I think it's going to work out just fine for that 

Finding a way to play it at home without disturbing everyone in the house is just a side issue really. I have other ways to practice. It would be nice to have a way to get used to the amp before I take it to a jam, but it's not essential I guess. I could always find somewhere I can play it loud, if it comes to that.

The amp sounds great at low volume, actually, so it's not a waste by any means. It just doesn't sound anything like the same amp at high volume, so it's not too useful in terms of getting used to how to dial it in, what settings it likes on my pedals, etc.

And I haven't completely given up on the idea of attenuation, I've just been cautious about it so far because my attenuator is only rated at 15 watts. 

I tried the amp dialed up to about 3 into that 15 watt load; it seemed to work fine. I wasn't fond of the sound I was getting out of the speakers, but a line out of the attenuator into a speaker simulation running on my computer and then some heavy-handed EQ'ing brought it into a 'sort of ok' territory. Not great by any means.

'Course that was before i realized how much the amp comes alive at 6 or 7 on the dial. I'm pretty sure a 15watt attenuator on a 23 watt amp is really NOT a good idea when it's cranked like that, so I'm not even going to try.

Back to the drawing board...


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## Church-Audio (Sep 27, 2014)

When ever you change the load on a output transformer you change the primary impedance of the transformer so it's better to go up on the primary impedance then go down. A 6v6 amp should be about the same as an el84 8k to 10k with the proper load connected to the speaker. If you use a lower tap say 4 ohms and put an 8 ohm load on it you will drive up the primary impedance to around 12k pretty safe for a 6v6 so use 8 ohms on the 4 ohm tap you should be fine. Another way to do it is a lowering of plate voltage to the phase inverter. But that's tricky.

Chris Church 
Church-audio 
amp repairs 
905-385-6872


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## keto (May 23, 2006)

You want a Silverface VibroChamp


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## traynor_garnet (Feb 22, 2006)

Which attenuator are you using?

TG


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## parkhead (Aug 14, 2009)

open the dog house and look at the filter caps. 
if there are anything other than 16mfd caps under there recap the amp with the proper values 
that should brown it out and reduce the need to crank it to get fat tones 

Personally for home use I would look at lowering the filtering even more 
but that is beyond the scope of general discussion 

when I hear that an amp needs to be cranked to 7 to get TONE I always suspect it has been over filtered and over-biased somewhere in its past life. 


P


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## nonreverb (Sep 19, 2006)

Try replacing the 5AR4 with a 5U4 rectifier. It will drop between 15V and 20V more from the B+ and has a more sluggish reponse when loaded. Might just take off enough to make a difference.
Don't worry about the extra filament current either, as the power tranny can take it.


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## mhammer (Nov 30, 2007)

A naïve question: How much of the OP's "sweet spot" is a sweet spot in the front end or the power stage, versus the speakers? Speakers have a tendency to change tonal quality at different output levels.

If what we're chasing here is the way the speakers sound at a particular output level, then maybe the requirement is to alter how loud the speakers sound, rather than feed them with less power, via some electronic tinkering. Possible to simply stick a closed baffle over one of the speakers so that the amp sees the same old load, and divides up the signal between the two speakers, but you only (mostly) hear one?


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## Church-Audio (Sep 27, 2014)

Tubes like a range of load impedance from the opt.
el84 6v6 7-12k primary impedance
el34 50 watt 4k 100 watt 1.8 to 2 k
6l6 4.2 to 6.8k 30 -40 watt 100 watt 4k to 5k 
so the load impedance has a direct relationship to the primary Change your speaker impedance drastically change the primary impedance and so the math is done for you when you have taps on the secondary its a no brainer when you don't it's not the end of the world you just need to know the range you can play with with each amount and type of tube in the power section. I use a bk precision 879b impedance meter that uses an ac signal of 100hz 150hz 1k or 10k so you can get an idea of performance at different settings.


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## ampaholic (Sep 19, 2006)

How about trying different preamp tubes. Maybe a 5751?


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## Church-Audio (Sep 27, 2014)

Different preamp tubes also effect breakup. The ken fisher master volume mod can work in these amps all you need is a few caps and a dual 250k pot. Works ok.... I am not a huge fan of attenuators. They can stress a vintage amp out big time if you dime the amp all the time.


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## jb welder (Sep 14, 2010)

Amprepair said:


> I am not a huge fan of attenuators. They can stress a vintage amp out big time if you dime the amp all the time.


For sure. For a vintage amp with original (and perhaps rare) output transformer, playing flat out can put your OT in danger, and your power tube life is the same as playing flat out into a speaker. Arcing can also become an issue.
The post phase inverter master volume (PPIMV) Amprepair mentioned is one of the most preferred master volume methods.
The version 2 (larmar) with 2M2 safety resistors does not even require the extra caps. A 250K dual pot replaces the 220K bias feed resistors, with 2M2 resistors added across the 2 sides of the pot. The extra resistors ensure you don't lose bias if the wiper of the pot has bad contact.
This shows the circuit in something other than a deluxe, but the principle is the same.


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## Church-Audio (Sep 27, 2014)

The other issue too that dummy loads for the most part are not reactive loads. They are pretty constant over the frequency response of an amp. Weber makes some reactive loads that use a motor assembly of a speaker. To act as a load these are the best loads to use on an amp if you are going to load it down.


Chris


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