Your questions I cannot answer but this i ask of you. What are the symptoms? Can you link the schematic you found?Hi all, used to be a member several years ago but lost access to my account so have just been lurking since but have been having trouble with a Trace Elliot bass head I am fixing for a friend. I hope someone might be able to enlighten me!
It is a Trace Elliot GP7 AH150 head from the (roughly) mid 90's and I have not been able to find a schematic, the internet is filled with examples of another similar GP7 head but it is not this one. In all my searches the only proof I ever found of this amp even existing was a single listing on a second-hand site. So I traced out the schematic myself (just power amp the preamp is fine) and realised it looked familiar. While searching for schematics I found one titled "Trace Elliot GP7 150-300watt SM" which seems to be fairly available and I assumed was for the newer looking version which is all over the place, however the final pages of this schematic depict an alternative power amp section using MOSFETS of similar (essentially the new equivalent) type to the amp I have. After tracing out the power amp I realised that it was essentially identical (have not confirmed all component values) to the suggested design in the schematics. This seemed strange to me as it seems they originally designed the amp using MOSFETS as in the one I have, they then changed to a different design known as the Bi-polar Bear using BJTs but then offered an apparently improved design based upon an older model!
While this is all very strange and interesting (to me at least!) it's not particularly relevant to my question. Sorry if I have taken a while to get to the point but here it is...
The design in the schematic is slightly different from the amp I have, the most notable difference being the introduction of a load of crap that if I'm totally honest have no idea what it's doing there. I have outlined this area in red on the image attached. If someone could please help me figure out:
1. What this arrangement is known as and what its purpose is?
2. Can it be omitted and if so what adjustments might need to be made?
3. Do I need to re-evaluate my life for not knowing this?
Also if anyone owns or has worked on this amp it would be interesting to know if the power section of your model uses K135s and J50s (like my friends), BJTs or BUZ901/6s.
I'd happily spend months mucking about with this amp, it's what I like to do. However some people like to make music...
Any help much is appreciated, and much respect to anyone selflessly sharing knowledge!
As far as going from Mosfets to Bipolars it sounds similar to what was done on some Hartke 3500's.