pointy sine wave

[apa]

I have an amplifier (a modified Traynor YSR-1) that seems to have less
headroom than it should. With a 1K tone at the input I see a good sine
wave with a scope on the output. As I turn up the gain the shape top
half of the wave remains pretty much the same but the bottom half gets
narrower and narrower until it becomes a sharp point. This happens
before the onset of clipping.

What might this be an indication of (not component wise but in terms
of interpreting the wave form)?

I've found a few resources for interpreting symmetrical changes in
square waves. Are there any good ones for making sense of the changes
is a sine wave observed on a scope (especially asymmetric changes in
the waveform)?

Thanks, Andy

[Don Pearce]

On 12 Apr 2007 08:23:14 -0700, "apa" > wrote:

>I have an amplifier (a modified Traynor YSR-1) that seems to have less
>headroom than it should. With a 1K tone at the input I see a good sine
>wave with a scope on the output. As I turn up the gain the shape top
>half of the wave remains pretty much the same but the bottom half gets
>narrower and narrower until it becomes a sharp point. This happens
>before the onset of clipping.
>
>What might this be an indication of (not component wise but in terms
>of interpreting the wave form)?
>
>I've found a few resources for interpreting symmetrical changes in
>square waves. Are there any good ones for making sense of the changes
>is a sine wave observed on a scope (especially asymmetric changes in
>the waveform)?
>
>Thanks, Andy

The amplifier certainly has a fault; the word "modified" may be a
clue.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Scott Dorsey]

apa > wrote:
>I have an amplifier (a modified Traynor YSR-1) that seems to have less
>headroom than it should. With a 1K tone at the input I see a good sine
>wave with a scope on the output. As I turn up the gain the shape top
>half of the wave remains pretty much the same but the bottom half gets
>narrower and narrower until it becomes a sharp point. This happens
>before the onset of clipping.
>
>What might this be an indication of (not component wise but in terms
>of interpreting the wave form)?

This is distortion. It's actually the _opposite_ of clipping, in that
the gain is increasing at higher levels. If it's asymmetric, it's almost
certainly a bias issue.

>I've found a few resources for interpreting symmetrical changes in
>square waves. Are there any good ones for making sense of the changes
>is a sine wave observed on a scope (especially asymmetric changes in
>the waveform)?

Break all feedback loops, and find the stage where the waveform is going
asymmetric. If it's a single-ended stage, it's a bias issue. If it is
a push-pull stage, something is wrong on one side of it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[apa]

On Apr 12, 11:42 am, (Scott Dorsey) wrote:
> apa > wrote:
> >I have an amplifier (a modified Traynor YSR-1) that seems to have less
> >headroom than it should. With a 1K tone at the input I see a good sine
> >wave with a scope on the output. As I turn up the gain the shape top
> >half of the wave remains pretty much the same but the bottom half gets
> >narrower and narrower until it becomes a sharp point. This happens
> >before the onset of clipping.
>
> >What might this be an indication of (not component wise but in terms
> >of interpreting the wave form)?
>
> This is distortion. It's actually the _opposite_ of clipping, in that
> the gain is increasing at higher levels. If it's asymmetric, it's almost
> certainly a bias issue.

Thanks Scott.
That makes good sense.



>
> >I've found a few resources for interpreting symmetrical changes in
> >square waves. Are there any good ones for making sense of the changes
> >is a sine wave observed on a scope (especially asymmetric changes in
> >the waveform)?
>
> Break all feedback loops, and find the stage where the waveform is going
> asymmetric. If it's a single-ended stage, it's a bias issue. If it is
> a push-pull stage, something is wrong on one side of it.
> --scott
> --
> "C'est un Nagra. C'est suisse, et tres, tres precis."

[Mark]

On Apr 12, 11:23 am, "apa" > wrote:
> I have an amplifier (a modified Traynor YSR-1) that seems to have less
> headroom than it should. With a 1K tone at the input I see a good sine
> wave with a scope on the output. As I turn up the gain the shape top
> half of the wave remains pretty much the same but the bottom half gets
> narrower and narrower until it becomes a sharp point. This happens
> before the onset of clipping.
>
> What might this be an indication of (not component wise but in terms
> of interpreting the wave form)?
>
> I've found a few resources for interpreting symmetrical changes in
> square waves. Are there any good ones for making sense of the changes
> is a sine wave observed on a scope (especially asymmetric changes in
> the waveform)?
>
> Thanks, Andy

with an output load or unloaded?

Mark

[apa]

On Apr 12, 3:54 pm, "Mark" > wrote:
> On Apr 12, 11:23 am, "apa" > wrote:
>
>
>
> > I have an amplifier (a modified Traynor YSR-1) that seems to have less
> > headroom than it should. With a 1K tone at the input I see a good sine
> > wave with a scope on the output. As I turn up the gain the shape top
> > half of the wave remains pretty much the same but the bottom half gets
> > narrower and narrower until it becomes a sharp point. This happens
> > before the onset of clipping.
>
> > What might this be an indication of (not component wise but in terms
> > of interpreting the wave form)?
>
> > I've found a few resources for interpreting symmetrical changes in
> > square waves. Are there any good ones for making sense of the changes
> > is a sine wave observed on a scope (especially asymmetric changes in
> > the waveform)?
>
> > Thanks, Andy
>
> with an output load or unloaded?
>
> Mark

loaded with a 10 ohm resistor.

[Mark]

On Apr 12, 6:01 pm, "apa" > wrote:
> On Apr 12, 3:54 pm, "Mark" > wrote:
>
>
>
>
>
> > On Apr 12, 11:23 am, "apa" > wrote:
>
> > > I have an amplifier (a modified Traynor YSR-1) that seems to have less
> > > headroom than it should. With a 1K tone at the input I see a good sine
> > > wave with a scope on the output. As I turn up the gain the shape top
> > > half of the wave remains pretty much the same but the bottom half gets
> > > narrower and narrower until it becomes a sharp point. This happens
> > > before the onset of clipping.
>
> > > What might this be an indication of (not component wise but in terms
> > > of interpreting the wave form)?
>
> > > I've found a few resources for interpreting symmetrical changes in
> > > square waves. Are there any good ones for making sense of the changes
> > > is a sine wave observed on a scope (especially asymmetric changes in
> > > the waveform)?
>
> > > Thanks, Andy
>
> > with an output load or unloaded?
>
> > Mark
>
> loaded with a 10 ohm resistor.- Hide quoted text -
>
> - Show quoted text -

try it without a load...

if it cleans up, then you prob have a driver or output transistor that
has failed OPEN...

Mark