HRM needs some Lovin'

Overdrive Special, Steel String Singer, Dumbleland, Odyssey, Winterland, etc. -
Members Only

Moderators: pompeiisneaks, Colossal

Post Reply
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

Re: HRM needs some Lovin'

Post by fred.violleau »

norburybrook wrote:Is your Chassis anodised?

You really need to dremell away the anodising for your ground points on the chassis and I would add a separate earth connection from the output jacks etc if you're expecting them to ground through the chassis.


Marcus
Marcus, I don’t know if the chassis is anodised. I will check and also I will try to scratch the surface to have a better grounding.

Thanks!



Humble and Dumble,

Fred.
User avatar
norburybrook
Posts: 3290
Joined: Mon Jan 06, 2014 12:47 am
Location: London
Contact:

Re: HRM needs some Lovin'

Post by norburybrook »

I spent nearly a week chasing a bad hum on a build only to find it was the switchcraft jacks on the output not grounding properly through a black anodised chassis, I had ground the anodising away from the earth points on the chassis but didn't think about the jacks as I presumed they'd earth with tightening the nuts. Adding a ground lead cured it immediately. I had tried everything until that point.



M
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

Re: HRM needs some Lovin'

Post by fred.violleau »

Marcus, Thanks for sharing! I will definitely watch for the ground issues then.

I have tried to keep moving and see what comes up.
So far, I have wired the switch for half/full power, pretty much everything that goes on the power tubes, and I still miss the 15K for the bias pot.Choke is not connected to the B+.

20180115 DumblePower section.jpg
I made a little schematic of the power supply of the amp. I did not want to change it at first, but voltages appear to be high so I might have to change the values of the resistors. I put the voltages and the value of each component butI am missing the value of the blue filter cap. Can't read it, but some pros here might help.

PowerSectionFinal.jpg
I will appreciate any comment as this is a first for me and I may have done some mistakes.

My build includes an active FX loop in the chassis. So I will have to add some B+ supply.

Here are a few questions :
1- In calculating the current drop across resistors after standby switch, I suppose I have to add all the resistor's value to determine the total resistance (R1+R2+R5+R6+R7+R8) and then use Ohm's law to get how much each resistor would have the current drop.

2- Why is there a 10W 510 ohms ciment resistor feeding B+2 as I did not see it on many schematics, and voltage is not dropping..

3- If I want to add power supply for my FX loop, I need to extend my B+ rail. Can i do so with the existing PT? using 2x22uf caps and resistors to manage current voltages? OR should I use a separate transformer feeding the FX Loop?

Again thanks for your help, little steps at a time, it seem things are moving along !

Humble and Dumble

Fred.
You do not have the required permissions to view the files attached to this post.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: HRM needs some Lovin'

Post by martin manning »

fred.violleau wrote: Tue Jan 16, 2018 1:12 amI made a little schematic of the power supply of the amp. I did not want to change it at first, but voltages appear to be high so I might have to change the values of the resistors. I put the voltages and the value of each component butI am missing the value of the blue filter cap.
You need a cap to ground for the B+5 node, another 22u. The bias supply filter should be 100u.
fred.violleau wrote: Tue Jan 16, 2018 1:12 am1- In calculating the current drop across resistors after standby switch, I suppose I have to add all the resistor's value to determine the total resistance (R1+R2+R5+R6+R7+R8) and then use Ohm's law to get how much each resistor would have the current drop.
It's not that simple, because the current varies along the series of resistors. If you know or can estimate the current draw from each B+ node you can determine the current flowing through each resistor and its expected voltage drop. But wait a minute...
fred.violleau wrote: Tue Jan 16, 2018 1:12 am2- Why is there a 10W 510 ohms ciment resistor feeding B+2 as I did not see it on many schematics, and voltage is not dropping..
Presumably the 510R was placed there to reduce the downstream voltage, but you are not seeing that because you have almost no current flowing through it. You are testing the power supply in isolation, I guess? You might want to adjust its value later to get the preamp voltages into line. Notice that right now you are exceeding the voltage rating of the filters. They will take a little overage, and the voltage may drop sufficiently once you get some current flowing, but it might still be a problem at start-up.
fred.violleau wrote: Tue Jan 16, 2018 1:12 am3- If I want to add power supply for my FX loop, I need to extend my B+ rail. Can i do so with the existing PT? using 2x22uf caps and resistors to manage current voltages? OR should I use a separate transformer feeding the FX Loop?
Make a branch off from the screen node, say a 47-100k resistor, a 33u cap to ground, a 100k resistor, and another 33u cap. Adjust the value of the first resistor to get the voltage at the first cap to about 360V with the loop tube in the circuit.
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

HRM needs some Lovin'

Post by fred.violleau »

Martin thanks a lot for the feedback!
martin manning wrote: You need a cap to ground for the B+5 node, another 22u. The bias supply filter should be 100u .
This node used to feed a transformer for the reverb in the old amp(which never worked btw). I will add a cap to ground the node.
martin manning wrote: Presumably the 510R was placed there to drop some voltage, but you are not seeing any because you have almost no current flowing through it. You are testing the power supply in isolation, I guess?
Yes: no tubes in the sockets, nor is the preamp board connected. I am testing with one probe on the chassis and the other on the node.
martin manning wrote: Notice that right now you are exceeding the voltage rating of the filters. They will take a little overage, and the voltage may drop sufficiently once you get some current flowing, but it might still be a problem at start-up.
I did notice, more than 1000v AC and over 500v DC.. I also read about the voltage peaks at startup and the issues of the standby switch. Would it be fixed if I added a resistor in parallel to the standby switch as mentioned here :
http://www.valvewizard.co.uk/standby.html

martin manning wrote:
fred.violleau wrote: Tue Jan 16, 2018 1:12 am3- If I want to add power supply for my FX loop, I need to extend my B+ rail. Can i do so with the existing PT? using 2x22uf caps and resistors to manage current voltages? OR should I use a separate transformer feeding the FX Loop?
Make a branch off from the screen node, say a 47-100k resistor, a 33u cap to ground, a 100k resistor, and another 33u cap. Adjust the value of the first resistor to get the voltage at the first cap to about 360V with the loop tube in the circuit.
Order for filter caps and resistors on the way!
On the power board, it seems the resistors in place are mainly 1W. Should I replace these with 2W? How can I tell the wattage of the resistors besides visual inspection?

Humble and Dumble,

Fred.
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

Re: HRM needs some Lovin'

Post by fred.violleau »

I was wondering: on the HRM layout, there is an OD trimmer (250k A) on the chassis in series with another OD trimmer on the preamp board (250k also). As I am trying to expose all the controls to get the best tone flexibility, should I get rid of the pot on the preamp board and just replace the OD trimmer with a 500k linear pot?

Is it usable?


Humble and Dumble,

Fred.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: HRM needs some Lovin'

Post by martin manning »

Hi Fred, got a link to the layout you are looking at?
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

HRM needs some Lovin'

Post by fred.violleau »

martin manning wrote:Hi Fred, got a link to the layout you are looking at?
I am referring to the ceriatone HRM schematic


Humble and Dumble,

Fred.
User avatar
martin manning
Posts: 13080
Joined: Sun Jul 06, 2008 12:43 am
Location: 39°06' N 84°30' W

Re: HRM needs some Lovin'

Post by martin manning »

Not that they are any sort of expert on D-style amps, but there is a newer version of C-tone HRM with a rear panel OD entrance trim. The old one has the configuration you describe and the newer one has a 100k trim on the board and a 25k pot on the rear panel (with the same 4k7 to ground). Clearly they wanted a much finer adjustment. Personally I would just stick to the board-mounted trimmer, and set it to taste.
jam-mill
Posts: 222
Joined: Sun Nov 17, 2013 8:37 pm
Location: San Diego, CA

Re: HRM needs some Lovin'

Post by jam-mill »

The on-board 250K trimmer seems as if it is a mistake and probably should be removed when/if using a pot mounted on the rear panel.

EDIT: I see the mistake now; the latest layout has a 250K pot on the back panel instead of 25K.

-jack
John 15:12-13
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

Re: HRM needs some Lovin'

Post by fred.violleau »

Hey guys,

I am working on the HRM tonestack.
I made a little drawing of the layout and tried to avoid using a little board for the OD tonestack.
I will put it out on the front plate.
I have added as Martin's recommendation the OD TS lift as well.

Please feel free to comment and advise on my proposition.
HRM tonestack with lift.jpg
Thanks again for your help!

Fred.
You do not have the required permissions to view the files attached to this post.
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

HRM needs some Lovin'

Post by fred.violleau »

I am also trying to figure out which HRM setting to choose from
I organized a little comparison charts of the HRM OD trimmer values that one can find on this forum :
HRM Flavors.PNG
Normster's is 200k resistor and then a singleo 25K trimmer on the board

Ceriatone's take is 100k resistor, 250k pot and 250k OD trimmer with a 4k7 resistor to ground

I would like to keep just one OD trrim pot that gives me the largest usable palette.

How changing the combination of the resistor and OD trimmer affects the tone and the drive level?
Does more resistance leads to larger audio frequency spectrum + larger range of OD?
it seems to me that a 25k pot vs. a250 pot would trim down the high frequencies

Any suggestions ?

Modified -----

Looks like there are tons of threads already tackling the subject [emoji6]
http://ampgarage.com/forum/viewtopic.ph ... 7&start=15

http://ampgarage.com/forum/viewtopic.php?t=23791

Looks like 200k resistor + 100K trimmer is the gold standard!

Fred.
You do not have the required permissions to view the files attached to this post.
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

Re: HRM needs some Lovin'

Post by fred.violleau »

A little update of my whereabouts:

B+ rail extended

Image

Wired pots and relays:

Image

Getting ready to load the preamp board:

Image

A view of the front:

Image


Humble and Dumble,

Fred.
ChopSauce
Posts: 1038
Joined: Wed Mar 15, 2017 12:08 pm
Location: So Paris, France

Re: HRM needs some Lovin'

Post by ChopSauce »

Chi va piano, va sano e va lontano ... 8)

I'm glad to see some progress here -
fred.violleau
Posts: 503
Joined: Tue Jun 06, 2017 12:20 pm
Location: Montreal, Canada

HRM needs some Lovin'

Post by fred.violleau »

Grazie Mille @ChopSauce!

I had friends from Corsica who’s moto was « doucement le matin et pas trop vite l’après-midi » [emoji6]

I wish I had more time to go faster, but one makes it with the time he has.

My biggest mistake was probably to start my build without having all the components at hand...

And as it is my first build, I realize it takes a lot of planning before soldering anything, trying to figure out the best layout possible, cables routing, etc...

But I just love it!

I hope I will enjoy the end result.

Humble and Dumble,

Fred.
Post Reply