JMI 30/4 vs Vox Herritage AC30 H2

[Rolf Tjernell]

Hi guys,,,

I love the sound from EF86 amps!
Are any of you more versed in amplifier construction?
I am thinking specifically of the components in the circuit in JMI 30/4, and what a fantastic amplifier by the way!
In your opinion, are there any similarities in the construction of circuit boards and the choice of components:
JMI 30/4 vs Vox Herritage AC30 H2.
I think they sound different despite the legacy!

Cheers
//Rolf

[rogercook]

Hi Rolf,

A quick look at the schematic for the AC30H2 confirms the EF86 channel is not the same as the AC30/4. I've never actually seen inside an AC30H2 but it is probably built on printed circuit boards whereas the AC30/4 was built the old fashioned way on tagboards. Personally I don't think the method of construction makes much difference if any to the sound but tagboards are easier to repair and more robust in my view.

Cheers

Roger

[grip]

Feb 5, 2022 13:48:31 GMT rogercook said:

Hi Rolf,

A quick look at the schematic for the AC30H2 confirms the EF86 channel is not the same as the AC30/4. I've never actually seen inside an AC30H2 but it is probably built on printed circuit boards whereas the AC30/4 was built the old fashioned way on tagboards. Personally I don't think the method of construction makes much difference if any to the sound but tagboards are easier to repair and more robust in my view.

Cheers

Roger

Hi Roger,
There's an "under the hood" picture of the AC30H2 here (EF86 looks massive though):

www.voxshowroom.com/uk/amp/ac30h2_2007_hood.html

Kind regards,


Chris

[rogercook]

Ah! They've wrapped the EF86 in heatshrink sleeving to damp the glass envelope and combat it's tendency to go microphonic.

[garystrat]

Hi Rolf,

There seem to be a lot of general similarities between the two, and indeed the AC30 range (the main difference being the phasing out of the EF86 circuit on non Heritage models). The EF86 is described as driving the EL84s in the power amp differently, providing a darker more aggressive sound without so much of the chime or compression.

www.voxshowroom.com/uk/amp/ac30-4.html

www.premierguitar.com/gear/vox-heritage-collection-ac30h2-review

My understanding from reading the above is that the Vox AC30 H2 has a switch mode that changes EF86 operation from Pentode to Triode, the reviewer goes on to state “The pentode mode does indeed put out a sweet high gain tone, but the triode mode has a less vibrant response and sounds dull in comparison. Personally, this option doesn’t appeal to me because I don’t see why you’d want to run a Pentode circuit in triode mode”.

I must admit that I didn’t fully get the point of that, this is possibly what Roger noticed in the schematics?

Regards

Gary

Sorry Roger, our posts crossed.

[rogercook]

Yes Gary, something like that! It has that triode/pentode switch and some fancy switching described as "brightness". As you say I don't really see why you'd want to run the EF86 in triode mode. Certainly for the early Shads sound the EF86 channel is a great option and of course the ECC83 input for the later material. I haven't looked in detail at the rest of the circuit though.

[Rolf Tjernell]

Thank you for your interest and your comments ...
Somewhere I have either heard or read that there were several options when it comes to the circuit for EF86.
But I no longer remember where or in what context. Circuits 1, 3 and so on ...

In my Vox Treble 1964, a colleague mounted an EF86 preamp which is a copy of Ronnie Gustafsson's EF86 circuit that originated in the Roberto Pistolesi modification.

Cheers
// Rolf

[philc]

All my files are with my 50th Anniversary AC30H2, I'll let you decide whether the tone stands up to the original early Shadows recordings

The two channels (Top boost & EF86) are excellent, the EF86 channel has the original tone setting but also a VOX upgrade, the channel has the original sound, the only other tone controls that work with it is the top boost, I rarely us it but if I do it's very little and just to add a smudging of brightness. When using this channel the top boost channel can also be added by just turning up the volume.

As for the Pentode and Triode switch, it works with both channels but it's your choice as to what sound you need.

EF86 Channel app.box.com/s/360tf075b9w3mctbgvisqw9gi6jf0lno

Top Boost Channel app.box.com/s/b6i8fzkcb18kpdapfbu2mtfu667vvwo1

Phil

[Rolf Tjernell]

Phil,,,
Nice and accurate sounds, Happy Birthday really stands out.
Fantastic presence in the guitar.

Cheers
//Rolf

[Kurt Fröberg]

Hi guys,

Phil, your recordings are as usual excellent with spot on playing and all the backing and recording. Both these tunes represent for me "The Holy grail" of The Shadows sound.
Regarding the tone it is very close to the original, especially for Atlantis.
For Happy Birthday I think you can get even closer using the bridge pickup in all the verses exept for the higher octave verse. It sounds to me like you use the middle pickup through the whole song.

Best regards
Kurt

[philc]

Thanks Rolf.

Thanks Kurt, to be honest, I can't remember what pickups I used, but the soundfiles were posted to give an idea what the AC30H2 sounds like.....however! To get close to the original recordings, more has to be done than just plug in and play, so it's not just the amp giving that sound.

Phil

[rogerbayliss]

I owned an AC30H2 mahogany case for a number a of years and it had a great sound on both the top boost and ef86 channels and everyone at our club played through it I think over time and said how good it sounded. I loved the EF86 channel with the brilliance switch deployed. The triode mode was a complete change of tone to me , more rounded and lost its edge, such that I never used it for Shadows sounds.

If I remember right , Amanda Hambridge modded my brilliance circuit so it more closely followed the original circuit. It was a great sounding amp handwired with tag boards.

One of problems with many modern Voxes, is that they have to follow CE certification and as such a number of components differ from original 60's designs, such as filter caps, and signal passing caps are different values and so on.

Some people go to great lengths to modify the circuits , changing capacitors and other components to get them nearer to 60's spec and characteristics. The transformers used are often average etc.

As such, you are unlikely to buy a modern amp off Vox that will be the same as the early models. In fact the circuit designs changed frequently in the early years as well ! So unlikely any Vox will be identical.

As far as EF86 sound went , the Shadows only used it for a relatively small number of tunes I believe and the brilliance circuit too. The top boost circuit got used much more.

These days I own an AC15HW1 with blue speaker and it sounds great with top boost and Normal Channel.