Wayne's BA 2018 linestage

Hey everyone,

I just finished this preamp and there is too much gain (I get a hiss on the speakers - white noise).

I was reading that "gain set by ratio of R16/R17".

I'm using the preamp input as Balanced with R20 @ 10K and R18 @ 27K as per suggested in the thread earlier.

For a balanced input, is the gain still determined by R16/R17 in that scenario? Looking at the schematic, R17 ties to the negative phase of to the XLR terminal.

Thanks!!
Antoine
 
Thanks @RainfallSky,

That's exactly my config: BAL input and SE output. Sorry I wasn't clear. In that configuration, as I understand, you simply wire the XLR:

1 - Chassis
2 - IN+,
3 - IN-

Which is what I have right now.

The reason I was asking about gain, is that the preamp is super clear when playing on headphones (I did the "big" Toshiba outputs) and no hissing or anything there.

Problem happens when I plug it to the big amp, then I hear hissing about 4-5 feet away from speakers. It's annoying enough that I want to quiet it.

Bias-wise, the pre-amp biasses perfectly (can reach very close to 0V on each channel). So I don't think it's a build problem. But I'm happy to be proven wrong! :)
 
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The reason I was asking about gain, is that the preamp is super clear when playing on headphones (I did the "big" Toshiba outputs) and no hissing or anything there.

Problem happens when I plug it to the big amp, then I hear hissing about 4-5 feet away from speakers. It's annoying enough that I want to quiet it.

Can you please post a photo of how everything is connected?
I am convinced there should be now hissing with this linestage.. so something could be done to eleminate it.

I tryed to simulate it but not sure I did everything right.
That look on a board like:
left side of the board: +IN to XLR pin 2
right side of the board: -IN to XLR pin 3
left side -IN connect to right side +IN
no -IN to GND jumpers on both board (not connected).
Both sides share GND also with PSU.

Ltspice is happy run it with no errors.
But still not sure everything is correct..
 
Thanks for the help @RainfallSky!

I was trying to eliminate possible sources of noise so I cut the wires to the source selection (Will rewire later 😅).

The left channel goes to left (1-2-3 from xlr to IN+/-/Gnd of board) and right goes to the other channel of the board.

Shields of the cable goes to chassis.

I messed with Pin 1 to chassis and floating and it didn't make a difference.

Outputs are RCAs.

I tried headphones in tbe RCA jacks (with a shenaniganned adapter) and that sounds fantastic. It also sounds fantastic on the amp, just hissing.

I coupled the transistors for heat sharing and put a heatsink on the toshibas.

644C4C52-6F10-4BD9-BD5A-89702F3985DD.jpeg
 
Hey everyone,

I just finished this preamp and there is too much gain (I get a hiss on the speakers - white noise).

I was reading that "gain set by ratio of R16/R17".

I'm using the preamp input as Balanced with R20 @ 10K and R18 @ 27K as per suggested in the thread earlier.

For a balanced input, is the gain still determined by R16/R17 in that scenario? Looking at the schematic, R17 ties to the negative phase of to the XLR terminal.

Thanks!!
Antoine
what amp exactly, and what gain it's having?
if there is too much (sum) gain of preamp and amp, hiss is likely possible, and logical
 
what amp exactly, and what gain it's having?
if there is too much (sum) gain of preamp and amp, hiss is likely possible, and logical
Thanks for jumping in everyone.

The amplifier is the Wolverine amp from this forum (and they have absolutely no hiss at all when I connect other inputs. Only I can connect one input and SE only.

I was looking at a preamp as a way to have balanced input come in (which the BA18 allow) as well as many input sources with a nice knob.

I connected the headphones to the RCA connector (via an adapter) to make sure the test is fair.

When testing the components individually (preamp and amp) there is no hiss. Only when connecting both together, which is why I thought it was a gain issue.

Also the speakers are Klipsch Heresy IV, which are quite efficient.

Unless from the pic I shared you see a grounding problem, but I'd expect a hum in that case, the noise sounds like white noise only.

Thank you!!
 
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so, simple calculus sez that hiss is what you can expect, with so excessive gain, feeding Klipsch speakers

read What is Gain Structure?

few pics missing, but you'll get it
Awesome, thank you for sharing! I had never heard of that concept before, and it makes a lot of sense.

What do you suggest to remediate the "problem"? I'm really enjoying the sound of the BA18, just don't like the hiss :)
 
Awesome, thank you for sharing! I had never heard of that concept before, and it makes a lot of sense.

What do you suggest to remediate the "problem"? I'm really enjoying the sound of the BA18, just don't like the hiss :)

as I remember , Wayne sez that thingie is stable with lesser gain, can't remember was it 1* or 2* mentioned specifically

however - if you decrease gain of preamp, it'll sound different ..... only you can tell how much of change you are going to hear and is it to your liking

besides preamp, you can change gain of amp; same applies regarding change in sound

probably best way is to use unity gain preamp, simpler topology than Wayne's (this one)
 
as I remember , Wayne sez that thingie is stable with lesser gain, can't remember was it 1* or 2* mentioned specifically

however - if you decrease gain of preamp, it'll sound different ..... only you can tell how much of change you are going to hear and is it to your liking

besides preamp, you can change gain of amp; same applies regarding change in sound

probably best way is to use unity gain preamp, simpler topology than Wayne's (this one)
Awesome, thank you for the input, much appreciating the learning experience! :)