I'm thinking of building preamp as my first point to point project (I built a Tubelab SSE last year), and the JEL76 preamp has caught my eye.
JE Labs Arkiv (up to 2008): JE Labs phono and line preamp
I'm working on a BOM and getting familiar with the schematic and a few things have popped up that I was hoping someone who has built this, or is familiar with the preamp, could help verify for me (mostly about power supply).
1. I can't read the lower rating values of the chokes on the schematic.
Would Hammond 193C (20H, 100 DC MA, 181 Ohms, Max 600v) and 193B (12H, 100 DC MA, 155 Ohms, Max 600v) work?
2. What are the capacitor values on the CRC of the 6.3v heaters? I'm seeing 10kuf 10V?
3. Could someone explain the circuit that floats the ground of the 6.3v heater tap? I'm thinking diodes (and if so what value and direction), but this part of the schematic is not so clear to me.
4. B+ on the power schematic is stated at ~290v, but on the linestage schematic its listed at 280v. How critical is this?
I'm also considering the Wauwatosa Sofrito or Muchedumbre preamps if anyone wants to comment on any of these.
Sofrito Preamplifier – wauwatosa tube factory
Muchedumbre Buffer Preamp – wauwatosa tube factory
Thanks so much for the help!
-Jeff
JE Labs Arkiv (up to 2008): JE Labs phono and line preamp
I'm working on a BOM and getting familiar with the schematic and a few things have popped up that I was hoping someone who has built this, or is familiar with the preamp, could help verify for me (mostly about power supply).
1. I can't read the lower rating values of the chokes on the schematic.
Would Hammond 193C (20H, 100 DC MA, 181 Ohms, Max 600v) and 193B (12H, 100 DC MA, 155 Ohms, Max 600v) work?
2. What are the capacitor values on the CRC of the 6.3v heaters? I'm seeing 10kuf 10V?
3. Could someone explain the circuit that floats the ground of the 6.3v heater tap? I'm thinking diodes (and if so what value and direction), but this part of the schematic is not so clear to me.
4. B+ on the power schematic is stated at ~290v, but on the linestage schematic its listed at 280v. How critical is this?
I'm also considering the Wauwatosa Sofrito or Muchedumbre preamps if anyone wants to comment on any of these.
Sofrito Preamplifier – wauwatosa tube factory
Muchedumbre Buffer Preamp – wauwatosa tube factory
Thanks so much for the help!
-Jeff
1: looks like 100mA to me.
2: 10,000uF
3: no diodes; just connect the "-6" output to the floating/offset voltage divider.
4:not very critical. 280 or 290 probably wouldn't make any noticeable difference .
Just m 2cts based on a quick reading of the schematic. Looks pretty straightforward/ easy build.
2: 10,000uF
3: no diodes; just connect the "-6" output to the floating/offset voltage divider.
4:not very critical. 280 or 290 probably wouldn't make any noticeable difference .
Just m 2cts based on a quick reading of the schematic. Looks pretty straightforward/ easy build.
How much gain do you need? What output impedance do you need?
The JE Labs circuit has a gain stage connected to a cathode follower. This will provide gain plus a low output impedance. The Sofrito is a single gain stage, which may not have low enough output impedance to drive the following stages. Conversely, the Muchedumbre has slightly less than unity gain (ie no gain) but a low output impedance.
Hey guys, thanks so much for the responses.
After some consideration, I've come to the conclusion that I really don't need a lot of gain. I'm driving my amp now with no problem from either of my sources. Switching out cables is the main problem.
I've decided on the Muchedumbre as it seems to best fit my needs. Parts have been ordered, just waiting on delivery.
After some consideration, I've come to the conclusion that I really don't need a lot of gain. I'm driving my amp now with no problem from either of my sources. Switching out cables is the main problem.
I've decided on the Muchedumbre as it seems to best fit my needs. Parts have been ordered, just waiting on delivery.