Responses have provided great info regarding square waves and scopes. There are also responses describing ways to improve the amp. The amp looks fine as is (as far as I can tell from the provided info). The bandwidth and square wave response needs no improvement. Avoid changing anything.
It's a very informative thread, especially given the lack of an actual question to start it off. Interesting that the 250k pot might be a bit of a bottleneck - the amp was originally designed with 6V6 output tubes and a 6SN7 driver, the Lacewood 2.0 amp from Cascadetubes.com. I upgraded the tubes and output transformers without changing any other parts, now I wonder if a 100k pot would be a better choice. But, as you say, I'd rather change nothing.
Thanks all
w
Thanks all
w
Gentlemen, yes, this thread is a nice example for good information of basic problems.
Today it seems I am in didactic mode :
Post 1: as others said for a simple tube amp this is a quite nice 10 kHz square wave.
Consider the bandwidth of the simple scope also - as said in post 18 and 19 and good
advice in post 37.
Post 5: the 1 kHz wave also looks good. Set the input switch to dc and show the result.
The hf ringing you see is from some transformer resonance. It looks small for me but
will increase without load as said in post 10.
Post 6: which frequency ? With the given remarks it should be 1 kHz.
Post 8 : the explanation is square wave contains a sequence of frequencies up to infinity
(with deceasing level) and this signal can never be transferred in a perfect way. The hf
information is in the edges - see post 14, 38 and others. The flat part contains information
about frequencies even lower than the fundamental.
Post 10: yes we should look at the response of your scope to the input signal from the
generator, confirmed in post 11 and 25.
Post 15 : post 10 is fine, except "tweak feedback" ..
Post 24 : for a test like this it is perfectly adequate to use direct wiring and no probes.
Remember this is a speaker output, no hf device (remark to post 26 also).
Post 26 : I think it is more like nine harmonics ..
Post 27 : you should not expect perfection from cheap and simple set ups.
...
Out of curiosity, how high is the gain in your amp at full volume setting ?
Today it seems I am in didactic mode :
Post 1: as others said for a simple tube amp this is a quite nice 10 kHz square wave.
Consider the bandwidth of the simple scope also - as said in post 18 and 19 and good
advice in post 37.
Post 5: the 1 kHz wave also looks good. Set the input switch to dc and show the result.
The hf ringing you see is from some transformer resonance. It looks small for me but
will increase without load as said in post 10.
Post 6: which frequency ? With the given remarks it should be 1 kHz.
Post 8 : the explanation is square wave contains a sequence of frequencies up to infinity
(with deceasing level) and this signal can never be transferred in a perfect way. The hf
information is in the edges - see post 14, 38 and others. The flat part contains information
about frequencies even lower than the fundamental.
Post 10: yes we should look at the response of your scope to the input signal from the
generator, confirmed in post 11 and 25.
Post 15 : post 10 is fine, except "tweak feedback" ..
Post 24 : for a test like this it is perfectly adequate to use direct wiring and no probes.
Remember this is a speaker output, no hf device (remark to post 26 also).
Post 26 : I think it is more like nine harmonics ..
Post 27 : you should not expect perfection from cheap and simple set ups.
...
Out of curiosity, how high is the gain in your amp at full volume setting ?
thanks for all the info. I'm not sure how to measure the gain - I only have a pair of 4-ohm resistors in 5w and they sing pretty loud with the test waves on em - I haven't turned the volume up past 50%
sound sources are a DIY DAC streamer and a turntable with a DIY EAR834p preamp, which has a considerably higher output than the DAC.
"I'm not sure how to measure the gain" - compare input and output level on your scope.
I do not talk about output power - turn down the volume of the generator if it is too high.
Gain is (output voltage / input voltage), easy to see with square wave, but with sine and
triangle also.
I do not talk about output power - turn down the volume of the generator if it is too high.
Gain is (output voltage / input voltage), easy to see with square wave, but with sine and
triangle also.
Here is a 1kHz wave direct from my source to the scope.
Also trying to figure out scope terminology. So, it's set at 2v. Is that 2v for every Horizontal line away from the center(zero) line? And 0.2ms, is that per (vertical) division as well?
Anyway, here's the same signal run thru the amp with the volume pot open:
So not quite 2v gain?
Also trying to figure out scope terminology. So, it's set at 2v. Is that 2v for every Horizontal line away from the center(zero) line? And 0.2ms, is that per (vertical) division as well?
Anyway, here's the same signal run thru the amp with the volume pot open:
So not quite 2v gain?
This sees to indicate a gain of only 1.5 ..
For a power amp you would expect 10 .. 30,
but here we have only a single driver stage.
For a power amp you would expect 10 .. 30,
but here we have only a single driver stage.
It shouldn't be that little. Are you sure that the 470k resistance is really 470k and not just 4.7k?
Sensitivity should be something like 0,5V rms for full power . Full power would be something like 3,5V rms / 4ohm , the output tube is old school triode and is "lazy" 🙂 So I would expect 7 overall gain ...
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"Are you sure that the 470k resistance is really 470k and not just 4.7k?"
This would result in low bass output, it is not, see 1 kHz square wave.
"Whitout feedback like in schematic from post1 , the gain should be huge"
Don't forget the "gain reduction" in the optr.
This would result in low bass output, it is not, see 1 kHz square wave.
"Whitout feedback like in schematic from post1 , the gain should be huge"
Don't forget the "gain reduction" in the optr.
I corrected the response , not the output transformer step down voltage ratio is important but the output tube - old school triode
It is relatively "huge" using a modern pentode like EL84
It is relatively "huge" using a modern pentode like EL84
Or it's just clipping. The square wave signal is sneaky 🙂
Turn the volume pot down until the amplifier signal is +/- 4V. Then measure the amplitude at the potentiometer output.
Turn the volume pot down until the amplifier signal is +/- 4V. Then measure the amplitude at the potentiometer output.
Depa, editing your post 50 later makes my reply useless.
"The square wave signal is sneaky" : yes, it is 12 Vpp, not
sure it is clipped, the test should be repeated with sine or
triangle wave.
"The square wave signal is sneaky" : yes, it is 12 Vpp, not
sure it is clipped, the test should be repeated with sine or
triangle wave.
Now that is clear, much better than on AliExpess.
The kit costs more than the assembled version? That's unusual.
The numbers in circles are the pins of the double triode not voltages ... grid is 0V , cathode 1.7V and so on , of course the clipping possibility is real .
hi...please put vol of your amp to max ......and control sig amplitud by sig generator ... check a gain 10khz sq.