Barcus-Berry Standard Pre-Amp Model 1330-1  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
turbofeedus
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Post by turbofeedus »

Hey all, picked up this preamp last week. Came to me with a pretty bad crackle/hiss. Haven't sorted that out yet, but I did up a schematic.
I verified the transistor pinouts and gain with a DCA55.
Diodes are 1N7xx, forward voltage is 0.78V.
Enjoy and feel free to ask questions.
More pics here.
bb1330-1-3.JPG
drawings.jpg
1330-1 schematic.jpg

Axldeziak
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Post by Axldeziak »

Are there any visible markings on the Bass pot inductor? (Is it painted over?) Measurement, perhaps?

turbofeedus
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Post by turbofeedus »

Axldeziak wrote:Are there any visible markings on the Bass pot inductor? (Is it painted over?) Measurement, perhaps?
Unfortunately not, and as far as I know, measuring for inductance is complicated.
I'd probably just start with a 500mH like this, and go from there.

Updated schematic with a couple corrections.
1330-1 schematic.jpg

Manfred
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Post by Manfred »

Unfortunately not, and as far as I know, measuring for inductance is complicated.
Not realy using a LCR-meter.

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Post by Axldeziak »

I may have found a few clues as to what the ITS30326 is. Seems the style of JFet, round, white on the sides with a black top was produced by Siliconix in the mid 70's and was known as the E series.
From there I was able to find mention of E230 Siliconix fets being used in early Barcus Berry amps. The model number was later changed to J230. Looking in a copy of the 1986 Siliconix FET Databook the J230 is listed alongside the J231, and J232 as being N-Channel "Audio and Sub-Audio Amplifiers."

turbofeedus
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Post by turbofeedus »

Manfred wrote:
Unfortunately not, and as far as I know, measuring for inductance is complicated.
Not realy using a LCR-meter.
Don't have one of those unfortunately.
Axldeziak wrote:I may have found a few clues as to what the ITS30326 is. Seems the style of JFet, round, white on the sides with a black top was produced by Siliconix in the mid 70's and was known as the E series.
From there I was able to find mention of E230 Siliconix fets being used in early Barcus Berry amps. The model number was later changed to J230. Looking in a copy of the 1986 Siliconix FET Databook the J230 is listed alongside the J231, and J232 as being N-Channel "Audio and Sub-Audio Amplifiers."
Nice, ultimately it doesn't matter much in this context. It's just being used as a buffer, so any modern NJFET should work ok; J113, 2N5484, etc.

Manfred
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Post by Manfred »

Don't have one of those unfortunately.
I see, perhaps there is repair shop in your area you can aks for measurement.

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Post by Manfred »

The treble and bass controls are in the feedback loop of the gain circuit.
I ran a simulation of the bass control where I have inserted the control circuit into the feedback loop of an inverting OP-Amp amplifier.
I have found the following center frequencies depending on the inductance of the coil.
Frequency Versus Inductance.jpg
I made a PCB-Copy for retracing the schematic.
The coil on the very right of the layout is not marked
BarcusBerryStdPreAmpModel1330_1Layout.JPG
Ready to print PDF-files:
BarcusBerryStdPreAmpPCB-ComponetSide.pdf
(13.11 KiB) Downloaded 16 times
BarcusBerryStdPreAmpPCB_SolderSide.pdf
(4.17 KiB) Downloaded 16 times
Sprint-Layout 6.0 - file:
BarcusBerryStdPreAmpModel1330-1.zip
(15.57 KiB) Downloaded 15 times

turbofeedus
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Post by turbofeedus »

Manfred wrote:The treble and bass controls are in the feedback loop of the gain circuit.
I ran a simulation of the bass control where I have inserted the control circuit into the feedback loop of an inverting OP-Amp amplifier.
I have found the following center frequencies depending on the inductance of the coil.
Frequency Versus Inductance.jpg
I made a PCB-Copy for retracing the schematic.
The coil on the very right of the layout is not marked
BarcusBerryStdPreAmpModel1330_1Layout.JPG
Ready to print PDF-files:
BarcusBerryStdPreAmpPCB-ComponetSide.pdf
BarcusBerryStdPreAmpPCB_SolderSide.pdf
Sprint-Layout 6.0 - file:
BarcusBerryStdPreAmpModel1330-1.zip
Awesome work Manfred! I did call around and no-one had an LCR meter. I'd loe to get my hand on one of these:
https://www.amazon.com/PEAK-Atlas-LCR45 ... 897&sr=1-5

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ppluis0
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Post by ppluis0 »

Hi turbofeedus,

You (and all of us...)can build an inexpensive inductance meter presented in this link: http://electronics-diy.com/inductance-meter.php

Cheers,
Jose

Manfred
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Post by Manfred »

Hi turbofeedus,

I own the LCR45 and am very satisfied with it.
it also measures the impedance and shows real part, imaginary part, absolute value and phase angle. If you are familiar with these expressions of electrical engineering then I can recommend the device, if not then I would consider an LCR meter device with a lower price to be sufficient.

turbofeedus
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Post by turbofeedus »

ppluis0 wrote:Hi turbofeedus,

You (and all of us...)can build an inexpensive inductance meter presented in this link: http://electronics-diy.com/inductance-meter.php

Cheers,
Jose
I'll check that out, thanks.
Manfred wrote:Hi turbofeedus,

I own the LCR45 and am very satisfied with it.
it also measures the impedance and shows real part, imaginary part, absolute value and phase angle. If you are familiar with these expressions of electrical engineering then I can recommend the device, if not then I would consider an LCR meter device with a lower price to be sufficient.
They sound vaguely familiar :D I have the DCA55 and really like it, so I'm familiar with using Peak products.

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Post by Manfred »

They sound vaguely familiar :D I have the DCA55 and really like it, so I'm familiar with using Peak products.
Then the LCR45 is a good choice :thumbsup

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Post by turbofeedus »

Manfred wrote:
They sound vaguely familiar :D I have the DCA55 and really like it, so I'm familiar with using Peak products.
Then the LCR45 is a good choice :thumbsup
Couldn't swing the ~$120, so I ordered a cheap but well reviewed LCR meter off Amazon. Should be here tomorrow. Allegedly measures down to 200uH, so we'll see what happens.

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Post by turbofeedus »

Wasn't able to get a good reading with the LCR meter.
Important to remember, this unit started with problems, perhaps the inductor is part of those issues.
Regardless, either the inductor is more than 20H, seems unlikely, or something else is wrong.
inductor-1.JPG

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Post by Manfred »

Such a large inductance is not possible in this size.
Can you measure the DC resistance maybe you did not have good contact to the coil terminals?

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Post by turbofeedus »

Manfred wrote:Such a large inductance is not possible in this size.
Can you measure the DC resistance maybe you did not have good contact to the coil terminals?
Duh, don't know why I didn't think to test that. Yep, it's open.
Only thing valuable about this now is the dimensions which are ~13mm long and ~7mm diameter.

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Post by VivMeLol »

What do those back to back diodes at input do?

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Post by plush »

VivMeLol wrote:What do those back to back diodes at input do?
They are present in case input voltage swing exceeds supply voltage (i.e. input overvoltage protection).

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ppluis0
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Post by ppluis0 »

turbofeedus wrote:Duh, don't know why I didn't think to test that. Yep, it's open.
Only thing valuable about this now is the dimensions which are ~13mm long and ~7mm diameter.
Perhaps it's time to make several speculations to guess what is the correct value of this inductor.

I'm not have luck using software simulators, so my best guess is that that coil must have a value of 1 to 2 mili henries. :roll:

Cheers,
Jose

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