amp design frequency response - louder at 12th fret than at nut.

[walkman]

Hi all.

Can frequency shaping with small cathode caps and small interstage caps result in noticably louder notes around the 12th fret (or any frequency) and above rather than an overall reduction of bass?

Is it more likely that this is due to the particular amp speaker guitar? Actually it could be useful for a volume boost from open chords to lead lines. Notes around the nut and in the lower strings if anything lack clarity and punch. The amp is single ended with a mid cut and no feedback pentode into half triode into pentode similar to el84.

Any general comments rather than a schematic analysis at this point.

[Chuck H]

I take it this is a phenomenon that is actually happening and not a performance request?

General comments...

Resonant peak? You would likely have the same affect on all guitar positions for "that note" and not just the twelfth fret. This is hard to accommodate without schematic analysis though

Acoustic feedback? It's always possible that the guitar and amp have a symbiotic resonance. If this were the case it would only present itself with the one guitar. Possibly only in that one room.

The amp has no idea what position you're playing in. Wolfing notes and ringing notes are almost always related to the guitar itself. Only the guitar knows what position you're playing in and there are all sorts of resonant peaks that differ from instrument to instrument. From a physical, rather than electrical standpoint it is much more possible to have note anomalies sensitive to position. It may not be evident with other amps because they have a different frequency accent than the amp in question. It's possible (probable) that the guitar has acoustically resonant characteristics that are especially evident with that particular amp.

[J M Fahey]

In a vibrating string main resonances happen at different points along it, but you can count on strong ones at half string length.

12th fret and above means strong vibrations happen just above the typical pickup position or near itīs sensitive area, so naturally those strings "sound louder".

Itīs not an amplifier not even pickup (by itself) problem but a pickup *position* one.

[Chuck H]

In a vibrating string main resonances happen at different points along it, but you can count on strong ones at half string length.

12th fret and above means strong vibrations happen just above the typical pickup position or near itīs sensitive area, so naturally those strings "sound louder".

Itīs not an amplifier not even pickup (by itself) problem but a pickup *position* one.

I agree, but... I assumed by the nature of the post that this was being observed by walkman as a new experience with this particular amp. I don't think the OP is a complete greenie with guitars and amps or I might have asked "Does this happen with other guitars in that amp? and "Does the guitar you're hearing this on do the same with other amps", etc.

[walkman]

Yes I should have said that I hadn’t noticed this with the same guitar with a different amp ( yamaha thr5.

I’ve a few more guitars I can test with but I think I noticed it more because I had not played it for a while as I’d lent it to a friend.

The coupling caps are 5n6 and 4n7 so there is a fair bit of bass shaved off. Bypass caps are less than 5uf on the preamp stages and 22uf on the output pentode. Currently I’m running into 10” GB style speaker in a small open back cab. I do recall the same effect running into a quad of GB clones but didn’t think much of it at the time perhaps due to the generally fuller sound of the quad.

As for the loudness it starts to be more prominent from the 9/10th fret onwards then reduces slightly by 13/14th.

I was wondering if I may have created some sort of high mid peak / emphasis. If so would like to experiment ‘tuning’ it and balancing the lower fret response.

I accept that it may well be the guitar and the pickup location in combination with the room / speaker position

[Chuck H]

As for the loudness it starts to be more prominent from the 9/10th fret onwards then reduces slightly by 13/14th.

I was wondering if I may have created some sort of high mid peak / emphasis. If so would like to experiment ‘tuning’ it and balancing the lower fret response.

I accept that it may well be the guitar and the pickup location in combination with the room / speaker position

That^^^^^^^^^^^^^^^^^^^^^^^^^^^

From an electronic standpoint the amp has no idea what position you're playing in. If the amp were (directly) responsible for any resonances the ringing of these notes would not be specific to neck position. Any and every note played in those positions that rings, and can be created elsewhere in another position on the instrument, would. Meaning the phenomenon would be strictly note specific and not position specific.

[J M Fahey]

Thatīs the point.
Check whether it happens in about same neck area (what you said seems to favor that) in which case mine could be one explanation, or whether it happens with same frequencies, no matter where on the neck.
Also if your guitar has 2 or 3 pickups, check whether sensitive position varies.
Say, between neck and bridge pickups.

I donīt consider you green by any means, quite the opposite , but since you ask, I offer my theory

[walkman]

Thanks for the replies guys... it never hurts to ask and usually around here there are very well thought out and enlightening answers.

I will do some more testing over the next few days with different pickup positions and guitars and let you know what I find.