Some Discussion on Amp EQs

[JimmyM]

Ah, OK. For some reason that didn't pop out at me when I first read it, but it could have been that I'm extremely tired but can't sleep Thanks Charlie.

 

[BassyBill]

I think post #1 in this thread is possibly the most epic opening post I have ever seen in any discussion on the forum.

It's this sort of stuff that really makes TalkBass what it is. Thanks for taking the time and trouble to share this expert info.

 

[joelb79]

Incredible thread.

 

[arai]

Really awesome thread. Thanks for sharing.

 

[One Drop]

This really makes my understanding of the different stacks much deeper and more easily related to how I practice using them. Wonderful and useful thread!

The thought of a Hiwatt clone amp with a mid control like the SVT seems like it would make a holy grail combination. Has no one done this before?

 

[dunwichamps]

Don't know which is correct, but I like saying "Baxandall" more than "James" so I stick with it

Very interesting thread as a longtime SVT/B-15 lover. Were your results directly from the preamp of an SVT or were they coming out of the output transformer? The reason I ask is that most folks say that the SVT won't be flat sounding with knobs at noon. I don't know how to test mine but I have compared it to an amp that has pretty flat response with knobs at noon and ended up with a couple knobs pretty far off noon on the SVT to match tones. But from what I've heard out of the post-EQ DI on SVT's, they do come across to my ears as flatter than through the cab.

This is actually a good point. There are so many factors which control the overall system EQ (bass + pedals + amp + cab + room). Its entirely possible that given all these factors, that the sound coming out of the cab may not be perceived to be flat despite the controls being at noon.

Given all these other factors I tried to be as consistent as possible and only do the preceding driver stage for each EQ. It would be very difficult to simulate beyond the phase inverters as the transformers are very complex and much harder to model accurately in LTSpice.

 

[dunwichamps]

I think post #1 in this thread is possibly the most epic opening post I have ever seen in any discussion on the forum.

It's this sort of stuff that really makes TalkBass what it is. Thanks for taking the time and trouble to share this expert info.

Incredible thread.

Really awesome thread. Thanks for sharing.

This really makes my understanding of the different stacks much deeper and more easily related to how I practice using them. Wonderful and useful thread!

The thought of a Hiwatt clone amp with a mid control like the SVT seems like it would make a holy grail combination. Has no one done this before?

thanks guys.

I can add the Hiwatt Tone Stack from the 60s/70s which is sort of a highly tweaked FMV style eq.

 

[Mr. Foxen]

Hiwatt one would be appreciated.

 

[dunwichamps]

Hiwatt one would be appreciated.

No problemo. Probably be put up later tonight. About to hit work and wont be out for a while.

 

[JimmyM]

This is actually a good point. There are so many factors which control the overall system EQ (bass + pedals + amp + cab + room). Its entirely possible that given all these factors, that the sound coming out of the cab may not be perceived to be flat despite the controls being at noon.

Given all these other factors I tried to be as consistent as possible and only do the preceding driver stage for each EQ. It would be very difficult to simulate beyond the phase inverters as the transformers are very complex and much harder to model accurately in LTSpice.

Very good...thanks for the further explanation. And thanks for a really interesting discussion.

 

[Passinwind]

I think post #1 in this thread is possibly the most epic opening post I have ever seen in any discussion on the forum.

It's this sort of stuff that really makes TalkBass what it is. Thanks for taking the time and trouble to share this expert info.

Here's another nice [Invalid or Expired Link Removed] from an old friend of mine, done back when ASCII diagrams were still uptown. Kind of the Cliffs Notes version of Nicks dissertation.

 

[father of fires]

Here's a discussion of the Hiwatt tone stack:

http://www.ampbooks.com/home/classic-circuits/cp103-tonestack-analysis/

There's some other decent stuff on this website as well.

 

[dunwichamps]

That's the earliest hiwatt stack. The one I'm talking about was in the late 60s into the 70s

See this scheme

http://hiwatt.org/Schematics/DR_Pre4Input_v0a.gif

Mhuss.com has pretty much all the info on hiwatts. Schemes, pics, history, everything.

 

[father of fires]

That's the earliest hiwatt stack. The one I'm talking about was in the late 60s into the 70s

I played around with the one in the link a long time ago. I would say it was very "glassy" sounding. I've never heard the new ones.

 

[Passinwind]

This is actually a good point. There are so many factors which control the overall system EQ (bass + pedals + amp + cab + room). Its entirely possible that given all these factors, that the sound coming out of the cab may not be perceived to be flat despite the controls being at noon.

Given all these other factors I tried to be as consistent as possible and only do the preceding driver stage for each EQ. It would be very difficult to simulate beyond the phase inverters as the transformers are very complex and much harder to model accurately in LTSpice.

Yep, and you'd need to measure the transformers yourself in most cases too. You can find a few Fender guitar amp LTspice models online that attempt to model everything, including the speaker in an open-back cab in one case.

Bass Gear Magazine posted SVT graphs that show frequency response at the output, both with controls at noon and also set to "nominal flat." It's well worth comparing those to the basic tone stack models.

 

[dunwichamps]

I played around with the one in the link a long time ago. I would say it was very "glassy" sounding. I've never heard the new ones.

the one you linked is originally something from Sound City used on the earliest Hiwatts I believe

See this scheme

http://hiwatt.org/Schematics/SC105.gif

By the time the late 60s rolled around they converted to a Bass Mids Treble stack closer to a FMV

 

[dunwichamps]

Yep, and you'd need to measure the transformers yourself in most cases too.

Bass Gear Magazine posted SVT graphs that show frequency response at the output, both with controls at noon and also set to "nominal flat." It's well worth comparing those to the basic tone stack models.

Of the OT Tap would give you even more info but then there is the cab. Probably easy to get a Ampeg fridge cab EQ but each cab is different.

 

[Passinwind]

Off the OT Tap would give you even more info but then there is the cab. Probably easy to get a Ampeg fridge cab EQ but each cab is different.

And then there's the room, of course.

 

[Passinwind]

I'd like to see the FMB set at 666 and at 2-10-2.

These AB763 Twin Reverb sims (courtesy of the Yahoo Groups LTspice forum) include the power amp section and an output transformer model. I'm showing the curves both pre-phase inverter and post-output transformer, with a resistive dummy load.

Normal Channel:
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Vibrato Channel:

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[JimmyM]

Here's a cool little video that advertises a line of A-Designs preamps but gets into a discussion about output transformers and the different tonal properties using different metals for them. Aimed at the layman, probably not quite as useful to the techies.