jcm900 preamp
hello, i got some time so i'm back with the pedals and recently i got some 12ax7 and a little bit bored with silicon, i started building preamps of recognized amps, i built the preamp of a jcm800 and all good, so now i want to build the jcm900 preamp, but I have a doubt about the signal input and the behavior/function of the marked line, I hope that someone who has some experience in this can help me
- Manfred
- Tube Twister
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This is a connection to the normally closed contact of the input jack.
If no instrument cable is plugged in, the grid of V1b is also connected to ground.
This is obviously to prevent noise or oscillation in the open state of the jack.
If no instrument cable is plugged in, the grid of V1b is also connected to ground.
This is obviously to prevent noise or oscillation in the open state of the jack.
- bmxguitarsbmx
- Cap Cooler
Go play a jcm900 before you put a bunch of work into it. I built a jcm900 some decades ago because it was presumably the highest gain circuit in the Aspen Pittman book. It was awful. I hated it. I was convinced I did something wrong. Spent forever swapping ceramic for silver mica and carbon comp for metal film. To no avail! For some stupid reason I ended up spending all my money on a jcm900 and it was at that moment I realized that I was an idiot. Still hate that amp. Still sorry to my buddy Tim, who bought it for $350. That was precisely the moment everything went wrong for him.
My 2 cents
My 2 cents
SL-X is much better.
- Cub
- Cap Cooler
The SL-X used to be my favourite of the JCM900 series and its specs certainly are attractive. Gain from 0 to 10 and then you can dial in an extra 12AX7 from 10 to 20 with the sensitivity pot for even more gain, what's not to like ?
But then I got to compare my 2100 SL-X with an earlier Master Volume model that uses a W005F bridge rectifier and an added 1N4007 instead of an extra tube. The lows were much tighter on the earlier amp and so much less hiss. I almost felt a bit cheated.
I always wondered if it would be possible to add a switch to it so the clipping from the rhythm and lead channels of the Silver Jubilee would be options as well. Carlos, that might be a fun little experiment for you to try !
Or would it be better to do it the other way around, a Silver Jub preamp with an added option for the W005F + 1N4007 clipping ?
On a side note, that bridge + 1 trick also works like a charm in a Boss DS-1 Distortion.
But then I got to compare my 2100 SL-X with an earlier Master Volume model that uses a W005F bridge rectifier and an added 1N4007 instead of an extra tube. The lows were much tighter on the earlier amp and so much less hiss. I almost felt a bit cheated.
I always wondered if it would be possible to add a switch to it so the clipping from the rhythm and lead channels of the Silver Jubilee would be options as well. Carlos, that might be a fun little experiment for you to try !
Or would it be better to do it the other way around, a Silver Jub preamp with an added option for the W005F + 1N4007 clipping ?
On a side note, that bridge + 1 trick also works like a charm in a Boss DS-1 Distortion.
I wish I were a chestnut tree, nourished by the sun.
With twigs and leaves and branches and conkers by the ton.
With twigs and leaves and branches and conkers by the ton.
- bmxguitarsbmx
- Cap Cooler
Now the Silver Jubilee I like