can SE bass be as good as PP ?

[Mickeystan]

Over the years I have built many different push pull power amplifiers and many have done an impressive job of bass response. On the other hand, I have not built many SE amplifiers. One SE amplifier I built about 4 years ago used a 300B for the output tube and was of the a direct reactance drive topology. This amplifier had a very stiff power supply and good quality output transformers. I must say even though I have not built many SE amplifiers, this amplifier pumps out wonderful bass when connected up to my Klipsch Forte II speakers. I think it has as good of bass as most any pushpull amplifier I have ever built or had the privilege of listening too. Good luck on any future builds.

Mickeystan

 

[Globulator]

The SRPP does a decent job of providing the voltage and current capability needed here, but the distortion is higher than an ordinary common cathode stage, and direct coupling is problematic. Nevertheless, the 300Beast was a nice sounding very dynamic amp.

I have since learned to use mosfet drivers for most of my tube amp designs. A mosfet follower can be directly coupled to the output tube grid eliminating the coupling cap and its associated overload issues. It can source amps of grid current if needed, and offers lower distortion than most vacuum tube cathode followers.

I must admit that a MOSFET follower is a very tempting thing. Solid current, no isolated filament voltages etc. I used one as a buffer for the GU50 grid voltage - the VR tubes just went mental connected directly to the screen grids - a decent mosfet solved it.

The powerdrive concept is very sound and solving blocking distortion is pretty important for an amp driven hard (like any SE with decent rock music going in). To replace a MOSFET properly with a tube (to keep it all-tube) I think a doubled up ECC88 would get you so far, but you'd need a much bigger tube to compete in real terms.

 

[MelB]

OK. Here are actual in room real life measurements.

I have an Anthem MRX-710 Receiver. It uses their own proprietary "Anthem Room Correction" kit to measure and correct your room for "perfect" sound at your listening position.

It comes with a calibrated usb microphone that you attach to a computer which then controls the Anthem Receiver. The program asks you to take 5 measurements around your listening area and then averages them. The fact that there is no "Uncorrected in-room response" on the graphs means there is no sub attached to the system.

I'm using the Anthem as a pre-amp and playing it through either a ~30 watt Single ended or a ~30 Push Pull home brew amp. Both amps have zero negative feedback around the output transformer.

So is there any measurable difference between the PP and the SE??? You decide.
To me it looks like the Single Ended amp actually has better control of the speakers(?). (It looks to EQ a bit better to me)

As far as actual listening I'm going to say the Push Pull sounds a bit punchier and listening to a bass guitar for example sounds a bit more defined with the Single Ended amp.

It's actually very interesting how the graph changes by just moving the mic a bit.

 

[Bigun]

OK. Here are actual in room real life measurements.

Fascinating - in addition to the PP vs SE bass, I find the 'Target Response' line very interesting.

 

[MelB]

The "Target Response" line can be changed as far as frequency correction range. I had it set at 25hz to 5000hz. You can not change the actual curve they have determined to be "ideal". The documentation also says anything above 5000hz can not be picked up reliably by the mic in a "living room" setting so there is no correction for frequencies above 5000hz.