Is it possible to bridge the inputs of a Dynacord Bass King amp?

[NoiseNinja]

If it should have gone past any ones attention with the numerous threads I managed to make by now about it, I recently bought a recently renovated old all tubes 50W Dynacord Bass King amp head produced in '64.

Anyone with knowledge about this amp would know that it was actually made with the purpose of functioning as an all round PA amp (despite it's name and the fact that it sounds beautiful as a dedicated bass amp).

That means that beside the usual jack instrument level input channel it comes with two XLR microphone level input channels.

Each of these channels by the way also have separate gain controls, as something unusual for amps made at that time.

My question is now:

Would it be possible with a patch cord with a male XLR plug in each end to bridge the two XLR channels and thereby obtain control over the extra channels to for instance increase the gain going into the power amp section to overdrive the power tubes?

Edit: Just realized those are not XLR connections but some kind of 5 pin female connections, which I guess would mean that the plugs needed to connect the channels would be 5 DIN male plugs, same as you use for MIDI.

 

[Roland GR 88]

Here's a schematic but I'm not an engineer

 

[NoiseNinja]

Here's a schematic but I'm not an engineer
View attachment 1086686

Thank you

Though:

1. I already got the schematics on a piece of paper that the seller was kind to include with the amp.

2. Sadly I am not an engineer either, or specifically well versed in electronics for that matter.

Appreciate your attempt at being helpful though, and maybe it will in fact help others who are not familiar with this specific amp to actually being able to answer my question.

 

[JimmyM]

Try it and get back with us on it.

 

[NoiseNinja]

Try it and get back with us on it.

I guess I should.

Just one thing then, are you 100% certain that I won't ruin anything by attempting so, like short cutting the two channels or blow the preamp tubes or similar?

Edit: Also just realized, those are not XLR connections. The female input connections have slightly smaller radius than a standard XLR and are 5 pin connections.

Anyone knows what type of plug they might be and what they would be called?

Edit 2: Found out my self by using the search term "5 pin male plug"... Seems to be the same plugs you use for MIDI called 5 Pin DIN Male.

 

[JimmyM]

I guess I should.

Just one thing then, are you 100% certain that I won't ruin anything by attempting so, like short cutting the two channels or blow the preamp tubes or similar?

Edit: Also just realized, those are not XLR connections. The female input connections have slightly smaller radius than a standard XLR and is 5 pin connections.

Anyone knows what type of plug they might be and what they would be called?

Edit 2: Found out my self by using the search term "5 pin male plug"... Seems to be the same plugs you use for MIDI called 5 Pin DIN Male.

I can't guarantee anything about an amp I never used, but people have been jumping channels for a very long time.

 

[Crater]

From looking at the schematic, all the inputs are in parallel and configured similarly. I can't see how you could harm the amp by bridging the inputs. Use pins 1(hot) and 2 (ground) on the DIN jacks to parallel the inputs. Each input has it's own tube, then a volume control, then they're combined, go through another gain stage, then through the tone stack and finally to the phase inverter and power amp.

I'm not an engineer either, but what does driving a train have to do with this?

 

[NoiseNinja]

From looking at the schematic, all the inputs are in parallel and configured similarly. I can't see how you could harm the amp by bridging the inputs. Use pins 1(hot) and 2 (ground) on the DIN jacks to parallel the inputs. Each input has it's own tube, then a volume control, then they're combined, go through another gain stage, then through the tone stack and finally to the phase inverter and power amp.

I'm not an engineer either, but what does driving a train have to do with this?

Thank you very much, I will try that out as soon as I got my hands on some DIN plugs.

 

[NoiseNinja]

So tried to connect the outputs just by sticking small jumper wires with exposed tips into the connector holes, but unfortunately it didn't seem to have any effect whatsoever.

So either it simply doesn't work, there's something wrong with the input plugs on the 2 other channels of the amp, or the wires I used might not have connected tight enough to make a proper connection.

All in all a pretty inconclusive tryout.

Anyway I think I just let it be with that in the first instance, unless someone who knows this particular amp and have tried it before can confirm that it will in fact work, and try to drive the input stage with my Joyo Orange Juice instead to hopefully get the breakup I kind of aiming for.

Under all circumstances I am actually pretty happy with the amp as it is, although I won't be able to try it at full power before I get it out to our rehearsal space, it got a really nice clean tone at least.

 

[Martin Beer]

Just connecting the two microphone channels together with a DIN cable won't work to bridge the channels on this amp, because it looks like there is only one input socket per channel and you need some way to get your bass signal in there. Linking channels with a single patch cable works where there is more than one input per channel, but on this amp you would need to make up some sort of splitter cable to connect the inputs together.
However, the amount of extra gain you can achieve this way is not much. Jumping channels together is most useful on amps that have two differently voiced channels like the bright/normal channels on an old Marshall or Bassman, where it allows you to mix the bright tone and the bassy tone together. You won't damage anything whatever way you connect those inputs together (the worst result is silence if you connect it wrongly), but it might not turn out to be very useful on this amp.

 

[NoiseNinja]

Just connecting the two microphone channels together with a DIN cable won't work to bridge the channels on this amp, because it looks like there is only one input socket per channel and you need some way to get your bass signal in there. Linking channels with a single patch cable works where there is more than one input per channel, but on this amp you would need to make up some sort of splitter cable to connect the inputs together.
However, the amount of extra gain you can achieve this way is not much. Jumping channels together is most useful on amps that have two differently voiced channels like the bright/normal channels on an old Marshall or Bassman, where it allows you to mix the bright tone and the bassy tone together. You won't damage anything whatever way you connect those inputs together (the worst result is silence if you connect it wrongly), but it might not turn out to be very useful on this amp.

Thank you for clarifying that.

Nice to know I don't have to worry myself about that then.

I guess I'll just go with driving the amp with my Joyo Orange Juice pedal, and hope it will push it into breakup.

As I haven't tried it on full power yet, since I live in an apartment, it is possible it will do so by it self once I get to turn it up at our rehearsal space.

I kind of doubt it though as it seem to be a super clean kind of amp, just like my first amp, which happened to be a Bass King T, with solid state preamp stage.

I love the tone of it though, really beautiful, it's not that, I just kind of need it to give off a little grid for the application I had in mind for it.

 

[Old Garage-Bander]

Just connecting the two microphone channels together with a DIN cable won't work to bridge the channels on this amp, because it looks like there is only one input socket per channel and you need some way to get your bass signal in there. Linking channels with a single patch cable works where there is more than one input per channel, but on this amp you would need to make up some sort of splitter cable to connect the inputs together.
However, the amount of extra gain you can achieve this way is not much. Jumping channels together is most useful on amps that have two differently voiced channels like the bright/normal channels on an old Marshall or Bassman, where it allows you to mix the bright tone and the bassy tone together. You won't damage anything whatever way you connect those inputs together (the worst result is silence if you connect it wrongly), but it might not turn out to be very useful on this amp.

+1 and then some.
I don't see how linking those two inputs together would do anything.
All three inputs are isolated from one another by their respective tube input stages.
Linking one or both of the mic inputs with the instrument input is not practical.
The mic inputs are balanced audio. The instrument input is unbalanced.
In general you can't just wire balanced to unbal directly without affecting the operation.
It can be done, but much magic is involved.
Mic input impedances, even with high Z (impedance) mics is still a lot lower than an instrument input.
Connecting the mic input may load down the instrument signal to the point of being unusable.
It can be done, but it's more trouble than it's worth and I still don't think you'll gain anything.