Ashdown ABM Neo 210 with sub issue

[blindboybenton]

Hi
Customer dropped this in to me saying that its been back to the place he brought it 3 times and then went back to ashdown.
The place he brought it from is now No longer trading and ashdown confirmed to me that its been back to them once

Anyway he say as ive fixed all of his other stuff ok, and he can't trust sending it away again


2017_02_13_12_17_32.mp3 audio

ABM EVO3 Main PCB Page 1 Schematic 2.pdf schematic
Its got a very strange fault. works perfectly until you press the sub s/w in and then you get a sort of delay on it. see sound clip above
checked with my workshop 3 cab's and customers so it aint the speaker
If you turn the the sub harmonics level is almost stops

I decided to to a block change.. Changed the jfet TR14 and IC 9 and i though while i was there changed Ic 8-10-11-12 op amps. all new parts,
My problem is i don't really understand the circuit.

i would welcome any thoughts

BBB

[Mick Bailey]

Cant get the schematic to load.

[blindboybenton]

ive just checked it on mine and once i click the link it downloads to the bottom of the browsers

ABM EVO3 Main PCB Page 1 Schematic 2 (1).pdf

[MarkusBass]

Have you noticed that there are two links to the schematic in your post? The first one is in the middle of the post and it's correct. The other one is at the end of your post (attachment) and this one does not work.

Mark

[blindboybenton]

Thanks. As long as One of them is working. People can read the schematic

[Jazz P Bass]

Follow the signal path.

It starts at R72, goes through TR13 into IC7A.

It's really difficult to see what the circuit is doing as there are no component values marked.

[blindboybenton]

Thanks jazz b. I'm home now so I will have to check tomorrow

[MarkusBass]

Actually it's not that difficult to understand what the circuit is doing.
Signal (either compressed, or not) is amplified by IC7-B. "Sub" signal is switched on by TR13 and amplified by IC7-A.
Then, it is directed to IC8-B which is Sallen-Key low pass filter. Signal is send to two wave rectifiers (IC11-A and IC10-A) and then to two comparators (IC10-B and IC11-B). Signal from outputs for comparators is send to CD4013 which is set up as frequency divider. The signal with divided frequency is used to switch TR14 on and off which modulates normal signal from IC7-A to IC12-B. On the output of this opamp you have original signal with twice lower frequency then the original signal. This signal is again filtered by Sallen-Key low pass filter (IC8-A) and mixed with IC14-B to original signal. IC12-A provides DC voltage to wave rectifiers and comparators. And that's all - very simple circuit. All you have to do it to check whether you have correct signal in all parts of the circuit. Start with a check what you have on output of CD4013. You have to provide low frequency signal to the amp (something like 200Hz).

Mark

[J M Fahey]

Which means: do not test it using guitar chords
I would inject an even lower frequency than Markus suggested: 100 Hz , and see what happens.
Does your customer use it for guitar?
In general octave division is a bad idea, and *murderous* on Bass.
EDIT: they have not solved "the problem" because there is no problem there, I hear some kind of tremolo in your sound sample and think the sub generator takes the lowest frequency it finds WHICH MAY BE WAY BELOW THE LOWEST FREQUENCY PLAYED, SINCE IT CAN BE THE BEATING BETWEEN 2 CLOSE FREQUENCIES and so just a few Hertz, and that modulates the chord being played.
So itīs an artifact of a properly working non linear circuit, used the wong way.
I clearly hear a slow tremolo, and no delay proper.

[nickb]

Actually it's not that difficult to understand what the circuit is doing.
Signal (either compressed, or not) is amplified by IC7-B. "Sub" signal is switched on by TR13 and amplified by IC7-A.
Then, it is directed to IC8-B which is Sallen-Key low pass filter. Signal is send to two wave rectifiers (IC11-A and IC10-A) and then to two comparators (IC10-B and IC11-B). Signal from outputs for comparators is send to CD4013 which is set up as frequency divider. The signal with divided frequency is used to switch TR14 on and off which modulates normal signal from IC7-A to IC12-B. On the output of this opamp you have original signal with twice lower frequency then the original signal. This signal is again filtered by Sallen-Key low pass filter (IC8-A) and mixed with IC14-B to original signal. IC12-A provides DC voltage to wave rectifiers and comparators. And that's all - very simple circuit. All you have to do it to check whether you have correct signal in all parts of the circuit. Start with a check what you have on output of CD4013. You have to provide low frequency signal to the amp (something like 200Hz).

Mark

and here's a picture with waveforms to go with the words...

[nickb]

Which means: do not test it using guitar chords
I would inject an even lower frequency than Markus suggested: 100 Hz , and see what happens.
Does your customer use it for guitar?
In general octave division is a bad idea, and *murderous* on Bass.
EDIT: they have not solved "the problem" because there is no problem there, I hear some kind of tremolo in your sound sample and think the sub generator takes the lowest frequency it finds WHICH MAY BE WAY BELOW THE LOWEST FREQUENCY PLAYED, SINCE IT CAN BE THE BEATING BETWEEN 2 CLOSE FREQUENCIES and so just a few Hertz, and that modulates the chord being played.
So itīs an artifact of a properly working non linear circuit, used the wong way.
I clearly hear a slow tremolo, and no delay proper.

Awesome +1000!

[blindboybenton]

Thanks Marcus. When in the workshop tomorrow I will pick it up again. Will let you know

[MarkusBass]

I've just listened to the audio sample and I surprised. Do you (and your customer) know that this is a bass guitar amp and it simply does not work with guitar? To make the "sub" circuit work, you need bass guitar, single (long) notes and strong signal. I case of doubts, go to youtube and search for a demo of an amp.
For example here there is one (I think it's the same circuit):

- listen at the sound at 4:34 (use headphones or good speakers). I would say that there is a big chance that there is nothing wrong with the amp. It was just used incorrectly. I wouldn't expect the "sub" section of this amp working correctly with guitar playing quiet chords.
BTW, this is very poor method of generating octave down signal. It because the signal is first converted to square signal a then filtered. And while changing the signal to square, it looses its tone. That's why this circuit is just a kind of toy - no serious bass player would use it .

Mark

[blindboybenton]

Thanks I have played bass though the amp. And it don't sound right.At present I only have a guitar in the workshop. The customer is a bass player and only uses a bass though it. I will let you all know when I check it tomorrow.
Bbb

[nickb]

BTW, this is very poor method of generating octave down signal. It because the signal is first converted to square signal a then filtered. And while changing the signal to square, it looses its tone. That's why this circuit is just a kind of toy - no serious bass player would use it .

Mark

Aw, man I think you're being a bit hard on the poor Ashdown designer guys

You may be overlooking what happens with that square wave. It is used to switch an invert/ non-invert of the original signal at the /2 rare so retaining it's essential character whilst halving the frequency. I think that was pretty smart of them.

I don't have a bass so I just test these using the low E string. I think it sounds nice with those sorts of frequencies.