Frequency response in small vs big amps (for DI use only)

[VintageCharlie]

Hi guys,

i apologize if this has been answered elsewhere, but i am wondering about this. Is a small tube amp (e.g. 2x EL84, 2x 6V6 amps) capable of producing the same or very close frequency response to their larger siblings (e.g. 4x EL84, 2x or 4x EL34, 6L6 amps) in a DI scenario (i would hook up the amp to a load and then take the line out signal into my DAW for recording)?
In this case the volume and ability to drive more speakers would not be relevant. As there are many variables, let's take AC15 and AC30 as an example. I love the sound of the AC30, but would prefer a compact and light DIY AC15 with just the top boost channel for this purpose. I assume they would not be the same as the larger OT in the AC30 would allow for better low end response and maybe even more highend extension. If i'd want the same or similar response from 2x EL84, would i need to incorporate an AC30 OT or something like an oversized AC15 OT?

I was always wondering about this also in general. To my understanding an OT will have a frequency response within it's specification while it is being used for it's specified wattage and when it goes beyound this, it will start to lose or narrow its bandwidth. So would for example the Radiospares type 30w output transformer, which was intended for hifi and supposed to be quite linear on the whole 20hz - 20khz spectrum at about 30w (if i recall correctly), be capable of giving an AC15 all the bandwidth that it needs in order to be equal/similar to an AC30? Or would the amp still need 4 output tubes to attain the same levels of low end response?

Thanks for any input!

[pdf64]

I agree that smaller amps seem to tend to lower spec OTs than bigger amps. I guess it helps to make ‘student’ grade amps cheaper than ‘pro’ grade amps.
RS DeLuxe OTs can be configured for an 8k primary, so would probably be an excellent, if expensive, choice for a high spec AC15.

[Phil_S]

Human voice is about 300 to 3400 Hz.
Guitar is 82 (low E) to about 4500Hz.
Bass guitar is about 40 to 4000Hz. (E = 41Hz)
A typical young person can actually hear 20 to 20,000Hz. By the time you are about 20 years old, the upper end declines to maybe 15,000Hz. At age 60, I expect you are lucky to hear 12,000Hz.
An audiologist generally won't test above 8,000Hz because the primary concern is hearing human speech.

I dunno about needing a 20 to 20,000Hz output transformer. It certainly wouldn't hurt. Maybe it adds some chime because it has good response in the harmonics? (Chime?)
I'd think you'd be beyond what you need if your OT was capable of 60Hz to 10,000Hz.

It's a trade off, money for Hz. How much are you willing to spend for something you can't hear?

If you don't believe me about hearing range, you can find an on line tone generator with a virtual slider that allows you to increase Hz of the tone until you can't hear it and it might be an eye opener.

Maybe this is TMI. I have tinnitus. The tone I hear is around 11KHz. It's been improving. Why? I used one of those tone generators and found out my range is down from around 12KHz to closer to 10.5KHz or maybe a little above that. I still hear the tone, but it is not so annoying now. It depends on the day. It is clear to me, in the not so distant future, age will cure my tinnitus. It will still be there, but I won't be able to hear it!

[R.G.]

There is no general rule of thumb. The specific design of the OT and circuits makes a huge difference, far more than the power rating of the amp. I have seen hifi/stereo tube amps down to about 15W with 20-20k, and 100W types as well. What makes a bigger difference is what the accountants at the amp factory said about buying cheaper versus more costly OTs and how the designer/players liked the tone controls. Those considerations are all over the map.

No general rule without exhaustive research.