I find this circuit extremely handy and I use it everywhere, all the time, everyday. Really, it is the Best Thing Since Sliced Bread.
Would folks be interested in a ready to run (RTR) GB for this preamp/buffer?
Briefly, provides balanced or SE in and balanced and SE output. Selectable gain of 0/6/14/20dB via DIP switches. On board ultra low noise +/-15v DCDC PSU requires only 12v from a wall wart.
Uses state of the art OPA1656 and OPA1637 opamps and balanced line drivers. Designed by Jhofland. Noise floor is an incredible -135dB (limit of my measurement).
Let’s start an interest list for a GB. I think I can offer these professionally assembled with genuine BOM and tested ready to go for $165ea. Includes all XLR/TRS jack (non locking), and premium RCA jacks.
I’ll need interest for at least 15 units to make this possible though.
Signup here with name / number of units / country.
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xrk971 / 2 / USA
Would folks be interested in a ready to run (RTR) GB for this preamp/buffer?
Briefly, provides balanced or SE in and balanced and SE output. Selectable gain of 0/6/14/20dB via DIP switches. On board ultra low noise +/-15v DCDC PSU requires only 12v from a wall wart.
Uses state of the art OPA1656 and OPA1637 opamps and balanced line drivers. Designed by Jhofland. Noise floor is an incredible -135dB (limit of my measurement).
Let’s start an interest list for a GB. I think I can offer these professionally assembled with genuine BOM and tested ready to go for $165ea. Includes all XLR/TRS jack (non locking), and premium RCA jacks.
I’ll need interest for at least 15 units to make this possible though.
Signup here with name / number of units / country.
———————-
xrk971 / 2 / USA
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In case someone is wondering what the value is here. The BOM from Mouser is $80 not including the RCA connectors or PCB. Add those and cost would be $115 to build it yourself. So you are getting a prebuilt and tested unit ready to be used in any project with high quality input connectors for $50 more than cost of DIY.
I’m going to go ahead and get a small batch of these ready to run panel mounted BTSB’s made by an assembly house and offer them in my shop once available in a few months. Price will probably be higher than what I offered with a group buy.
Can the panel mount be used for output also, or only input? I'm wondering if the dip switches swap direction
The title BTSB Panel Mount buffers are active buffers (use opamps), so the signal only goes one direction and is not bidirectional on the jacks. You want to be careful not to have an output going to your preamp output as that might damage the preamp.
I have another design for a passive version of this which could be bidirectional. But generally, XLR male is only used for input. There is the combo TRS inside the XLR which could be used both ways.
This is currently used in the Emerald Physics 600.2SE amp that I designed. It has a tube buffer version of the BTSB mounted as a separate PCB on the amp main floor plate. This is called the “BTSB Lite”. It has auto switching relays to disconnect the RCA’s for XLR/TRS priority and a 3.5kV galvanically isolated 12v DC/DC converter to drive the relays to prevent ground loops. It’s actually pretty slick and handy as a universal passive input board.
I have another design for a passive version of this which could be bidirectional. But generally, XLR male is only used for input. There is the combo TRS inside the XLR which could be used both ways.
This is currently used in the Emerald Physics 600.2SE amp that I designed. It has a tube buffer version of the BTSB mounted as a separate PCB on the amp main floor plate. This is called the “BTSB Lite”. It has auto switching relays to disconnect the RCA’s for XLR/TRS priority and a 3.5kV galvanically isolated 12v DC/DC converter to drive the relays to prevent ground loops. It’s actually pretty slick and handy as a universal passive input board.
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One place I have been considering the buffer is for a record output from my preamp after source selection before volume control. So for that setup se hard wire into the module, then connects to jacks for output. I was looking on my phone earlier so couldn't see the schematic well and now see the dips are to select between some resistors.
X: if there are not enough folks for the assembled GB, will you sell the bare PCB on your Etsy site?
Never mind ..I just saw they are there..
thanks,
pete
Just to be sure I understand this correctly:
- The boards are stereo, not mono
- The RCA and XLR jacks on the PCBs are the inputs, the outputs are on the pin connectors
- Both the RCA and XLR inputs are "live". Or does the board allow switching between RCA or XLR input? How?
Stereo and RCA for SE input, and XLR/TRS combo jacks for balanced input. There is a relay that automatically detects presence of XLR or TRS and gives that priority over RCA. So RCA jacks will be auto switched off if a balanced input plug is inserted. Outputs are balanced (3pin Molex KK or JST) and SE (2pin Molex KK or JST) and simultaneously output all the time. Output buffer for balanced is OPA1637 and SE is OPA1656.
The GB for this buffer is now closed and first units rolling off the assembly line. I should have them ready to ship by the end of the month from my shop. List price is $215ea ready to run.
You can see that OPA1656 opamps are used. I have upgrade the bootstrap caps to Nichicon Muse green bipolar. They are a bit big but I think worth the tight fit.
You can see that OPA1656 opamps are used. I have upgrade the bootstrap caps to Nichicon Muse green bipolar. They are a bit big but I think worth the tight fit.
Forgot to mention that these boards are in.
Some interesting news is that I tested them as high output buffer/preamps to drive the likes of 0dB gain amps like F4. The BTSB can provide outputs up to 52Vpp with balanced input and output. Setting gain at 20dB will require your preamp to be able to generate 1.4Vrms to reach 40Vpp:
Here is 49Vpp:
Here is 40Vpp - good enough to hit clip at 25W into 8ohms:
Some interesting news is that I tested them as high output buffer/preamps to drive the likes of 0dB gain amps like F4. The BTSB can provide outputs up to 52Vpp with balanced input and output. Setting gain at 20dB will require your preamp to be able to generate 1.4Vrms to reach 40Vpp:
Here is 49Vpp:
Here is 40Vpp - good enough to hit clip at 25W into 8ohms:
My shop is now taking preorders. Price is $430 each and units are fully built and tested ready to run. Comes with matched NOS 6N1P tubes.
https://www.etsy.com/listing/147415...499&click_sum=cca02e94&ref=shop_home_active_1
https://www.etsy.com/listing/147415...499&click_sum=cca02e94&ref=shop_home_active_1
Funny we have the same taste in meters, I have an extra pair of the little flukes and also the Owen scope. Sometimes it is nice not to worry about your probes being grounded.
Can never have too many meters! 😂
On the bench are my meters. These don’t include sound level SPL meters or IR thermometers or FLIR imager thermometers.
From left to right: BK 2706 - has thermocouple input for temperature (had this for 30 years), Fluke 101, Fluke 115, Fluke 116, Etekcity MSR C600 clamp on, Owon HDS242S scope/meter/function gen, and recent additions of LCR meters BM4070 for basic XO parts sorting and a nicer Ruoshui 4080 high resolution one with phase and variable excitation freq for measuring custom made inductors and capacitors. Almost all of these came from Amazon. The BK 2706, I got at Fry’s Electronics in Freemont CA when I was in grad school at Cal.
On the bench are my meters. These don’t include sound level SPL meters or IR thermometers or FLIR imager thermometers.
From left to right: BK 2706 - has thermocouple input for temperature (had this for 30 years), Fluke 101, Fluke 115, Fluke 116, Etekcity MSR C600 clamp on, Owon HDS242S scope/meter/function gen, and recent additions of LCR meters BM4070 for basic XO parts sorting and a nicer Ruoshui 4080 high resolution one with phase and variable excitation freq for measuring custom made inductors and capacitors. Almost all of these came from Amazon. The BK 2706, I got at Fry’s Electronics in Freemont CA when I was in grad school at Cal.
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