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Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 8:10 pm
by StrummersOfThunder
I know this comes up fairly frequently but Im reading a lot of conflicting opinions on this...

Still wondering if I should bite the bullet and replace the OT on my 62 tremolux with one that had multiple taps

Stock, it has 4ohm tap to match the original 2x10 cab
I'm running it into a single 1x12 cab at 8ohm

1. What effect will this have sound wise. Less volume ?
2. Bad for the amp /existing OT?

Cheers

Re: Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 8:35 pm
by JHorner
Less trouble/expense than a transformer swap?

https://www.tedweber.com/z-matcher/

Re: Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 8:45 pm
by StrummersOfThunder
JHorner wrote: Thu Jul 21, 2022 8:35 pm Less trouble/expense than a transformer swap?

https://www.tedweber.com/z-matcher/
That's pretty cool
Makes my brain hurt.

Re: Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 9:02 pm
by robthemac
Running an 8 Ohm load from a 4 Ohm tap should be fine, shouldn't it? Not harmful at least.

Re: Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 9:19 pm
by StrummersOfThunder
robthemac wrote: Thu Jul 21, 2022 9:02 pm Running an 8 Ohm load from a 4 Ohm tap should be fine, shouldn't it? Not harmful at least.
Yeh, that's the general consensus.
Less consistent are the thoughts around how it effects output

Re: Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 9:48 pm
by GrantB
100% mismatch is ok, I think ?? So, 16ohm speaker is ok off a 8 ohm tap. Right?

Re: Speaker / Amp impedance mismatch...

Posted: Thu Jul 21, 2022 10:06 pm
by robthemac
GrantB wrote: Thu Jul 21, 2022 9:48 pm 100% mismatch is ok, I think ?? So, 16ohm speaker is ok off a 8 ohm tap. Right?
And the amp is ok seeing a higher impedance cab than a lower impedance cab?

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 5:37 am
by Slowy
StrummersOfThunder wrote: Thu Jul 21, 2022 8:45 pm
JHorner wrote: Thu Jul 21, 2022 8:35 pm Less trouble/expense than a transformer swap?

https://www.tedweber.com/z-matcher/
That's pretty cool
Makes my brain hurt.
Skip Simmonds of 'The Truth About Vintage Amps' podcast reckons old Fenders don't react to impedance mismatches at all. As for output differences, the THD Flexi 50 I had recommended switching the impedance as a tone feature (not recommended on every amp). It's a long time ago but I think one had a slightly softer feel. It wasn't a huge change.

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 6:27 am
by StrummersOfThunder
Hard to imagine that they dont react 'at all' but i can imagine that the over engineered parts can cope with the extra stress.
Heres something curious....I actually DID swap out this transformer last year! Id forgotten as I got confused with the bandmaster which ha a weird old aussie made output transformer that I swapped out at the same time, then didnt use the tremolux for a long time. But when I was looking through my parts boxes I found two old output transformers ....durgh!!!! I think I may have too many amps.

Ive only wired the 8ohm tap but I might install a multitap switch using the extension speaker jack hole for a rotary switch.

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 7:06 am
by GrantB
Slowy wrote: Fri Jul 22, 2022 5:37 am
StrummersOfThunder wrote: Thu Jul 21, 2022 8:45 pm
JHorner wrote: Thu Jul 21, 2022 8:35 pm Less trouble/expense than a transformer swap?

https://www.tedweber.com/z-matcher/
That's pretty cool
Makes my brain hurt.
Skip Simmonds of 'The Truth About Vintage Amps' podcast reckons old Fenders don't react to impedance mismatches at all. As for output differences, the THD Flexi 50 I had recommended switching the impedance as a tone feature (not recommended on every amp). It's a long time ago but I think one had a slightly softer feel. It wasn't a huge change.
As long as there is a 100% mismatch. 4 and 8, 8 and 16 etc. So running 16ohm from a vintage 4ohm tap is a no go. At least that’s how I interpreted what he was saying

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 7:18 am
by StrummersOfThunder
GrantB wrote: Fri Jul 22, 2022 7:06 am
Slowy wrote: Fri Jul 22, 2022 5:37 am
StrummersOfThunder wrote: Thu Jul 21, 2022 8:45 pm

That's pretty cool
Makes my brain hurt.
Skip Simmonds of 'The Truth About Vintage Amps' podcast reckons old Fenders don't react to impedance mismatches at all. As for output differences, the THD Flexi 50 I had recommended switching the impedance as a tone feature (not recommended on every amp). It's a long time ago but I think one had a slightly softer feel. It wasn't a huge change.
As long as there is a 100% mismatch. 4 and 8, 8 and 16 etc. So running 16ohm from a vintage 4ohm tap is a no go. At least that’s how I interpreted what he was saying
I make a point of trusting people called 'Skip' without question

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 7:35 am
by calling card
robthemac wrote: Thu Jul 21, 2022 10:06 pm
GrantB wrote: Thu Jul 21, 2022 9:48 pm 100% mismatch is ok, I think ?? So, 16ohm speaker is ok off a 8 ohm tap. Right?
And the amp is ok seeing a higher impedance cab than a lower impedance cab?
Good question, I'd like to see tech opinion on.

I'd think high impedance would cause reduced current and voltage rise across OT, low impedance cause voltage drop and increased current. ??

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 7:55 am
by robthemac
calling card wrote: Fri Jul 22, 2022 7:35 am
robthemac wrote: Thu Jul 21, 2022 10:06 pm
GrantB wrote: Thu Jul 21, 2022 9:48 pm 100% mismatch is ok, I think ?? So, 16ohm speaker is ok off a 8 ohm tap. Right?
And the amp is ok seeing a higher impedance cab than a lower impedance cab?
Good question, I'd like to see tech opinion on.

I'd think high impedance would cause reduced current and voltage rise across OT, low impedance cause voltage drop and increased current. ??
Which sounds safer to my uneducated brain.

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 8:04 am
by calling card
I suppose it comes back to that 100% thing where OT can cope within that kind of floating parameter of impedance of up & down.

Re: Speaker / Amp impedance mismatch...

Posted: Fri Jul 22, 2022 8:07 am
by MikeC
Don't mismatch - safest.