Yet Another Color Preamp

This is a great circuit! I played around with the power supply and designed a PCB, mostly as an experiment. Did a quick plate build. Call it a proof of concept as I want to tweak case work and plate. Maybe even add remote with an R2R arduino volume control. Possibly try a tube rectified/regulated (glow tube) supply.

Anyways the color pre sounds amazing. It takes a slight edge off my KT88 push pull monoblocks. I run an EAR 834 clone through the color preamp as well. Maybe redundant in some sense, but it doesnt hurt. The meters actually helped with cartridge alignment and 1 khz test record. Tons of gain....

The pots on input are a good idea, especially with the inherent drive of the 834 clone. The real win with the preamp is streaming.

Happy to share the PCB files. The layout isnt perfect, but the results work well for me. YMMV as to my ideas on power supply. That said, I built a board out for the basement, no choke and 12V 4A laptop power supply feeding boost converter for HV.

7 comments

7 Comments

Timoun Dat-DJ-ONEVIBE

Sep 15

Hi ! stumbled upon this by chance while looking for other information, your post makes me curious: what is this "color preamp" for? It's an active volume control, OK, which is interesting in my case. If I understand correctly, it has a preamplification function, which can complement an RIAA EQ, but it is not an RIAA preamplifier? A kind of tube enhancer ? Could you explain why it seems to you redondant to plug it with EAR 834 clone ? Thanks you !

Edited

Timoun Dat-DJ-ONEVIBE

Sep 16

Replying to

regarding the use of a passive volume control in the EAR 834, what do you think is the best solution: use the pad provided on the circuit (next to the RCA output), or externalize it on the chassis between pcb output and RCA? In both cases, is the addition of the 68k resistor necessary (50k volume control = 68k resistor) ? If so, why? I don't know if you are familiar with this preamp. But thanks anyway!

Bob cooke

Sep 16

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Replying to

Hmm. My clone uses a 220k to ground on output. It is from tubes4hifi. I did see that circuit variation on line. I tried it, as an experiment and thought it sounded rolled off. If you like the sound it’s always nice to have the control on the phono. You can wire up a super simple system. (Eg direct to power amp) It depends on what equipment you have upstream as well.

Edited

Bob cooke

Sep 17

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Replying to

The preamp can take any line level. Too much signal, believe it will clip (check video).

Another idea might be to try zkit4 schematic from decware. Single tube color gain stage. I use this sometimes… one tube.

The pcb I made is roughly 4x7 inches.

I understand the concern regarding frequency response, impedances and so on. So long as the output stage of the phono “sees” correct resistance, it’s just a voltage divider imo.

Have fun!

Bob cooke

Feb 29

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300V boost converter for HV. 12V laptop supply at 4A with LM7806 regulator feeding heater supply filter caps.

Edited