Author Topic: Hudson Broadcast 24V Issues  (Read 288 times)

iamthesoyman

Hudson Broadcast 24V Issues
« on: January 26, 2021, 09:12:00 PM »
I'm having an issue with a pair of Hudson Broadcast builds using the layout from Tagboard effects here: http://tagboardeffects.blogspot.com/2016/12/hudson-electronics-broadcast.html

For additional reference, schematic is here: https://imgur.com/nrkQFyR

I have built the version with the charge pump in the top left corner, with the following substitutions:

- Using 3pdt footswitch instead of toggle for gain switching (I realize I lose one gain mode by doing this)
- Transistor 1 is a 2N5088 instead of a BC549C
- Transistor 2 is a 1T308B instead of OC71
- Mounted transformer on a daughterboard as I am using the 0.1" pitch vero, too large for the transformer.
- Charge pump is TI LT1054IP

When switched on, and on low gain, they seem to function properly. However as I increase the gain, some odd things start happening. Sometimes its a thudding oscillation, sometimes it's a high pitched whine, sometimes I can continue playing but the signal sounds kind of bitcrushed and a drone appears while I'm playing. Once the issues start, they persist even when I'm back at low gain settings. Some video links/sound clips are below:

https://youtu.be/U0jeKPP8cyc

https://youtu.be/rwEUCtEKQ2w

https://youtu.be/ZxaCIyp3Ou0

I have re-flowed and cut multiple times and traced the layout, I can't find any issues. Already checked all my offboard wiring, and the bypass switching is working correctly.
Pictures of the veroboard are here:

I have the 2n5088 in the Q1 position and the 1T308B in the Q2 position. Hfe is marked as 64 for the 1T308B's (purchased measured transistors) although I don't know the leakage.

DC voltages are:

White Pedal, supply is 26.8V:
2n5088: C - 18.7, B - 8.63, E - 8.4
1T308B: E - 18.9, B - 18.7, C - 10.1

Red Pedal, supply is 26.8V:
2n5088: C - 18.65, B - 8.66, E - 8.3
1T308B: E - 18.9, B - 18.63, C - 10.0

Charge pumps are TI LT1054IP's

My understanding is the Vbe of Si should be around 0.7V, mine are lower compared to that.

Any ideas on what could be causing this? If it's mis-biased transistors, what resistors should I look at adjusting ?

Thanks in advance !

EDIT:

See below for pictures of the veroboard, note that the sockets have been removed and trannies mounted directly to the board now. This seemed to help as before I sometime had no signal at all passing.










« Last Edit: January 27, 2021, 11:39:37 AM by iamthesoyman »

kaycee

Re: Hudson Broadcast 24V Issues
« Reply #1 on: January 27, 2021, 04:03:11 AM »
The gain switch is a 3 position toggle, it latches up, middle and down. Your footswitch has two positions, I'd guess this is the issue. If not you can google the schematic and find one with voltages for the trannies (my notes are in storage).

iamthesoyman

Re: Hudson Broadcast 24V Issues
« Reply #2 on: January 27, 2021, 07:50:09 AM »
The gain switch is a 3 position toggle, it latches up, middle and down. Your footswitch has two positions, I'd guess this is the issue. If not you can google the schematic and find one with voltages for the trannies (my notes are in storage).

If I'm just using one set of lugs for the gain switch, it should work the same but with one less gain option, shouldn't it ? The other two sets of lugs on the footswitch are used to switch between the 2 level potentiometers, switching lugs 2 and 3 simultaneously (lug 1 on both is grounded). Although looking at the Duocast schematic, it looks like all I need to do is switch lug 2.

duck_arse

Re: Hudson Broadcast 24V Issues
« Reply #3 on: January 27, 2021, 09:15:26 AM »
as someone once said, welcome to the forum.

as someone else once said a few times, can we see a circuit diagram so we know what you are talking to us about?

as a third person sometimes says, can we please, PLEASE, see photos of the thing you've built so as to compare it with the layout you are showing us?

and there was another someone who often says - you do know the BC*** transistors face the opposite way to the 2N**** transistors, don't you?
"I think we're done here."

"rule #1 - don't paraphrase."

'redundant legs don't grease the skids'

iamthesoyman

Re: Hudson Broadcast 24V Issues
« Reply #4 on: January 27, 2021, 11:44:25 AM »
as someone once said, welcome to the forum.

as someone else once said a few times, can we see a circuit diagram so we know what you are talking to us about?

as a third person sometimes says, can we please, PLEASE, see photos of the thing you've built so as to compare it with the layout you are showing us?

and there was another someone who often says - you do know the BC*** transistors face the opposite way to the 2N**** transistors, don't you?

Thanks, looking forward to spending some time here!

I have added the schematic and also pictures to my original post. Also, I have accounted for the facts that the 2n5088 needs to be flipped around, and also that the 1T308B pinout is not the same as the OC transistor. Originally I was using sockets, but they felt loose so I soldered the transistors right to the board. This seemed to help, as before I was hearing the same issues with the added issue of an intermittent signal.

kaycee

Re: Hudson Broadcast 24V Issues
« Reply #5 on: January 27, 2021, 12:55:54 PM »
The gain switch is a 3 position toggle, it latches up, middle and down. Your footswitch has two positions, I'd guess this is the issue. If not you can google the schematic and find one with voltages for the trannies (my notes are in storage).

If I'm just using one set of lugs for the gain switch, it should work the same but with one less gain option, shouldn't it ? The other two sets of lugs on the footswitch are used to switch between the 2 level potentiometers, switching lugs 2 and 3 simultaneously (lug 1 on both is grounded). Although looking at the Duocast schematic, it looks like all I need to do is switch lug 2.

Ok, regarding the gain switch, I understand what you have done, so regarding the operation of that, as long as you have the pole correctly identified then yes, you have just lost the low gain option. I don't really follow on the volume pots, are you switching between two volumes so that when you change gain you also change volume and can balance out?

If you have counted and have got the correct number of cuts, try going through checking the number on each line to identify a misplaced cut.

Looking at the top of your board, sorry to say, its a bit of a mess due to the over size capacitors you have used, there could be a short anywhere in there really. Might be time to cut your losses and start over with some lower voltage physically smaller capacitors. I'll put a picture of my build of the same layout below. I used a few extra columns to space out and drilled the perforations to take the transformer legs, using a couple of links to make good the connections.