• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

dynacord BA300

#281
Thanks Beate, I'll do that. (probably next weekend)

@ Muziekschuur: Thanks, it's big alright: sounds big and weighs a ton. And on the paint: I think it was one of those stickers from the music store. Some 'stickerverwijderaar' did the job already :)

And another question if I may: I can't make much sense of the reverb circuit. In the schematic's it looks like the connections are just for a footswitch, but there's also nothing I can recognise as a reverb circuit in the amp. Switching it on does not do much. Not that I reallly need reverb for bass, I'm just curious.
 
#282
Matthijs said:
@ Muziekschuur: Thanks, it's big alright: sounds big and weighs a ton.
Click to expand...

It is lightweight for a tube amp of this power (in terms of power/mass few really amps are better). And it is easier to carry around than my Mywatt 200 which has the same weight...

You might try to carry around a Hiwatt 100 or an old Orange. Or maybe just a Fender Twin Reverb. Then You know whats heavy...

(BTW: regarding modding these beasts: meanwhile i have learned that the amp can easily drive the heaters of 3 12Ax7 and a fourth if You replace the signal lamp by an LED)
 
#283
It took me a while to find the time to open it up and do some digging. Its not the tube stage. I disconnected the input and all of the hiss was gone. I tried the same inbetween the tone and the last tranisitor stage and the hiss definetely comes from that last transistor board.

I also tried using the input for the tube part as a poweramp input. I connected it to a pre and it was dead quiet, but a little low on signal. With the headphone out from my eden wt300 it worked just fine, with whatever noise there was coming from the eden.

Is there anything I could do to that last transistor stage? Am I right in thinking it is just a pre-amp stage to boost the signal inbetween the tone and the tube stages? I might just replace it with a more modern low-noise pre-amp stage.
 
#284
The last board. This is still the old circuitry from the mid 60s when the Gigant came out. IMO it must be designed new, especially the input stage.

The gain of the stage is a bit more than 60 (140 mV to 8.8 V). And it is noisy, especially the input stage of the board.

You have mainly the following choices (among others):

a) design some new schematics keep the old topology. Maybe a JFET input, maybe some lower noise design with bipolar transistors. (Noise sources are the transistors, especially the 1st one, and the resistors with their large values). If You'r lucky that is possible on the original motherboard.

b) use a new board with, e.g. an OpAmp instead. Even a TL072 or TL082 might do.

c) use a tube. You can use a pentode or a double triode - low to medium mu will be perfect. (I would probably design around an ECC82, or, for the fun of it, an EF86.
 
#285
Thank you Beate, that's really helpfull.

I think I prefer the idea of designing something new and keeping the old board, just in case.

I like the idea of a tube, but that's all new technology to me (you must have noticed :)). I'm going to do some research to find a good design. Is there a good source you can recommend?
 
Last edited:
#286
for the basics: How to design valve guitar amplifiers
and then: Tube CAD Journal (has some interesting ideas...)

You should take care of the limits of the heater section of the power transformer.

In the Gigant it drives 4 light bulbs of 0.3 A, in the other amps with that power stage like yours or mine, it drives only one bulb. So You have a capacity of 0.9 A (three ECC8x) or maybe four, if You replace the light bulb by an LED.
 
#288
If You are interested, here what i put into my G2000:

Preamp_Schem.png

and the frequency response

Preamp_Freq.png


Please note that R12/R13 is a pot of 100 kOhms (Gain) and R6 is a pot of 100 kOhms as well (Master). The tone stack is a tilt control with an adjustable mid control.
If You use it with ECC81, You need V1 selected tubes with low microphonics (a problem of the ECC81). A bit to my surprise the circuit works really well with an ECC83. Nice overdriven tone (You can overdrive the 2nd triode...) if desired. And the ECC83 has no problems with microphonics. Due to the small values of the gain pot the tonestack will see a relatively low driving impedance even with the ECC83 - that's desirable.

Meanwhile i added a switchable "bright cap" to the gain control and a switchable bass cut at ~70 Hz. You can use C8 or C7 for this.

The unusually small value of the volume pots has a reason: the G-2000 has custom concentric dual pots which i wanted to retain.
 
#290
My BA300 is completely quiet. I got there when I changed out the big capacitors from the powersection. Invalid Link Removed. These should be screw in capacitors to keep the unit Original and to keep it's chassis transportable. If you want to use cheap caps open the screw in ones and solder the new caps in there. The screw in option is mechanical very wize. Mine is the younger BA300. But both amps should be soundwize very similar. The amp can be driven by the new AMPEG scrambler pedal and then it will behave like an ampeg. Without you will have a great modern sound. When you push the amp it will give a dynacord growl. Wich are the end tubes being driven by a solidstate preamp wich stays clean... A very different but beautiful growl.
 
#292
For whatever it's worth, I picked up an Eminent EMT (1963?) last week to play through the matching 2x12 cab. I am trying to get back to guitar, and tried this with a Telecaster Thinline with humbuckers. Of course, as stock, there is no "modern" sounding distortion, but looking at the schematic, if I use the microphone channels and cascade the signal through three amplification stages before the tone stack, I should get plenty of overdrive.

The first issue is to root out the annoying buzz at C2 tone.
 
#293
@beate_r: Your schematic has me thinking about wether or not I want those extra controls on the front of the amp. I was planning on keeping the front original. The original tone stack is pretty usefull, so there's no real need for extra tone shaping. I can leave out your tone circuit, but I kind of like the idea of having a gain control. I might even make it switchable: just a low and a high gain setting that's internally trimmable. What will be the result of leaving out your tone stack? Would I need to do some additional compensation to get a fairly flat response? There's always the option of leaving it in, but also only with trimpots on the inside.
 
#294
The tone stack "eats" 9 dB of gain. Which means that You will be able to overdrive the 2nd stage quite easily.

I am going to retain the original look, at least on the long end (with 2 preamp, maybe even a 3rd...). That's why i am using the original pots, and that's the reason for the unusual design. My tonestack is a lot more flexible than the original one.
 

Latest posts

Top Bottom
Back