[81C4, Realtek ALC298, Speaker, Internal] Playback problem

I get thin tinny sound.
On ubuntu 19.10 I was able to work around this by running:
sudo hda-verb /dev/snd/hwC0D0 0x14 SET_CONNECT_SEL 0x0c
But that doesn't seem to work on 20.04 and I haven't been able to work out what I need to do to get sound working acceptably.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: alsa-base 1.0.25+dfsg-0ubuntu5
ProcVersionSignature: Ubuntu 5.4.0-29.33-generic 5.4.30
Uname: Linux 5.4.0-29-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: travis 36906 F.... pulseaudio
                      travis 207783 F.... alsamixer
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Thu May 14 00:58:56 2020
InstallationDate: Installed on 2020-05-09 (4 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
SourcePackage: alsa-driver
Symptom: audio
Symptom_AlsaPlaybackTest: ALSA playback test through plughw:PCH failed
Symptom_Card: Built-in Audio - HDA Intel PCH
Symptom_Jack: Speaker, Internal
Symptom_Type: None of the above
Title: [81C4, Realtek ALC298, Speaker, Internal] Playback problem
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/09/2018
dmi.bios.vendor: LENOVO
dmi.bios.version: 8GCN32WW
dmi.board.asset.tag: NO Asset Tag
dmi.board.name: LNVNB161216
dmi.board.vendor: LENOVO
dmi.board.version: SDK0R32862 WIN
dmi.chassis.asset.tag: NO Asset Tag
dmi.chassis.type: 31
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Lenovo YOGA C930-13IKB
dmi.modalias: dmi:bvnLENOVO:bvr8GCN32WW:bd10/09/2018:svnLENOVO:pn81C4:pvrLenovoYOGAC930-13IKB:rvnLENOVO:rnLNVNB161216:rvrSDK0R32862WIN:cvnLENOVO:ct31:cvrLenovoYOGAC930-13IKB:
dmi.product.family: YOGA C930-13IKB
dmi.product.name: 81C4
dmi.product.sku: LENOVO_MT_81C4_BU_idea_FM_YOGA C930-13IKB
dmi.product.version: Lenovo YOGA C930-13IKB
dmi.sys.vendor: LENOVO